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Fosamprenavir

Class: HIV Protease Inhibitors
VA Class: AM800
Chemical Name: C-[(3S)-tetrahydro-3-furanyl] ester [(1S,2R)-3-[[(4-aminophenyl)sulfonyl](2-methylpropyl)amino]-1-(phenylmethyl)-2-(phosphonooxy)propyl] carbamic acid disodium salt
Molecular Formula: C25H34N3Na2O9PS
CAS Number: 226700-80-7
Brands: Lexiva

Medically reviewed by Drugs.com on May 5, 2022. Written by ASHP.

Introduction

Antiretroviral; HIV protease inhibitor (PI).

Uses for Fosamprenavir

Treatment of HIV Infection

Treatment of HIV-1 infection in adults, adolescents, and certain pediatric patients ≥4 weeks of age; used in conjunction with other antiretrovirals.

Used in conjunction with low-dose ritonavir (ritonavir-boosted fosamprenavir) or without low-dose ritonavir (unboosted fosamprenavir); usually used in PI-based regimens that include a PI and 2 nucleoside reverse transcriptase inhibitors (NRTIs).

For initial treatment in antiretroviral-naive adults or adolescents, experts state fosamprenavir (with or without low-dose ritonavir) not recommended. Regimens that include unboosted fosamprenavir may be associated with virologic failure and may result in selection of mutations that confer resistance to fosamprenavir and darunavir; clinical trial data for ritonavir-boosted fosamprenavir more limited compared with data available for other ritonavir-boosted PIs.

For initial treatment in antiretroviral-naive pediatric patients, experts state ritonavir-boosted fosamprenavir not recommended in any age group because other more advantageous ritonavir-boosted PIs are available. Fosamprenavir (without low-dose ritonavir) also not recommended for pediatric patients of any age because of concerns related to inconvenient dosing and possibility of selection of resistance mutations.

Consider the following factors when initiating ritonavir-boosted fosamprenavir: Data insufficient to determine whether a regimen that includes ritonavir-boosted fosamprenavir is as effective as a regimen that includes the fixed-combination of lopinavir and ritonavir (lopinavir/ritonavir) in adults who previously received PIs (PI-experienced). Once-daily ritonavir-boosted fosamprenavir not recommended in PI-experienced adults or in any pediatric patient.

Postexposure Prophylaxis following Occupational Exposure to HIV (PEP)

Postexposure prophylaxis of HIV infection following occupational exposure (PEP) in health-care personnel and others exposed via percutaneous injury (e.g., needlestick, cut with sharp object) or mucous membrane or nonintact skin (e.g., chapped, abraded, dermatitis) contact with blood, tissue, or other body fluids that might contain HIV.

USPHS recommends a 3-drug regimen of raltegravir and emtricitabine and tenofovir disoproxil fumarate (tenofovir DF) as preferred regimen for PEP following occupational exposures to HIV. Fosamprenavir (with or without low-dose ritonavir) and 2 NRTIs can be considered an alternative regimen, but use for PEP only with expert consultation. Preferred dual NRTI option for PEP regimens is emtricitabine and tenofovir DF; alternatives are tenofovir DF and lamivudine, zidovudine and lamivudine, or zidovudine and emtricitabine.

Management of occupational exposures to HIV is complex and evolving; consult infectious disease specialist, clinician with expertise in administration of antiretroviral agents, and/or National Clinicians’ Postexposure Prophylaxis Hotline (PEPline at 888-448-4911) whenever possible. Do not delay initiation of PEP while waiting for expert consultation.

Postexposure Prophylaxis following Nonoccupational Exposure to HIV (nPEP)

Postexposure prophylaxis of HIV infection following nonoccupational exposure (nPEP) in individuals exposed to blood, genital secretions, or other potentially infectious body fluids that might contain HIV when the exposure represents a substantial risk for HIV transmission. Used in conjunction with other antiretrovirals.

When nPEP indicated in adults and adolescents ≥13 years of age with normal renal function, CDC states preferred regimen is either raltegravir or dolutegravir used in conjunction with emtricitabine and tenofovir DF (given as emtricitabine/tenofovir DF; Truvada); recommended alternative in these patients is ritonavir-boosted darunavir used in conjunction with emtricitabine/tenofovir DF.

CDC states that fosamprenavir is an alternative antiretroviral that can be used in nPEP regimens, but use in such regimens only with expert consultation.

Consult infectious disease specialist, clinician with expertise in administration of antiretroviral agents, and/or the National Clinicians’ Postexposure Prophylaxis Hotline (PEPline at 888-448-4911) if nPEP indicated in certain exposed individuals (e.g., pregnant women, children, those with medical conditions such as renal impairment) or if considering a regimen not included in CDC guidelines, source virus is known or likely to be resistant to antiretrovirals, or healthcare provider is inexperienced in prescribing antiretrovirals. Do not delay initiation of nPEP while waiting for expert consultation.

Fosamprenavir Dosage and Administration

Administration

Oral Administration

Administer orally with low-dose ritonavir (ritonavir-boosted fosamprenavir) or without low-dose ritonavir (unboosted fosamprenavir). (See Dosage under Dosage and Administration.)

Oral Suspension

Pediatric patients: Take with food.

Adults: Take without food.

If vomiting occurs soon after a dose (within 30 minutes), repeat dose.

Taste of the suspension can be improved by refrigeration.

Shake vigorously prior to each dose.

Tablets

Take with or without food.

Dosage

Available as fosamprenavir calcium; dosage expressed in terms of fosamprenavir.

Pediatric Patients

Children 4 weeks to 18 years of age: Dosage is based on weight. Do not exceed adult dosage.

Do not use once-daily regimen (with or without low-dose ritonavir) in pediatric patients.

Do not use twice-daily regimen (with low-dose ritonavir) in PI-experienced children <6 months of age.

Do not use twice-daily regimen (without low-dose ritonavir) in PI-naive or PI-experienced children <2 years of age.

Treatment of HIV Infection
Antiretroviral-naive Pediatric Patients
Oral

PI-naive children ≥4 weeks of age (oral suspension): Twice-daily regimen with low-dose ritonavir. (See Table 1.)

Table 1. Dosage of Ritonavir-boosted Fosamprenavir in PI-naive Pediatric Patients 4 Week of Age or Older1

Weight (kg)

Fosamprenavir Dosage (Oral Suspension)

Ritonavir Dosage

<11

45 mg/kg twice daily

7 mg/kg twice daily

11 to <15

30 mg/kg twice daily

3 mg/kg twice daily

15 to <20

23 mg/kg twice daily

3 mg/kg twice daily

≥20

18 mg/kg twice daily

3 mg/kg twice daily

PI-naive children ≥2 years of age (oral suspension): 30 mg/kg twice daily (without low-dose ritonavir).

PI-naive children weighing ≥39 kg (tablets): 700 mg twice daily with low-dose ritonavir (100 mg twice daily).

PI-naive children ≥2 years of age weighing ≥47 kg (tablets): 1.4 g twice daily (without low-dose ritonavir).

Antiretroviral-experienced Pediatric Patients
Oral

PI-experienced children ≥6 months of age (oral suspension): Twice-daily regimen with low-dose ritonavir. (See Table 2.)

Table 2. Dosage of Ritonavir-boosted Fosamprenavir in PI-experienced Pediatric Patients 6 months of Age or Older1

Weight (kg)

Fosamprenavir Dosage (Oral Suspension)

Ritonavir Dosage

<11

45 mg/kg twice daily

7 mg/kg twice daily

11 to <15

30 mg/kg twice daily

3 mg/kg twice daily

15 to <20

23 mg/kg twice daily

3 mg/kg twice daily

≥20

18 mg/kg twice daily

3 mg/kg twice daily

PI-experienced children ≥6 months of age weighing ≥39 kg (tablets): 700 mg twice daily with low-dose ritonavir (100 mg twice daily).

PI-experienced children ≥2 years of age or older weighing ≥47 kg (tablets): 1.4 g twice daily (without low-dose ritonavir).

Adults

Treatment of HIV Infection
Antiretroviral-naive Adults
Oral

1.4 g twice daily (without low-dose ritonavir).

1.4 g once daily with low-dose ritonavir (100 or 200 mg once daily). Alternatively, 700 mg twice daily with low-dose ritonavir (100 mg twice daily).

Antiretroviral-experienced Adults
Oral

PI-experienced adults: 700 mg twice daily with low-dose ritonavir (100 mg twice daily). Once-daily regimen not recommended.

Postexposure Prophylaxis following Occupational Exposure to HIV (PEP)†
Oral

1.4 g once daily with low-dose ritonavir (100 mg once daily). Alternatively, 1.4 g twice daily (without low-dose ritonavir). Use in conjunction with 2 NRTIs (see Postexposure Prophylaxis following Occupational Exposure to HIV under Uses).

Initiate PEP as soon as possible following occupational exposure to HIV (preferably within hours); continue for 4 weeks, if tolerated.

Prescribing Limits

Pediatric Patients

Treatment of HIV Infection
Oral

Maximum 1.4 g twice daily (without low-dose ritonavir) or 700 mg twice daily with low-dose ritonavir (100 mg twice daily). Do not exceed adult dosage.

Adults

Treatment of HIV Infection
Antiretroviral-naive Adults
Oral

Maximum 1.4 g once daily with low-dose ritonavir (200 mg once daily) or 700 mg twice daily with low-dose ritonavir (100 mg twice daily). Higher than recommended dosages of fosamprenavir and/or ritonavir associated with increased serum transaminase concentrations; higher dosages not recommended.

Antiretroviral-experienced Adults
Oral

Maximum 700 mg twice daily with low-dose ritonavir (100 mg twice daily). Higher than recommended dosages of fosamprenavir and/or ritonavir associated with increased serum transaminase concentrations; higher dosages not recommended.

Special Populations

Hepatic Impairment

Fosamprenavir (with or without low-dose ritonavir): Use with caution in patients with hepatic impairment. Dosage reductions necessary in adults; data not available to support dosage recommendations for pediatric patients.

Mild hepatic impairment (Child-Pugh score 5–6): In antiretroviral-naive adults, fosamprenavir 700 mg twice daily with low-dose ritonavir (100 mg once daily) or fosamprenavir 700 mg twice daily (without low-dose ritonavir). In PI-experienced adults, fosamprenavir 700 mg twice daily with low-dose ritonavir (100 mg once daily).

Moderate hepatic impairment (Child-Pugh score 7–9): In antiretroviral-naive adults, fosamprenavir 450 mg twice daily with low-dose ritonavir (100 mg once daily) or fosamprenavir 700 mg twice daily (without low-dose ritonavir). In PI-experienced adults, fosamprenavir 450 mg twice daily with low-dose ritonavir (100 mg once daily).

Severe hepatic impairment (Child-Pugh score 10–15): In antiretroviral-naive adults, fosamprenavir 300 mg twice daily with low-dose ritonavir (100 mg once daily) or fosamprenavir 350 mg twice daily (without low-dose ritonavir). In PI-experienced adults, fosamprenavir 300 mg twice daily with low-dose ritonavir (100 mg once daily).

Renal Impairment

Dosage adjustments not necessary.

Geriatric Patients

Select dosage with caution because of age-related decreases in hepatic, renal, and/or cardiac function and concomitant disease and drug therapy.

Cautions for Fosamprenavir

Contraindications

  • Known hypersensitivity to fosamprenavir, amprenavir (no longer commercially available in the US), or any ingredient in the formulation.

  • Concomitant use with drugs highly dependent on CYP3A4 for metabolism and for which elevated plasma concentrations are associated with serious and/or life-threatening events (e.g., alfuzosin, cisapride, ergot alkaloids, pimozide, sildenafil used for treatment of pulmonary arterial hypertension [PAH], lovastatin, simvastatin, midazolam, triazolam). (See Specific Drugs under Interactions.)

  • Concomitant use with drugs that may lead to loss of virologic response (e.g., rifampin, St. John's wort [Hypericum perforatum]). (See Specific Drugs under Interactions.)

  • Concomitant use of a ritonavir-boosted fosamprenavir regimen and flecainide or propafenone. (See Antiarrhythmic Agents under Interactions.)

Warnings/Precautions

Sensitivity Reactions

Dermatologic and Hypersensitivity Reactions

Rash (usually maculopapular and of mild to moderate intensity, with or without pruritus) reported. Severe and life-threatening skin reactions, including Stevens-Johnson syndrome, reported rarely.

Discontinue if severe or life-threatening rash or moderate rash accompanied by systemic symptoms occurs.

Sulfonamide Sensitivity

Because fosamprenavir contains a sulfonamide moiety, use with caution in patients with known sulfonamide allergy.

Potential for cross-sensitivity between sulfonamide drugs and fosamprenavir unknown.

Interactions

When ritonavir-boosted fosamprenavir is used, the usual cautions, precautions, and contraindications associated with ritonavir should be considered.

Serious, life-threatening, or fatal drug interactions or loss of virologic effect can occur with some drugs. (See Contraindications under Cautions and Specific Drugs under Interactions.)

Consider potential for drug interactions prior to and during ritonavir-boosted fosamprenavir therapy; review all drugs patient is receiving and monitor for adverse effects.

Hepatic Effects

HIV-infected patients with HBV or HCV coinfection or marked elevations in transaminase concentrations prior to fosamprenavir therapy may be at increased risk for developing transaminase elevations.

Perform appropriate laboratory tests to evaluate hepatic function prior to initiating fosamprenavir and monitor patients closely during treatment. (See Hepatic Impairment under Cautions.)

Use of fosamprenavir with ritonavir at higher than recommended dosages may result in elevated transaminase concentrations.

Hyperglycemic and Diabetogenic Effects

Hyperglycemia (potentially persistent), new-onset diabetes mellitus, or exacerbation of preexisting diabetes mellitus reported with use of PIs; diabetic ketoacidosis has occurred.

Monitor blood glucose and initiate or adjust dosage of insulin or oral hypoglycemic agents as needed.

Immune Reconstitution Syndrome

During initial treatment, patients who respond to antiretroviral therapy may develop an inflammatory response to indolent or residual opportunistic infections (e.g., Mycobacterium avium complex [MAC], M. tuberculosis, cytomegalovirus [CMV], Pneumocystis jirovecii [formerly P. carinii]); this may necessitate further evaluation and treatment.

Autoimmune disorders (e.g., Graves' disease, polymyositis, Guillain-Barré syndrome) also reported in the setting of immune reconstitution; time to onset is more variable and can occur many months after initiation of antiretroviral therapy.

Adipogenic Effects

Possible redistribution or accumulation of body fat, including central obesity, dorsocervical fat enlargement (buffalo hump), peripheral wasting, facial wasting, breast enlargement, and general cushingoid appearance. Mechanism and long-term consequences of fat redistribution unknown; causal relationship not established.

Evaluate patients for physical signs of fat redistribution.

Lipid Effects

Increases in triglyceride and cholesterol concentrations have occurred with ritonavir-boosted fosamprenavir. HIV infection itself is associated with lipid disorders.

Determine serum triglyceride and cholesterol concentrations prior to initiating fosamprenavir and periodically monitor during therapy; manage lipid disorders as clinically appropriate. (See HMG-CoA Reductase Inhibitors under Interactions.)

Hematologic Effects

Neutropenia has been reported with fosamprenavir; acute hemolytic anemia has been reported in at least one patient who received amprenavir (no longer commercially available in the US).

Hemophilia A and B

Spontaneous bleeding reported with PIs; causal relationship not established.

Increased hemostatic therapy (e.g., antihemophilic factor) may be needed.

Nephrolithiasis

Nephrolithiasis reported during postmarketing experience. If signs or symptoms of nephrolithiasis occur, consider temporarily interrupting or discontinuing fosamprenavir.

HIV Resistance

Possible amprenavir resistance in patients treated with fosamprenavir. The possible effect of fosamprenavir therapy on subsequent therapy with other PIs unknown.

Cardiovascular Effects

Postmarketing reports of myocardial infarction in patients receiving fosamprenavir. Possible association between cumulative exposure to fosamprenavir/amprenavir and increased risk of myocardial infarction. Higher relative risk of myocardial infarction reported with PIs compared with other antiretroviral drug classes, possibly due to ability of PIs to elevate serum lipid concentrations. HIV infection itself is associated with ischemic heart disease.

Monitor modifiable risk factors for cardiovascular disease (e.g., hypertension, diabetes, smoking) and manage as clinically appropriate. Individualize treatment, carefully considering risks and benefits of continued treatment.

Specific Populations

Pregnancy

Category C.

Antiretroviral Pregnancy Registry at 800-258-4263 or [Web].

Some experts state data insufficient to recommend routine use of fosamprenavir for initial treatment in antiretroviral-naive pregnant women; if the drug is used in pregnant women, these experts state ritonavir-boosted fosamprenavir must be used.

Lactation

Distributed into milk in rats; not known whether distributed into human milk.

Instruct HIV-infected women not to breast-feed because of risk of HIV transmission and risk of adverse effects in the infant.

Pediatric Use

Safety and efficacy not established in PI-naive children <4 weeks of age or in PI-experienced children <6 months of age.

In PI-naive infants, use only in those born at ≥38 weeks gestation who have attained postnatal age of ≥28 days.

Do not use once-daily regimen (with or without low-dose ritonavir) in pediatric patients.

Do not use twice-daily regimen (without low-dose ritonavir) in pediatric patients <2 years of age.

Experts state consider use of ritonavir-boosted fosamprenavir for initial treatment only in pediatric patients ≥6 months of age and only in special circumstances; experts also state do not use fosamprenavir (without low-dose ritonavir) in pediatric patients of any age. (See Treatment of HIV Infection under Uses.)

Adverse effects in pediatric patients similar to those reported in adults; vomiting and neutropenia reported more frequently than in adults.

Geriatric Use

Insufficient experience in those ≥65 years of age to determine whether they respond differently from younger adults.

Select dosage with caution because of age-related decreases in hepatic, renal, and/or cardiac function and concomitant disease and drug therapy.

Hepatic Impairment

Use with caution because concentrations may be increased; assess hepatic function prior to and periodically during therapy.

Dosage adjustments necessary in adults with hepatic impairment (Child-Pugh score 5 or greater); data not available to support dosage recommendations for pediatric patients. (See Hepatic Impairment under Dosage and Administration.)

Increased risk for further elevations in hepatic enzyme concentrations in HIV-infected patients with chronic HBV or HCV coinfection and those with marked increases in AST or ALT concentrations prior to fosamprenavir therapy.

Common Adverse Effects

Diarrhea, nausea, vomiting, headache, rash.

Interactions for Fosamprenavir

Amprenavir (active metabolite of fosamprenavir) is metabolized by CYP3A4.

Amprenavir inhibits CYP3A4 and also may induce CYP3A4.

Amprenavir does not inhibit CYP2D6, 1A2, 2C9, 2C19, or P2E1 or uridine glucuronosyltransferase (UDPGT).

Some interaction studies have been performed using fosamprenavir. These studies may not predict magnitude of interaction with ritonavir-boosted fosamprenavir.

Since fosamprenavir is metabolized to amprenavir, interactions reported with amprenavir (no longer commercially available in the US) also apply to fosamprenavir.

When fosamprenavir is used with low-dose ritonavir, consider interactions reported with low-dose ritonavir.

Drugs Affecting or Metabolized by Hepatic Microsomal Enzymes

Pharmacokinetic interactions likely with drugs that are inhibitors or substrates of CYP3A4 with possible alteration in metabolism of amprenavir and/or the other drug.

Drugs Affecting or Affected by P-glycoprotein Transport

Amprenavir is a substrate of and an inducer of P-glycoprotein (P-gp) transport system.

Specific Drugs

Drug

Interaction

Comments

Abacavir

Studies using amprenavir indicate pharmacokinetic interaction unlikely

In vitro evidence of synergistic antiretroviral effects

Alfuzosin

Potential for increased alfuzosin concentrations that could result in hypotension

Concomitant use with fosamprenavir (with or without low-dose ritonavir) is contraindicated

Antacids

Decreased amprenavir concentrations and AUC

Manufacturer of fosamprenavir states interaction not considered clinically important and makes no restrictions for concomitant use with antacids

Some experts recommend fosamprenavir be given simultaneously with or at least 2 hours before or 1 hour after antacids

Antiarrhythmic agents (amiodarone, dronedarone, flecainide, systemic lidocaine, propafenone, quinidine)

Possible increased antiarrhythmic agent concentrations

Potential for serious or life-threatening effects (e.g., cardiac arrhythmias) if ritonavir-boosted fosamprenavir used in patients receiving flecainide or propafenone

Potential for serious or life-threatening effects (e.g., cardiac arrhythmias) if fosamprenavir used in conjunction with amiodarone, systemic lidocaine, or quinidine

In patients receiving ritonavir-boosted fosamprenavir, concomitant use with flecainide or propafenone contraindicated

Caution if fosamprenavir used concomitantly with amiodarone, systemic lidocaine, or quinidine; antiarrhythmic concentration monitoring recommended

Amiodarone or dronedarone: Some experts state do not use concomitantly with fosamprenavir (with or without low-dose ritonavir)

Anticoagulants, oral

Apixaban, edoxaban, rivaroxaban: Increased anticoagulant concentrations

Dabigatran: Possible increased dabigatran concentrations

Warfarin: Possible altered warfarin concentrations

Apixaban, edoxaban, rivaroxaban: Avoid concomitant use

Dabigatran: Dosage adjustments not needed in patients with Clcr >50 mL/minute; avoid concomitant use in those with Clcr <50 mL/minute

Warfarin: Monitor INR, especially when initiating or discontinuing fosamprenavir; adjust warfarin dosage as needed

Anticonvulsants (carbamazepine, ethosuximide, lamotrigine, phenobarbital, phenytoin)

Carbamazepine, phenobarbital, phenytoin: Possible decreased amprenavir concentrations and decreased virologic response when used with unboosted fosamprenavir

Carbamazepine, phenobarbital: Possible increased carbamazepine concentrations and decreased amprenavir concentrations when used with ritonavir-boosted fosamprenavir

Ethosuximide: Possible increased ethosuximide concentrations

Lamotrigine: Possible decreased lamotrigine concentrations if used concomitantly with ritonavir-boosted fosamprenavir

Phenytoin: Increased amprenavir concentrations and decreased phenytoin concentrations when used with ritonavir-boosted fosamprenavir

Carbamazepine, phenobarbital, phenytoin: Use concomitantly with unboosted fosamprenavir with caution; some experts state do not use concomitantly with unboosted fosamprenavir

Carbamazepine, phenobarbital: If using ritonavir-boosted fosamprenavir, consider alternative anticonvulsant or monitor concentrations of the anticonvulsant and amprenavir and assess antiretroviral response

Ethosuximide: Monitor for ethosuximide toxicity

Lamotrigine: If used with ritonavir-boosted fosamprenavir, consider increasing lamotrigine dosage and monitoring lamotrigine concentrations; alternatively, consider alternative anticonvulsant

Phenytoin: Usual dosages of ritonavir-boosted fosamprenavir may be used, but monitor phenytoin concentrations and increase phenytoin dosage as needed

Antifungals, azoles (itraconazole, isavuconazonium, ketoconazole, posaconazole, voriconazole)

Itraconazole: Possible increased antifungal and amprenavir concentrations

Isavuconazonium (prodrug of isavuconazole): Possible increased isavuconazole concentrations and altered fosamprenavir concentrations if used concomitantly with fosamprenavir (without low-dose ritonavir)

Ketoconazole: Possible increased ketoconazole concentrations with fosamprenavir (with or without low-dose ritonavir)

Posaconazole: Decreased posaconazole AUC and increased amprenavir concentrations when used concomitantly with fosamprenavir (without low-dose ritonavir); increased posaconazole and amprenavir concentrations when used with ritonavir-boosted fosamprenavir

Voriconazole: Although specific data not available on interaction with ritonavir-boosted fosamprenavir, studies using low-dose ritonavir and voriconazole indicate decreased voriconazole concentrations; in addition, fosamprenavir (without low-dose ritonavir) possibly may result in increased concentrations of both drugs

Itraconazole: In patients receiving fosamprenavir (with or without low-dose ritonavir), consider monitoring itraconazole concentrations to guide dosage adjustments; in those receiving fosamprenavir (without low-dose ritonavir), may need to reduce antifungal dosage in those receiving >400 mg of itraconazole daily; in those receiving ritonavir-boosted fosamprenavir, itraconazole dosage >200 mg daily not recommended unless plasma concentrations are monitored

Isavuconazonium: If used with fosamprenavir (with or without low-dose ritonavir), consider monitoring isavuconazole concentrations and monitor for fosamprenavir-associated adverse effects and virologic response

Ketoconazole: In patients receiving fosamprenavir (without low-dose ritonavir), may need to reduce antifungal dosage in those receiving >400 mg of ketoconazole daily; in those receiving ritonavir-boosted fosamprenavir, use caution and ketoconazole dosage >200 mg daily not recommended

Posaconazole: If used with fosamprenavir (without low-dose ritonavir), monitor posaconazole concentrations; if used with ritonavir-boosted fosamprenavir, consider monitoring posaconazole concentrations and monitor for fosamprenavir-associated adverse effects

Voriconazole: Monitor for toxicities if used with fosamprenavir (without low-dose ritonavir); do not use with ritonavir-boosted fosamprenavir unless potential benefits outweigh risks; if used with ritonavir-boosted fosamprenavir, consider monitoring voriconazole concentrations and adjusting voriconazole dosage accordingly

Antimycobacterials (bedaquiline, rifabutin, rifampin, rifapentine)

Bedaquiline: Possible increased bedaquiline concentrations; clinical importance unknown

Rifabutin: 150 mg every other day with ritonavir-boosted fosamprenavir results in increased amprenavir concentrations and increased rifabutin metabolite concentrations compared with rifabutin 300 mg daily alone

Rifampin: Studies using amprenavir indicate decreased amprenavir concentrations; possible decreased antiretroviral efficacy and increased risk of antiretroviral resistance

Rifapentine: Possible decreased fosamprenavir concentrations

Bedaquiline: Use concomitantly with ritonavir-boosted fosamprenavir with caution and only if potential benefits outweigh risks; monitor for QTc interval prolongation and liver dysfunction

Rifabutin: If fosamprenavir (without low-dose ritonavir) used with rifabutin, reduce rifabutin dosage by at least 50% (150 mg once daily or 300 mg 3 times weekly has been suggested); if ritonavir-boosted fosamprenavir used with rifabutin, reduce rifabutin dosage by at least 75% (maximum dosage of 150 mg once every other day or 3 times weekly); monitor for neutropenia by performing CBCs weekly and as clinically indicated; monitor for antimycobacterial response and consider therapeutic drug monitoring

Rifampin: Concomitant use contraindicated

Rifapentine: Concomitant use not recommended

Antiplatelet agents (ticagrelor, vorapaxar)

Ticagrelor, vorapaxar: Increased antiplatelet agent concentrations expected

Ticagrelor, vorapaxar: Avoid concomitant use

Antipsychotics (lurasidone, perphenazine, pimozide, quetiapine, risperidone, thioridazine)

Lurasidone: Potential for serious and/or life-threatening adverse effects if used concomitantly with ritonavir-boosted fosamprenavir

Perphenazine, risperidone, thioridazine: Possible increased antipsychotic concentrations if used concomitantly with ritonavir-boosted fosamprenavir

Pimozide: Possible increased pimozide concentrations; potential for serious and/or life-threatening effects (e.g., cardiac arrhythmias)

Quetiapine: Increased quetiapine concentrations expected

Lurasidone: Concomitant use with ritonavir-boosted fosamprenavir contraindicated; if concomitant use with unboosted fosamprenavir necessary, reduce lurasidone dosage

Perphenazine, risperidone, thioridazine: If used with ritonavir-boosted fosamprenavir, initiate antipsychotic at lowest dosage and adjust maintenance dosage; monitor for toxicities associated with the antipsychotic

Pimozide: Concomitant use contraindicated

Quetiapine: Initiate quetiapine at lowest dosage and titrate as needed; if initiating fosamprenavir (with or without low-dose ritonavir) in patient receiving quetiapine, reduce quetiapine to one-sixth of original dosage; monitor for efficacy and adverse effects of quetiapine

Atazanavir

Ritonavir-boosted fosamprenavir: Decreased atazanavir concentrations and AUC; no change in amprenavir concentrations and AUC

Fosamprenavir (without low-dose ritonavir): No data

In vitro evidence of synergistic antiretroviral effects

Fosamprenavir (with or without low-dose ritonavir): Appropriate dosages for concomitant use with respect to safety and efficacy not established

Avanafil

Possible increased avanafil concentrations and AUC if used concomitantly with fosamprenavir (with or without low-dose ritonavir)

If avanafil used for treatment of erectile dysfunction, do not exceed avanafil dosage of 50 mg once every 24 hours; concomitant use with ritonavir-boosted fosamprenavir not recommended

β-adrenergic blocking agents (atenolol, labetalol, metoprolol, nadolol, sotalol, timolol)

Metoprolol, timolol: Possible increased concentrations of the β-blocker

Metoprolol, timolol: Decrease in β-blocker dosage may be needed based on clinical response; consider using certain β-blockers not metabolized by CYP isoenzymes (e.g., atenolol, labetalol, nadolol, sotalol)

Benzodiazepines (alprazolam, clonazepam, clorazepate, diazepam, flurazepam, midazolam, triazolam)

Midazolam or triazolam: Possible increased concentrations of midazolam or triazolam; potential for serious and/or life-threatening effects (e.g., prolonged or increased sedation or respiratory depression)

Other benzodiazepines: Possible increased concentrations of alprazolam, clonazepam, clorazepate, diazepam, flurazepam

Midazolam or triazolam: Manufacturer of fosamprenavir states that concomitant use is contraindicated; some experts state a single parenteral dose of midazolam can be used with caution in a monitored situation for procedural sedation; consider an alternative benzodiazepine metabolized by non-CYP pathways (e.g., lorazepam, oxazepam, temazepam)

Other benzodiazepines: Clinical importance of pharmacokinetic interaction unknown; a decrease in benzodiazepine dosage may be needed

Bosentan

Increased bosentan concentrations

In patients already receiving fosamprenavir (with or without low-dose ritonavir) for ≥10 days, initiate bosentan using a dosage of 62.5 mg once daily or every other day based on individual tolerability

In patients already receiving bosentan, discontinue bosentan for at least 36 hours prior to initiating fosamprenavir (with or without low-dose ritonavir); after ≥10 days of fosamprenavir, resume bosentan using a dosage of 62.5 mg once daily or every other day based on individual tolerability

Buprenorphine

No clinically important pharmacokinetic interactions

Ritonavir-boosted fosamprenavir: Dosage adjustments not necessary; clinical monitoring recommended; if route of buprenorphine administration changed from transmucosal to subdermal implantation, monitor patient to ensure effect of buprenorphine is adequate and not excessive

Buspirone

Increased buspirone concentrations expected

Use low dosage of buspirone with caution and titrate based on clinical response

Calcium-channel blocking agents (diltiazem, felodipine, nifedipine, nicardipine, nimodipine, verapamil, amlodipine, nisoldipine, isradipine)

Possible increased concentrations of calcium-channel blocking agent

Use concomitantly with caution; clinical monitoring recommended

Cisapride

Possible increased cisapride concentrations; potential for serious and/or life-threatening effects (e.g., cardiac arrhythmias)

Concomitant use contraindicated

Clarithromycin

Ritonavir-boosted fosamprenavir: Possible increased clarithromycin concentrations

Studies using amprenavir indicate increased amprenavir concentrations and AUC and slightly decreased clarithromycin concentrations

Fosamprenavir (without low-dose ritonavir): Dosage adjustment not needed

Ritonavir-boosted fosamprenavir: Consider alternative macrolide (e.g., azithromycin); if used concomitantly, monitor for clarithromycin-related toxicities

Ritonavir-boosted fosamprenavir: Some experts recommend reduce clarithromycin dosage by 50% if Clcr 30–60 mL/minute and reduce by 75% if Clcr <30 mL/minute

Colchicine

Increased colchicine concentrations

Patients with renal or hepatic impairment: Concomitant use of colchicine and ritonavir-boosted fosamprenavir not recommended

Colchicine for treatment of gout flares: In those receiving ritonavir-boosted fosamprenavir, use initial colchicine dose of 0.6 mg followed by 0.3 mg 1 hour later and repeat dose no earlier than 3 days later; in those receiving fosamprenavir (without low-dose ritonavir), use initial colchicine dose of 1.2 mg and repeat dose no earlier than 3 days later

Colchicine for prophylaxis of gout flares: In those receiving ritonavir-boosted fosamprenavir, decrease colchicine dosage to 0.3 mg once daily in those originally receiving 0.6 mg twice daily or decrease dosage to 0.3 mg once every other day in those originally receiving 0.6 once daily; in those receiving fosamprenavir (without low-dose ritonavir), decrease colchicine dosage to 0.3 mg twice daily or 0.6 mg once daily in those originally receiving 0.6 mg twice daily or decrease dosage to 0.3 mg once daily in those originally receiving 0.6 mg once daily

Colchicine for treatment of familial Mediterranean fever (FMF): In those receiving ritonavir-boosted fosamprenavir, use maximum colchicine dosage of 0.6 mg daily (may be given as 0.3 mg twice daily); in those receiving fosamprenavir (without low-dose ritonavir), use maximum colchicine dosage of 1.2 mg daily (may be given as 0.6 mg twice daily)

Corticosteroids (beclomethasone, budesonide, dexamethasone, fluticasone, methylprednisolone, prednisolone, prednisone, triamcinolone)

Beclomethasone (orally inhaled, intranasal): Clinically important pharmacokinetic interactions not expected

Budesonide or fluticasone (orally inhaled, intranasal): Increased corticosteroid concentrations; may result in adrenal insufficiency, including Cushing's syndrome

Methylprednisolone, prednisolone, triamcinolone (intra-articular or other local injections): Increased corticosteroid concentrations; may result in adrenal insufficiency, including Cushing's syndrome

Budesonide or prednisone (systemic): Increased corticosteroid concentrations; may result in adrenal insufficiency, including Cushing's syndrome

Dexamethasone (systemic): Possible decreased amprenavir concentrations and decreased antiretroviral efficacy

Budesonide or fluticasone (orally inhaled, intranasal): Do not use concomitantly unless potential benefits of inhaled corticosteroid outweigh risks of systemic corticosteroid adverse effects; consider alternative (e.g., beclomethasone), especially when long-term corticosteroid use anticipated

Methylprednisolone, prednisolone, triamcinolone (intra-articular or other local injections): Do not use concomitantly; consider alternative nonsteroidal therapies; if intra-articular corticosteroid required, use alternative antiretroviral that does not alter CYP3A4 activity (e.g., dolutegravir, raltegravir)

Budesonide or prednisone (systemic): Do not use concomitantly unless potential benefits outweigh risks of systemic corticosteroid adverse effects

Dexamethasone (systemic): Use concomitantly with caution; consider alternative corticosteroid for long-term use

Daclatasvir

No effect on daclatasvir concentrations if used concomitantly with fosamprenavir (with or without low-dose ritonavir)

Dosage adjustments not needed

Darunavir

Data not available regarding concomitant use of darunavir and fosamprenavir (with or without low-dose ritonavir)

Delavirdine

Studies using amprenavir indicate possible increased amprenavir concentrations and AUC and possible decreased delavirdine plasma concentrations and AUC; possible decreased antiretroviral efficacy and increased risk of antiretroviral resistance

In vitro evidence of synergistic antiretroviral effects

Concomitant use contraindicated

Didanosine

In vitro evidence of synergistic antiretroviral effects

Dolutegravir

Ritonavir-boosted fosamprenavir: Decreased dolutegravir concentrations and AUC; effect on fosamprenavir pharmacokinetics unlikely

No in vitro evidence of antagonistic antiretroviral effects with amprenavir

Ritonavir-boosted fosamprenavir: In integrase strand transfer inhibitor-naive (INSTI-naive) patients, use dolutegravir 50 mg twice daily; in INSTI-experienced patients with documented or suspected INSTI resistance, consider alternative to ritonavir-boosted fosamprenavir whenever possible

Efavirenz

Substantially decreased amprenavir concentrations if used with fosamprenavir (without low-dose ritonavir); additional pharmacokinetic interactions if used with ritonavir-boosted fosamprenavir

In vitro evidence of synergistic antiretroviral effects

Fosamprenavir (without low-dose ritonavir): Appropriate dosages for concomitant use with respect to safety and efficacy not established

Ritonavir-boosted fosamprenavir: Use usual efavirenz dosage with fosamprenavir 1.4 g once daily and ritonavir 300 mg once daily or, alternatively, fosamprenavir 700 mg twice daily and ritonavir 100 mg twice daily

Elbasvir and grazoprevir

Fixed combination of elbasvir and grazoprevir (elbasvir/grazoprevir): No data

Elvitegravir

Cobicistat-boosted elvitegravir: Altered concentrations of elvitegravir, cobicistat, and/or fosamprenavir if used with fosamprenavir (with or without low-dose ritonavir)

Cobicistat-boosted elvitegravir: Do not used concomitantly with fosamprenavir (with or without low-dose ritonavir)

Eplerenone

Increased eplerenone concentrations expected

Experts state concomitant use contraindicated

Ergot alkaloids (dihydroergotamine, ergotamine, methylergonovine)

Possible increased concentrations of ergot alkaloids and potential for serious and/or life-threatening effects such as ergot toxicity (peripheral vasospasm and ischemia of the extremities and other tissues)

Concomitant use contraindicated

If treatment of uterine atony and excessive postpartum bleeding is indicated in a woman receiving fosamprenavir, use methylergonovine maleate (Methergine) only if alternative treatments cannot be used and if potential benefits outweigh risks; use methylergonovine at lowest dosage and shortest duration possible

Estrogens/progestins

Hormonal contraceptive containing ethinyl estradiol 35 mcg with norethindrone 0.5 mg per tablet: Decreased ethinyl estradiol and norethindrone concentrations with ritonavir-boosted fosamprenavir; clinically important increase in serum transaminase concentrations

Hormonal contraceptives: Possible loss of virologic response if used with fosamprenavir (without low-dose ritonavir)

Subdermal implants containing etonogestrel, transdermal systems containing ethinyl estradiol and norelgestromin: No data

Hormonal contraceptives: Consider alternative or additional contraception methods or consider alternative antiretroviral regimen

Subdermal implants containing etonogestrel, transdermal systems containing ethinyl estradiol and norelgestromin: Consider alternative or additional methods of contraception or consider alternative antiretroviral regimen

Etravirine

Fosamprenavir (with or without low-dose ritonavir): Substantially increased amprenavir concentrations

Fosamprenavir (with or without low-dose ritonavir): Do not administer concomitantly

Flibanserin

Increased flibanserin concentrations expected

Experts state concomitant use contraindicated

Fluvoxamine

Possible altered fosamprenavir concentrations

Consider alternative antidepressant or alternative antiretroviral therapy

Histamine H2-receptor antagonists (cimetidine, famotidine, nizatidine, ranitidine)

Decreased amprenavir plasma concentrations and AUC; possible decreased antiretroviral efficacy

Use concomitantly with caution; administer fosamprenavir (without low-dose ritonavir) at least 2 hours before the H2-receptor antagonist; consider using ritonavir-boosted fosamprenavir

HMG-CoA reductase inhibitors (statins)

Atorvastatin, lovastatin, rosuvastatin, simvastatin: Increased concentrations and AUCs of the statin; increased risk of statin-associated adverse effects, including myopathy and rhabdomyolysis

Atorvastatin: Do not exceed atorvastatin dosage of 20 mg daily in patients receiving fosamprenavir (with or without low-dose ritonavir); carefully titrate atorvastatin dosage; use lowest necessary dosage with close monitoring for adverse effects

Lovastatin: Concomitant use with fosamprenavir (with or without low-dose ritonavir) contraindicated

Pitavastatin: Dosage adjustments not necessary

Rosuvastatin: Dosage adjustments not necessary

Simvastatin: Concomitant use with fosamprenavir (with or without low-dose ritonavir) contraindicated

Immunosuppressive agents (cyclosporine, everolimus, sirolimus, tacrolimus)

Increased concentrations of immunosuppressive agent expected

Monitor immunosuppressive agent concentrations; some experts state initiate immunosuppressive agent with adjusted dosage to account for potential increased concentrations, monitor for toxicities, consult a specialist if needed

Indinavir

Fosamprenavir: Possible increased amprenavir concentrations and AUC; effect on indinavir concentrations not well established

Ritonavir-boosted fosamprenavir: Concomitant use not evaluated

In vitro evidence of additive antiretroviral effects

Fosamprenavir (with or without low-dose ritonavir): Appropriate dosages for concomitant use with respect to safety and efficacy not established

Ivabradine

Increased ivabradine concentrations expected

Experts state concomitant use contraindicated

Lamivudine

Studies using amprenavir indicate no evidence of pharmacokinetic interaction

In vitro evidence of synergistic antiretroviral effects

Ledipasvir and sofosbuvir

Fixed combination of ledipasvir and sofosbuvir (ledipasvir/sofosbuvir): Pharmacokinetic interactions not expected if used concomitantly with fosamprenavir (with or without low-dose ritonavir)

Concomitant use of ledipasvir/sofosbuvir and HIV antiretroviral regimen that includes ritonavir-boosted fosamprenavir and tenofovir DF: Possible increased tenofovir concentrations; safety of increased tenofovir concentrations not established

Ledipasvir/sofosbuvir: Dosage adjustments not needed if used concomitantly with fosamprenavir (with or without low-dose ritonavir)

Concomitant use of ledipasvir/sofosbuvir and HIV antiretroviral regimen that includes ritonavir-boosted fosamprenavir and tenofovir DF: Consider alternative HCV treatment or an alternative antiretroviral regimen; if concomitant use necessary, monitor patient for tenofovir-associated adverse effects

Lopinavir/ritonavir

Fosamprenavir: Decreased amprenavir concentrations and AUC; no change in lopinavir concentrations or AUC

Ritonavir-boosted fosamprenavir: Decreased amprenavir concentrations and AUC; altered lopinavir concentrations and AUC (decreased or increased)

Increased incidence of adverse effects reported

In vitro evidence of additive antiretroviral effects

Fosamprenavir (with or without low-dose ritonavir): Concomitant use not recommended; appropriate dosages for concomitant use with respect to safety and efficacy not established

Maraviroc

Increased maraviroc concentrations and AUC; decreased amprenavir concentrations and AUC

No in vitro evidence of antagonistic antiretroviral effects

Recommended maraviroc dosage is 150 mg twice daily with usual dosage of ritonavir-boosted fosamprenavir; do not use unboosted fosamprenavir

Methadone

Decreased methadone concentrations; opiate withdrawal unlikely but may occur

Methadone dosage may need to be adjusted; monitor for opiate withdrawal and increase methadone dosage as clinically indicated

Nelfinavir

Studies using amprenavir indicate concomitant use may affect pharmacokinetics of both drugs; concomitant use of ritonavir-boosted fosamprenavir and nelfinavir not evaluated

In vitro evidence of additive antiretroviral effects

Appropriate dosages for concomitant use with respect to safety and efficacy not established

Nevirapine

Fosamprenavir (without low-dose ritonavir): Decreased amprenavir AUC and increased nevirapine AUC

Ritonavir-boosted fosamprenavir (twice-daily regimen): Decreased amprenavir AUC and increased nevirapine AUC

Ritonavir-boosted fosamprenavir (once-daily regimen): Concomitant use with nevirapine not studied

In vitro evidence of additive antiretroviral effects

Fosamprenavir (without low-dose ritonavir): Concomitant use not recommended

RItonavir-boosted fosamprenavir (twice-daily regimen): Use usual nevirapine dosage with fosamprenavir 700 mg twice daily and ritonavir 100 mg twice daily

Ombitasvir, paritaprevir, ritonavir, and dasabuvir

Fosamprenavir (without low-dose ritonavir): Concomitant use with fixed combination of ombitasvir, paritaprevir, and ritonavir (ombitasvir/paritaprevir/ritonavir) with dasabuvir may result in increased paritaprevir and amprenavir concentrations

Ritonavir-boosted fosamprenavir: Increased paritaprevir concentrations expected if used concomitantly with ombitasvir/paritaprevir/ritonavir with dasabuvir; possible increased amprenavir concentrations

Fosamprenavir (without low-dose ritonavir): If used concomitantly with ombitasvir/paritaprevir/ritonavir with dasabuvir, dosage adjustments not established but fosamprenavir manufacturer states consider fosamprenavir 1.4 g once daily

Ritonavir-boosted fosamprenavir: Concomitant use with ombitasvir/paritaprevir/ritonavir with dasabuvir not recommended

Proton-pump inhibitors (esomeprazole, lansoprazole, omeprazole, pantoprazole, rabeprazole)

Esomeprazole: When used with fosamprenavir (without low-dose ritonavir), no change in amprenavir concentrations or AUC, and increased esomeprazole AUC; when used with ritonavir-boosted fosamprenavir, clinically important pharmacokinetic interaction unlikely

Can be administered at the same time as proton-pump inhibitors with no change in plasma amprenavir concentrations

Dosage adjustments of fosamprenavir (with or without low-dose ritonavir) not needed

Raltegravir

Fosamprenavir (with or without low-dose ritonavir): Decreased concentrations and AUCs of raltegravir and amprenavir

Fosamprenavir (with or without low-dose ritonavir): Appropriate dosage for concomitant use with respect to safety and efficacy not established; some experts state dosage adjustments not necessary

Rilpivirine

Possible increased rilpivirine concentrations; not expected to affect amprenavir concentrations

Some experts state dosage adjustments not necessary

Ritonavir

Increased plasma concentrations and AUC of amprenavir

Concomitant low-dose ritonavir used for therapeutic advantage (ritonavir-boosted fosamprenavir); increased potential for drug interactions since ritonavir is a potent inhibitor of CYP3A4 and also inhibits CYP2D6

In vitro evidence of additive antiretroviral effects

When ritonavir-boosted fosamprenavir is used in a once-daily regimen, recommended dosage is fosamprenavir 1.4 g once daily with ritonavir 100 or 200 mg once daily; when used in a twice-daily regimen, recommended dosage is fosamprenavir 700 mg twice with ritonavir 100 mg twice daily

Once-daily regimen of ritonavir-boosted fosamprenavir not recommended in PI-experienced patients

St. John’s wort (Hypericum perforatum)

Possible decreased amprenavir concentrations; possible decreased antiretroviral efficacy and increased risk of antiretroviral resistance

Concomitant use contraindicated

Salmeterol

Possible increased salmeterol concentrations and increased risk of salmeterol-associated adverse cardiovascular effects, including QT interval prolongation, palpitations, and sinus tachycardia

Concomitant use not recommended

Saquinavir

Decreased amprenavir concentrations

In vitro evidence of synergistic antiretroviral effects

Appropriate dosages for concomitant use with respect to safety and efficacy not established

Selective serotonin-reuptake inhibitors (SSRIs)

Paroxetine: Decreased SSRI concentrations with ritonavir-boosted fosamprenavir

Paroxetine: Titrate dosage of the SSRI based on clinical response and tolerability

Sildenafil

Possible increased sildenafil concentrations and increased risk of sildenafil-associated adverse effects (e.g., hypotension, syncope, visual disturbances, prolonged erection)

Sildenafil (Revatio) for treatment of pulmonary arterial hypertension (PAH): Concomitant use with fosamprenavir (with or without low-dose ritonavir) is contraindicated; fosamprenavir manufacturer states that a safe and effective dose for concomitant use not established

Sildenafil for treatment of erectile dysfunction: If used concomitantly with fosamprenavir (with or without low-dose ritonavir), do not exceed sildenafil dosage of 25 mg once every 48 hours and closely monitor for sildenafil-associated adverse effects (e.g., hypotension, syncope, visual disturbances, prolonged erection)

Simeprevir

Fosamprenavir (without low-dose ritonavir): Possible altered simeprevir concentrations; altered amprenavir concentrations not expected

Ritonavir-boosted fosamprenavir: Increased simeprevir concentrations expected; altered amprenavir concentrations not expected

Concomitant use with fosamprenavir (with or without low-dose ritonavir) not recommended

Stavudine

In vitro evidence of synergistic antiretroviral effects

Suvorexant

Increased suvorexant concentrations expected

Experts state concomitant use not recommended

Tadalafil

Possible increased tadalafil concentrations and increased risk of tadalafil-associated adverse effects (e.g., hypotension, syncope, visual disturbances, prolonged erection)

If tadalafil (Adcirca) is initiated for treatment of PAH in patients who have been receiving fosamprenavir (with or without low-dose ritonavir) for ≥1 week, use initial tadalafil dosage of 20 mg once daily and, if tolerated, increase dosage to 40 mg once daily

If fosamprenavir (with or without low-dose ritonavir) is indicated in patient already receiving tadalafil (Adcirca) for treatment of PAH, discontinue tadalafil for at least 24 hours prior to initiating fosamprenavir; after ≥1 week of the antiretroviral agent, resume tadalafil at dosage of 20 mg once daily and, if tolerated, increase dosage to 40 mg once daily

If tadalafil is used for treatment of erectile dysfunction in patients already receiving fosamprenavir (with or without low-dose ritonavir), do not exceed tadalafil dosage of 10 mg once every 72 hours and closely monitor for tadalafil-related adverse effects (e.g., hypotension, syncope, visual disturbances, prolonged erection, syncope)

If tadalafil is used for treatment of benign prostatic hyperplasia, do not exceed tadalafil dosage of 2.5 mg once daily

Tenofovir

No change in amprenavir concentrations with ritonavir-boosted fosamprenavir

In vitro evidence of synergistic antiretroviral effects

Tipranavir

Possible decreased amprenavir concentrations if used concomitantly with ritonavir-boosted tipranavir

Concomitant use with ritonavir-boosted tipranavir not recommended

Trazodone

Possible increased trazodone concentrations with fosamprenavir (with or without low-dose ritonavir)

Increased risk of trazodone-associated adverse effects

Use concomitantly with caution; consider reduced trazodone dosage; use lowest possible trazodone dosage and monitor for adverse CNS and cardiovascular effects

Tricyclic antidepressants (amitriptyline, desipramine, imipramine, nortriptyline)

Amitriptyline, desipramine, imipramine, nortriptyline: Possible increased concentrations of the tricyclic antidepressant

Amitriptyline, desipramine, imipramine, nortriptyline: Use lowest possible antidepressant dosage; titrate antidepressant dosage based on clinical assessment and/or antidepressant concentrations

Vardenafil

Possible increased vardenafil concentrations and increased risk of vardenafil-associated adverse effects (e.g., hypotension, syncope, visual disturbances, prolonged erection)

If fosamprenavir (with or without low-dose ritonavir) is used in patients receiving vardenafil for treatment of erectile dysfunction, do not exceed vardenafil dosage of 2.5 mg once every 72 hours and closely monitor for vardenafil-related adverse effects (e.g., hypotension, syncope, visual changes, prolonged erection)

Zidovudine

Studies using amprenavir indicate possible increased amprenavir AUC; possible increased zidovudine plasma concentrations and AUC

In vitro evidence of synergistic antiretroviral effects

Zolpidem

Ritonavir-boosted fosamprenavir: Possible increased zolpidem concentrations

Ritonavir-boosted fosamprenavir: Experts state initiate using low dosage of zolpidem; dosage reduction may be needed

Fosamprenavir Pharmacokinetics

Absorption

Bioavailability

Fosamprenavir calcium is a prodrug of amprenavir (no longer commercially available in the US).

Absolute oral bioavailability of amprenavir after administration of fosamprenavir calcium has not been established; peak amprenavir concentrations attained 1.5–4 hours after administration of the prodrug.

When a single 1.4-g dose is administered on an empty stomach as tablets or the oral suspension, amprenavir exposure (AUC) is similar, but peak amprenavir concentrations are 14.5% higher with the suspension compared with the tablet.

Food

Tablets: Administration of fosamprenavir calcium tablets with food has no effect on bioavailability of amprenavir.

Suspension: Administration of fosamprenavir calcium suspension with food (i.e., standardized high-fat meal) reduces peak plasma concentrations of amprenavir by 46%, delays time to peak plasma concentration by 0.72 hours, and reduces AUC by 28% compared with administration in the fasting state.

Distribution

Extent

Amprenavir crosses the placenta and is distributed into milk in animals. Not known whether drug crosses human placenta or is distributed into human milk.

Plasma Protein Binding

90% bound to plasma proteins, primarily to α1-acid glycoprotein.

Elimination

Metabolism

Following oral administration, fosamprenavir calcium is rapidly and almost completely hydrolyzed to amprenavir and inorganic phosphate in the intestinal epithelium during absorption.

Amprenavir is metabolized in liver principally by CYP3A4.

Elimination Route

About 14% of an oral dose excreted in urine and 75% eliminated in feces as metabolites. Only minimal amounts eliminated unchanged in urine or feces.

Half-life

Amprenavir elimination half-life approximately 7.7 hours.

Special Populations

Following administration of ritonavir-boosted fosamprenavir, AUC of amprenavir increased 22, 70, or 80% in those with mild, moderate, or severe hepatic impairment, respectively. Plasma protein binding decreased in these individuals.

Pharmacokinetics not studied to date in patients with impaired renal function, but renal impairment not expected to have a clinically important effect on pharmacokinetics.

Pharmacokinetics studied in pediatric patients 2–5 years of age receiving fosamprenavir 30 mg/kg twice daily, patients 6–11 years of age receiving fosamprenavir 18 mg/kg and ritonavir 3 mg/kg twice daily, and in those 12–18 years of age receiving fosamprenavir 700 mg and ritonavir 100 mg twice daily.

Stability

Storage

Oral

Oral Suspension

5–30°C; avoid freezing.

Tablets

Tight container at 25°C (may be exposed to 15–30°C).

Actions and Spectrum

  • Fosamprenavir calcium is a prodrug of amprenavir (no longer commercially available in the US) and has little or no antiretroviral activity until hydrolyzed in vivo to amprenavir.

  • Amprenavir, a PI, inhibits replication of HIV-1 by interfering with HIV protease.

  • HIV-1 with reduced susceptibility to amprenavir were selected in vitro and have emerged during therapy with fosamprenavir.

  • Varying degrees of cross-resistance occur among PIs; only limited data available to date regarding cross-resistance between amprenavir and other PIs.

Advice to Patients

  • Critical nature of compliance with HIV therapy and importance of remaining under the care of a clinician. Importance of taking as prescribed; do not alter or discontinue antiretroviral regimen without consulting clinician.

  • Importance of using in conjunction with other antiretrovirals–not for monotherapy.

  • Antiretroviral therapy is not a cure for HIV infection; opportunistic infections and other complications associated with HIV disease may still occur. Sustained decreases in plasma HIV RNA have been associated with reduced risk of progression to AIDS and death.

  • Advise patients that effective antiretroviral regimens can decrease HIV concentrations in blood and genital secretions and strict adherence to such regimens in conjunction with risk-reduction measures may decrease, but cannot absolutely eliminate, the risk of secondary transmission of HIV to others. Importance of continuing to practice safer sex (e.g., using latex or polyurethane condoms to minimize sexual contact with body fluids), never sharing personal items that can have blood or body fluids on them (e.g., toothbrushes, razor blades), and never reusing or sharing needles.

  • Importance of reading patient information provided by the manufacturer.

  • If a dose is missed, take the dose as soon as it is remembered and take next dose at regularly scheduled time. If a dose is skipped, do not take a double dose to make up for the missed dose.

  • When the oral suspension is used, advise adults to take the preparation on an empty stomach. Advise children to take the oral suspension with food. Refrigeration of the suspension may improve the taste.

  • When the oral suspension is used, repeat dose if vomiting occurs within 30 minutes of ingestion.

  • Importance of patients informing their clinician if they are allergic to sulfonamides.

  • Redistribution/accumulation of body fat may occur, with as yet unknown long-term health effects.

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal products (e.g., St. John’s wort), as well as any concomitant illnesses.

  • Advise patients receiving selective phosphodiesterase type 5 (PDE5) inhibitors (e.g., avanafil, sildenafil, tadalafil, vardenafil) that they may be at increased risk of PDE5 inhibitor-associated adverse effects (e.g., hypotension, syncope, visual disturbances, priapism) and that any symptoms should be promptly reported to their clinician. Fosamprenavir should not be used concomitantly with sildenafil used for treatment of pulmonary arterial hypertension (PAH).

  • Importance of women using a reliable nonhormonal (e.g., barrier) method of contraception because of the potential interaction with hormonal contraceptives.

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed. Advise HIV-infected women not to breast-feed.

  • Importance of advising patients of other important precautionary information. (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

Fosamprenavir Calcium

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Suspension

50 mg (of fosamprenavir) per mL

Lexiva

ViiV

Tablets, film-coated

700 mg (of fosamprenavir)

Fosamprenavir Calcium Tablets

Lexiva

ViiV

AHFS DI Essentials™. © Copyright 2022, Selected Revisions May 15, 2017. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

† Use is not currently included in the labeling approved by the US Food and Drug Administration.

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