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Drug Interactions between atazanavir and fosamprenavir

This report displays the potential drug interactions for the following 2 drugs:

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Interactions between your drugs

Moderate

atazanavir fosamprenavir

Applies to: atazanavir and fosamprenavir

MONITOR: Coadministration with fosamprenavir may decrease the plasma concentrations of atazanavir, even in the presence of low-dose ritonavir as a pharmacokinetic booster. The mechanism has not been described. In 22 study subjects, administration of atazanavir (300 mg once a day) with fosamprenavir/ritonavir (700 mg/100 mg twice a day) for 10 days decreased the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of atazanavir by 24% and 22%, respectively, compared to administration of atazanavir with ritonavir alone (300 mg/100 mg once a day) for 10 days. The clinical significance of these changes is unknown. In a study consisting of patients who have been intolerant to or have failed lopinavir/ritonavir, 14 patients who received atazanavir/fosamprenavir/ritonavir (150 or 200 mg/700 mg/100 mg twice a day, with or without nucleoside reverse transcriptase inhibitors) for 24 weeks all demonstrated plasma trough concentrations of atazanavir and amprenavir well above the minimum acceptable concentrations. In addition, the patients tolerated the regimen and had good antiretroviral response. At 24 weeks, 10 patients (60%) achieved HIV RNA levels below 400 copies/mL, and four had less than 50 copies/mL. Four patients required concomitant statins because of hyperlipidemia, which is a known side effect of protease inhibitors, in particular ritonavir. One patient developed grade 3 hyperlipidemia at week 8 and discontinued ritonavir with improvement. Three patients who did not tolerate ritonavir were switched to atazanavir/fosamprenavir (400 mg/700 mg twice a day), which also yielded good tolerance and antiretroviral response. Atazanavir reportedly does not significantly affect the pharmacokinetics of amprenavir from fosamprenavir.

MANAGEMENT: Appropriate dosages of atazanavir, fosamprenavir, and ritonavir with respect to safety and efficacy have not been established when used in combination. Limited data suggest that an atazanavir dosage of 150 or 200 mg twice daily may be adequate in combination with fosamprenavir 700 mg and ritonavir 100 mg twice daily. Therapeutic drug monitoring is recommended if this regimen is used, and antiretroviral response should be monitored closely.

References (3)
  1. (2003) "Product Information. Lexiva (fosamprenavir)." GlaxoSmithKline
  2. Ray JE, Marriott D, Bloch MT, McLachlan AJ (2005) "Therapeutic drug monitoring of atazanavir: surveillance of pharmacotherapy in the clinic." Br J Clin Pharmacol, 60, p. 291-9
  3. Khanlou H, Bhatti L, Farthing C (2006) "Interaction between atazanavir and fosamprenavir in the treatment of HIV-infected patients." J Acquir Immune Defic Syndr, 41, p. 124-5

Drug and food interactions

Moderate

atazanavir food

Applies to: atazanavir

ADJUST DOSING INTERVAL: Administration of atazanavir with food enhances oral bioavailability and reduces pharmacokinetic variability. According to the manufacturer, administration with a light meal increased the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of a single 400 mg dose of atazanavir by 57% and 70%, respectively, relative to the fasting state. Administration with a high-fat meal resulted in a mean increase of 35% in atazanavir AUC and no change in Cmax compared to fasting. The coefficient of variation of AUC and Cmax decreased by approximately one-half when given with either a light or high-fat meal compared to the fasting state.

MANAGEMENT: To ensure maximal oral absorption, atazanavir should be administered with or immediately after a meal.

References (1)
  1. (2003) "Product Information. Reyataz (atazanavir)." Bristol-Myers Squibb
Moderate

fosamprenavir food

Applies to: fosamprenavir

ADJUST DOSING INTERVAL: Food may reduce the systemic bioavailability of amprenavir from fosamprenavir oral suspension. The mechanism of interaction has not been described. According to the product labeling, administration of fosamprenavir oral suspension (1400 mg single dose) with a high-fat meal (967 kcal, 67 g fat, 33 g protein, 58 g carbohydrate) reduced amprenavir peak plasma concentration (Cmax) by 46% and systemic exposure (AUC) by 28% compared to administration in a fasted state. The time to reach peak plasma level (Tmax) was delayed by 0.72 hours. In contrast, the same high-fat meal did not affect the pharmacokinetics of amprenavir from fosamprenavir tablets.

MANAGEMENT: Fosamprenavir suspension should be administered on an empty stomach in adults, but with food in pediatric patients to aid palatability and compliance. If emesis occurs within 30 minutes after dosing the suspension, the dose should be repeated. Fosamprenavir tablets may be taken with or without food.

References (1)
  1. (2003) "Product Information. Lexiva (fosamprenavir)." GlaxoSmithKline

Therapeutic duplication warnings

Therapeutic duplication is the use of more than one medicine from the same drug category or therapeutic class to treat the same condition. This can be intentional in cases where drugs with similar actions are used together for demonstrated therapeutic benefit. It can also be unintentional in cases where a patient has been treated by more than one doctor, or had prescriptions filled at more than one pharmacy, and can have potentially adverse consequences.

Duplication

Protease inhibitors

Therapeutic duplication

The recommended maximum number of medicines in the 'protease inhibitors' category to be taken concurrently is usually one. Your list includes two medicines belonging to the 'protease inhibitors' category:

  • atazanavir
  • fosamprenavir

Note: In certain circumstances, the benefits of taking this combination of drugs may outweigh any risks. Always consult your healthcare provider before making changes to your medications or dosage.

See also

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Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.
Unknown No interaction information available.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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