Skip to main content

Drug Interactions between saquinavir and sildenafil

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

Edit list (add/remove drugs)

Interactions between your drugs

Major

saquinavir sildenafil

Applies to: saquinavir and sildenafil

CONTRAINDICATED: Coadministration with protease inhibitors (PIs), especially ritonavir, may significantly increase the plasma concentrations of sildenafil. The mechanism is PI inhibition of CYP450 3A4, the isoenzyme primarily responsible for the metabolic clearance of sildenafil. In 14 healthy volunteers, administration of a single 100 mg dose of sildenafil during treatment with ritonavir (500 mg twice a day for 7 days) increased the mean sildenafil peak plasma concentration (Cmax) and systemic exposure (AUC) by 300% and 1000%, respectively, compared to administration alone. At 24 hours, sildenafil plasma levels were still approximately 200 ng/mL as opposed to about 5 ng/mL with sildenafil alone. In a parallel study, saquinavir (soft gelatin capsule 1200 mg three times a day for 7 days) increased single-dose sildenafil Cmax and AUC by 140% and 210%, respectively, in 14 healthy volunteers. No change in safety or tolerability of sildenafil was observed with either PI. In six HIV-infected patients stabilized on triple antiretroviral therapy containing indinavir (800 mg three times a day), the AUC of a single 25 mg dose of sildenafil was 4.4 times higher than dose-normalized data from historical controls. The patients experienced headache, flushing, dyspepsia and rhinitis, and there was a mean maximal decrease in blood pressure of 14/10 mmHg. The interaction was also suspected in the death of a 47-year-old man who used sildenafil (25 mg) during treatment with ritonavir and saquinavir.

MANAGEMENT: A safe and effective dosage of sildenafil has not been established for the treatment of pulmonary arterial hypertension when used in the presence of protease inhibitors. Due to the potential for increased sildenafil-associated adverse events including visual disturbances, hypotension, prolonged erection and syncope, this use is considered contraindicated. When used for erectile dysfunction, a lower starting dose of 25 mg should be considered for patients treated with saquinavir. For patients receiving other PIs, the maximum dosage of sildenafil should not exceed a single dose of 25 mg in any given 48-hour period. Patients should be advised to promptly notify their doctor if they experience pain or tightness in the chest or jaw, irregular heartbeat, nausea, shortness of breath, visual disturbances, syncope, or prolonged erection (greater than 4 hours).

References

  1. (2001) "Product Information. Norvir (ritonavir)." Abbott Pharmaceutical
  2. (2001) "Product Information. Crixivan (indinavir)." Merck & Co., Inc
  3. (2001) "Product Information. Viracept (nelfinavir)." Agouron Pharma Inc
  4. (2001) "Product Information. Viagra (sildenafil)." Pfizer U.S. Pharmaceuticals
  5. (2001) "Product Information. Agenerase (amprenavir)." Glaxo Wellcome
  6. Barry M, Mulcahy F, Merry C, Gibbons S, Back D (1999) "Pharmacokinetics and potential interactions amongst antiretroviral agents used to treat patients with HIV infection." Clin Pharmacokinet, 36, p. 289-304
  7. Nandwani R, Gourlay Y (1999) "Possible interaction between sildenafil and HIV combination therapy." Lancet, 353, p. 840
  8. Hall MCS, Ahmad S (1999) "Interaction between sildenafil and HIV-1 combination therapy." Lancet, 353, p. 2071-2
  9. Merry C, Barry MG, Ryan M, Tjia JF, Hennessy M, Eagling VA, Mulcahy F, Back DJ (1999) "Interaction of sildenafil and indinavir when co-administered to HIV-positive patients." AIDS, 13, f101-7
  10. Warrington JS, Shader RI, vonMoltke LL, Greenblatt DJ (2000) "In vitro biotransformation of sildenafil (Viagra): Identification of human cytochromes and potential drug interactions." Drug Metab Disposition, 28, p. 392-7
  11. Muirhead GJ, Wulff MB, Fielding A, Kleinermans D, Buss N (2000) "Pharmacokinetic interactions between sildenafil and saquinavir/ritonavir." Br J Clin Pharmacol, 50, p. 99-107
  12. (2001) "Product Information. Fortovase (saquinavir)." Roche Laboratories
  13. Hyland R, Roe GH, Jones BC, Smith DA (2001) "Identification of the cytochrome P450 enzymes involved in the N-demethylation of sildenafil." Br J Clin Pharmaacol, 51, p. 239-48
  14. (2003) "Product Information. Reyataz (atazanavir)." Bristol-Myers Squibb
  15. (2003) "Product Information. Lexiva (fosamprenavir)." GlaxoSmithKline
  16. (2005) "Product Information. Revatio (sildenafil)." Pfizer U.S. Pharmaceuticals Group
  17. (2006) "Product Information. Prezista (darunavir)." Ortho Biotech Inc
  18. (2011) "Product Information. Victrelis (boceprevir)." Schering-Plough Corporation
  19. (2011) "Product Information. Incivek (telaprevir)." Vertex Pharmaceuticals
View all 19 references

Switch to consumer interaction data

Drug and food interactions

Moderate

saquinavir food

Applies to: saquinavir

ADJUST DOSING INTERVAL: Food significantly increases the absorption of saquinavir.

MONITOR: Coadministration with grapefruit juice may increase the plasma concentrations of saquinavir. The primary mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In eight healthy volunteers, ingestion of 400 mL of grapefruit juice prior to administration of a 600 mg dose of saquinavir mesylate increased the area under the plasma concentration-time curve and oral bioavailability of saquinavir by 50% and 100%, respectively, compared to water; however, the increase is not considered clinically relevant. A high degree of intersubject variability in the grapefruit juice effect was also observed. The extent to which this interaction may occur with the saquinavir free base soft gelatin capsule is unknown. However, the saquinavir soft gelatin capsule formulation is no longer commercially available.

MANAGEMENT: Saquinavir mesylate should be taken with meals or within 2 hours after eating to enhance bioavailability. Patients should be advised to avoid the consumption of large amounts of grapefruit and grapefruit juice during saquinavir therapy unless otherwise directed by their doctor, as the interaction is unreliable and subject to a high degree of interpatient variation.

References

  1. (2001) "Product Information. Invirase (saquinavir)." Roche Laboratories
  2. Kupferschmidt HHT, Fattinger KE, Ha HR, Follath F, Krahenbuhl S (1998) "Grapefruit juice enhances the bioavailability of the HIV protease inhibitor saquinavir in man." Br J Clin Pharmacol, 45, p. 355-9
  3. Bailey DG, Malcolm J, Arnold O, Spence JD (1998) "Grapefruit juice-drug interactions." Br J Clin Pharmacol, 46, p. 101-10
  4. Eagling VA, Profit L, Back DJ (1999) "Inhibition of the CYP3A4-mediated metabolism and P-glycoprotein-mediated transport of the HIV-I protease inhibitor saquinavir by grapefruit juice components." Br J Clin Pharmacol, 48, p. 543-52
  5. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  6. Cerner Multum, Inc. "Australian Product Information."
View all 6 references

Switch to consumer interaction data

Moderate

sildenafil food

Applies to: sildenafil

GENERALLY AVOID: Coadministration with grapefruit juice may slightly increase the oral bioavailability and delay the onset of action of sildenafil. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In a randomized, crossover study with 24 healthy male volunteers, ingestion of 250 mL of grapefruit juice one hour before and concurrently with a 50 mg dose of sildenafil increased the mean area under the plasma concentration-time curve (AUC) of sildenafil and its pharmacologically active N-desmethyl metabolite by 23% and 24%, respectively, compared to water. Peak plasma concentrations (Cmax) were unaltered, but the time to reach sildenafil Cmax was prolonged by 0.25 hour. The observed increase in sildenafil bioavailability is unlikely to be of clinical significance in most individuals. However, pharmacokinetic interactions involving grapefruit juice are often subject to a high degree of interpatient variability and may be significant in the occasional susceptible patient. Indeed, one subject in the study had a 2.6-fold increase in sildenafil concentrations.

MANAGEMENT: It may be advisable to avoid administration of sildenafil with grapefruit juice to prevent potential toxicity and delay in onset of action.

References

  1. Jetter A, Kinzig-Schippers M, Walchner-Bonjean M, et al. (2002) "Effects of grapefruit juice on the pharmacokinetics of sildenafil." Clin Pharmacol Ther, 71, p. 21-29

Switch to consumer interaction data

Therapeutic duplication warnings

No warnings were found for your selected drugs.

Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.

See also

Report options

Loading...
QR code containing a link to this page

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.

Medical Disclaimer