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Drug Interactions between sildenafil and Vaprisol

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

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Interactions between your drugs

Moderate

sildenafil conivaptan

Applies to: sildenafil and Vaprisol (conivaptan)

GENERALLY AVOID: Coadministration with conivaptan may significantly increase the plasma concentrations of phosphodiesterase-5 (PDE5) inhibitors. The mechanism is conivaptan inhibition of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of these agents. Although the interaction has not been specifically studied, high plasma levels of PDE5 inhibitors (e.g., due to high doses or interaction with other potent 3A4 inhibitors such as protease inhibitors) have been associated with increased PDE5 adverse effects such as headache, flushing, dyspepsia, rhinitis, visual disturbances, hypotension, and even death. In pharmacokinetic studies with other drugs that are primarily metabolized by CYP450 3A4 such as midazolam, simvastatin, and amlodipine, conivaptan has increased systemic exposure (AUC) by 2- to 3-fold.

MANAGEMENT: Use of PDE5 inhibitors should preferably be avoided in patients treated with conivaptan. Patients currently using PDE5 inhibitors should consider an interruption during administration of conivaptan, and allow an appropriate amount of time following completion of conivaptan therapy before resuming these medications.

References

  1. Nandwani R, Gourlay Y (1999) "Possible interaction between sildenafil and HIV combination therapy." Lancet, 353, p. 840
  2. Hall MCS, Ahmad S (1999) "Interaction between sildenafil and HIV-1 combination therapy." Lancet, 353, p. 2071-2
  3. 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
  4. 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
  5. 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
  6. (2006) "Product Information. Vaprisol (conivaptan)." Cumberland Pharmaceuticals Inc
View all 6 references

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Drug and food interactions

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

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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.

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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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