OBJECT DRUGS

Phosphodiesterase Inhibitors:

• Sildenafil (Viagra, etc.)
• Tadalafil (Cialis, etc.)
• Vardenafil (Levitra, etc.)

PRECIPITANT DRUGS

Enzyme Inhibitors:

• Amiodarone (Cordarone, etc.)
• Amprenavir (Agenerase)
• Aprepitant (Emend)
• Atazanavir (Reyataz)
• Cimetidine (Tagamet, etc.)
• Conivaptan (Vaprisol)
• Cyclosporine (Neoral, etc.)
• Darunavir (Prezista)
• Delavirdine (Rescriptor)
• Dronedarone (Multaq)
• Grapefruit
• Indinavir (Crixivan)
• Nelfinavir (Viracept)
• Ritonavir (Norvir)
• Saquinavir (Invirase)
• Telaprevir (Incivek)

Comment:

The phosphodiesterase inhibitors appear to be metabolized by CYP3A4 and concurrent administration with CYP3A4 inhibitors could produce increased plasma concentrations. Increased side effects may occur during coadministration with CYP3A4 inhibitors.

Class 3: Assess Risk & Take Action if Necessary

• Consider Alternative:
• Cimetidine: Famotidine (Pepcid), nizatidine (Axid), and ranitidine (Zantac) have minimal effects on drug metabolism.
• Grapefruit: Orange juice does not appear to inhibit CYP3A4.
• Monitor: Monitor for phosphodiesterase inhibitor toxicity including visual disturbances, hypotension, and syncope. Reduced dose of the phosphodiesterase inhibitor may be required.