OBJECT DRUGS

Phosphodiesterase Inhibitors:

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

PRECIPITANT DRUGS

Antimicrobials:

• Ciprofloxacin (Cipro, etc.)
• Clarithromycin (Biaxin, etc.)
• Erythromycin (E-Mycin, etc.)
• Fluconazole (Diflucan)
• Itraconazole (Sporanox, etc.)
• Ketoconazole (Nizoral, etc.)
• Posaconazole (Noxafil)
• Quinupristin (Synercid)
• Telithromycin (Ketek)
• Troleandomycin (TAO)
• Voriconazole (Vfend)

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 with concurrent CYP3A4 inhibitors.

Class 3: Assess Risk & Take Action if Necessary

• Consider Alternative:
• Azole Antifungals: Itraconazole and ketoconazole are potent inhibitors of CYP3A4; fluconazole appears weaker, but in larger doses it also inhibits CYP3A4. Terbinafine (Lamisil) does not appear to affect CYP3A4, and would not be expected to interact with phosphodiesterase inhibitors.
• Macrolide Antibiotics: Unlike erythromycin, clarithromycin and troleandomycin, azithromycin (Zithromax) and dirithromycin* do not appear to inhibit CYP3A4. (*not available in US)
• Telithromycin: The use of azithromycin (Zithromax) or a quinolone antibiotic other than ciprofloxacin should be considered.
• Monitor: Monitor for phosphodiesterase inhibitor toxicity including visual disturbances, hypotension, and syncope. Reduced dose of the phosphodiesterase inhibitor may be required.