Phosphodiesterase Type 5 Inhibitors

Phosphodiesterase type 5 inhibitors (PDE5) inhibitors include sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis).

• How PDE5 inhibitors work: Following sexual stimulation, PDE5 inhibitors increase blood flow to the penis, causing an erection.
  
  
• Who should not use these medications: Persons with allergy to PDE5 inhibitors should not use them. Concurrent use of nitrate medications (for example, nitroglycerin [Nitro-Bid, Nitro-DUR, Nitroderm, Nitrogard, Nitrolingual, Nitrostat], isosorbide mononitrate [ISMO], or isosorbide dinitrate [Isordil, ISDN, Sorbitrate]) increases the potential for excessively low blood pressure. Taking nitrates is an absolute contraindication to the use of these medicines.
  
  
• Use: The prescribed tablet strength is swallowed 15-60 minutes before sexual activity. Viagra and Levitra work best if taken without having eaten food within the last 2 hours. Cialis may be taken without regard to food. Cialis has a longer duration of increased sensitivity for developing an erection (up to 24-36 h) compared with Viagra and Levitra (up to 4-12 h).
  
  
• Drug or food interactions: Some drugs that may increase PDE5 inhibitors’ effect include erythromycin (E-Mycin, Ery-Tab), ketoconazole (Nizoral), itraconazole (Sporanox), indinavir (Crixivan), and ritonavir (Norvir). When PDE5 inhibitors are given to men taking nitrate medications (see above), excessively low blood pressure may occur. Low blood pressure has also been shown to occur when PDE5 inhibitors are taken with other drugs that lower blood pressure, such as terazosin (Hytrin), doxazosin (Cardura), prazosin (Minipress), alfuzosin (Uroxatral), or tamsulosin (Flomax).
  
  
• Side effects: Common adverse effects include headache, flushing, runny nose, stomach pain, back pain (Cialis), and indigestion. Lower doses are used for individuals with liver and/or kidney disease. PDE5 inhibitors may cause dizziness or a sudden drop in blood pressure. Men with heart disease require a doctor’s evaluation before use and, possibly, lower PDE5 doses. Some men (<2%) experience prolonged or painful erections. Visual problems (for example, blurred vision, increased sensitivity to light, bluish haze, or temporary difficulty distinguishing between blue and green) may occur.