Table 2

Comparison of PDE5 inhibitors

CHARACTERISTICSILDENAFIL (VIAGRA)TADALAFIL (CIALIS)VARDENAFIL (LEVITRA)
Onset≤ 30–60 min≥ 30–60 min≤ 30–60 min
Peak effect1 h2 h1 h
Duration> 4 h36 h> 4 h
Available doses25, 50, 100 mg2.5, 5, 10, 20 mg5, 10, 20 mg
Usual starting dose50 mg10 mg (see Comments regarding daily dosing)10 mg
Maximum dose100 mg20 mg20 mg
Cost per 8 doses (usual dose)$105$125$110
Effect of fatty mealDelay onset by 60 min; might decrease effectMeal has no effectDelay onset by 60 min; might decrease effect
Unique consideration“Blue vision” effect more commonVery long actingQT interval drug interactions (eg, TCAs)
Monitor (baseline)Liver, renalLiver, renalLiver
Contraindications5History of MI in past 90 d or stroke in past 6 mo; angina: unstable or occurring with sexual activity; nitrate use; hypotension (BP < 90/50 mm Hg) or uncontrolled hypertension (BP > 170/100 mm Hg); priapism, retinitis pigmentosa; history of NAION; previous PDE5 inhibitor allergy
Common side effectsHeadache, flushing (approximately 10%); dyspepsia, dizziness, rhinitis, altered, hazy, or blurred vision (< 10%); myalgia (possibly more with tadalafil)
Serious side effectsRare: prolonged erection (< 4 h), priapism
Very rare or uncertain: NAION, MI, hearing loss18
Drug interactions (common and important; not exhaustive)Drugs that cause hypotension (α1 blockers, 19 nitrates, vasodilators): increased hypotensive effect, heart rate, and MI risk
Nitrate washout time required: 24 h for sildenafil and vardenafil; 48 h for tadalafil
CYP 3A4 inhibitors (eg, azole antifungals, erythromycin, grapefruit juice, protease inhibitors, verapamil): increased levels of the PDE5
CommentsPDE5 inhibitors might be effective in several ED-associated conditions such as diabetes,20 spinal cord injury,21 and follow-up to treatment for prostate cancer22
Moderate to high doses are useful to ensure initial treatment success; however, consider lower dose if the patient is elderly, has hepatic or renal dysfunction (vardenafil does not require dose adjustment for renal function), or is taking concomitant CYP 3A4 inhibitors
Because of tadalafil’s long action, daily dosing of 2.5–5 mg (or 5–10 mg 3 times/wk) might be an option for some; use lowest effective dose23,24
  • BP—blood pressure, CYP—cytochrome P450, ED—erectile dysfunction, MI—myocardial infarction, NAION—nonarteritic ischemic optic neuropathy, PDE5—phosphodiesterase 5, TCA—tricyclic antidepressant.

  • Data from Brien and Trussell,5 Tsertsvadze et al,16 Downey,17 the FDA Drug Safety Newsletter,18 Kloner,19 Vardi and Nini,20 Giuliano et al,21 Miles et al,22 Roehrborn et al,23 and Kloner et al.24