Absolute Contraindications:
(1) nitrate exposure (chronic nitrate therapy, short-acting nitrate therapy, or inhaled nitrates) can result in a potentially fatal drop in blood pressure
(2) nonselective alpha-antagonists (doxazosin, terazosin)
Relative Contraindications (potentially hazardous):
(1) patients with active coronary ischemia who are not on nitrates
(2) patients with congestive heart failure and borderline low blood pressure and borderline low volume status
(3) patients on complicated multi-drug, anti-hypertensive regimens
(4) patients taking medications which may prolong the half-life of Viagra (erythromycin, clarithromycin, cimetidine, ketoconazole, itraconazole, mibefradil, ritonavir, saquinavir)
(5) patients with organ dysfunction that can prolong the half-life of Viagra (severe liver or renal diseases)
(6) retinitis pigmentosa or other hereditary retinal degeneration
(7) nonarteritic anterior ischemic optic neuropathy
