Visual Effects. About 2.5% of men experience abnormal visual effects that include seeing a blue haze, temporary increased brightness, and even temporary vision loss in a few cases. Experts believe that visual disturbances are related to the inhibition of phosphodiesterase enzymes in the retina, but the effect appears to be temporary and insignificant, lasting a few minutes to several hours. Men at risk for eye problems who take PDE5 inhibitors regularly should have frequent eye examinations with an ophthalmologist. Men should also see an eye doctor if visual problems last more than a few hours.
In 2005, the FDA began investigating reports of partial vision loss in men who took sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis). The vision loss was caused by non-arteric anterior ischemic optic neuropathy (NAION), a condition that occurs from poor blood flow to optic nerves. However, experts note that erectile dysfunction is itself linked to the same vascular problems that cause NAION. Patients who suffer from diabetes, high blood pressure, and heart disease are at higher risk for erectile dysfunction as well as other vascular problems such as NAION. Information concerning vision loss has been added to the labels of these drugs, but the risk of blindness appears small. Still, patients who use this medication and experience a sudden loss of vision should immediately stop taking the drug and contact their doctor.
Seizures. There have been a few reports of seizures in men taking sildenafil. These are rare occurrences and it is not clear if there is any causal association.
Risk of Priapism. PDE5 inhibitors pose a very low risk for priapism in most men. (Priapism is sustained, painful, and unwanted erection.) Exceptions are young men with normal erectile function.
Interactions with Other Drugs. In addition to serious interactions with nitrates, PDE5 inhibitors may also interact with certain antibiotics, such as erythromycin, and acid blockers, such as cimetidine (Tagamet). Patients should tell their doctor about any medications they are taking.
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