Browse Prescribing Notes by Therapeutic Subcategory

Erectile dysfunction is treated by phosphodiesterase type 5 inhibitors or PDE5 inhibitors (sildenafil, tadalafil, vardenafil) or prostaglandin E₁ (alprostadil). The PDE5 inhibitors are selective for cyclic guanosine monophosphate (cGMP) phosphodiesterase type 5, an enzyme that helps control the rate of degradation of cGMP. Sexual stimulation causes the release of nitric oxide in the corpus cavernosum, resulting in increased levels of cGMP. This leads to the relaxation of smooth muscle, and allows increased blood flow into the penis. By inhibiting the activity of PDE5, cGMP levels are increased, facilitating the erectile process. Alprostadil is prostaglandin E₁, given by intracavernous injection or as an intraurethral suppository. It induces erection by relaxation of trabecular smooth muscle and by dilation of cavernous arteries. This leads to expansion of lacunar spaces and entrapment of blood by compressing the venules against the tunica albugineam (ie, corporal veno-occlusive mechanism). The efficacy of yohimbine is controversial. Unlike newer medications, which are used prior to intercourse, it must be taken on a daily basis.