Erectile dysfunction

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Erectile dysfunction is a condition in which a male cannot obtain or maintain an erect penis.^[1][2] It can result from a wide range of medical conditions, both physical and psychological. Physical causes include diabetes, radical prostatectomy, vascular insufficiency, nerve damage, or insufficient cyclic guanine monophosphate (cGMP) levels. Psychological causes include stress, post-traumatic stress disorder (PTSD), depression, situational anxiety, and relationship problems.

Diagnosis[edit]

Erectile dysfunction is often diagnosed using the Sexual Health Inventory for Men (SHIM) test, a validated questionnaire that is widely used in urology clinics to evaluate and assess treatment efficacy for erectile dysfunction (ED).^[3]

Additional tests may be necessary to determine the underlying causes of the condition.

Treatment[edit]

Clinical practice guidelines by the American College of Physicians address management.^[4][5][6]

Phosphodiesterase type 5 inhibitors[edit]

(CC) Image: David E. Volk
cGMP

(CC) Image: David E. Volk
sildenafil

Sildenafil (Viagra®), vardenafil (Levitra®) and tadalafil (Cialis®), may treat erectile dysfunction^[7] and as well as pulmonary hypertensive, are selective phosphodiesterase type 5 (PDE-5) inhibitors that bind selectively to PDE-5 and inhibit the binding and subsequent degradation of cyclic GMP (cGMP). Normally, erection results from increased cGMP levels produced by guanylate cyclase, which in turn is upregulated by nitric oxide release after stimulation. By decreasing the degradation of cGMP by PDE-5 enzymes increases the levels of cGMP in the corpus cavernosum and its supply vessels, relaxes the smooth muscle, and enables an erection. Viagra (sildenafil) was the first blockbuster drug for ED treatment in this class, although vardenafil is more potent in vitro. Both sildenafil and vardenafil have structural similarity to cGMP (and the unselective PDE inhibitor caffeine), with which they compete for binding of PDE-5 enzymes. Tadalafil is significantly different in structure but is thought to act by the same mechanism.

Tadalafil^[8][9] and vardenafil^[10] can be taken once a day although this schedule is approved by the Food and Drug Administration only for tadalafil.

83% of men who used sildenafil had at least one episode of intercourse as compared to 45% who received placebo according to a systematic review of randomized controlled trials of using sildenafil.^[11] Few randomized controlled trials have compared the different phosphodiesterase inhibitors.^{[12][13][14][15]}

References[edit]