Phosphodiesterase Inhibitors: Treatment of Erectile Dysfunction

PDE5 inhibitors (1/4): basic pharmacology, side effects, contraindications
PDE5 inhibitors (2/4): Sildenafil
PDE5 inhibitors (3/4): Tadalafil
PDE5 inhibitors (4/4): Vardenafil

Review Literature: (Hatzimouratidis and Hatzichristou, 2007).

Indications for Phosphodiesterase Inhibitors

PDE5 inhibitors are used for the medical treatment of erectile dysfunction.

PDE5 Inhibitors: Mode of Action

The phosphodiesterase type 5 plays a crucial role in the inactivation of the signal transduction for the penile erection. Inhibition of the phosphodiesterase type 5 causes a preponderance of the erectile signal transduction and thus an improvement in erection. The mode of action requires thus for an erection a sufficient sexual stimulation, some innervation of the penis and an anatomical intact erectile tissue.

All phosphodiesterase inhibitors for the treatment of erectile dysfunction inhibit potent and highly specific the type 5 phosphodiesterase. The strong treatment effect and the favorable side effect profile make PDE5 inhibitors the first choice treatment option of erectile dysfunction.

Side Effects of Phosphodiesterase Inhibitors

Nervous system:

Headaches (very often). Dizziness (often).

Eyes:

Visual impairment like blurring or disturbed color vision (often). Eye pain.

Cardiovascular system:

Palpitations, flushing (often). Rarely clinically significant cardiac arrhythmia, angina pectoris or cardiac death (the causality of phosphodiesterase inhibitors in cardiac death is difficult to assess).

Other side effects of phosphodiesterase inhibitors:

Stuffy nose (often). Heartburn or dyspepsia (occasionally). Rarely prolonged erection (priapism). Very rarely severe allergic skin reactions.

Drug Interactions with Phosphodiesterase Inhibitors

Nitrates:

Phosphodiesterase inhibitors potentiate the blood pressure lowering effects of nitrates. Co-administration of nitrates and phosphodiesterase inhibitors is contraindicated.