Sildenafil

Sildenafil belongs to the group of phosphodiesterase-5 inhibitors. It has a vasodilatory effect and is used to treat erectile dysfunction (erectile dysfunction). Originally developed as a treatment for angina pectoris, the drug is also used to treat pulmonary arterial hypertension. Preparations containing sildenafil are usually administered as tablets and are available only on prescription in Germany, Austria and Switzerland.

Pharmacodynamics

Sildenafil is an inhibitor of the enzyme phosphodiesterase-5. Phosphodiesterase causes a breakdown of the neurotransmitter cGMP. This substance causes a slackening of the muscles at the erectile tissue of the penis and promotes the inflow of blood. Thus, if PDE-5 is inhibited, the rate of degradation of cGMP decreases (levels of cGMP remain elevated) and the erection can be better maintained.

Pharmacokinetics

Sildenafil is rapidly absorbed from the gastrointestinal tract and reaches its maximum blood concentration 30-60 minutes after ingestion. Sildenafil is approximately 96% protein bound and has a half-life of approximately 3-5 hours. Sildenafil is broken down in the cells of the liver by enzymes of the CYP450 family. It is then mostly excreted in the stool.

Drug interactions

It may interact with drugs that are also metabolized by the CYP450 enzyme system. These include ketoconazole, itraconazole, sequinavir, erythromycin, and cimetidine. The potent CYP3A4 inhibitor ritonavir may result in excessive plasma levels of sildenafil. When taken concomitantly, life-threatening side effects are the possible consequence.

Side effects

Possible side effects are flushing, dizziness, headache, dyspepsia, nasal congestion and visual disturbances. In case of overdose, similar side effects may occur, but they are usually more severe.

There is no evidence that sildenafil is carcinogenic or genotoxic. Sildenafil should be administered to pregnant women and nursing mothers (for the treatment of pulmonary arterial hypertension) only in extreme emergencies.