Tadalafil

Tadalafil is a vasodilator and blood pressure-lowering phosphodiesterase-5 inhibitor and is used to treat erectile dysfunction, benign enlargement of the prostate, and pulmonary hypertension. Unlike other similarly acting drugs such as sildenafil (Viagra), tadalafil has a better and longer-lasting effect and is more suitable for daily dosing.

Pharmacodynamics

Tadalafil inhibits the enzyme phosphodiesterase-5, which delays the breakdown of the neurotransmitter cGMP. This triggers a relaxation of the smooth muscle in the penis, causing the blood vessels to dilate and allowing more blood to flow into the corpus cavernosum. As a result, an erection can be produced or maintained longer and stronger.

The drug also causes the smooth muscle of the pulmonary vessels to relax, lowering blood pressure in the pulmonary arteries.

In benign enlargement of the prostate, tadalafil reduces smooth muscle cell growth, helping to reduce prostate size and relieve symptoms.

Pharmacokinetics

The maximum plasma concentration of tadalafil is reached after approximately 2 hours and is 94% bound to plasma proteins. The half-life is 15-17.5 hours. In the liver, the drug is metabolized by the enzyme CYP3A4 and excreted mainly in the stool and 30% in the urine.

Drug Interactions

Since tadalafil enhances the antihypertensive effect of nitrates, NO donors, amyl nitrite, and other antihypertensive agents, the agents should not be used concomitantly. Interactions may also occur with drugs that are also degraded by CYP3A4.

Side effects

Possible side effects include headache, dizziness, dyspepsia (upper abdominal discomfort), back pain, infection of the pharyngeal mucosa, and facial flushing, as well as low blood pressure and visual disturbances.

Toxicological data

Symptoms of overdose are similar to typical side effects.