Alprostadil

Alprostadil, also known as prostaglandin E1 (PGE1), is a naturally occurring prostaglandin in the body that is also used as a drug. In infants with congenital heart defects, it is administered by slow injection into a vein to open the ductus arteriosus until surgery can be performed. By injection into the penis or insertion into the urethra, it is used to treat erectile dysfunction.

Prostaglandin E1 was first isolated in 1957 and approved for medical use in 1981. It is on the World Health Organization's list of essential medicines.

Pharmacodynamics

Alprostadil (prostaglandin E1) is produced endogenously to relax vascular smooth muscle and cause vasodilation. In adult males, the vasodilatory effects of alprostadil on the cavernous arteries and corpus cavernosum smooth muscle result in rapid arteriolar inflow and dilation of the corpus cavernosum, leading to erection.

In infants, the vasodilatory effects of alprostadil increase pulmonary and systemic blood flow. In congenital heart disease, the effects of alprostadil lead to increased oxygenation of tissues, especially lower body organs such as the kidneys. This can critically prolong the infant's survival time until surgery is possible.

Pharmacokinetics

The absolute bioavailability of alprostadil is not precisely known. It is bound in plasma primarily to albumin (81%). Alprostadil must be infused continuously because it is metabolized very rapidly. Up to 80% of circulating alprostadil may be metabolized in one pass through the lungs, mainly by beta and omega oxidation. Metabolites are excreted primarily by the kidneys, and elimination is essentially complete within 24 hours of administration. The elimination half-life is 5 to 10 minutes (after a single dose), in healthy adults and neonates.

Side effects

Common side effects of alprostadil may include:

• mild pain in the penis, urethra, or testicles
• redness of the penis
• warmth or burning in the urethra

A doctor should be informed immediately if you experience any of the following symptoms:

• a feeling of dizziness, as if you might faint
• bleeding after the injection
• a painful erection that lasts 4 hours or longer
• new or worsening pain in your penis
• severe redness, swelling, tenderness, nodules under the skin
• unusual shape or curvature of the erect penis