Singapore Drugs Database

Indication

For palliative, not definitive, therapy to temporarily maintain the patency of the ductus arteriosus until corrective or palliative surgery can be performed in neonates who have congenital heart defects and who depend upon the patent ductus for survival. Also for the treatment of erectile dysfunction due to neurogenic, vasculogenic, psychogenic, or mixed etiology.

Mechanism of Action

Alprostadil causes vasodilation by means of a direct effect on vascular and ductus arteriosus (DA) smooth muscle, preventing or reversing the functional closure of the DA that occurs shortly after birth. This is because, as a form of prostaglandinE1 (PGE1) it has multiple effects on blood flow. This results in increased pulmonary or systemic blood flow in infants. In cyanotic congenital heart disease, alprostadil's actions result in an increased oxygen supply to the tissues. In infants with interrupted aortic arch or very severe aortic coarctation, alprostadil maintains distal aortic perfusion by permitting blood flow through the DA from the pulmonary artery to the aorta. In infants with aortic coarctation, alprostadil reduces aortic obstruction either by relaxing ductus tissue in the aortic wall or by increasing effective aortic diameter by dilating the DA. In infants with these aortic arch anomalies, systemic blood flow to the lower body is increased, improving tissue oxygen supply and renal perfusion. When administered by intracavernosal injection or as an intraurethral suppository, alprostadil acts locally to relax the trabecular smooth muscle of the corpora cavernosa and the cavernosal arteries. Swelling, elongation, and rigidity of the penis result when arterial blood rapidly flows into the corpus cavernosum to expand the lacunar spaces. The entrapped blood reduces the venous blood outflow as sinusoids compress against the tunica albuginea.

Pharmacokinetics

Absorption

The absolute bioavailability of alprostadil has not been determined.

Distribution

Metabolism

Alprostadil must be infused continuously because it is very rapidly metabolized. As much as 80% of the circulating alprostadil may be metabolized in one pass through the lungs, primarily by beta- and omega-oxidation.

Elimination

Toxicity

Oral, mouse: LD₅₀ = 186 mg/kg; Oral, rat: LD₅₀ = 228 mg/kg. Apnea, bradycardia, pyrexia, hypotension, and flushing may be signs of drug overdosage.

Active Ingredient/Synonyms

(11alpha,13e,15S)-11,15-Dihydroxy-9-oxoprost-13-en-1-oic acid | (13e)-(15S)-11alpha,15-Dihydroxy-9-oxoprost-13-enoate | 11alpha,15alpha-Dihydroxy-9-oxo-13-trans-prostenoic acid | Alprostadil | Alprostadil Alfadex | Alprostadilum | Befar | PGE-1 | PGE₁ | PGE1 α-CD | Prostaglandin e1 | Alprostadil |