Indications: maintenance of patency in congenital heart defects (ductus arteriosus) in neonates prior to corrective surgery; erectile dysfunction.

Cautions: history of haemorrhage, avoid in hyaline membrane disease, monitor arterial pressure. priapism— patients should be instructed to report any erection lasting 4 hours or longer—anatomical deformations of penis, follow up regularly to detect signs of penile fibrosis, discontinuation the drug if angulation, cavernosal fibrosis or Peyronie's disease develop.

Contra-indications: in sickle cell anaemia, multiple myeloma or leukaemia; not to be used with other agents for erectile dysfunction, in patients with penile implants or when sexual activity medically inadvisable; urethral application also contra-indicated in urethral stricture, severe hypospadia, severe curvature, balanitis, urethritis.

Side Effects: apnoea (particularly in infants under 2 kg), flushing, bradycardia, hypotension, tachycardia, cardiac arrest, oedema, diarrhoea, fever, convulsions, disseminated intravascular coagulation, hypokalemia; cortical proliferation of long bones, weakening of the walls of the ductus arteriosus and pulmonary artery may follow prolonged use, gastric-outlet obstruction reported penile pain, priapism, reactions at injection site include haematoma, haemosiderin deposits, penile rash, penile oedema, penile fibrosis, haemorrhage, inflammation; other local reactions include urethral burning and bleeding, penile warmth, numbness, penile or urinary-tract infection, irritation, sensitivity, phimosis, pruritus, erythema, venous leak, abnormal ejaculation; systemic effects reported include testicular pain and swelling, scrotal disorders, changes in micturition (including haematuria), nausea, dry mouth, fainting, hypotension (very rarely circulatory collapse) or hypertension, rapid pulse, vasodilatation, chest pain, supraventricular extrasystole, peripheral vascular disorder, dizziness, weakness, localised pain (buttocks, legs, genital, perineal, abdominal), headache, pelvic pain, back pain, influenza- like syndrome, swelling of the leg veins.

Dose: by intravenous infusion, initially 50-100 nanograms/kg/minute, then decreased to lowest effective dose. [but lower dose such as 10 nanograms/kg/minute may be effective and safer].