Prostaglandin and Leukotriene Drugs

Prepared and reviewed by the PrepElephant Academic Review Team

First published 2 Oct 2026 · Spot an error?

On this page

Direct answer
What you must remember
One pathway, four unrelated prescriptions
Where students slip
Frequently asked questions
Related topics

Direct answer

Arachidonic acid released from membrane phospholipids by phospholipase A2 feeds two enzymatic highways — cyclo-oxygenase yielding prostaglandins and thromboxane, 5-lipoxygenase yielding leukotrienes — and both carry licensed drugs. From the COX branch: alprostadil (PGE1) to keep the ductus open in duct-dependent congenital heart disease; misoprostol (PGE1 analogue, 200 micrograms four times daily) for NSAID ulcer prophylaxis and, with mifepristone, medical termination; carboprost 250 micrograms intramuscularly for postpartum haemorrhage; latanoprost 0.005 percent eye drops for glaucoma; and the prostacyclin family for pulmonary hypertension. From the 5-LOX branch, montelukast 10 mg at bedtime and zileuton block leukotriene action or synthesis. Adverse-effect logic is receptor physiology: uterine cramping, diarrhoea, flushing, fever.

What you must remember

Biosynthetic map: phospholipase A2 → arachidonic acid → COX-1/COX-2 → PGG2/PGH2 → PGE2, PGF2alpha, PGI2 (prostacyclin), TXA2; parallel 5-LOX → LTC4/D4/E4 (cysteinyl leukotrienes, the slow-reacting substance of anaphylaxis).
Misoprostol 200 micrograms QID: the only established cytoprotective agent against NSAID ulcers; contraindicated in pregnancy unless used for termination — a boxed-warning drug in most pharmacopoeias.
Obstetric utility ladder: dinoprostone (PGE2) gel for cervical ripening; misoprostol for medical abortion with mifepristone 200 mg; carboprost 250 micrograms IM for refractory PPH when oxytocin and ergometrine fail.
Latanoprost 0.005 percent once nightly: increases uveoscleral outflow; unique adverse effects — longer, darker eyelashes and irreversible iris pigmentation.
Alprostadil: IV infusion 0.01-0.05 micrograms/kg/min keeps the ductus open in neonates with duct-dependent lesions awaiting surgery; the opposite task — closing a symptomatic patent ductus in a preterm infant — belongs to indomethacin or paracetamol.
Prostacyclin drugs: epoprostenol (short half-life minutes, continuous infusion, platelet inhibition) for WHO functional class III-IV pulmonary hypertension; oral selexipag is a prostacyclin receptor agonist.
Leukotriene modifiers: montelukast 10 mg HS (4 mg granules in infants, 5 mg in children 6-14) and zafirlukast 20 mg BD block CysLT1; zileuton inhibits 5-LOX itself (liver monitoring) — strongest evidence in aspirin-exacerbated respiratory disease.
Warning worth quoting: montelukast carries a boxed warning (US FDA, 2020) for neuropsychiatric events — agitation, dream abnormalities, depression — relevant to Indian practice where it is heavily prescribed.

One pathway, four unrelated prescriptions

A neonatologist infuses alprostadil in a cyanotic newborn with transposition, keeping the ductus open until the balloon atrial septostomy; the same prostaglandin chemistry that the obstetrician exploits two floors up to ripen a cervix and the gastroenterologist exploits to protect an arthritic patient's gastric mucosa from diclofenac. An ophthalmologist prescribes latanoprost for glaucoma and warns about iris darkening in brown eyes. A chest physician reaches for montelukast in a young asthmatic with nasal polyps and aspirin sensitivity — the Samter triad — because in that phenotype leukotrienes drive both bronchospasm and polyposis. Four consultants, one membrane lipid. The unifying viva answer: cells everywhere convert arachidonic acid on demand, so administering a single eicosanoid or blocking a single receptor produces entirely organ-specific medicine.

Where students slip

The most common mistake is misplacing misoprostol's indications — it is cytoprotective in the stomach, ripens the cervix, aborts with mifepristone, and treats PPH, four different doses and routes on one drug card. The second slip is confusing "prostaglandins cause diarrhoea" trivia with mechanism: PGE and PGF receptor activation drives intestinal smooth muscle and secretions, which is why misoprostol and carboprost share gastrointestinal adverse effects. Third, candidates forget the aspirin angle on both sides: aspirin blocks COX but shunts substrates toward leukotrienes in susceptible patients — explaining both the Samter triad and why montelukast specifically rescues it.

Frequently asked questions

Which prostaglandin keeps the ductus arteriosus open, and which closes it?

Alprostadil (PGE1) infusion maintains ductal patency in duct-dependent congenital heart disease, while indomethacin or paracetamol promote closure in preterm patent ductus.

What is the dose of misoprostol for NSAID ulcer prophylaxis?

200 micrograms four times daily with food (or 400 micrograms twice daily), reduced to 100 micrograms QID for intolerance; never in pregnancy except for obstetric indications.

Which drug is added for refractory postpartum haemorrhage after oxytocin and ergometrine?

Carboprost, 15-methyl PGF2alpha, 250 micrograms intramuscularly every 15-90 minutes up to 8 doses; avoided in asthma (PGF2alpha is a bronchoconstrictor).

Why is latanoprost given at night, and what are its signature adverse effects?

Once-nightly dosing matches its long uveoscleral-outflow effect; signature effects are darker longer lashes, irreversible iris pigmentation and conjunctival hyperaemia.

Which leukotriene drug class suits aspirin-exacerbated respiratory disease?

Cysteinyl leukotriene receptor antagonists (montelukast, zafirlukast) or the 5-lipoxygenase inhibitor zileuton, since aspirin-driven leukotriene overproduction underlies the bronchospasm and polyposis.