A pregnant woman with a history of bronchial asthma is in the third stage of labor. Which drugs should be avoided in managing postpartum hemorrhage in this mother?

Correct Answer: B. Carboprost

Carboprost (15-methyl-PGF2α) is a potent prostaglandin F analogue used for postpartum hemorrhage, but it is absolutely contraindicated in asthmatic patients because it causes severe bronchospasm. Prostaglandin F compounds trigger mast cell degranulation and increase airway smooth muscle contractility via FP receptor activation, precipitating life-threatening bronchospasm in asthmatics. In a pregnant asthmatic woman in the third stage of labor, carboprost poses an unacceptable risk of acute respiratory compromise. The other uterotonic agents (methylergonovine, oxytocin, dinoprostone) do not carry this bronchospasm risk. Methylergonovine is safe in asthma; oxytocin has no bronchospastic effect; dinoprostone (PGE2) causes bronchodilation rather than bronchoconstriction. Per Indian obstetric guidelines and KD Tripathi pharmacology, carboprost is the only agent in this list with a documented contraindication in asthma. The discriminating principle is that PGF2α analogues are bronchoconstrictors, making them dangerous in reactive airway disease, whereas PGE2 analogues are bronchodilators.

Why the other options are wrong

A. Methyl ergometrine — Methylergonovine (ergot alkaloid) is safe in asthma and is actually a preferred first-line agent for postpartum hemorrhage in asthmatic mothers. It works via α-adrenergic and serotonergic mechanisms on uterine smooth muscle, with no bronchospastic effect. The NBE trap is pairing ergot alkaloids with contraindications (they have many—hypertension, coronary disease, sepsis—but asthma is NOT one). C. Oxytocin — Oxytocin is the safest uterotonic in asthma, with no bronchospastic or bronchodilator effects. It acts on oxytocin receptors on uterine myometrium and is the gold standard for PPH in asthmatic patients. The trap is that students may confuse oxytocin's side effects (water intoxication, hypotension) with respiratory risk, but respiratory compromise is not a feature. D. Dinoprostone — Dinoprostone (PGE2) is a bronchodilator, not a bronchoconstrictor, and is safe in asthma. It is used for cervical ripening and labor induction. The NBE trap is grouping all prostaglandins together; students must recall that PGE2 (dinoprostone) causes bronchodilation while PGF2α (carboprost) causes bronchospasm—opposite effects.

High-Yield Facts

Mnemonics

PG Bronchomotor Effects PGF = Bronchoconstriction (F for 'Foe' to airways); PGE = Bronchodilation (E for 'Ease'). Use when choosing prostaglandins in asthma. Asthma + PPH = OXY first In asthmatic postpartum hemorrhage: OXYtocin is safest, then methylergonovine (if no HTN), then dinoprostone. Never carboprost. Recall: OXY = oxygen-friendly.

NBE Trap

NBE pairs prostaglandins together to trap students who assume all PGs are equivalent. The critical distinction is that PGF2α (carboprost) causes bronchospasm while PGE2 (dinoprostone) causes bronchodilation—opposite effects that flip the safety profile in asthma.

Clinical Pearl

In Indian obstetric practice, when an asthmatic mother presents with postpartum hemorrhage, oxytocin (10 IU IV) is the first choice, followed by methylergonovine if blood pressure permits. Carboprost must be explicitly avoided because even a single dose can trigger life-threatening bronchospasm in the immediate postpartum period when the mother is already physiologically stressed.

_Reference: KD Tripathi Pharmacology Ch. 62 (Oxytocics); Harrison Ch. 297 (Asthma in pregnancy); Robbins Ch. 24 (Pregnancy complications)_