Prostaglandins in Obstetrics

Prostaglandins ripen the cervix, contract the uterus and open the cervix for miscarriage and termination. Misoprostol (PGE1 analogue), dinoprostone (PGE2) and carboprost (15-methyl PGF2 alpha) are used. They are cheap, stable and effective, but cause hyperstimulation, so use needs careful selection and monitoring.

Mechanism. They activate EP and FP receptors, remodel cervical collagen, soften and dilate the cervix, and cause myometrial contraction. Effects begin within 30 minutes and cannot easily be reversed.

Pharmacokinetics. Misoprostol: oral onset in 8 to 12 minutes, sublingual absorption faster and longer lasting, vaginal absorption slower with sustained effect. Dinoprostone: absorbed locally from gel or controlled-release insert. Carboprost: intramuscular onset within 15 minutes.

Induction of labour.

• Misoprostol 25 micrograms vaginally every 4 to 6 hours, or 25 micrograms orally every 2 hours (as solution), maximum 6 doses in 24 hours; do not use higher doses at term.
• Dinoprostone 10 mg vaginal insert released over 24 hours, or gel 1 to 2 mg intravaginally and repeat after 6 hours.
• Balloon catheter is an alternative that avoids hyperstimulation.

Miscarriage and termination.

• Early pregnancy loss: misoprostol 800 micrograms vaginally or sublingually; repeat after 3 hours if needed.
• Medical termination up to 12 weeks: mifepristone 200 mg orally, then misoprostol 800 micrograms vaginally, buccally or sublingually 24 to 48 hours later.
• Later gestation: misoprostol 400 micrograms every 3 hours, up to 5 doses, under supervision.
• Cervical priming before surgery: misoprostol 400 micrograms vaginally 3 hours before.

Postpartum haemorrhage. Misoprostol 800 micrograms sublingually; carboprost 250 micrograms intramuscularly every 15 minutes up to 8 doses.

Storage. Misoprostol tablets are stable at room temperature; dinoprostone products need refrigeration or freezing by product.

• First-line. Misoprostol for early pregnancy loss and termination; dinoprostone or misoprostol for induction with an unfavourable cervix; carboprost for atony that does not respond to oxytocin.
• Alternative. Balloon catheter or mechanical dilators; manual vacuum aspiration for incomplete miscarriage.
• Specialist. Late termination, intrauterine death, induction after previous caesarean (usually mechanical methods or oxytocin only).
• Emergency. Atonic PPH when other agents fail.

Selection. Avoid misoprostol and dinoprostone in women with a uterine scar. Check foetal heart rate and contractions before and after each dose, and keep the patient in the facility for at least 30 minutes after a dose.

Contraindications. Previous caesarean or major uterine surgery (induction); uterine anomaly; regular painful contractions already present; non-reassuring foetal status; placenta praevia; unexplained vaginal bleeding; hypersensitivity. Carboprost: asthma, cardiac, renal or liver disease. Dinoprostone: asthma, glaucoma (relative).

Serious adverse effects.

• Uterine hyperstimulation with foetal heart rate change, uterine rupture, meconium passage.
• Fever, shivering, nausea, vomiting, diarrhoea.
• Carboprost: bronchospasm, hypertension, flushing.
• Heavy bleeding or incomplete expulsion in miscarriage and termination.

Major interactions. Oxytocin (wait 6 hours after dinoprostone gel and 30 minutes after pessary removal); NSAIDs reduce prostaglandin effect but are used for pain; ergometrine adds uterine effect.

Common prescribing errors.

• Repeating doses too soon.
• Using high misoprostol doses at term.
• Giving misoprostol in a scarred uterus.
• Starting oxytocin too early after dinoprostone.
• Discharging without safety advice after miscarriage management.

Special groups.

• Pregnancy: used only for induction or pregnancy loss; teratogenic risk (limb and cranial defects) if pregnancy continues after use for abortion.
• Breastfeeding: compatible; transient diarrhoea in infant possible.
• Children and adolescents: dose as adults.
• Older adults: not applicable.
• Kidney and liver: avoid carboprost in severe disease.
• East Africa: misoprostol is an affordable, heat-stable option for PPH and miscarriage care; laws and facility rules on abortion differ, so follow national law; counsel on bleeding and when to seek help.

Monitoring. Contractions and foetal heart rate; bleeding and pain; temperature; respiratory rate with carboprost; ultrasound or symptoms to confirm completion.

Referral and escalation. Tachysystole; foetal compromise; heavy bleeding; infection signs; failed expulsion; scar tenderness.

Comparison with alternative classes. Prostaglandins ripen the cervix and work without infusion pumps, but cannot be switched off. Oxytocin is easier to control but ineffective on an unripe cervix. Balloon catheters have fewer hyperstimulation events.