MRCOG Part 1: Pharmacology
Pharmacology is one of the four highest-yield subjects in MRCOG Part 1, with approximately 131 questions. Questions focus heavily on drugs used in obstetrics and gynaecology — their mechanisms of action, side effects, contraindications and pharmacokinetics.
Topics Covered
Oxytocics & Uterotonic Drugs
- ›Oxytocin — mechanism, receptor, pharmacokinetics, ADH-like effects
- ›Ergometrine and syntometrine — mechanism, contraindications
- ›Carboprost (prostaglandin F2α) — use in PPH, contraindications (asthma)
- ›Misoprostol (prostaglandin E1) — uses in O&G
- ›Mifepristone — mechanism as progesterone receptor antagonist
Tocolytics
- ›Nifedipine — calcium channel blocker, first-line tocolytic
- ›Atosiban — oxytocin receptor antagonist
- ›Beta-agonists (salbutamol, ritodrine) — mechanism and side effects
- ›Indomethacin — COX inhibitor, ductal effects limit use after 32 weeks
Antibiotics in Obstetrics & Gynaecology
- ›Penicillins — mechanism (beta-lactam), Group B Strep prophylaxis
- ›Cephalosporins — spectrum, cross-reactivity with penicillin
- ›Metronidazole — anaerobes and protozoals, use in BV, trichomoniasis
- ›Clindamycin — use in BV, mechanism
- ›Macrolides — erythromycin for Chlamydia, clarithromycin
- ›Tetracyclines — contraindicated in pregnancy (fetal bones/teeth)
Pharmacokinetics
- ›Volume of distribution, bioavailability, half-life
- ›First-pass metabolism and hepatic extraction ratio
- ›Protein binding — changes in pregnancy (albumin falls)
- ›Renal clearance — GFR increases in pregnancy affecting renally cleared drugs
- ›Drug metabolism — CYP450 enzymes, inducers and inhibitors
Other O&G Pharmacology
- ›Antihypertensives in pregnancy — labetalol, methyldopa, nifedipine (safe); ACEi contraindicated
- ›Magnesium sulphate — eclampsia prevention, mechanism, toxicity signs
- ›Corticosteroids — betamethasone/dexamethasone for fetal lung maturity
- ›Heparin and LMWH — anticoagulation in pregnancy
- ›Anti-D immunoglobulin — mechanism and indications
- ›Combined oral contraceptive pill — mechanism, contraindications (WHO criteria)
Exam Tips for Pharmacology
Know oxytocin pharmacokinetics: it is a peptide, given IV/IM, short half-life ~3–5 min, has ADH-like activity (water retention risk).
Drug contraindications in pregnancy are very commonly tested — know the teratogenic and fetotoxic drugs by trimester.
Magnesium sulphate toxicity: loss of patellar reflexes first, then respiratory depression — know the levels.
Mechanism-of-action questions are common: be clear on receptor types (beta-2, oxytocin receptor, prostaglandin receptor).
Antibiotic spectrum is tested: know which antibiotics cover anaerobes, which are safe in pregnancy.
Recommended Book
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