Drugs in Pregnancy
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Direct answer
Isotretinoin, warfarin, thalidomide, valproate, methotrexate and mycophenolate form the core list of established human teratogens that FMGE expects verbatim, alongside the class-based bans: ACE inhibitors and angiotensin receptor blockers in the second and third trimesters (renal failure, oligohydramnios, skull hypoplasia), tetracyclines (enamel and bone), and live vaccines. The old FDA letters A, B, C, D and X are still the examination currency in India even though the United States replaced them in 2015 with narrative labelling, so the answer to a category question is still "X for known fetal harm". The constructive half of the chapter matters just as much: paracetamol for pain, penicillins and cephalosporins for infection, labetalol–methyldopa–nifedipine for blood pressure, low-molecular-weight heparin for thrombosis, lamotrigine or levetiracetam for epilepsy, and iron with folic acid as the national programme staple.
What you must remember
- Known teratogens by trimester logic: weeks 3 to 8 post-conception are organogenesis, the window of structural teratogenicity; before week 3 the all-or-none rule applies; after week 8, growth and functional harm (for example fetal NSAID effects) dominate.
- Category X examples worth memorising: isotretinoin (retinoic-acid embryopathy — contraception from one month before to one or more months after), thalidomide (phocomelia), warfarin (nasal hypoplasia, stippled epiphyses), valproate (neural tube defects), methotrexate, mycophenolate (ear and digit anomalies), live vaccines, oestrogens and statins.
- ACE inhibitors and ARBs: contraindicated throughout pregnancy, classically fetopathic after the first trimester — switch to labetalol, methyldopa, long-acting nifedipine or hydralazine; switching from one ACE inhibitor to another is the planted wrong option.
- NSAIDs in the third trimester constrict the ductus arteriosus and reduce amniotic fluid; high-dose aspirin adds bleeding and kernicterus risk — paracetamol is the analgesic default at any stage.
- Anticoagulation: low-molecular-weight heparin throughout (warfarin only in special mechanical-valve decisions made by specialists); direct oral anticoagulants are contraindicated.
- Epilepsy: lamotrigine and levetiracetam preferred; valproate worst; folic acid 5 mg daily from before conception; do not withdraw an effective drug during pregnancy.
- Anti-infective safety: penicillins, cephalosporins, azithromycin and clindamycin acceptable; nitrofurantoin avoided near term (haemolysis); sulphonamides near term (kernicterus risk); tetracyclines avoided; metronidazole acceptable after the first trimester.
- Thyroid: propylthiouracil in the first trimester, carbimazole later; levothyroxine dose rises 25–30 per cent in pregnancy.
- Antiemetics: doxylamine with pyridoxine is the established first line; ondansetron is used when needed.
- Indian programme points: the IFA tablet provides 100 mg elemental iron with 500 microgram folic acid daily for at least 100 days in pregnancy under Anaemia Mukt Bharat; tetanus toxoid immunisation is safe and routine; codeine is contraindicated in late pregnancy and breastfeeding.
A worked pathway: planning pregnancy on valproate
A 26-year-old with juvenile myoclonic epilepsy on valproate attends pre-conception counselling. Step one switches the drug before conception — levetiracetam or lamotrigine, re-titrated with myoclonus watched, since seizure freedom on the current drug must not be traded carelessly for a theoretical gain. Step two starts folic acid 5 mg daily immediately and continues through at least the first trimester. Step three plans pregnancy care: anomaly scan at 18–20 weeks, dose monitoring as pregnancy pharmacokinetics change clearance, and a delivery plan noting bleeding risk with enzyme inducers. Step four commits to breastfeeding with reassurance, and step five reviews contraception until control is stable on the new regimen.
The companion scenario the exam prefers is shorter: a hypertensive woman on telmisartan discovers she is eight weeks pregnant. The answer is not switching to enalapril (same class, same fetopathy) but crossing to labetalol or extended-release nifedipine immediately, confirming the switch worked, and screening fetal growth and amniotic fluid at the anomaly scan. Every chronic-therapy swap in pregnancy follows this cross-class logic.
Where students slip
Switching within the banned class is the commonest wrong option — an ACE inhibitor or ARB swapped for another ACE inhibitor or ARB helps no fetus. Second, warfarin is "corrected" to a direct oral anticoagulant, which is equally contraindicated; the answer is low-molecular-weight heparin. Third, the trimester reasoning is ignored: metronidazole withheld through all three trimesters for a trichomoniasis that needs treating, or an NSAID continued casually at 34 weeks. Fourth, the epilepsy question is answered "stop the drug" — the correct movement is switch if needed, continue always, supplement always. Fifth, category arithmetic: the stem asks which of the listed drugs is category X and the candidate picks a category D ACE inhibitor in the second trimester; the letter depends on evidence of fetal harm, and both answers are "wrong in pregnancy" but only one is X. Finally, iodine-containing cough mixtures and live vaccines slip through wellness visits unchecked.
Frequently asked questions
Which antihypertensives are safe in pregnancy?
Labetalol, methyldopa, extended-release nifedipine and hydralazine; ACE inhibitors, ARBs and direct renin inhibitors are contraindicated, producing fetal renal failure and oligohydramnios.
Which analgesic is preferred throughout pregnancy?
Paracetamol at any stage; NSAIDs are avoided especially in the third trimester because they constrict the ductus arteriosus and reduce amniotic fluid.
Which anticoagulant is used in pregnancy?
Low-molecular-weight heparin, which does not cross the placenta; warfarin causes embryopathy and fetal bleeding, and direct oral anticoagulants are contraindicated.
Which anti-epileptics are preferred in pregnancy?
Lamotrigine and levetiracetam with 5 mg folic acid before conception; valproate carries the highest neural tube and neurodevelopmental risk and is avoided where possible.
Which antibiotics should be avoided near term?
Nitrofurantoin (haemolysis), sulphonamides (kernicterus risk) and tetracyclines throughout; penicillins, cephalosporins and azithromycin remain acceptable.
Why is propylthiouracil preferred in early pregnancy?
It crosses the placenta least and lacks carbimazole's teratogenic signal; after the first trimester, carbimazole resumes because propylthiouracil's hepatotoxicity accumulates.