Drugs in Pregnancy & Lactation

Drugs in Pregnancy & Lactation

1. Definition, scope & clinical framing

• Pregnancy is the "last true therapeutic orphan" — because of ethical, medicolegal, and fetal-safety concerns, very few pharmacokinetic (PK), pharmacodynamic (PD), or clinical trials are conducted in pregnant individuals, so most drug labels carry the boilerplate "no adequate and well-controlled studies in pregnant women… use only if clearly needed" (Atkinson 4e Ch.23, pp.425–6).
• The clinician's task is risk–benefit balance: the fetal risk of a drug (chiefly teratogenesis) must be weighed against the risk to mother and fetus of the untreated maternal disease — a consideration that is frequently and wrongly omitted, leaving pregnant women under-treated (Atkinson 4e Ch.23, p.425; DiPiro 12e Ch.99, p.1293).
• General principle (Indian PG framing): drugs should generally be avoided in pregnancy; if required, used cautiously, balancing risk vs benefit for both mother and child — for many diseases one or two agents are known to be reasonably safe (e.g. methyldopa for hypertension, chloroquine for malaria) (Padmaja 7e Ch.63, p.735).
• Two compelling reasons to study drugs in pregnancy: (1) rising maternal age at first pregnancy → more women with pre-existing disease needing continued therapy; (2) gestational physiology alters PK, so blind extrapolation of non-pregnant data risks under-dosing (loss of efficacy) or over-dosing (toxicity) and worsens pregnancy outcome (Atkinson 4e Ch.23, pp.425–6).
• Baseline (background) risk: even with no known teratogenic exposure, the population risk of a major congenital malformation is ~3% (Katzung: ~3%; DiPiro: 3–5%); minor anomalies add another 7–14% (Katzung 16e Ch.59, p.1114; DiPiro 12e Ch.99, p.1293; Atkinson 4e Ch.23, p.442).
• Drugs cause <1% of all birth defects — ~65–80% are of unknown cause, ~15% chromosomal, ~5% single-gene, ~10% other environmental (irradiation, maternal disease, infection); fewer than 30 drugs are proven human teratogens (Katzung 16e Ch.59, p.1113; DiPiro 12e Ch.99, p.1293; Atkinson 4e Ch.23, p.442).
• Counselling matters: because ~50% of pregnancies are unplanned and many patients assume every drug is a teratogen, evidence-based counselling demonstrably prevents unnecessary terminations (Katzung 16e Ch.59, pp.1113–4).