Prescribing in pregnancy and lactation: altered pharmacokinetics, teratogenicity, risk categories and milk transfer
How pregnancy changes drug handling (lamotrigine, levothyroxine, renally cleared drugs), placental transfer and timing of teratogenic risk, the Australian pregnancy categories and their limits, and how to estimate infant exposure through breast milk.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Pregnancy raises plasma volume, GFR and the activity of several hepatic enzymes, and lowers albumin. Many drugs need higher doses in pregnancy and lower doses again after delivery.
- Drugs cross the placenta if they are small, lipophilic and unionised. Heparins and insulin don't; IgG monoclonal antibodies do, late in pregnancy.
- Timing decides the type of harm: all-or-none before organogenesis, malformations during weeks 3 to 8 after conception, functional and growth effects later.
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Sources
- Australian categorisation system for prescribing medicines in pregnancy, and Prescribing medicines in pregnancy databaseAU/NZTherapeutic Goods Administration, 2025
- Therapeutic Guidelines: Prescribing in special populations (pregnancy and breastfeeding)AU/NZTherapeutic Guidelines Ltd, 2026
- Australian Medicines HandbookAU/NZAustralian Medicines Handbook Pty Ltd, 2026
- Drugs and Lactation Database (LactMed)US National Library of Medicine, 2026
- Pregnancy-induced changes in pharmacokinetics: a mechanistic-based approachClinical Pharmacokinetics (Anderson, 2005;44:989-1008), 2005
- Safety information 2024-SI-007: sodium valproate use in men (paternal exposure)AU/NZNSW Health Clinical Excellence Commission, 2024
- Last updated
- 14 November 2026
What changed
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