Suggestions for Prescribing Medication in Pregnant Women
- Use medication only if absolutely indicated.
- Avoid initiating therapy during the first trimester if not essential during first trimester.
- Select a medication with a proven track record in human pregnancy.
- Use a single agent whenever possible.
- Use the lowest effective dose.
- Discourage the use of over-the-counter drugs that might interact with prescription medications.
Modified from: Norwitz ER, Greenberg JA. Antibiotics in pregnancy: are they safe? Rev Obstet Gynecol. 2009 Summer;2(3):135-6. PMID: 19826569
Factors that Determine the Extent of Placental Transfer
- Molecular weight: Drugs with molecular weights (MW) less than 500 D appear to cross the placenta easily, drugs with MW greater than 500 have incomplete transfer across the human placenta. Drugs with very high MW , such as insulin with a M.W ~ 5800 do not normally cross the placenta.
- pKa: Strongly dissociated acids transfer incompletely, though not always predictably.
- Placental physiology: Blood flow and gestational age affect transfer.
- Enzyme and transporter activity: For example placental 11beta-hydroxysteroid dehydrogenase 2 (11beta-HSD2) enzyme inactivates prednisolone by interconversion into prednisone , and ABC transporters pump tenofovir disoproxil fumarate from trophoblast back to maternal circulation.
- Protein binding: Has limited impact on placental drug transfer.
Prescription Drugs of Choice During Pregnancy Medications recommended as first line agents during pregnancy by various organizations and authorities .
Recommended Resources
- BUMPS: Best Use of Medicines in Pregnancy
- Breastfeeding and Maternal Medication (WHO, 2002)
- DailyMed – official prescription drug information.
- Drugs.com
- Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk Classic text by Briggs GG, Freeman RK, Yaffe S.J.
- Drug Safety in Lactation Prescriber Update
- InfantRisk Center
- MotherToBaby Fact Sheets
- LactMed – database on drugs and lactation.
- Prescribing medicines in pregnancy database Australia
- Reprotox Fee required
- RX List Pill Identification Tool
References
- Pacifici GM, Nottoli R. Placental transfer of drugs. Clin Pharmacokinet. 1995;28(3):235-69. PMID: 7758253
- Menon RK et al. Transplacental passage of insulin. N Engl J Med. 1990;323(5):309-15. PMID: 2195347
- van Runnard Heimel PJ et al. Transplacental passage of prednisolone. Placenta. 2005;26(10):842-5. PMID: 16226134
- Neumanova Z et al. Tenofovir and efflux transporters. AIDS. 2014;28(1):9-17. PMID: 24413260
- Hemauer SJ et al. Placental transporters and glyburide efflux. Am J Obstet Gynecol. 2010;202(4):383.e1-7. PMID: 20350646
- ACOG Practice Bulletin No.153: Nausea and vomiting of pregnancy. Obstet Gynecol. 2015;126:e12–24. PMID: 26287788