The Basics
What is Metformin?
Used to treat and prevent type 2 diabetes.
Brand names for Metformin
Actoplus Met
How Metformin is classified
Hypoglycemic Agents, Biguanides
Metformin During Pregnancy
Metformin pregnancy category
Category CNote that the FDA has deprecated the use of pregnancy categories, so for some medications, this information isn’t available. We still think it’s useful to list historical info, however, given what a common proxy this has been in the past.
What we know about taking Metformin while pregnant
There are no adequate and well-controlled studies of ACTOPLUS MET or its individual components in pregnant women. Animal studies using pioglitazone show increased rates of post-implantation loss, delayed development, reduced fetal weights, and delayed parturition at doses 10 to 40 times the maximum recommended human dose. ACTOPLUS MET should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Taking Metformin While Breastfeeding
What are recommendations for lactation if you're taking Metformin?
Data from well-conducted studies indicate that metformin levels in milk are low and infants would receive less than 0.5% of their mother’s weight-adjusted dosage. Milk metformin levels are relatively constant during maternal metformin use, so timing of breastfeeding with respect to the administration times is of little benefit. Although the dose in milk is low, metformin is sometimes detectable in low levels in the serum of breastfed infants. One sizeable prospective study found no adverse effects in breastfed infants. Metformin should be used with caution while nursing newborn and premature infants and those with renal impairment.
Maternal / infant drug levels
Data from well-conducted studies indicate that metformin levels in milk are low and infants would receive less than 0.5% of their mother’s weight-adjusted dosage. Milk metformin levels are relatively constant during maternal metformin use, so timing of breastfeeding with respect to the administration times is of little benefit. Although the dose in milk is low, metformin is sometimes detectable in low levels in the serum of breastfed infants. One sizeable prospective study found no adverse effects in breastfed infants. Metformin should be used with caution while nursing newborn and premature infants and those with renal impairment.
Possible effects of Metformin on milk supply
In a study of 250 women who received metformin 500 mg to 2 grams daily in either the immediate- or extended-release formulation for polycystic ovary syndrome, information on breastfeeding was available on 164 women. Of these, 97 (59%) were successful at breastfeeding, 27 (17%) failed, and 40 (27%) made no attempt to breastfeed. Of the 124 who attempted to breastfeed, 78% were successful. Failures were attributed to poor milk production in 4 women, demands of multiple births, infant prematurity, cleft palate and mastitis.[8]
In a follow-up to a placebo-controlled study on metformin use during pregnancy in women with polycystic ovary syndrome, women were asked about the duration and extent of breastfeeding. No difference in breastfeeding in the duration of exclusive or partial breastfeeding was observed between the women who received metformin during pregnancy and those who received placebo.[9]
Possible alternatives to Metformin
Acarbose, Glipizide, Glyburide, Insulin, Miglitol.
List of References
Lactation sources: Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK501922/1. Hale TW, Kristensen JH, Hackett LP et al. Transfer of metformin into human milk. Diabetologia. 2002;45:1509-14. PMID: 12436333
2. Hale T, Kristensen J, Hackett L et al. Transfer of metformin into human milk. Adv Exp Med Biol. 2004;554:435-6. PMID: 15384618
3. Gardiner SJ, Kirkpatrick CM, Begg EJ et al. Transfer of metformin into human milk. Clin Pharmacol Ther. 2003;73:71-7. PMID: 12545145
4. Briggs GG, Ambrose PJ, Nageotte MP et al. Excretion of metformin into breast milk and the effect on nursing infants. Obstet Gynecol. 2005;105:1437-41. PMID: 15932841
5. Eyal S, Easterling TR, Carr D et al. Pharmacokinetics of metformin during pregnancy. Drug Metab Dispos. 2010;38:833-40. PMID: 20118196
6. Glueck CJ, Salehi M, Sieve L, Wang P. Growth, motor, and social development in breast- and formula-fed infants of metformin-treated women with polycystic ovary syndrome. J Investig Med 2006;54 (suppl 2):S376. Abstract 21. DOI: doi:10.2310/6650.2005.x0015
7. Glueck CJ, Salehi M, Sieve L, Wang P. Growth, motor, and social development in breast- and formula-fed infants of metformin-treated women with polycystic ovary syndrome. J Pediatr. 2006;148:628-32.e2. PMID: 16737874
8. Thatcher SS, Jackson EM. Pregnancy outcome in infertile patients with polycystic ovary syndrome who were treated with metformin. Fertil Steril. 2006;85:1002-9. PMID: 16580387
9. Vanky E, Nordskar J, Leithe H et al. Breast size increment during pregnancy and breastfeeding in mothers with polycystic ovary syndrome: a follow-up study of a randomised controlled trial on metformin versus placebo. BJOG. 2012;19:1403-9. PMID: 22827167
Disclaimer: This material is provided for educational purposes only and is not intended for medical advice, diagnosis, or treatment. Consult your healthcare provider with any questions.
