Transfer of metformin into human milk

In the past decade Type II diabetes has increased by 30%, particularly in younger people, including pregnant women (Rosenbloom et al. 1998, 1999). In addition, the use of metformin for treating polycystic ovarian syndrome (PCOS) has increased (Knockenhauer et al. 1998). PCOS affects approximately 5% of reproductive age patients. Metformin has been found to improve ovulatory function in insulin-resistant women with PCOS, to reduce first trimester miscarriage (Glueck et al. 2001), and to decrease the progression from impaired glucose tolerance to Type II diabetes mellitus (Inzucchi 2002). Therefore using metformin while breastfeeding is important, although to date no data are available on transfer of metformin into human milk or to the breastfed infant. The aim of this study was to characterize milk/plasma ratio (M/P) and infant dose for metformin in breastfeeding women and determine plasma concentrations and any effects in their infants. The hypothesis is that maternal metformin use is safe for the breastfed infant.