Chlormethiazole treatment and breast feeding

Four mothers receiving chlormethiazole for pre-eclampsia and their babies were the subjects of the investigation. Blood samples at delivery and blood and breast milk samples in the postpartum period were analysed for chlormethiazole. Concentrations ranged from 1.340 to 1.640 micrograms/g of sample of umbilical artery blood at birth, and fell to 0.010 to 0.153 micrograms/g in capillary blood 20 to 26 hours later. After the start of breast feeding, chlormethiazole in the babies was detectable in only 3 out of 27 serial blood samples and was 0.018, 0.009 and 0.006 micrograms/g. The highest calculated amount of chlormethiazole ingested at a breast feed was 37.2 micrograms. It is suggested that breast feeding should not be delayed solely on account of chlormethiazole therapy.