Fetal Risk Summary
No reports linking the use of colistimethate with congenital defects have been located. The drug crosses the placenta at term (1).
Colistimethate was not teratogenic in rats at IM doses of 4.15 or 9.3 mg/kg (about 0.13 and 0.30 times the maximum recommended human dose on a mg/m2 basis [MRHD]) (2). The same weight doses in rabbits (about 0.25 and 0.55 times the MRHD) resulted in talipes varus in 2.6% and 2.9% of the fetuses, respectively. Increased resorption of rabbit embryos occurred at the highest dose.
Breast Feeding Summary
Colistimethate is excreted into breast milk. The milk:plasma ratio is 0.170.18 (3). Although this level is low, three potential problems exist for the nursing infant: modification of bowel flora, direct effects on the infant, and interference with the interpretation of culture results if a fever workup is required.
- MacAulay MA, Charles D. Placental transmission of colistimethate. Clin Pharmacol Ther 1967;8:57886.
- Product information. Coly-Mycin. Monarch Pharmaceuticals, 2000.
- Wilson JT. Milk/plasma ratios and contraindicated drugs. In Wilson JT, ed. Drugs in Breast Milk. Australia (Balgowlah):ADIS Press, 1981:789.