RESUMEN
OBJECTIVE: To investigate the excretion of gentamicin into human breast milk and resulting serum gentamicin levels in nursing newborn infants. METHODS: Women delivered by cesarean received gentamicin, 240 mg/day (80 mg intramuscularly three times a day) for 5 days postpartum. On day 4, maternal serum samples were collected 1 and 7 hours after gentamicin administration. Milk samples were collected 1, 3, 5, and 7 hours following administration. The infants were fed 1 hour after gentamicin administration, and serum samples were collected from the newborns 1 hour later. The concentrations of gentamicin were measured by a fluorescence polarization immunoassay. RESULTS: The mean (+/- standard deviation) maternal serum gentamicin levels at 1 and 7 hours were 3.94 +/- 1.12 and 1.02 +/- 0.78 microgram/mL, respectively. Milk gentamicin levels were: 0.42 +/- 0.26, 0.48 +/- 0.17, 0.49 +/- 0.17, and 0.41 +/- 0.25 microgram/mL at 1, 3, 5, and 7 hours, respectively. The mean milk:plasma gentamicin ratios were 0.11 and 0.44 at 1 and 7 hours, respectively. The correlation between maternal peak serum levels and milk levels was not statistically significant (P > .05). Detectable (above 0.27 microgram/mL) gentamicin levels were found in five of the ten newborn serum samples, with a mean level of 0.41 +/- 0.05 microgram/mL. CONCLUSION: Gentamicin is transferred into breast milk, and half of nursing newborn infants have detectable serum gentamicin levels.