Maternal-fetal pharmacological activity of amikacin

Thirty healthy gravid patients of six to 20 weeks' gestation each received a single dose of 7.5 mg of amikacin/kg within 24 hr prior to elective hysterectomy. The half-life (t1/2) of amikacin in maternal serum was 2.07 hr. The mean peak concentration of amikacin in the sera of these patients was slightly lower than that in nonpregnant adults. Two-thirds of the placental samples had amikacin concentrations of greater than or equal to 8 microng/g during the 20-hr interval between drug injection and delivery time. In fetal kidney the concentration of amikacin peaked at a level of 22.4 microng/g at 12 hr after administration. The peak concentration of amikacin in fetal urine was 24 microng/ml, and the t1/2 was 3.2 hr. High levels of the drug in fetal urine and low levels in fetal serum (less than 4 microng/ml) and amniotic fluid (less than 3 microng/ml) were unrelated to high levels found in fetal kidney. Levels of amikacin in fetal lung were 1.4-8.0 microng/g during intervals of 1-16 hr between administration of the drug and time of delivery. With the increasing number of drugs available for use, both potential benefits and risks for the fetus must be considered when prescribing an antibiotic to treat the infected gravid patient, and it should be kept in mind that low levels in body fluid may not be equated with safety.