Influence of Body Weight, Ethnicity, Oral Contraceptives and Pregnancy on the Pharmacokinetics of Azithromycin in Women of Child-Bearing Age

Women of child-bearing age commonly receive azithromycin for treatment of community acquired infections, including during pregnancy. This study determined azithromycin pharmacokinetics (PKs) in pregnant and nonpregnant women and identified covariates contributing to PK variability. Plasma samples were collected using a sparse sampling strategy in pregnant women, 12-40 weeks gestational age, and nonpregnant women of child bearing age receiving oral azithromycin for treatment of infection. PK data from extensive sampling conducted on 12 healthy women were also included. Plasma samples were assayed for azithromycin by high performance liquid chromatography. Population data were analyzed by nonlinear mixed effects modeling. The population analysis included 53 pregnant and 25 non12 pregnant women. A three compartment model with first order absorption and a lag time provided the best fit of the data. Lean body weight, pregnancy, ethnicity and co-administration of oral contraceptives were covariates identified as significantly influencing the oral clearance of azithromycin and, except for oral contraceptive use, intercompartmental clearance between the central and second peripheral compartment. No other covariate relationships were identified. Compared to non-pregnant women not receiving oral contraceptives, a 21% to 42% higher dose adjusted, azithromycin area under the plasma concentration-time curve (AUC) occurs in non- African American women who are pregnant or receiving oral contraceptives. Conversely, azithromycin AUC is similar between pregnant, African American women and non-pregnant women not receiving oral contraceptives. Although higher maternal and fetal azithromycin exposure suggests that lower doses be administered to non-African American women during pregnancy, consideration of azithromycin pharmacodynamics during pregnancy should guide any dose adjustments.