Placental passage of clarithromycin surpasses other macrolide antibiotics

Objective: Infection of the amnion cavity with Ureaplasma urealyticum continues to be a therapeutic challenge. The transplacental transfer rates of macrolide antibiotics are low, and tetracyclines and quinolones are contraindicated in pregnancy. The aim of this study was to investigate placental transfer of clarithromycin in a well-studied placental perfusion model to determine whether clarithromycin surpasses the transfer rate of other macrolide antibiotics in similar models. Study Design: Ten placentas that were obtained immediately after delivery were perfused with clarithromycin (3 μg/mL) plus a reference substance (antipyrine). Open circulation placental preparations were used to evaluate steady-state pharmacodynamics and transplacental gradient formation. Drug concentrations were measured by high-performance liquid chromatography. Results: The mean transplacental transfer of clarithromycin was 6.1% (95% CI, 1.8%). Conclusion: Because of its enhanced placental passage compared with other macrolide antibiotics, clarithromycin that is given after the first trimester (after embryogenesis) may be an appropriate candidate in treatment trials of genital mycoplasma and ureaplasma infections during pregnancy. (Am J Obstet Gynecol 2003;188:816-9.)