The full, clinically endorsed recommendation should be obtained from Lareb.   

Rationale for drug selection  

Azithromycin is used for bacterial infections in pregnancy, such as Chlamydia trachomatis. As pregnancy-induced changes change the pharmacokinetics of some drugs, dose adjustments might be needed.

Pharmacokinetics of azithromycin in pregnancy 

Available pharmacokinetic studies indicate that plasma concentration of azithromycin during pregnancy is very similar to the non-pregnant state. In the case of azithromycin, pregnancy-related changes in hepatic enzymes and renal handling do not translate into a consistent change in maternal plasma concentrations. Additionally, the drug distributes extensively into tissues, with tissue concentrations greatly exceeding plasma levels after oral dosing, and this pattern does not appear different in pregnancy. Therefore, dose adjustments during pregnancy might not be necessary. The placental transfer of azithromycin appears to be variable, with placental perfusion experiments showing minimal transfer, while in-vivo studies report neonatal levels that are approximately 50–80% of maternal levels. Maternal-foetal PBPK provided additional evidence on the minimal differences in between nonpregnant and pregnant individuals at various gestational ages. This supported the dosing decision-making.

Benefits and risks with the proposed drug adjustments 

Based on the validated PBPK model simulations the plasma concentrations of azithromycin are very similar between nonpregnant and pregnant populations. Azithromycin accumulates in tissue, and there is no evidence to suggest that this process differs significantly between the nonpregnant and pregnant states. Therefore, no dose adjustments are proposed.

In short 

Azithromycin pharmacokinetics appear unchanged in pregnancy. Overall safety data are reassuring, Consult Lareb for the model-informed dosing recommendations.