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PK studies to guide dosing of azithromycin (AZ) for pregnancy specific conditions, such as preterm premature rupture of membranes (PPROM), and data on accumulation of AZ in fetal compartment are lacking. We aim to evaluate feasibility of non-invasive collection of amniotic fluid (AF), validate an assay for AZ in AF, and describe concentration of AZ in the amniotic cavity over one week following a single maternal dose.


Patients with PPROM treated with 1g AZ PO once and wore underwear lining pads to collect AF as it leaked. AF strained from each pad, up to 10cc collected, centrifuged and frozen.

Calibration curve established using range of 1 to 200 ng/mL, with Azithromycin-D3 as internal standard. Spiked standards and samples were extracted with plasma to ACN ratio as 1:2, and centrifuged. The clean supernatant was subjected to LCMS runs using Thermo-Orbitrap coupled with Dionex 3000 UHPLC system under +ve ion mode and sample 5µL injection volume. The chromatographic separations were done using HSS XSelect C18 reverse phase column using 50:50 water and ACN with 0.1% FA as mobile phase, flow rate of 0.250 mL/min. The linearity equation (y= 10945x, r2>0.99) established using average of 8 injections over 4 days; 2 injections per day. AZ from AF samples was quantitated in duplicate and expressed as concentration/time profile.


Five patients were enrolled. Mean gestational age on admission with PPROM was 27.5 ±2.3wk with a median latency of 7 days [IQR 4-13]. A median of 2 samples/day [IQR 1-3] were collected per participant. Azithromycin was quantified in duplicate; intra-assay coefficient of variation was 17%. Azithromycin concentration was <60ng/ml after day 3. Azithromycin concentration was positively correlated with IL-8 (r=0.38, p=0.03), IL1a (r=0.39, p=0.03), and IL-1b (r=0.36, p=0.04) in amniotic fluid.


This simple technique for noninvasive collection of AF allows for precise quantification of AZ in AF with LCMS. AZ persists in the fetal compartment for at least seven days after a single maternal dose, although not necessarily at an adequate inhibitory concentration.

Publication Date



pregnancy, pharmacology, PPROM


Medicine and Health Sciences | Obstetrics and Gynecology


Presented at the 2021 American Society for Clinical Pharmacology and Therapeutics Annual Meeting

Noninvasive amniotic fluid sampling to establish PK of azithromycin in pregnancy