Pharmacokinetics of 250 μg anti‐D IgG in the third trimester of pregnancy: An observational study

Abstract

OBJECTIVE: We present a pharmacokinetic study evaluating a single intramuscular dose of 250 μg anti-D immunoglobulin in the third trimester of pregnancy. The aim of the study was to determine the kinetic profile and duration of detectable levels of anti-D. DESIGN: Prospective observational study. SETTING: Antenatal outpatient clinic. POPULATION: Healthy Rhesus D (RhD)-negative pregnant women with an RHD-positive fetus. METHODS: Serial plasma anti-D quantitations following antenatal administration of anti-D immunoglobulin were performed using flow cytometry. Kinetic profiles for anti-D levels were generated from the concentration values at predetermined sampling time points. The half-lives were calculated by linear regression analysis. Main outcome measures. Time vs. concentration profile, half-life and anti-D concentration ≥1 ng/mL close to term. RESULTS: The maximal plasma concentration of anti-D was usually seen at 3-10 days postinjection, with a median value of 25 ng/mL. The half-life varied between individuals, with a median of 23 days. We found detectable levels of anti-D IgG within two weeks of parturition in 11 of 12 women. CONCLUSIONS: The preparation of anti-D immunoglobulin used in the present study, if administrated in pregnancy week 28-30, is associated with detectable levels of anti-D in most women at the time of delivery. Although the half-time is 23 days, it is uncertain whether all mothers have adequate anti-D concentrations at term. Alternative strategies may be evaluated in the future, with repeated administration of antenatal prophylaxis at term rather than conventional postpartum administration of anti-D.