Bioavailability of hCG after intramuscular or subcutaneous injection in obese and non-obese women

Abstract

Background: Obese women require higher gonadotrophin doses for ovarian stimulation and to trigger ovulation. The bioavailability of a drug is affected by its route of administration. Herein, the bioavailability of hCG was compared after intramuscular (i.m.) or subcutaneous (s.c.) injection in obese and non-obese women. Methods: Twenty four Chinese women, 12 with a body mass index (BMI) ≥28 kg/m2 and 12 with a BMI of 20-25 kg/m2 were recruited as the obese and non-obese groups respectively. A single hCG injection was given intramuscularly on one occasion, and subcutaneously on a second occasion, separated by 4 weeks. Blood samples were taken at intervals for the pharmacokinetic study of hCG. Results: Examination of the hCG plasma concentration-time curve showed the area under the curve (AUC) and maximum concentration (Cmax) of hCG to be significantly higher after i.m. injection than after s.c. injection in both the obese and non-obese groups. However, the AUC and Cmax values in obese women were significantly lower than in non-obese women, irrespective of whether i.m. or s.c. dosing was employed. Conclusions: Intramuscular dosing of hCG provided better bioavailability than s.c. dosing, but bioavailability was significantly less in obese women than in non-obese women.