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

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) greater than or equal to28 kg/m(2) and 12 with a BMI of 20-25 kg/m(2) 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 (C-max) 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 C-max 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.