This is sort of interesting...you have two studies of hCG administration routes and they appear to have completely opposite findings and a third which shows IM and SC administration of hCG to be equivalent...apparently it doesn't really matter how you inject it...
Hum Reprod. 2003 Nov;18(11):2294-7.
Bioavailability of hCG after intramuscular or subcutaneous injection in obese and non-obese women.
Chan CC, Ng EH, Chan MM, Tang OS, Lau EY, Yeung WS, Ho PC.
Department of Obstetrics and Gynaecology, Queen Mary Hospital, The University of Hong Kong, SAR, China. firstname.lastname@example.org
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.
Twenty four Chinese women, 12 with a body mass index (BMI) >/==" BORDER="0">28 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.
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.
Intramuscular dosing of hCG provided better bioavailability than s.c. dosing, but bioavailability was significantly less in obese women than in non-obese women.
Fertil Steril. 2003 Apr;79(4):881-5.
Subcutaneous versus intramuscular administration of human chorionic gonadotropin during an in vitro fertilization cycle.
Stelling JR, Chapman ET, Frankfurter D, Harris DH, Oskowitz SP, Reindollar RH.
Department of Obstetrics and Gynecology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston IVF, Boston, Massachusetts, USA. email@example.com
To confirm that hCG levels in follicular fluid and serum would be comparable between i.m. and s.c. administration of purified hCG.
In a prospective study, serum and follicular fluid levels of hCG after an i.m. or s.c. injection of 10,000 IU of hCG were evaluated 36 hours after injection, that is, at the time of oocyte retrieval.
This study was carried out in a university-affiliated IVF program.
Forty women undergoing oocyte retrieval were entered into the study at the time of egg retrieval, that is, 36 hours after hCG administration.
S.c. or i.m. injection of hCG.
MAIN OUTCOME MEASURE(S):
Serum and follicular fluid concentrations of hCG were evaluated 36 hours after injection at the time of oocyte retrieval.
There was a significantly higher serum hCG level in the s.c. group (348.6 +/- 98 IU/L) vs. the i.m. group (259.0 +/- 115 IU/L) and a significantly higher follicular fluid hCG level in the s.c. vs. the i.m. group (233.5 +/- 85 vs. 143.4 +/- 134 IU/L).
After purified hCG administration via the s.c. route, both serum and follicular fluid levels are greater compared with the i.m. route.
Hum Reprod. 1998 Jun;13(6):1461-4.
A randomized three-way cross-over study in healthy pituitary-suppressed women to compare the bioavailability of human chorionic gonadotrophin (Pregnyl) after intramuscular and subcutaneous administration.
Mannaerts BM, Geurts TB, Odink J.
Clinical Development Department, NV Organon, Oss, The Netherlands.
The objective of this study was to compare the bioavailability of s.c. and i.m. administration of human chorionic gonadotrophin (HCG; Pregnyl). In a randomized, single-centre, three-way cross-over study, 18 healthy pituitary-suppressed volunteers were assigned to single HCG injections of 5000 and 10,000 IU i.m. and 10,000 IU s.c. Rate (Cmax, t(max)) and extent [area under curve from zero to infinity (AUC(0-infinity))] of absorption of HCG were determined. Serum immunoactive HCG increased from 0.4-0.5 IU/l at baseline to mean peak concentrations, which were reached 20 h after injection of 156 IU/l with 5000 IU i.m., of 307 IU/l with 10,000 IU i.m. and of 339 IU/l with 10,000 IU s.c. Eight days after administration, < 10% of the maximum HCG activity was found for each regimen. The elimination half-life (t(1/2)) was on average 32-33 h, irrespective of the treatment regimen. Intramuscular and s.c. injections of 10,000 IU HCG were bioequivalent with respect to AUC(0-infinity). The Cmax and t(max) were also similar between the two administration routes but bioequivalence could not be proven due to intersubject variability. Intramuscular doses of 5000 IU and 10,000 IU HCG were dose-proportional. Since s.c. HCG is bioequivalent to i.m. HCG with respect to extent of absorption (its major pharmacokinetic variable) and is well tolerated, the s.c. administration route may be effectively and safely used in assisted reproduction. Moreover, since s.c. injection can be performed by the patients themselves, acceptability may be enhanced.