Serum Levels of levonorgestrel and sex hormone binding globulin following vaginal and oral administration of combined steroid contraceptive tablets

ABSTRACT

Ten women were treated daily with a standard dose contraceptive tablet [Neovlar, Shiring] consisting of 0.25 mg levonorgestrel in combination with 0.05 mg of ethinylestradiol. Five women used the tablet vaginally while the other five used it orally. Blood samples were taken frequently during the first day of treatment and after one and two hours from taking the tablets on treatment days 7 and 14. Serum levonorgestrel [LNG] levels were measured by radioimmunoassay and sex hormone binding globulin [SHBG] was quantitated by means of charcoal assay. On the first day, peak concentration of LNG of 5.1 ng/ml was reached after two hours in the oral group whereas in the vaginal group the peak concentration [2.2 ng/ml] was reached after four hours. After 24 hours, mean serum levels of LNG were 1.1 and 0.69 ng/ml in the oral and vaginal groups, respectively. In both groups, mean LNG concentrations increased dramatically on day 7 and 14 compared to the first day. There was no significant difference between the two groups in LNG concentrations, except after 2 hours on the first day. SHBG levels were increased after one day of treatment. By day 14 of treatment, there was a 3.5 to 4.5 folds rise in SHBG levels from pretreatment values in both groups. However, there was no significant difference in SHBG levels between the two groups throughout the study. A high correlation was found between serum levels of SHBG and LNG in both the vaginal and oral groups. The results suggested that increase in serum LNG levels in women receiving combined contraceptive tablets either vaginally or orally is due to the increased levels of SHBG. The presence of a measurable concentration of LNG up to 24 hours after taking the tablet in the vaginal group is consistent with the previously reported clinical contraceptive efficacy of combined contraceptive pills when given vaginally