Serum steroid binding protein concentrations, distribution of progestogens, and bioavailability of testosterone during treatment with contraceptives containing desogestrel or levonorgestrel**Supported by a grant from Organon Scientific Development Group, Oss, The Netherlands.

The oral administration of 150 μg desogestrel and 30 μg ethinyl estradiol (EE2) increases (P< 0.001) serum concentrations of sex-hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG), whereas treatment with 150 μg levonorgestrel and 30 μg EE2only increases serum CBG concentrations. No changes in serum albumin concentrations occurred during or after treatment with either preparation, and increases in SHBG and CBG returned to the pretreatment values 1month after treatment ceased. The serum distribution of levonorgestrel was unchanged during treatment, whereas the increase in serum SHBG concentrations after treatment with the preparation containing desogestrel decreased (P< 0.001) the percentage of non-protein-bound 3-keto-desogestrel and the percentage of albumin-bound 3-keto-desogestrel but increased (P< 0.001) the SHBG-bound fraction. Oral contraceptives containing either progestogen decrease the mean serum non-protein-bound testosterone concentrations, especially during treatment with desogestrel (P< 0.001), and desogestrel may therefore be the more appropriate progestogen for the treatment of women prone to androgenic side effects.