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  • Title: The relative bioavailability of levonorgestrel and ethinylestradiol when administered in tablet and capsule form.
    Author: Back DJ, Killick SR, Stevenson PJ, Shenoy N, Elstein M, Cohen M.
    Journal: Contraception; 1987 Sep; 36(3):321-6. PubMed ID: 3119288.
    Abstract:
    The relative bioavailability of levonorgestrel (LNG) and ethinylestradiol (EE2) administered as a conventional tablet (150/30) or capsule has been assessed in a randomized two-period crossover study in 9 healthy volunteer women. Serum concentrations were monitored for 24h post-dosing. There was no significant difference in any of the pharmacokinetic parameters determined for either steroid. Hence the relative bioavailability is similar after tablet and capsule formulations. 9 female volunteers, aged 18-38 years participated in this study contrasting the bioavailability of levonorgestrel (LNG) and ethinylestradiol (EE2). Each subject received a combination of LNG (150mcg) and EE2 (30mcg) in a soft gelatin capsule form and in tablet form, in random sequence on separate occasions in each of 2 consecutive menstrual cycles. Blood samples were drawn at 0, 0.5, 1, 1.5, 1, 1.5, 3, 4, 5, 6, 7, 8, and 24 hours, and measured by radioimmunoassay after clotting and serum. There was no significant difference in the kinetics of either steroid when data for capsule vs. tablet form were compared. LNG is almost completely bioavailable, while EE2 has a bioavailability of 50% with extensive presystemic metabolism occurring principally in the intestinal wall. However, this study demonstrates no significant improvement in the bioavailability when comparing a capsule with a tablet formulation. The capsule formulation therefore offered little potential for reducing the total steroid dose or maintaining a more constant blood level of contraceptive steroid.
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