Progestogen pharmacokinetics

Significant differences in the pharmacokinetics of prednisolone amongst menopausal women have been described (SEDA-21, 419 412). The postmenopausal women had reduced unbound clearance (30%), reduced total clearance, and an increased half-life. Similar results are seen in the postmenopausal women who took estrogen or estrogen-progestogen therapy. 

Valproic acid, which is not an enzyme inducer, has no detectable effect on the pharmacokinetics of progestogens and estrogens (332). 

Jnng-Hoffmann C, Kuhl H. Interaction with the pharmacokinetics of ethinylestradiol and progestogens contained in oral contraceptives. Contraception 1989 40(3) 299-312. 

Krattenmacher, R. (2000) Drospirenone pharmacology and pharmacokinetics of a unique progestogen. Contraception, 62, 29-38. 

Pharmacokinetic data show that the progestogen component (levonorg-estrel, norethisterone) of combined oral contraceptives is not affected by ampicillin, clarithromycin, doxycycline, metronidazole, moxi-floxacin, or tetracycline. There is no reason to expect that the contraceptive efficacy of the various progestogen-only methods (tablets, implants, injections, lUDs) would be affected by antibacterials that alter gut flora and do not induce liver enzymes. 

---