Oral Contraception

Combination oral contraceptives act by suppression of gonadotropins. Although the primary mechanism of this action is inhibition of ovulation, other alterations include changes in the cervical mucus (which increase the difficulty of sperm entry into the uterus) and the endometrium (which reduce the likelihood of implantation).

Receptor binding studies, as well as studies in animals and humans, have shown that norgestimate and 17-deacetyl norgestimate, the major serum metabolite, combine high progestational activity with minimal intrinsic androgenicity.^90-93 Norgestimate, in combination with ethinyl estradiol, does not counteract the estrogen-induced increases in sex hormone binding globulin (SHBG), resulting in lower serum testosterone.^90,91,94

Pharmacokinetics

Absorption

Norgestimate (NGM) and ethinyl estradiol (EE) are rapidly absorbed following oral administration. Norgestimate is rapidly and completely metabolized by first-pass (intestinal and/or hepatic) mechanisms to norelgestromin (NGMN) and norgestrel (NG), which are the major active metabolites of norgestimate. Mean pharmacokinetic parameters for NGMN, NG and EE during three cycles of administration of ORTHO TRI-CYCLEN® Lo are summarized in Table 1. These results indicate that: (1) Peak serum concentrations of NGMN and EE were generally reached by 2 hours after dosing; (2) Accumulation following multiple dosing of the 180 µg NGM / 25 µg dose is approximately 1.5 to 2 fold for NGMN and approximately 1.5 fold for EE compared with single dose administration, in agreement with that predicted based on linear kinetics of NGMN and EE; (3) The kinetics of NGMN are dose proportional following NGM doses of 180 to 250 µg; (4) Steady-state conditions for NGMN following each NGM dose and for EE were achieved during the three cycle study; (5) Non-linear accumulation (4.5-14.5 fold) of norgestrel was observed as a result of high affinity binding to SHBG, which limits its biological activity.¹⁰⁰ The effect of food on the pharmacokinetics of ORTHO TRI-CYCLEN® Lo has not been studied. Table 1 provides a summary of norelgestromin, norgestrel and ethinyl estradiol pharmacokinetic parameters.

Table 1: Mean (SD) Pharmacokinetic Parameters of ORTHO TRI-CYCLEN® Lo During a Three Cycle Study

Distribution

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