home > drugs a-z list > jadelle (levonorgestrel implants (unavailable in us)) drug center > jadelle (levonorgestrel implants (unavailable in us)) drug - clinical pharmacology

Levonorgestrel is a totally synthetic and biologically active progestin that exhibits no significant estrogenic activity and is highly progestational. The absolute configuration conforms to that of D-natural steroids.

At least two mechanisms are active in preventing pregnancy: ovulation inhibition and thickening of the cervical mucus. Other mechanisms may add to these contraceptive effects.

Pharmacokinetics

Absorption

Levonorgestrel is delivered directly into interstitial fluids from the subdermal implants. However, the bioavailability of levonorgestrel after insertion of Jadelle® (levonorgestrel implants (unavailable in us)) implants compared with intravenous administration is not known. After placement of Jadelle® implants, maximum levonorgestrel concentrations are reached in about 2 to 3 days, with the mean ± standard deviation being 772 ± 414 pg/mL at 2 days. After the initial phase, mean levonorgestrel concentrations slowly decline to approximately 435 ± 172 pg/mL at 1 month, 357 ±155 pg/mL at 6 months, and 280 ± 123 pg/mL at 3 years. Concentrations at 4 and at 5 years are similar to those at 3 years.

TABLE 1: Serum Concentrations During Jadelle® Use

Serum levonorgestrel concentrations were found to be inversely related to body weight. Serum levonorgestrel concentrations in women weighing more than 70 kg were approximately half as high as in women weighing less than 50 kg.

Because of the range in serum concentrations and variation in individual response, serum concentrations alone are not predictive of the risk of pregnancy in an individual woman. Serum levonorgestrel concentrations in Jadelle® (levonorgestrel implants (unavailable in us)) users are substantially below those generally observed in users of oral contraceptives containing the progestins norgestrel or levonorgestrel.

Distribution

Levonorgestrel in serum is primarily protein bound. Approximately half is bound to sex hormone binding globulin (SHBG) and half to albumin. SHBG concentrations are depressed by levonorgestrel within a few days of administration, with resultant decreases in circulating levonorgestrel concentrations.

Metabolism

Levonorgestrel metabolic pathways have been only partially delineated. 16β-hydroxylation is an identified pathway of metabolism. Concentrations of metabolites in circulation soon exceed those of levonorgestrel, mostly as conjugated sulfates. Metabolic clearance rates may differ among individuals by several fold, which is believed to account in part for the wide variation observed in levonorgestrel serum concentrations among implant users.

Excretion

The elimination half-life of levonorgestrel is approximately 13 to 18 hours. Levonorgestrel and its metabolites are primarily excreted in the urine (40% to 68%) and about 16% to 48% are excreted in feces. After removal of the implants, levonorgestrel concentrations decrease below 100 pg/mL by 96 hours and below sensitivity of the assay by 5 days to 2 weeks.

Special Populations

Race

Studies were conducted among women of different races in Asia, North and South America, Europe and Africa. However, data on race were not collected in the clinical trials with Jadelle® (levonorgestrel implants (unavailable in us)) implants.

Hepatic Insufficiency

No formal studies have evaluated the effect of hepatic disease on the disposition of levonorgestrel. However, since levonorgestrel is metabolized in the liver, use in patients with markedly impaired liver function or liver disease is not recommended.

Renal Insufficiency

No formal studies have evaluated the effect of renal disease on the disposition of levonorgestrel.

Drug-Drug Interactions

See "DRUG INTERACTIONS" under PRECAUTIONS.

Last reviewed on RxList: 12/29/2008
This monograph has been modified to include the generic and brand name in many instances.