Levonorgestrel-only emergency contraceptive pills are reported to have an 89% effectiveness rate if taken within the recommended 72 hours after sex. The efficacy of the drug decreases by 50% for each 12 hour delay in taking the dose after the emergency contraceptive regimen has been started. Skin patch
Estradiol with levonorgestrel in the form of a skin patch is used under the brand name Climara Pro for hormone replacement therapy in postmenstrual women, treating symptoms such as hot flashes or osteoporosis. The simultaneous delivery of a progestogen such as levonorgestrel is necessary for the protection of the endometrium. Intrauterine device
The levonorgestrel intrauterine system (LNG-IUS) is a type of long-term birth control that releases the progestin into the uterine cavity. Levonorgestrel is released at a constant, gradual rate of 0.02 mg per day by the polydimethylsiloxane membrane of the device, which renders it effective for up to five years. Because it is inserted directly into the uterus, levonorgestrel is present in the endometrium in much higher concentrations that would result from a LNG-containing oral pill; the LNG-IUS delivers 391 ng of levonorgestrel to the inner uterine region while a comparable oral contraceptive delivers only 1.35 ng. This high level of levonorgestrel impedes the function of the endometrium, making it hostile for sperm transport, fertilization, and implantation of an ovum. Implant
Subcutaneous implants of levonorgestrel have been marketed as birth control implants under the brand names Norplant and Jadelle and are available for use in some countries. Contraindications
Known or suspected pregnancy is a contraindication of levonorgestrel as an emergency contraceptive.
It is a weakly androgenic progestin and in women may cause androgenic biochemical changes and side effects such as decreased sex hormone-binding globulin (SHBG) levels, decreased HDL cholesterol levels, weight gain, and acne.In combination with a potent estrogen like ethinylestradiol however, all contraceptives containing androgenic progestins are negligibly androgenic in practice and in fact can be used to treat androgen-dependent conditions like acne and hirsutism in women. This is because ethinylestradiol causes a marked increase in SHBG levels and thereby decreases levels of free and hence bioactive testosterone, acting as a functional antiandrogen. Nonetheless, contraceptives containing progestins that are less androgenic increase SHBG levels to a greater extent and may be more effective for such indications. Levonorgestrel is currently the most androgenic progestin that is used in contraceptives, and contraceptives containing levonorgestrel may be less effective for androgen-dependent conditions relative to those containing other progestins that are less androgenic. Other activity
Levonorgestrel stimulates the proliferation of MCF-7 breast cancer cells in vitro, an action that is independent of the classical PRs and is instead mediated via the progesterone receptor membrane component-1 (PGRMC1). Certain other progestins act similarly in this assay, whereas progesterone acts neutrally. It is unclear if these findings may explain the different risks of breast cancer observed with progesterone and progestins in clinical studies. Pharmacokinetics
The bioavailability of levonorgestrel is approximately 95% (range 85 to 100%). The plasma protein binding of levonorgestrel is about 98%. It is bound 50% to albumin and 48% to SHBG.