Levonorgestrel

Levonorgestrel is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand name Plan B among others, it is useful within 72 hours. This should not be confused with EllaOne which can be effective within 120 hours (5 days) of unprotected sex. The more time that has passed since sex, the less effective the medication becomes, and it does not work after pregnancy (implantation) has occurred. It decreases the chances of pregnancy by 57 to 93%. In an intrauterine device (IUD), such as Mirena among others, it is effective for the long-term prevention of pregnancy. A levonorgestrel-releasing implant is also available in some countries.
Common side effects include nausea, breast tenderness, headaches, and increased, decreased, or irregular menstrual bleeding. When used as an emergency contraceptive, if pregnancy occurs, there is no evidence that its use harms the baby. It is safe to use during breastfeeding. Birth control that contains levonorgestrel will not change the risk of sexually transmitted infections. It is a progestin and has effects similar to those of the hormone progesterone. It works primarily by preventing ovulation and closing off the cervix to prevent the passage of sperm.
Levonorgestrel was patented in 1960 and introduced for medical use together with ethinylestradiol in 1970. It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. It is available as a generic medication. In the United States, levonorgestrel-containing emergency contraceptives are available over the counter (OTC) for all ages. In 2016, it was the 223rd most commonly prescribed medication in the United States, with more than two million prescriptions.
Medical uses.
Birth control.
At low doses, levonorgestrel is used in monophasic and triphasic formulations of combined oral contraceptive pills, with available monophasic doses ranging from 100 to 250 µg, and triphasic doses of 50 µg/75 µg/125 µg. It is combined with the estrogen ethinylestradiol in these formulations.
At very low daily dose of 30 µg, levonorgestrel is used in some progestogen-only pill 
formulations.
Levonorgestrel is the active ingredient in a number of intrauterine devices including Mirena and Skyla. It is also the active ingredient in the birth control implants Norplant and Jadelle.
One of the more common forms of contraception that contains only levonorgestral is an IUD. One IUD, the Mirena is a small hollow cylinder containing levonorgestral and polydimethylsiloxane and covered with a release rate controlling membrane.
Emergency birth control.
Levonorgestrel is used in emergency contraceptive pills (ECPs), both in a combined Yuzpe regimen which includes estrogen, and as a levonorgestrel-only method. The levonorgestrel-only method uses levonorgestrel 1.5 mg (as a single dose or as two 0.75 mg doses 12 hours apart) taken within 3 days of unprotected sex, with one study indicating that beginning as late as 120 hours (5 days) after intercourse could be effective.
The primary mechanism of action of levonorgestrel as a progestogen-only emergency contraceptive pill is, according to International Federation of Gynecology and Obstetrics (FIGO), to prevent fertilization by inhibition of ovulation and thickening of cervical mucus. FIGO has stated that: "review of the evidence suggests that LNG [levonorgestreol] ECPs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling." In November 2013, the European Medicines Agency (EMA) approved a change to the label saying it cannot prevent implantation of a fertilized egg.
Other studies still find the evidence to be unclear. While it is unlikely that emergency contraception affects implantation it is impossible to completely exclude the possibility of post-fertilization effect.
In November 2013, the EMA also approved a change to the label for HRA Pharma's "NorLevo" saying: "In clinical trials, contraceptive efficacy was reduced in women weighing 75 kg [165 pounds] or more, and levonorgestrel was not effective in women who weighed more than 80 kg [176 pounds]." In November 2013 and January 2014, the FDA and the EMA said they were reviewing whether increased weight and body mass index (BMI) reduce the efficacy of emergency contraceptives.
An analysis of four WHO randomised clinical trials, published in January 2017, showed pregnancy rates of 1.25% (68/5428) in women with BMI under 25, 0.61% (7/1140) in women with BMI between 25 and 30, and 2.03% (6/295) in women with BMI over 30. These values yield an eight-fold reduction in efficacy for women with BMI over 30 compared to women with BMI under 25. However, emergency contraceptives remain effective regardless of BMI.
Hormone therapy.
Levonorgestrel is used in combination with an estrogen in menopausal hormone therapy. It is used under the brand name "Klimonorm" as a combined oral tablet with estradiol valerate and under the brand name "Climara Pro" as a combined transdermal patch with estradiol.
Available forms.
As a type of emergency contraception, levonorgestrel is used after unprotected intercourse to reduce the risk of pregnancy. However, it can serve different hormonal purposes in its different methods of delivery. It is available for use in a variety of forms:
By mouth.
Levonorgestrel can be taken by mouth as a form of emergency birth control. The typical dosage is either 1.5 mg taken once or 0.75 mg taken 12–24 hours apart. The effectiveness in both methods is similar. The most widely used form of oral emergency contraception is the progestin-only pill, which contains a 1.5 mg dosage of levonorgestrel. 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 5 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.
Side effects.
After an intake of 1.5 mg levonorgestrel in clinical trials, very common side effects (reported by 10% or more) included: hives, dizziness, hair-loss, headache, nausea, abdominal pain, uterine pain, delayed menstruation, heavy menstruation, uterine bleeding, and fatigue; common side effects (reported by 1% to 10%) included diarrhea, vomiting, and painful menstruation; these side effects usually disappeared within 48 hours. However, the long term side effects common with oral contraceptives such as arterial disease are lower with levonorgestrel than in combination pills.
Levonorgestrel as a contraceptive intrauterine device is associated with a higher risk of breast cancer than with non-use.
Overdose.
Overdose of levonorgestrel as an emergency contraceptive has not been described. Nausea and vomiting might be expected.
Interactions.
If taken together with drugs that induce the CYP3A4 cytochrome P450 liver enzyme, levonorgestrel may be metabolized faster and may have lower effectiveness. 
These include, but are not limited to barbiturates, bosentan, carbamazepine, felbamate, griseofulvin, oxcarbazepine, phenytoin, rifampin, St. John's wort and topiramate.
Pharmacology.
Levonorgestrel (LNG) is a progestin and has effects similar to those of the hormone progesterone. It works primarily by preventing ovulation and closing off the cervix to prevent the passage of sperm.
Pharmacodynamics.
Levonorgestrel is a progestogen; that is, an agonist of the progesterone receptor (PR), the main biological target of the progestogen sex hormone progesterone. It is also a weak agonist of the androgen receptor (AR), the main biological target of the androgen sex hormone testosterone. Levonorgestrel has no other important hormonal activity, including no estrogenic, glucocorticoid, or antimineralocorticoid activity. The lack of significant mineralocorticoid or antimineralocorticoid activity with levonorgestrel is in spite of a relatively high affinity for the mineralocorticoid receptor of as much as 75% of that of aldosterone. Due to its progestogenic activity, levonorgestrel has antigonadotropic effects, and is able to suppress fertility and gonadal sex hormone production in both women and men.
Androgenic activity.
Levonorgestrel is a weakly androgenic progestin and in women may cause androgenic side effects such as decreased sex hormone-binding globulin (SHBG) levels, decreased cholesterol levels, weight gain, and acne. In combination with a potent estrogen like ethinylestradiol however, all contraceptives containing androgenic progestins are negligibly androgenic in clinical practice and can in fact 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 relative extent and may be more effective for such indications. Levonorgestrel is currently the most androgenic progestin that remains 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.
Antigonadotropic effects.
In men, levonorgestrel causes marked suppression of circulating testosterone levels secondary to its antigonadotropic effects. Because of this, and due to its androgenic activity being only weak and hence insufficient for purposes of androgen replacement in males, levonorgestrel has potent functional antiandrogenic effects in men, and is able to produce associated adverse effects like decreased libido and erectile dysfunction among others. In relation to this, levonorgestrel has been combined with an androgen like testosterone or dihydrotestosterone when it has been studied as a hormonal contraceptive in men.
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. Levonorgestrel is metabolized in the liver, via reduction, hydroxylation, and conjugation (specifically glucuronidation and sulfation). Oxidation occurs primarily at the C2α and C16β positions, while reduction occurs in the A ring. 5α-Dihydrolevonorgestrel is produced as an active metabolite of levonorgestrel by 5α-reductase. The elimination half-life of levonorgestrel is 24 to 32 hours, although values as short as 8 hours and as great as 45 hours have been reported. About 20 to 67% of a single oral dose of levonorgestrel is eliminated in urine and 21 to 34% in feces.
Chemistry.
Levonorgestrel, also known as 17α-ethynyl-18-methyl-19-nortestosterone or as 17α-ethynyl-18-methylestr-4-en-17β-ol-3-one, is a synthetic estrane steroid and a derivative of testosterone. It is the C13β or levorotatory stereoisomer and enantiopure form of norgestrel, the C13α or dextrorotatory isomer being inactive. Levonorgestrel is more specifically a derivative of norethisterone (17α-ethynyl-19-nortestosterone) and is the parent compound of the gonane (18-methylestrane) subgroup of the 19-nortestosterone family of progestins. Levonorgestrel acetate and levonorgestrel butanoate are C17β esters of levonorgestrel. It has a molecular weight of 312.45 g/mol and a partition coefficient (logP) of 3.8.
History.
Norgestrel ("rac"-13-ethyl-17α-ethynyl-19-nortestosterone), the racemic mixture containing levonorgestrel and dextronorgestrel, was discovered by Hughes and colleagues at Wyeth in 1963 via structural modification of norethisterone (17α-ethynyl-19-nortestosterone). It was the first progestogen to be manufactured via total chemical synthesis. Norgestrel was introduced for medical use as a combined birth control pill with ethinylestradiol under the brand name "Eugynon" in Germany in 1966 and under the brand name "Ovral" in the United States 1968, and as a progestogen-only pill under the brand name "Ovrette" in the United States in 1973. Following its discovery, norgestrel had been licensed by Wyeth to Schering AG, which separated the racemic mixture into its two optical isomers and identified levonorgestrel (13β-ethyl-17α-ethynyl-19-nortestosterone) as the active component of the mixture. Levonorgestrel was first studied in humans by 1970, and was introduced for medical use in Germany as a combined birth control pill with ethinylestradiol under the brand name "Neogynon" in August 1970. A more widely used formulation, containing lower doses of ethinylestradiol and levonorgestrel, was introduced under the brand name "Microgynon" by 1973. In addition to combined formulations, levonorgestrel was introduced as a progestogen-only pill under the brand names "Microlut" by 1972 and "Microval" by 1974. Many other formulations and brand names of levonorgestrel-containing birth control pills have also been marketed.
Levonorgestrel, taken alone in a single high dose, was first evaluated as a form of emergency contraception in 1973. It was the second progestin to be evaluated for such purposes, following a study of quingestanol acetate in 1970. In 1974, the Yuzpe regimen, which consisted of high doses of a combined birth control pill containing ethinylestradiol and norgestrel, was described as a method of emergency contraception by A. Albert Yuzpe and colleagues, and saw widespread interest. Levonorgestrel-only emergency contraception was introduced under the brand name "Postinor" by 1978. Ho and Kwan published the first study comparing levonorgestrel only and the Yuzpe regimen as methods of emergency contraception in 1993 and found that they had similar effectiveness but that levonorgestrel alone was better-tolerated. In relation to this, the Yuzpe regimen has largely been replaced as a method of emergency contraception by levonorgrestrel-only preparations. Levonorgestrel-only emergency contraception was approved in the United States under the brand name "Plan B" in 1999, and has also been marketed widely elsewhere throughout the world under other brand names such as "Levonelle" and "NorLevo" in addition to "Postinor". In 2013, the Food and Drug Administration approved "Plan B One-Step" for sale over-the-counter in the United States without a prescription or age restriction.
Levonorgestrel has also been introduced for use as a progestogen-only intrauterine device under the brand names "Mirena" and "Skyla" among others, as a progestogen-only birth control implant under the brand names "Norplant" and "Jadelle", as a combined oral tablet with estradiol valerate for menopausal hormone therapy under the brand name "Klimonorm", and as a combined transdermal patch with estradiol for menopausal hormone therapy under the brand name "Climara Pro". Ester prodrugs of levonorgestrel such as levonorgestrel acetate and levonorgestrel butanoate have been developed and studied as other forms of birth control such as long-acting progestogen-only injectable contraceptives and contraceptive vaginal rings, but have not been marketed for medical use.
Society and culture.
Generic names.
"Levonorgestrel" is the generic name of the drug and its , , , , , and , while "lévonorgestrel" is its . It is also known as "d-norgestrel", "d(–)-norgestrel", or "-norgestrel", as well as by its developmental code names "WY-5104" (Wyeth) and "SH-90999" (Schering AG).
Brand names.
Levonorgestrel is marketed alone or in combination with an estrogen (specifically ethinylestradiol, estradiol, or estradiol valerate) under a multitude of brand names throughout the world, including "Alesse", Altavera, Alysena, Amethia, Amethyst, Ashlyna, Aviane, Camrese, Chateal, "Climara Pro", "Cycle 21", Daysee, Emerres, Enpresse, Erlibelle, "Escapelle", Falmina, Introvale, Isteranda, "Jadelle", "Jaydess", Jolessa, "Klimonorm", Kurvelo, Kyleena, Lessina, "Levlen", Levodonna, "Levonelle", Levonest, Levosert, Levora, Liletta, "Loette", "Logynon", "LoSeasonique", Lutera, Lybrel, Marlissa, "Microgynon", "Microlut", "Microvlar", Min-Ovral, "Miranova", "Mirena", My Way, Myzilra, Next Choice, "Nordette", Norgeston, NorLevo, "Norplant", One Pill, Option 2, Orsythia, Ovima, Ovranette, "Plan B", "Plan B One-Step", Portia, "Postinor", "Postinor-2", Preventeza, Ramonna, "Rigevidon", Quartette, Quasense, "Seasonale", "Seasonique", "Skyla", Sronyx, Tri-Levlen, "Trinordiol", Triphasil, "Triquilar", "Tri-Regol", Trivora, and Upostelle, among many others. These formulations are used as emergency contraceptives, normal contraceptives, or in menopausal hormone therapy for the treatment of menopausal symptoms.
As an emergency contraceptive, levonorgestrel is often referred to colloquially as the "morning-after pill".
Availability.
Levonorgestrel is very widely marketed throughout the world and is available in almost every country.
Accessibility.
Levonorgestrel-containing emergency contraception is available over-the-counter in some countries, such as the United States.
A policy update in 2015, required all Indian Health Services-run pharmacies, clinics, and emergency departments to have Plan B One-Step in stock, to distribute it to any woman (or her representative) who asked for it without a prescription, age verification, registration or any other requirement, to provide orientation training to all staff regarding the medication, to provide unbiased and medically accurate information about emergency contraception, and to make someone available at all times to distribute the pill in case the primary staffer objected to providing it on religious or moral grounds.
Research.
Levonorgestrel has been studied in combination with androgens such as testosterone and dihydrotestosterone as a hormonal contraceptive for men.