|Systematic (IUPAC) name|
|Routes||Implant; insert (extended-release); oral|
|Metabolism||Hepatic via CYP3A4|
|Half-life||36 ± 13 hours|
|Excretion||Renal: 45%; Fecal:32%|
|ATC code||G03 G03|
|Mol. mass||312.446 g/mol|
|(what is this?)|
Levonorgestrel (or l-norgestrel or D-norgestrel) (Plan B, Next Choice, Postinor, "the morning after pill," and others) is a second generation progestin (synthetic progestogen) used as an active ingredient in some hormonal contraceptives, including combined oral contraceptive pills, progestogen only pills, emergency contraceptive pills, intrauterine systems, contraceptive implants, and hormone replacement therapy.
It is on the World Health Organization's List of Essential Medicines, a list of the most important medication needed in a basic health system.
At low doses, levonorgestrel is used in monophasic and triphasic formulations of combined oral contraceptive pills, with available monophasic doses ranging from 100-250 µg, and triphasic doses of 50 µg/75 µg/125 µg.
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 FIGO, to prevent fertilization by inhibition of ovulation. The International Federation of Gynecology and Obstetrics (FIGO) has issued a statement 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 for HRA Pharma's NorLevo saying it cannot prevent implantation of a fertilized egg.
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.
Levonorgestrel is the active ingredient in the Mirena & Skyla (Jaydess) intrauterine system.
Hormone replacement therapy
After intake of levonorgestrel 1.5 mg in clinical trials, very common effects (reported by 10% or more) included: dizziness, headache, nausea, abdominal pain, uterine pain, delay of menses, heavy menses, uterine bleeding, or fatigue; common effects (reported by 1% to 10%) included diarrhea, vomiting, or painful menses; these effects usually disappeared within 48 hours.
Levonorgestrel (levo=left) is one form of a hormone that exists in two mirror image left and right forms. (See Chirality (chemistry).)
Its in vitro relative binding affinities at human steroid hormone receptors are: 323% that of progesterone at the progesterone receptor, 58% that of testosterone at the androgen receptor, 17% that of aldosterone at the mineralocorticoid receptor, 7.5% that of cortisol at the glucocorticoid receptor, and <0.02% that of estradiol at the estrogen receptor.
There are many brand names of levonorgestrel-only ECPs, including: Escapelle, Plan B, Levonelle, Glanique, NorLevo, Postinor-2, i-pill, "Next Choice" and 72-HOURS.
- "WHO Model List of EssentialMedicines". World Health Organization. October 2013. Retrieved 22 April 2014.
- Trussell, James; Schwarz, Eleanor Bimla (2011). "Emergency contraception". In Hatcher, Robert A.; Trussell, James; Nelson, Anita L.; Cates, Willard Jr.; Kowal, Deborah; Policar, Michael S. Contraceptive technology (20th revised ed.). New York: Ardent Media. pp. 113–145. ISBN 978-1-59708-004-0. ISSN 0091-9721. OCLC 781956734. p. 121:
Mechanism of action
When used as a regular or emergency method of contraception, copper-releasing IUCs act primarily to prevent fertilization. Emergency insertion of a copper IUC is significantly more effective than the use of ECPs, reducing the risk of pregnancy following unprotected intercourse by more than 99%.2,3 This very high level of effectiveness implies that emergency insertion of a copper IUC must prevent some pregnancies after fertilization.
Emergency contraceptive pills
To make an informed choice, women must know that ECPs—like the birth control pill, patch, ring, shot, and implant,76 and even like breastfeeding77—prevent pregnancy primarily by delaying or inhibiting ovulation and inhibiting fertilization, but may at times inhibit implantation of a fertilized egg in the endometrium. However, women should also be informed that the best available evidence indicates that ECPs prevent pregnancy by mechanisms that do not involve interference with post-fertilization events.
ECPs do not cause abortion78 or harm an established pregnancy. Pregnancy begins with implantation according to medical authorities such as the US FDA, the National Institutes of Health79 and the American College of Obstetricians and Gynecologists (ACOG).80
Ulipristal acetate (UPA). One study has demonstrated that UP can delay ovulation.81... Another study found that UPA altered the endometrium, but whether this change would inhibit implantation is unknown.82
Progestin-only emergency contraceptive pills. Early treatment with ECPs containing only the progestin levonorgestrel has been show to impair the ovulatory process and luteal function.83–87
Combined emergency contraceptive pills. Several clinical studies have shown that combined ECPs containing ethinyl estradiol and levonorgestrel can inhibit or delay ovulation.107–110
- RCOG Faculty of Sexual & Reproductive Healthcare, Clinical Effectiveness Unit (January 2012). Clinical guidance: emergency contraception. London: Royal College of Obstetricians and Gynaecologists. ISSN 1755-103X. Retrieved 2012-04-30. p.3:
How does EC work?
In 2002, a judicial review ruled that pregnancy begins at implantation, not fertilisation.8 The possible mechanisms of action should be explained to the patient as some methods may not be acceptable, depending on individual beliefs about the onset of pregnancy and abortion.
Copper-bearing intrauterine device (Cu-IUD). Copper is toxic to the ovum and sperm and thus the copper-bearing intrauterine device (Cu-IUD) is effective immediately after insertion and works primarily by inhibiting fertilisation.9–11 A systematic review on mechanisms of action of IUDs showed that both pre- and postfertilisation effects contribute to efficacy.11 If fertilisation has already occurred, it is accepted that there is an anti-implantation effect,12,13
Levonorgestrel (LNG). The precise mode of action of levonorgestrel (LNG) is incompletely understood but it is thought to work primarily by inhibition of ovulation.16,17
Ulipristal acetate (UPA). UPA’s primary mechanism of action is thought to be inhibition or delay of ovulation.2
- UNDP/UNFPA/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP) (March 25, 2010). "Fact sheet on the safety of levonorgestrel-alone emergency contraceptive pills (LNG ECPs)". Geneva: World Health Organization.
Can LNG ECPs cause an abortion?
LNG ECPs do not interrupt an established pregnancy or harm a developing embryo.15 The evidence available to date shows that LNG ECP use does not prevent a fertilized egg from attaching to the uterine lining. The primary mechanism of action is to stop or disrupt ovulation; LNG ECP use may also prevent the sperm and egg from meeting.16
- Speroff, Leon; Darney, Philip D. (2011). "Special uses of oral contraception: emergency contraception, the progestin-only minipill". A clinical guide for contraception (5th ed.). Philadelphia: Lippincott Williams & Wilkins. pp. 153–166. ISBN 978-1-60831-610-6. p. 155:
Emergency postcoital contraception
Mechanism and efficacy
- Belluck, Pam (June 6, 2012). "No abortion role seen for morning-after pill". The New York Times. p. A1.
Belluck, Pam (June 6, 2012). "Drug's nickname may have aided politicization". The New York Times. p. A14.
- International Federation of Gynecology and Obstetrics (FIGO) and International Consortium for Emergency Contraception (ICEC) (April 4, 2011). "Mechanism of action: How do levonorgestrel-only emergency contraceptive pills (LNG ECPs) prevent pregnancy?". London: International Federation of Gynecology and Obstetrics.
Levonorgestrel-only emergency contraceptive pills:
• Interfere with the process of ovulation;
• May possibly prevent the sperm and the egg from meeting.
Implications of the research:
• Inhibition or delay of ovulation is LNG ECPs principal and possibly only mechanism of action.
• Review of the evidence suggests that LNG-ECs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling.
• The fact that LNG-ECs have no demonstrated effect on implantation explains why they are not 100% effective in preventing pregnancy, and are less effective the later they are taken. Women should be given a clear message that LNG-ECs are more effective the sooner they are taken.
• LNG ECPs do not interrupt a pregnancy (by any definition of the beginning of pregnancy). However, LNG ECPs can prevent abortions by reducing unwanted pregnancies.
- Belluck, Pam (November 26, 2013). "New birth control label counters lawsuit claim; European authorities found that a drug like Plan B One-Step cannot prevent fertilized eggs from implanting in the womb". The New York Times. Retrieved March 5, 2014.
HRA Pharma (November 2013). "NorLevo 1.5 mg tablet Patient Information Leaflet (PIL)". Dublin: Irish Medicines Board. Retrieved March 5, 2014. "NorLevo works by stopping your ovaries from releasing an egg. It cannot stop a fertilized egg from attaching to the womb."
HRA Pharma (November 2013). "5.1 Pharmacodynamic properties". "NorLevo 1.5 mg tablet Summary of Product Characteristics (SPC)". Dublin: Irish Pharmaceutical Healthcare Association. Retrieved March 5, 2014.
European Medicines Agency (January 24, 2014). "Review of emergency contraceptives started". London: European Medicines Agency. Retrieved March 5, 2014.
- Glasier, Anna; Cameron, Sharon T.; Blithe, Diana; Scherrer, Bruno; Mathe, Henri; Levy, Delphine; Gainer, Erin; Ulmann, Andre (October 2011). "Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel". Contraception 84 (4): 363–367. doi:10.1016/j.contraception.2011.02.009. PMID 21920190.
- Trussell, James; Raymond, Elizabeth G.; Cleland, Kelly (February 2014). "Emergency contraception: a last chance to prevent unintended pregnancy". Princeton: Office of Population Research at Princeton University, Association of Reproductive Health Professionals. Retrieved April 9, 2014.
- HRA Pharma (November 2013). "4.8 Undesireable effects". "NorLevo 1.5 mg tablet Summary of Product Characteristics (SPC)". Dublin: Irish Pharmaceutical Healthcare Association. Retrieved April 9, 2014.
- Edgren RA, Stanczyk FZ (1999). "Nomenclature of the gonane progestins". Contraception 60 (6): 313. doi:10.1016/S0010-7824(99)00101-8. PMID 10715364.
- Sitruk-Ware R (2006). "New progestagens for contraceptive use". Hum Reprod Update 12 (2): 169–78. doi:10.1093/humupd/dmi046. PMID 16291771.
- Trussell, James; Cleland, Kelly (2007-04-10). "Emergency Contraceptive Pills Worldwide". Princeton University. Retrieved 2007-05-28.
- Levonelle manufacturer's product information from Schering
- Monograph for levonorgestrel - Uk Medicines Information
- U.S. National Library of Medicine: Drug Information Portal - Levonorgestrel