Products
Levonorgestrel is commercially available as the so-called morning-after pill in tablet form (e.g., NorLevo, generics). It is available under a doctor’s care. Since 2002, it may also be sold in pharmacies for emergency contraception after structured professional counseling and dispensing documentation. Levonorgestrel is also contained in other hormonal contraceptives. These are tablets containing ethinyl estradiol (the “pill”) and intrauterine devices (“IUDs”). This article refers to emergency contraception.
Structure and properties
Levonorgestrel (C21H28O2, Mr = 312.5 g/mol) is a white to almost white crystalline powder that is practically insoluble in water. It is the D-enantiomer of norgestrel, a racemate of D- and L-norgestrel.
Effects
Levonorgestrel (ATC G03AC03) inhibits or delays ovulation. It is no longer effective if the egg has already implanted and does not cause abortion. If pregnancy occurs or already exists despite emergency contraception, the drug poses no risk to the baby. Levonorgestrel can prevent most, but not all, unintended pregnancies. It is less reliable than continuous use of an oral contraceptive. Levonorgestrel does not provide further protection until the end of the cycle. Therefore, a barrier method (such as a condom) should be used.
Indications
For emergency contraception within 72 hours (= 3 days) of unprotected intercourse or identifiable failure of mechanical methods, or in other circumstances.
Dosage
According to the SmPC. The tablet is taken as a single dose before meals within 72 hours (= 3 days) after unprotected sexual intercourse. Preferably within 12 hours and generally as soon as possible. Efficacy decreases rapidly over time. Levonorgestrel can be taken at any time during the menstrual cycle. If vomiting occurs within three hours of taking the tablet, the active substance is not fully absorbed. Therefore, another tablet should be obtained and taken immediately, possibly in combination with an antiemetic.
Contraindications
- Hypersensitivity
- Severe liver dysfunction
- Pregnancy
Full precautions can be found in the drug label.
Interactions
CYP3A4 is involved in the biotransformation of levonorgestrel. Therefore, the degradation of CYP inducers may be increased and the efficacy of the drug may be reduced. CYP inducers include, for example, phenobarbital, phenytoin, primidone, carbamazepine, rifabutin, rifampicin, griseofulvin, ritonavir, and drugs containing St. John’s wort. In this case, the use of a copper IUD is possible.
Adverse effects
With the exception of bleeding disorders, adverse effects are transient but may last up to two days because levonorgestrel has a long half-life of 43 hours. Nausea, lower abdominal pain, headache, fatigue, dizziness, and breast tenderness are very common. Menstrual irregularities such as spotting, irregular or increased bleeding, are also very common. Menstruation may occur earlier or later. Diarrhea and vomiting are common.
