ADR that result in revision of patient information
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| The United Kingdom: Levonorgestrel-containing emergency hormonal contraception: advice on interactions with hepatic enzyme inducers and contraceptive efficacy |
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The Medicines and Healthcare products Regulatory Agency (MHRA) advised that medicines or herbal remedies that induce CYP3A4 enzymes reduce blood levels of levonorgestrel, may reduce emergency contraceptive efficacy.
The MHRA issued updated advice for healthcare professionals:
• women seeking emergency contraception who have used cytochrome P450 3A4 (CYP3A4) enzyme inducers within the last 4 weeks, should:
- preferably use a non-hormonal emergency contraceptive—ie, a copper intrauterine device
- if this is not an option, double the usual dose of levonorgestrel from 1.5 milligrams to 3 milligrams (ie, 2 packs)
• for these women:
- provide advice on highly effective ongoing contraception that is not affected by hepatic enzyme-inducing drugs
- advise them to have a pregnancy test to exclude pregnancy after use of levonorgestrel-containing emergency contraception
- advise them to seek prompt medical advice if they do become pregnant
This updated advice is in line with existing guidance from UK experts in sexual and reproductive health, and applies to both prescription and non-prescription supply which will help ensure that women receive consistent advice. Product information for healthcare professionals and women and the outer packaging for levonorgestrel emergency contraception are being updated with this advice.
Levonorgestrel-containing emergency contraception is used to prevent unintended pregnancy when taken within 72 hours (3 days) of unprotected intercourse or failure of a contraceptive method. The sooner it is taken after having unprotected sex, the more effective it will be. In the UK, levonorgestrel-containing emergency contraception is available with or without a prescription as a single 1500 microgram tablet, or on prescription as two 750 microgram tablets taken as a single dose.
Concomitant use of liver enzyme inducers—mainly inducers of CYP3A4 enzymes—increases the metabolism of levonorgestrel. Examples of enzyme inducers that reduce plasma levonorgestrel levels are some medicines used to treat:
• epilepsy (eg, barbiturates, primidone, phenytoin, carbamazepine)
• tuberculosis (eg, rifampicin, rifabutin)
• HIV (eg, ritonavir, efavirenz)
• fungal infections (eg, griseofulvin)
Concomitant administration of the antiretroviral efavirenz (used to treat HIV) reduces plasma levels (AUC) of levonorgestrel by around 50%. Data are not available for all CYP3A4 enzyme inducers; however, studies of levonorgestrel-containing combined hormonal contraceptives show that other hepatic enzyme-inducing medicines or herbal medicines may produce similar reductions in plasma levels. These contraceptive products already contain advice on additional or alternative methods of contraception.
Herbal remedies that contain St John’s wort (Hypericum perforatum) also reduce levonorgestrel levels.
Elevated levels of CYP3A4 enzymes can persist for up to 4 weeks after cessation of the enzyme-inducing medicine. This decrease in plasma levonorgestrel may reduce contraceptive efficacy of levonorgestrel-containing emergency hormonal contraceptives.
Exposure during pregnancy to some of the enzyme-inducing medicines listed above has been associated with an increased risk of birth defects. It is therefore important to provide advice on highly effective forms of regular contraception for women who take these medicines, and to exclude pregnancy after use of levonorgestrel-containing emergency contraception.
Please refer to the following website in MHRA for details:
http://www.gov.uk/drug-safety-update/levonorgestrel-containing-emergency-hormonal-contraception-advice-on-interactions-with-hepatic-enzyme-inducers-and-contraceptive-efficacy
In Hong Kong, there are 37 registered pharmaceutical products containing levonorgestrel, of which 30 products are prescription only medicines, including 29 products containing levonorgestrel 0.75mg/tablet or 1.5mg /tablet and 1 intrauterine device; while 7 products are over-the-counter medicines containing levonorgestrel 0.15mg/tablet or below. So far, the Department of Health (DH) has not received any adverse drug reaction report related to levonorgestrel. In view of the above MHRA announcement, letters to inform local healthcare professionals will be issued, and the matter will be discussed by the Registration Committee of the Pharmacy and Poisons Board.
Ends/ Saturday, September 17, 2016
Issued at HKT 12:30
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