Emergency contraception containing levonorgestrel may interact with liver enzyme inducers

Interactions between drugs and contraceptives, especially emergency contraceptive pills, are of concern, as these interactions can reduce the effectiveness of contraception. The following article outlines the effects of liver enzyme inducers on emergency contraceptive pills containing levonorgestrel.

Emergency contraceptive pills containing levonorgestrel are used to prevent unwanted pregnancy, the pill is taken within 72 hours (3 days) of unprotected sex or no contraception. The sooner you take it after unprotected sex, the more effective it is at preventing pregnancy.
Levonorgestrel-containing emergency contraceptives are available over-the-counter as a single 1500 microgram tablet, or by prescription as two 750 microgram tablets taken as a single dose.

Inducers of liver enzymes are drugs that, when taken with other classes of drugs, can have the following effects:
Decrease the bioavailability of other drugs metabolized by those enzymes Increase the bioavailability of drugs to be metabolized Concomitant use of liver enzyme inducers, mainly CYP3A4 inducers, increases the metabolism of levonorgestrel.
Research has shown that co-administration of the antiretroviral efavirenz (used in the treatment of HIV) reduces levonorgestrel plasma AUC (blood concentration over time) by approximately 50%. Studies of combined hormonal contraceptives containing levonorgestrel indicate that other hepatic enzyme inducers or herbal medicines may similarly reduce plasma concentrations. Elevated levels of the enzyme CYP3A4 may persist for up to 4 weeks after discontinuation of enzyme inducers. This decrease in levonorgestrel plasma concentrations may reduce the contraceptive efficacy of levonorgestrel-containing emergency hormonal contraceptives.
Examples of enzyme inducers that decrease levonorgestrel plasma concentrations:
Antiepileptic drugs (eg, barbiturates, primidone, phenytoin, carbamazepine) Tuberculosis drugs (eg rifampicin, rifabutin) Drugs to treat HIV (eg, ritonavir, efavirenz) Fungal drugs (eg, griseofulvin) Herbal medicines containing St John's wort (Hypericum perforatum) also reduce levonorgestrel levels. Doctors recommend that patients adjust the dose of emergency contraceptive pills containing levonorgestrel if taking concomitant medications that induce liver enzymes. For women who are unable or unwilling to use an IUD, or who wish to use emergency contraception who have used a liver enzyme inducer in the past 4 weeks, the usual dose of levonorgestrel should be doubled. usually (1.5 milligrams to 3 milligrams) to compensate for the decrease in plasma levonorgestrel. Other instructions for use are the same as for the usual dose.

There is no increased risk of side effects from taking higher doses in these cases. Users and healthcare professionals are advised to report any suspected side effects of levonorgestrel, including any that are thought to be related to a double dose of the ECP. grant .

Tell your doctor, pharmacist or nurse if you are currently taking medicine to treat any of the following conditions, or have taken a medicine for these conditions in the past 4 weeks:
Seizures (for example: barbiturates, primidone, phenytoin, or carbamazepine) Tuberculosis (eg, rifampicin, rifabutin) HIV (eg, ritonavir, efavirenz) Fungal infections (eg, griseofulvin) Herbal medicines containing St John's wort (Hypericum perforatum) ) If you are taking any medicines or herbal remedies and are not sure if they could affect levonorgestrel emergency contraception, tell your doctor or pharmacist.

Advice for women taking levonorgestrel emergency contraception:
Levonorgestrel emergency contraception can not prevent pregnancy every time. It works best if taken earlier, preferably within 12 hours of having sex. See your doctor or pharmacist for advice on effective birth control methods. Take a pregnancy test to make sure you're not pregnant if your period doesn't come at the right time or if you suspect you might be pregnant. If the test results indicate that you are pregnant (even after taking levonorgestrel), see your doctor as soon as possible to make sure you get the best care Read the leaflet that comes with it. with levonorgestrel to understand the medication and any potential side effects. The above is not all information about emergency contraceptive pills containing levonorgestrel. In case of needing further advice, customers can contact their doctor or pharmacist for appropriate indications.

Reference source: gov.uk