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Contraception - emergency - Management
What drug interactions can occur with oral ulipristal acetate emergency contraception
Ulipristal acetate is metabolised via cytochrome P450, in particular CYP3A4.
- Liver enzyme inducers
- CYP3A4 inducers such as rifampicin, phenytoin, phenobarbital, carbamazepine, ritonavir, St John's wort, non-nucleoside reverse transcriptase inhibitors (such as efavirenz, nevirapine, etravirine) and modafinil, may reduce plasma concentrations of ulipristal acetate, resulting in a decrease in its efficacy.
- Enzyme induction wears off slowly and effects on the plasma concentrations of ulipristal acetate may occur even if the enzyme inducer was stopped 2–3 weeks before.
- Liver enzyme inhibitors
- CYP3A4 inhibitors such as protease inhibitors (ritonavir, indinavir, nelfinavir), macrolide antibiotics (erythromycin, clarithromycin), azole antifungals (ketoconazole, itraconazole, fluconazole), nefazodone, verapamil and cimetidine may increase exposure to ulipristal acetate. The clinical relevance of this is unknown.
- Drugs that increase gastric pH
- Concomitant use is not recommended. Drugs that increase gastric pH like proton pump inhibitors, antacids and H2 receptor antagonists may reduce the plasma concentration of ulipristal acetate and may decrease its efficacy.
- Other contraceptives
- Ulipristal acetate binds with high affinity to the progesterone receptor so it may interfere with the action of progestogen-containing products.
- The contraceptive action of combined hormonal contraceptives and progesterone-only contraception may be reduced.
- Concomitant use of ulipristal acetate and emergency contraception containing levonorgestrel is not recommended.
[ABPI Medicines Compendium, 2009; FSRH Clinical Effectiveness Unit, 2009]
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