Oral contraceptives and antibacterials: unintended pregnancies
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Oral contraceptives and antibacterials: unintended pregnancies A drug interaction between oral contraceptives and non-enzyme-inducing antibacterials reduces the efficacy of the contraceptives and results in risk of unintended pregnancies, according to findings of a UK study published in BMJ Evidence-Based Medicine. Data from adverse event reports to the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) between 1963 and July 2018 were used to compare rates of unintended pregnancies in patients taking oral contraceptives who received non-enzyme-inducing antibacterials (amoxicillin, ampicillin, cefalexin, ciprofloxacin, erythromycin, metronidazole, nitrofurantoin, oxytetracycline or trimethoprim; n=74 623), enzyme-inducing drugs known to reduce contraceptive efficacy (carbamazepine, eslicarbazepine acetate, griseofulvin, nevirapine, oxcarbazepine, phenobarbital, phenytoin, primidone, rifabutin, rifampicin, ritonavir or topiramate; 38 872), or control drugs not expected to reduce contraceptive efficacy (citalopram, ibuprofen, lansoprazole, loperamide, loratadine, paracetamol, propranolol, theophylline or zolpidem; 65 578). Unintended pregnancies were reported significantly more frequently in patients who received non-enzyme-inducing antibacterials than in those who received control drugs (62 vs 9 per 100 000; odds ratio [OR] 6.7; 95% CI
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