Marineni Srujana*, V. Sai Chitra Prathyusha, Gadde Thanuja
Ratnam Institute of Pharmacy, Pidathapoluru, Nellore
A B S T R A C T
Objective: To evaluate the evidence on possible drug interactions between antibiotics (tetracycline’s, penicillin’s, Rifampin, cephalosporin’s) and oral contraceptives (OCs) that may lead to OC failure. The number of accidental pregnancies occurring in oral contraceptive (OC) users who are concurrently taking certain antibiotics and antifungal agents exceeds the 1% failure rate associated with OCs, suggesting some form of drug interaction. Although the risk of pregnancy due to OC-antibiotic interactions is extremely small, OC users prescribed antibiotics should be warned to use condoms or spermicides until the antibiotics are discontinued. Data Sources: MEDLINE and Lexis/Nexis Medical Library searches for 1966-1999 using the key word “oral contraceptives,” cross-indexed with the terms “antibiotics,” “adverse effects,” and “pregnancy,” and Medline search using the additional MeSH term “drug interactions.” No language restrictions were used. Data Extraction: Studies reporting oral contraceptive pharmacokinetics, mechanisms, incidence, implicated antibiotics and clinical consequences of antibiotic/oral contraceptive drug interactions. Data Analysis: Rifampin is the only antibiotic that has been reported to reduce plasma estrogen concentrations. When taking rifampin, oral contraceptives cannot be relied upon and a second method of contraception is mandatory. OC failure is found in women using preparations containing 30μg of ethinylestradiol and 150 μ g of levonorgestrel. Amoxicillin, ampicillin, griseofulvin, metronidazole and tetracycline have been associated with contraceptive failure in three or more clinical cases. Other antibiotics are most likely safe to use concomitantly with oral contraceptives. Conclusion: Oral contraceptives cannot be relied upon for birth control while taking rifampin. Rifampin is the only antibiotic has been reported lower plasma estrogen concentrations.
Keywords: Rifampin, Antibiotics, Drug interactions, Oral contraceptives, ethinylestradiol, levonorgestrel.