Ampicillin with oral contraceptives

Drug Interactions Contraceptive effects are decreased when "the pill" is taken with ANTIDIOTICS (ampicillin, isoniazid, neomycin, pen V, rifampin, sulfonamides, tetracycline) or CNS AGENTS (barbiturates, benzodiazepines, phenytoin). Contraceptives increase the effects of corticosteroids and worsen side effects of tricyclic antidepressants. Oral contraceptives decrease the effectiveness of oral anticoagulants, anticonvulsants, and oral hypoglycemic agents. 

Joshi JV, Joshi UM, Sankholi GM, Krishna U, Mandlekar A, Chowdhury V, Hazari K, Gupta K, Sheth UK, Saxena BN. A study of interaction of low-dose combination oral contraceptive with ampicillin andmettonidazole. Contraception (1980) 22, 643-52. 

The use of a penicillin (unspecified) was implicated in 32 pregnancies in women taking an oral contraceptive (unspecified) in the adverse reactions register of the CSM in the UK for the years 1968 to 1984 (a fiuther 31 cases were attributed to other antihacterials). In an earlier review, the penicillins in 15 cases of contraceptive failure were named as ampicillin (alone or with fusidic acid, tetracycline or flncloxacillin), amoxicillin, talampicillin, phenoxymethylpenicillin (one also with oxytetracycline) and penicillin . A survey of contraceptive failure descrihed failures due to amoxicillin (16 cases), flncloxacillin, phenoxymethylpenicillin, pivampicillin (3 cases) and amoxicillin with phenoxymethylpenicillin (1 case), and a follow-up survey identified 9 further cases involving amoxicillin and one with penicillin . Another similar survey descrihed a total of 17 cases with amoxicillin and 5 cases with penicillin , and a follow-up survey identified 8 further cases with amoxicillin and 1 case with penicillin . ... 

Ampicillin has also been thought to reduce the effect of oral contraceptives. Here, however, the evidence is much weaker than with the other drugs mentioned above. Pregnancies were reported (122 ) to have occurred in 3 patients taking oral contraceptives while on ampicillin. In no case was there any failure of compliance to the regimen, nor did any patient suffer from diarrhoea or vomiting as a result of the ampicillin treatment. 

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