Objective: To estimate the frequency of cholestatic hepatitis of uncertain origin occurring among persons who had recently received flucloxacillin, a drug which has recently been reported as causing cholestatic hepatitis, and to compare this frequency with that related to oxytetracycline, a drug which has seldom been reported as causing this disorder.
Design: A retrospective cohort study using data automatically recorded on general practitioners' office computers.
Setting: Some 600 general practices in the United Kingdom.
Subjects: 132,087 people who received flucloxacillin and 145,844 people who received oxytetracycline.
Main outcome measure: Clinically documented cholestatic hepatitis of uncertain origin diagnosed 1-45 days after a prescription for flucloxacillin, 46-90 days after a prescription for flucloxacillin and, for comparison, 1-45 days after a prescription for oxytetracycline.
Results: There were 10 cases of cholestatic hepatitis of uncertain origin diagnosed within 45 days of receiving flucloxacillin that were either characteristic of or consistent with a syndrome recently described as being associated with this drug; there was one such case 46-90 days after a prescription for flucloxacillin; there were three such cases 1-45 days after a prescription for oxytetracycline.
Conclusion: Flucloxacillin is a likely cause of cholestatic hepatitis. The risk is estimated to be in the range of 7.6 per 100,000 users (95% confidence interval, 3.6-13.9).