In a meta-analysis of five placebo controlled studies conducted between 1971 and 1980, closure or improvement of fistulas was observed in 54% of treated patients (22 of 41) and in 21% of patients taking placebo (six of 29) (odds ratio 4.44 [95% CI 1.50 to 13.20]). A duration of treatment of more than 17 weeks was the strongest determinant of response of the active disease to the drug. Present et al, in a placebo controlled study, reported closure of 31% (nine of 29) versus 6% (one of 17) of fistulas and improvement of 29% (seven of 24) versus 18% (three of 17) of fistulas in patients treated with 6-MP versus placebo. Two subsequent uncontrolled studies in 1985 and 1991 reported closure rates of 37% and 23%, and improvement rates of 27% and 40% in 41 and 35 patients, respectively. The mean time to response with AZA 2.0 to 2.5 mg/kg or with 6-MP 1.5 mg/kg ranged from 3.1 to 4.5 months, with 20% of patients taking more than four months for improvement to be observed. Relapse occurred in all eight patients whose treatment was discontinued after closure of their fistulas. An uncontrolled study with an intravenous loading dose of AZA showed a closure rate of 54% (seven of 13), with a time to response of less than four weeks. However, a controlled trial of oral AZA with or without initial intravenous loading resulted in similar rates of complete response of active Crohn’s disease after eight, 12 and 16 weeks. Whether this observation also applies to closure or improvement of fistulas is unknown but is probable. Learn how to save money – buy antibiotics online to enjoy your shopping and your treatment.