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Chapter 40, Question 1.
Number needed to treat
Consider the following summary of the methods and findings of a study in a paper by Abdus Salam et al in the Lancet (1998; 352: 522-526).
Background Infections caused by multiply resistant Shigella species are a major cause of childhood morbidity and mortality in Third World countries. A randomized double-blind study was undertaken to test the effects of ciprofloxacin treatment in children with shigella dysentry.
Methods The efficacy and toxic effects of ciprofloxacin suspension (10mg/kg) every 12 h for 5 days, maximum individual dose 500mg) were compared with those of pivmecillinam tablets (15-20 mg/kg every 8h for 5 days, maximum individual dose 300mg). 143 children aged 2-15 years with dysentry of 72h or less duration were enrolled in the study. Patients stayed in hospital for 6 days, and were followed up 7, 30 and 180 days after hospital discharge. Joint symptoms and function were assessed daily for 6 days. Clinical success was defined as the absence of frank dysentry on day 3, and on day 5 no bloody-mucoid stools, one or no watery stool, six or fewer total stools, and no fever. If no shigella were isolated from faecal samples on day 3 or thereafter, treatment was judged bacteriologically successful. Secondary endpoints of interest were duration of fever, duration of abdominal pain, and the total number of stools for each patient in the study period.
Statistical analysis Differences in proportions were tested with the Chi-squared test with continuity correction or Fisher's Exact test if the predicted size of any cell was five or less. Differences in continuous variables were assessed with Student's t-test or the Mann-Whitney U test otherwise. All tests of significance were two-tailed.
Findings 13 patients were excluded since they did not meet eligibility criteria; 10 withdrew before day 5. Thus 120 patients (60 in each group) completed the study. Treatment was clinically successful in 48 of 60 patients who received ciprofloxacin and in 39 of 60 patients who received pivmecillinam (difference in percentages = 15.0%, 95% CI for difference = -0.7% to 30.8%, P=0.10). Treatment was bacteriologically successful in all of the patients who received ciprofloxacin, and in 54 of the patients who received pivmecillinam (difference in percentages = 10.0%, 95% for difference = 2.4% to 17.6%, P=0.03). Joint pain began in 18% of patients who received ciprofloxacin and 22% of patients who received pivmecillinam (P>0.2), and no patient had signs of arthritis. The median number of stools during the study was 35 in the ciprofloxacin group and 36 in the pivmecillinam group (P>0.2).
Interpretation Ciprofloxacin suspension and pivmecillinam had the same clinical efficacy in this trial. Ciprofloxacin had greater bacteriological efficacy and was not associated with the development of arthropathy. It can be concluded that ciprofloxacin is an effective and safe drug for use in multiply resistant childhood shigellosis.
Select all of the following statements which you believe to be true.