Intended for healthcare professionals

Endgames Statistical Question

Placebos and sham treatments

BMJ 2015; 351 doi: (Published 10 July 2015) Cite this as: BMJ 2015;351:h3755
  1. Philip Sedgwick, reader in medical statistics and medical education,
  2. Carwyn Hooper, senior lecturer in medical ethics and law
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  1. Correspondence to: P Sedgwick p.sedgwick{at}

The effectiveness of topical chloramphenicol in preventing wound infection after minor dermatological surgery was evaluated. A randomised placebo controlled superiority trial was performed.1 Participants were patients with high risk sutured wounds who had undergone minor surgery. The intervention was a single application of topical chloramphenicol ointment to the sutured wound immediately after suturing. Chloramphenicol ointment is an antibiotic indicated for the treatment of bacterial conjunctivitis, but it is often used as prophylaxis for, or treatment of, wound infection, although little evidence exists for its effectiveness. The control treatment was placebo ointment, which consisted of a mixture of soft white and liquid paraffin with no known anti-infective properties. In total, 972 patients were recruited and randomised to topical chloramphenicol ointment (n=488) or placebo (n=484). All participants were instructed to follow standard management, keeping their wound dry and covered for 24 hours after surgery.

The primary outcome was infection on the agreed day of removal of sutures or sooner if the patient re-presented with a perceived infection. The percentage of participants with an infection in the topical chloramphenicol group was significantly lower than in the placebo group (6.6% v 11.0%; difference −4.4%, 95% confidence interval −7.9% to −0.8%; P=0.010). Although the application of a single dose of topical chloramphenicol to high risk sutured wounds after minor surgery produced a statistically significant reduction in the infection rate, the researchers concluded that the reduction …

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