Effect of periodic letters on evidence-based drug therapy on prescribing behaviour: a randomized trial

Background: The effect of regular and expected printed educational materials on physician prescribing behaviour has not been studied. We sought to measure the impact of a series of evidence-based drug therapy letters mailed to physicians in British Columbia on prescribing to newly treated patients. Methods: A paired, cluster randomized community design was used. The study population included 499 physicians from 24 local health areas in British Columbia. Local health areas were paired by number of physicians, and 1 of each pair was randomly selected and its physicians assigned to an intervention group or a control group. The intervention was 12 issues of an evidence-based series called Therapeutics Letter. Physicians in the control group (n = 241) received the letters 3-8 months after physicians in the intervention group (n = 258). The impact on prescribing to newly treated patients (defined as patients who had not previously made a claim for any medication from the class of drugs profiled in the letter) was analyzed using the drug claims database of BC Pharmacare, a publicly funded drug benefits program that covered all seniors and people receiving social assistance. Results: The probability of prescribing a drug recommended in the Therapeutics Letter rather than another drug in the same class increased by 30% in the 3 months after the mailing of the letter relative to the preceding 3 months, adjusted for any before-after changes in the control group (relative risk 1.30; 95% confidence interval 1.13-1.52). No letter achieved statistical significance on its own. However, 11 of the 12 letters produced prescribing changes in the predicted direction such that the overall result was significant when their effect was combined. Interpretation: The combined effect of an ongoing series of printed letters distributed from a credible and trusted source can have a clinically significant effect on prescribing to newly treated patients.