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Independent prescribing advice affects doctors' behaviour
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     A series of printed letters from a credible and trusted source had a clinically significant impact on doctors?prescribing of drugs to newly treated patients, a new study has found (CMAJ 2004;171:1057-61).

    Researchers from Canada and the United States found that the probability of prescribing a drug recommended in Therapeutics Letter (www.ti.ubc.ca), rather than another drug in the same class, increased by 30% in the three months after the mailing of the letter, relative to the preceding three months, adjusted for any before-after changes in the control group (relative risk 1.30; 95% confidence interval 1.13 to 1.52). No single letter achieved statistical significance, but 11 of the 12 letters did so when their effect was combined.

    Therapeutics Letter is published every two months and targets problematic therapeutic issues; it is distributed to most practising doctors in British Columbia. It includes a literature review and the development of a message relating to drugs in different therapeutic categories by working groups of the University of British Columbia抯 therapeutics initiative. A draft of the letter is reviewed by experts in the particular therapeutics area being reviewed and members of the university抯 scientific information and education committee. The therapeutics initiative is a member of the International Society of Drug Bulletins, the publications of which are financially and intellectually independent of the pharmaceutical industry.

    Between 1994 and 1997, the university抯 therapeutics initiative did a randomised controlled trial with Therapeutics Letter and reported in 1998 that two letters on the treatment of primary hypertension did not produce a significant change in prescribing (Lancet 1998;352:943-8).

    But the current study showed that the letter did change doctors?prescribing behaviour. The authors give two possible reasons for the different results. "At least two factors may have contributed to the observed significant impact on prescribing. First, counting only newly-treated patients increased the sensitivity of demonstrating a change in prescribing?Second, combining the effects of a series of letters created a larger sample than would have been available for any one letter."

    The study looked at 12 of the first 20 issues of the letter, distributed between October 1994 and December 1997.

    Impact was measured using the drug claims database of British Columbia Pharmacare, a publicly funded drug benefit programme, which covered all people aged 65 and older and those receiving social support.

    The study抯 source population comprised all British Columbia residents aged 66 years or older between 1993 and 1998 who were living at home or in a continuing care institution and who had been eligible for Pharmacare coverage for at least one year.

    A younger source population was chosen to measure the impact of a letter on the management of asthma. The letter had to provide a clear message that could be predicted to result in a change in prescribing behaviour, and any predicted change had to be measurable within the limitations of the database available for analysis.

    The authors acknowledge limitations to their study, including the selection criteria for patients and the impossibility of including follow ups longer than three months and thus the sustainability of the impact on prescribing.(Quebec David Spurgeon)