Physicians who participate in pharmaceutical company-sponsored clinical trials are more likely to prescribe the sponsor company drugs, but still keep within treatment guidelines, according to a new study looking at asthma studies.

Pharmaceutical companies are frequently involved in clinical trials in general practice, and this may trigger an increase in the use of the sponsoring company's products due to the physicians' experience with these products, according to the researchers. This effect may be further strengthened by close physician-company cooperation, which may create physician loyalty toward the company, they suggest.

But until now the effect of participation in company-sponsored studies on drug preferences has not been evaluated in primary care, according to Morten Andersen of the University of Southern Denmark, who headed the study.

Andersen and colleagues investigated the effects of physicians participating in a pharmaceutical company-sponsored clinical trial that was aimed at improving patients' use of asthma medicine. The study compared 10 practices that were conducting the trial on asthma medicine with 165 control practices in Denmark. The study included 5,439 patients treated with asthma drugs from the trial-conducting practices and 59,574 patients from the control practices.

Overall the study found that trial-conducting practices were 26% more likely than the controls to use the trial sponsor's inhaled corticosteroid products, and the trial sponsor's share of the total prescribed volume of asthma drugs increased in trial-conducting practices compared with control practices by 6.7%.

"Our study confirms the hypothesis that physician involvement in clinical trials is a powerful tool for influencing company-specific drug preferences,” said Andersen. The work is published in the Journal of the American Medical Association (2006;295:2693).

Both trial-conducting and control practices had a gradually increased use of the trial sponsor's inhaled corticosteroids, from 74.8% to 81.5% in trial-conducting practices and 73.6% to 76.6% in the controls.

Overall, they found that the prevalence of inhaled steroid use among asthma patients increased by a similar margin in both groups, and there was no impact of participating in the trial on physicians' adherence to international treatment guidelines.

In an editorial accompanying the JAMA study, Bruce Psaty of the University of Washington, Seattle and Drummond Rennie of the University of California, San Francisco, said the finding may spark a new genre of research looking at physician/pharmaceutical company relationships.

"Agreeing to work as an investigator in industry-sponsored trials may represent a commitment to an effort that is more or less a scientific endeavor and, at the same time, a marketing initiative," they suggest.

Several mechanisms may be responsible for the finding that use of sponsor drugs increased, including the setting up of a ‘gift relationship’ through payments to the trial-conducting physicians, according to the researchers.

“If we had access to information on the costs of the trial, it would have been possible to evaluate if these trial costs were counterbalanced by the revenue from the trial sponsor's increased market share,”, they suggested.

But whether conducting a clinical trial can lead to minor improvements in guideline adherence can only be addressed in large-scale studies, they concluded.

Meanwhile, Psaty and Rennie say the study could also also syggest that the scientific rationale for launching thousands of small short-term trials remains unclear.

"The health of the public would be better served by the conduct of fewer small short-term studies and more well-designed large long-term trials, such as the Women's Health Initiative (WHI) and the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), that fully address the health risks and benefits of pharmacological therapies used for chronic conditions.

The findings from such studies provide a sensible evidence base for both clinical practice and industry marketing," they suggest.