How physicians choose drugs.

A drug choice model which includes the physician's attitudes, norms and personal experiences with drugs, was tested. One hundred and sixty-nine physicians were asked to estimate the model's components for the treatment of irritable bowel syndrome (IBS) and of renal colic. Given three drugs for both indications, the physicians gave their expectancies about the treatment outcomes, professional acceptability, patient demand and their personal experiences with the drugs. They also stated the value they assign to each of these components when choosing a drug for IBS and for renal colic. The influence of patient demand on the choice of a specific drug appeared to be negligible. The combined effect of the other three elements of the model predicted the stated drug of first choice correctly in 74% (for IBS) and 78% (for renal colic) of the cases, but further analysis showed that only the drug choices for renal colic were as reasoned as the model assumed. Expectancies and values about treatment outcomes determined the drug choice only in part. For choosing a drug for renal colic, the professional environment was more important. Moreover it was found that drug preferences were more related to expectancies about efficacy than to expectancies about side effects for both disorders. The findings can be useful when trying to change prescribing behaviour. Only a limited effect can be expected from the provision of technical drug information. Especially information about costs is unlikely to change prescribing easily, unless values and norms are changed as well. The importance of the professional environment implies that educational programmes in groups might be more effective than individual approaches.