Do clinical grant payment practices in phase 3 clinical trials influence subsequent clinical investigator prescribing behavior?

The advancement of science requires the cooperation of clinical investigators. Recent discourse, which attempts to relate pharmaceutical company grant payments to clinical investigators to subsequent preferential prescribing behavior, erodes the physician/patient relationship and may lead to an inadequate number of investigators. This study was designed to determine why the level of grant payments to Phase 3 clinical investigators differs for comparable levels of work and whether these differences are related to subsequent prescribing behavior of either the study drug or other drugs from the same sponsoring company. From a database of 100,000 investigator contracts, 2,108 U.S. physicians participating in Phase 3 trials at 2,897 clinical sites for new drugs launched in 1999-2000 were randomly selected in 10 outpatient indications. The relative grant amounts (RGAs) paid to the investigators were compared with their subsequent prescribing of the study drug and other sponsor company drugs for a period of six months after study drug introduction. The RGA is the payment percentile represented by the absolute cost per patient grant paid to any specific investigator compared with other similar studies, including such considerations as the number of patient visits, the number and types of medical procedures performed, the investigator's geographic location, and whether the study was conducted at the investigator's office or hospital. Linear regression correlations were calculated between study, investigator, and drug characteristics with the RGA, and the correlation between the RGA and subsequent prescribing behavior of the study drug and other drugs from the sponsor company at three and six months after study drug product launch. Five variables were statistically significantly related to the RGA received by an investigator: compound therapeutic novelty, the number of similar studies being conducted at same time, investigator clinical research experience, and the inverse of drug class prescription volume. Most significantly, investigators' post-study prescribing behavior was not related to RGA. Drug development and market forces explain the RGA, but RGA is not related to subsequent sponsor or study drug prescribing.