Do too many cooks spoil the broth? Multiple physician involvement in medical management of elderly patients and potentially inappropriate drug combinations

To determine (a) whether the risk of a potentially inappropriate drug combination (PIDC) increases with the number of physicians involved in the medical management of an elderly patient and (b) whether the risk of a PIDC is reduced if a patient has a single primary care physician or a single dispensing pharmacy, or both. Cross-sectional retrospective provincial database study. A regionally stratified random sample of 51,587 elderly medicare registrants in Quebec who (a) visited at least one physician in 1990, (b) were not living in a health care institution for the entire year and (c) had been dispensed at least one prescription for a cardiovascular drug, a psychotropic drug or a nonsteroidal anti-inflammatory drug (NSAID). Information on all physician visits and drugs dispensed during 1990. Physician claims were used to identify the number of physicians involved in a patient's management and whether the patient had one primary care physician. Prescription claims were used to identify the number of PIDCs, prescribing physicians and dispensing pharmacies. The prevalence of PIDCs ranged from 4.0% (among those in the NSAID group) to 20.3% (among those in the psychotropic drug group). Of the PIDCs identified, 17.6% to 25.8% resulted from contemporaneous prescribing by different physicians. The number of prescribing physicians was the most important risk factor for a PIDC in all drug groups (odds ratio [OR] 1.44 to 1.71). The presence of a single primary care physician lowered the risk for cardiovascular and psychotropic PIDCs (OR 0.70 and 0.79 respectively) but not for NSAID PIDCs (OR 0.94). The use of a single dispensing pharmacy lowered the risk of a PIDC in all drug groups (OR 0.68 to 0.79). The greater the number of physicians prescribing medications for an elderly patient, the greater is the risk that the patient will receive a PIDC. A single primary care physician and a single dispensing pharmacy may be "protective" factors in preventing PIDCs.