Drug interactions in cancer inpatients

Abstract

8146 Background: Patients with advanced cancer usually receive various classes of drugs. Although little has been published on this subject, there seems to be general consensus that drug interactions are associated with the number of medications a patient receives. We attempted to quantify the frequency of potential drug interactions not related to chemotherapy in our institution. Methods: Charts of 100 consecutive cancer patients who had been admitted between May and October 2003 were reviewed. Patients were excluded if they received chemotherapy and/or hormone therapy during hospital stay. Patients could have only one monthly admission analyzed. All drugs in the orders were tabulated, irrespective of whether they were actually administered. Interactions were screened with Drug Interaction Facts softwear and manually by the authors. Potential interactions were graded by their levels of severity (severe, moderate, and minor) and significance (1 to 5, with 1 representing the highest level of evidence).Results: Median age, length of stay and number of prescribed drugs per patient were 67 years (range, 20 to 94 years), 6 days (range, from less than one to 81 days), and 8 drugs (range, one to 20 drugs), respectively. 180 potential interactions were detected, with a median of one per patient per admission (range, none to 11 interactions). Of 100 patients, 63 presented any potential interaction, of which 18.3% were classified as severe, 56.7% as moderate, and 25% as minor. Approximately 7%, 18%, 13%, 52%, and 11% of potential interactions were graded as level 1, 2, 3, 4, and 5, respectively. Univariate analyses demonstrated that age (P=0.026), number of medications (P<0.0001) and length of stay (P=0.001) were correlated with potential interactions. In multivariate analysis, prescriptions with 5 or more drugs (risk ratio of 6.4, 95% CI: 1.82 to 22.56; P=0.004) and hospital stay of 7 or more days (risk ratio of 3.4, 95% CI:1.23 to 9.46; P=0.019) remained independently associated with potential interactions.Conclusions: Potential drug interactions are common among inpatients with advanced cancer. Length of hospital stay and number of prescribed drugs were risk factors in multivariated analyses. No significant financial relationships to disclose.