Drug interactions in ambulatory cancer patients receiving cancer-directed therapy

Abstract

6129 Background: Cancer patients (pts) are susceptible to drug interactions (DI) because they receive multiple medications. Here we evaluate the epidemiology of potential DI in cancer patients. Methods: Ambulatory, adult pts with solid malignancies who were receiving antineoplastic treatment completed a questionnaire about drugs taken in the previous month. Drug Interactions Facts software was used to screen for potential DI and to classify them in terms of severity (major, moderate and minor, where major is a life-threatening interaction) and level of scientific evidence (1 to 5, with 1 being the highest level). Summary statistics and logistic regression were used to describe the results. Results: Between Sept -Dec 2005, 183 pts completed the questionnaire: median age was 61 (range 26–88), and 114 (62%) were women. Cancer sites included breast 63 (35%), gastrointestinal 45 (25%), and genitourinary 36 (20%). Treatment intent was palliative in 139 (60%). Most pts (76%) were receiving chemotherapy; 111 (66%) had at least one co-morbid condition, and 72 (47%) had abnormal liver and/or renal function. The median number of drugs per pt was 5 (range 0–16). Among the 183 pts, 131 potential DI were identified of which 65 (50%) were due to pharmacokinetic interactions. Sixteen (12%) of all potential DI were major, 94 (72%) were moderate, and 21 (16%) were minor. Fourteen (11%), 54 (41%), 5 (4%), 42 (32%), and 16 (12%) were supported by levels 1,2,3,4,5 of evidence respectively. Most potential DI involved non-chemotherapy agents such as warfarin, antihypertensives, and anti-inflammatory drugs. In multivariate analyses, number of comorbidities (p= .0001), number of drugs (p= .005), and cancer type (p= .03) were significant risk factors for DI. Conclusion: PotentialDI are common in oncology, and usually involve non-chemotherapeutic drugs. Risk factors for potential DI include comorbid illness, number of medications and type of cancer. Oncologists should be aware of such an important issue. No significant financial relationships to disclose.