Prevalence of the Coprescription of Clinically Important Interacting Drug Combinations Involving Oral Anticancer Agents in Singapore: A Retrospective Database Study

Background There has been a recent increase in the availability and use of oral anticancer agents (OAAs). Drug–drug interactions (DDIs) involving OAAs pose a major concern in oncology practice due to these drugs' narrow therapeutic indices and potential for compromised efficacy and fatal adverse events. Objective To assess the prevalence of the coprescription of potentially interacting drug combinations involving OAAs in Singapore. Methods A retrospective review of physicians' electronic prescription records between the years 2007 and 2009 was performed in the largest cancer center in Singapore. An overall prevalence rate of potential DDIs and a prevalence rate for each individual DDI pair were calculated. Logistic regression was used to identify risk factors for potential DDIs. Results Fifty-eight clinically significant DDIs were selected for evaluation from Drug Interaction Facts and Micromedex DrugDex. A total of 39,772 OAA prescriptions prescribed to 8837 patients were reviewed. Potential DDI coprescription was found in 5.4% of the patients on OAAs and in 4.7% of the OAA prescriptions. The drug pair prescribed to the largest number of patients was prednisolone and aspirin. About half (53.3%) of the observed DDIs were found on the same prescription. On multivariate analysis, older patients, males, and those taking prednisolone had a higher risk for potential DDIs. Conclusion Although limited by the data available, the analysis of prescription records found that ∼5% of patients taking OAAs in Singapore were exposed to ≥1 potentially interacting drug combination.