Potential drug–drug interactions between anti-cancer agents and community pharmacy dispensed drugs

Objective of the study To identify the prevalence of potential drug–drug interactions between hospital pharmacy dispensed anti-cancer agents and community pharmacy dispensed drugs. Setting A retrospective cohort study was conducted on the haematology/oncology department of the internal medicine ward in a large teaching hospital in Amsterdam, the Netherlands. Method Prescription data from the last 100 patients treated with anti-cancer agents were obtained from Paracelsus, the chemotherapy prescribing system in the hospital. The community pharmacy dispensed drugs of these patients were obtained by using OZIS, a system that allows regionally linked pharmacies to call up active medication on any patient. Both medication lists were manually screened for potential drug–drug interactions by using several information sources on interactions, e.g. Pubmed, the Flockhart P450 table, Micromedex and Dutch reference books. Main outcome measure Prevalence of potential drug–drug interactions between anti-cancer agents provided by the hospital pharmacy and drugs dispensed by the community pharmacy. Results Ninety-one patients were included in the study. A total of 31 potential drug–drug interactions were found in 16 patients, of which 15 interactions were clinically relevant and would have required an intervention. Of these interactions 1 had a level of severity ≥D, meaning the potential drug–drug interaction could lead to long lasting or permanent damage, or even death. The majority of the interactions requiring an intervention (67%) had a considerable level of evidence (≥2) and were based on well-documented case reports or controlled interaction studies. Most of the potential drug–drug interactions involved the antiretroviral drugs (40%), proton pump inhibitors (20%) and antibiotics (20%). The anti-cancer drug most involved in the drug–drug interactions is methotrexate (33%). Conclusion This study reveals a high prevalence of potential drug–drug interactions between anti-cancer agents provided by the hospital pharmacy and drugs dispensed by the community pharmacy. It shows us there is need for an optimal medication surveillance mechanism to detect potential drug–drug interactions between these two groups of medication, especially because of the high toxicity of anticancer drugs and thus the severe consequences these interactions can have for the patient.