Background A previous retrospective study into drug-drug interactions between anticancer agents administered in our hospital and drugs dispensed in community pharmacy identified a prevalence of clinically relevant interactions of 18%. Based on these findings The authors developed a continuous screening programme for all chemotherapy patients.

Purpose To identify drug-drug interactions between cytotoxic agents and community pharmacy-dispensed medicines prior to the start of chemotherapy, and to develop clinical rules for their management.

Materials and methods Prior to chemotherapy, a medicines review was performed on the current medicines list from the community pharmacy. Both ambulatory and inpatient oncology patients were included from June 2010 until September 2011. 365 patients were screened in total 412 times.

Results 80 potentially relevant interactions were observed in 57 patients (16%). The most frequent interactions, their possible clinical effects and proposed management were: A) coumarin with cytostatics (n=17), resulting in possibly increased anticoagulation. Clinical management involves additional INR (international normalised ratio) checks. B) protease inhibitors with anthracyclines and Vinca alkaloids (n=13) resulting in possibly increased toxicity. Management consists of prophylactic GCSF (granulocyte colony-stimulating factor) and monitoring for neuropathy. C) ciprofloxacin with anthracyclines, podophyllotoxins and oxazaphosphorines (n=8), leading to reduced exposure to fluoroquinolones. In the case of prophylactic treatment, no action is needed, whereas in therapeutic use, switching to another antibiotic should be considered. Overall, 24 interactions involved CYP-inducing or inhibiting co-treatment. In 11 of these, a switch to a non-CYP-affecting drug was feasible. In 3 cases, antiepileptics or antidepressants were involved, requiring additional monitoring of serum levels. These results warrant timely interaction screening, preferably days before the start of chemotherapy.

Conclusions The high prevalence of potential drug-drug interactions between anticancer agents and community-dispensed drugs makes clear the need for optimal medicines surveillance and data exchange between the hospital and the community.