Cancer patients are often treated with numerous concomitant medications other than antineoplastic agents. Recent studies have shown a high prevalence of drug-drug interactions (DDIs) among these patients, some of them considered as clinically relevant due to potential changes on the efficacy and toxicity of the anticancer therapy. We aimed to determine clinically relevant DDIs leading to pharmaceutical intervention in ambulatory cancer patients treated at our centre.
A sample size of 149 subjects was calculated based on an expected percentage of 11% of patients with clinically relevant DDIs. Patients starting a new anticancer therapy were asked to participate in this trial. Information of the use of concomitant medications with antineoplastic agent(s), including over-the-counter drugs, was collected by the oncologist through a structured interview. DDIs were identified using the LexiComp Handbook and a software programme available at www.drugs.com. If a clinically relevant DDI was recognized by the clinical pharmacist, a recommendation was sent to the prescribing oncologist who decided whether to carry out the suggested intervention or not.
The mean age of the patients was 57.5 ± 13.6 years, and 74.5% (n = 111) of them were female. The majority of patients had solid tumours (98.6%), specifically: breast (53.7%), followed by gastrointestinal (23.5%) and genitourinary malignancies (6.7%). Seventy-two patients (47.7%) had an underlying comorbidity other than cancer, mainly high blood pressure (n = 52) and diabetes mellitus (n = 23). The median number of medications per patients was 3 (range: 0 – 12). A total of 37 clinically relevant interactions were detected in 26 patients (17.4%; 95% Confidence Interval: 14.3 – 20.5). Of these interactions, 11 (29.7%) were considered of high risk (category D), leading to therapy modifications in 100% of cases, as suggested by the clinical pharmacist. The principal mechanism of DDIs was pharmacokinetic (70.3%), followed by pharmacodynamic (19%), and unknown in the remaining cases (10.7%).
Clinically relevant DDIs were frequently detected in this prospective study. A multidisciplinary approach is required to identify and avoid potentially harmful DDIs.
Clinical trial identification
Legal entity responsible for the study
University of Costa Rica. Caja Costarricense de Seguro Social.
All authors have declared no conflicts of interest.