Background and importance Selective cyclin dependent kinase (CDK) inhibitors, palbociclib and ribociclib, were recently approved to treat advanced or metastatic breast cancer. The hospital pharmacist plays an important role in the revision of the treatment at consultation, in order to ensure the safety and effectiveness of the treatment.

Aim and objectives To analyse potential drug interactions (PDI) before starting palbociclib or ribociclib treatment and to evaluate physician acceptance of pharmacist recommendations.

Material and methods This was a retrospective observational study including all patients who started treatment with palbociclib or ribociclib in a second level hospital until September 2019. At the beginning of treatment, the pharmacist interviewed patients and reviewed their medication in the pharmaceutical consultation. All PDI detected were analysed, making an intervention as therapeutic recommendations.

PDI were identified using Lexicomp, Stockley’s Drug Interactions, Micromedex and CheckTheMeds. PDI were classified as moderate (pharmacological effects must be controlled) or severe (drug combination should be avoided). Follow-up of the recommendations was made 1 month after the beginning of treatment at the pharmaceutical consultation.

Results Twenty-eight patients started palbociclib (50%) or ribociclib (50%) treatment in our hospital (95.9% women; mean age 63.6±9.8 years). Sixteen (57%) were polymedicated; the average number of medications per patient (not including endocrine and CDK inhibitors therapy) was 6.25. Thirty-one PDI were detected in 18 different patients (64.3%). There were 14 (45.2%) severe PDI and 17 (54.8%) moderate PDI. The most common types of drugs involved were statins (22.6%), proton pump inhibitors (22.6%), antidepressants (12.9%) and pyrazolones (16.1%).

Eleven severe PDIs were accepted (78.6%). Moderate recommendations led to a reduction in antidepressant dosage (5.9%) and two change of drugs involved in the interaction (11.8%).

Conclusion and relevance This study showed that more than half of patients that started treatment with CDK inhibitors has at least one PDI. Clinical pharmacists are essentials in detecting PDI, which is a positive influence on physician prescriptions and patient treatment outcomes, improving the safety and effectiveness of the oncological treatment.

References and/or acknowledgements No conflict of interest.