Background and Importance Potential interactions are detected with new oral treatments for prostate cancer. Interactions with these drugs need to be reviewed in elderly people are fragile, polypathological and polymedicated

Aim and Objectives To detect and analyse the interactions between the selective inhibitor of the enzyme 17α-hydroxylase(abiraterone) and the androgen receptor inhibitors (apalutamide and enzalutamide) with the chronic medication of patients who come to the outpatient clinic.

Material and Methods Observational and transversal study carried out in the Outpatient Unit(UPE) for two months (July-August 2022) in an area reference hospital.

The pharmacist conducted a clinical interview with all patients receiving treatment with abiraterone, apalutamide, and enzalutamide who came to pick up their medication at the outpatient clinic. In necessary cases, we rely on the computerised electronic prescription. In addition, age, disease classification and treatment start date were collected.

The data collected was analysed using the Lexicomp database, which classifies interactions into 5 categories according to the recommendation: Category A and B (No follow-up necessary), C(Monitor the patient), D(Consider modification of therapy) and X. (Avoid combination). The interactions of categories C, D and X have been considered. The degree of rigor and the reliability rating were also collected.

Results A total of 69 men were interviewed. The mean age was 77 years, all older than 60 years. 31 patients were receiving treatment with apalutamide, 26 with abiraterone and 12 with enzalutamide. The patients had a mean of 12.6 ± 15.1 months of treatment. 88.5% took 5 or more medications.

A total of 709 lines of treatment were analysed, finding that 66.6% of the patients presented an interaction in their treatments, 1.9 interactions per patient.

According to the severity of the interactions, 76.2% (91) were C, 10.1% (12) D and 12.7% (15) category X. 63.5% of the interactions were with apalutamide, 26.2% with enzalutamide and 10.1% with abiraterone. 4 pharmacological groups are responsible for category D interactions and 1 is responsible for category X interactions (proton pump inhibitors).

Conclusion and Relevance

• The study has allowed us to detect a high number of interactions, although the proportion of patients with clinically relevant interactions is low.

• The pharmacist plays a very important role in the prevention, detection and monitoring of interactions in this group of patients.

Conflict of Interest No conflict of interest