Background and importance The concomitant administration of abiraterone with corticoids is necessary to manage adverse events related to mineralocorticoid effect. A proper adherence to both therapies is needed to reach effectiveness in metastatic prostate cancer (mPC).

Aim and objectives To measure and compare adherence to abiraterone and concomitant corticoids in patients with mPC.

Material and methods Retrospective observational study, which included patients under treatment with abiraterone, and corticosteroid (prednisone/dexamethasone) that attended the Outpatient Pharmaceutical Care Unit (OPCU) between March 2020 and February 2021. Abiraterone is dispensed in the hospital pharmacy and concomitant treatment with corticoid is dispensed in the community pharmacy.

Full treatment adherence was measured by combining two indirect methods: dispensing registration and the Morisky–Green (MG) test. Patients with a dispensing record greater than 95% and a score in the MG questionnaire of 4 were considered adherent.

To obtain data, the Ambulatory Information System (AIS) was used, which includes electronic prescriptions, and reports of dispensations in the community pharmacy as well as the dispensing registration system of the hospital pharmacy.

Statistical analysis: qualitative variables were expressed percentagewise and compared using the Chi-square test.

Results Thirty patients were included, with an average age of 74 (SD 10.8) years. Of them 50% were aged over 80 years. The average number of drugs per patient was 9.9 (SD 3.7) so 85% were polymedicated patients (drugs >6). Of the 30 patients treated with abiraterone, 2 died and 2 abandoned the treatment.

Of those aged over 80 years, 69.2% were abiraterone adherents whereas under 80 the figure was 84.6% (p<0.352). In those over 80, 46.2% were corticoid adherents

Polymedicated patients were 72% abiraterone-adherent, while non-polymedicated patients were 100% adherent (p<0.234). Polymedicated patients were 40.9% corticoid-adherent.

By dispensation recounts 84% abiraterone and 46% corticosteroid were adherent patients; while according to the MG test, 85% abiraterone and 81% corticosteroid were adherent patients.

Combining both methods, adherence data were observed to be higher in patients treated with abiraterone compared with corticoids (77% vs 42%), with no significant statistically difference (p=0.147)

Conclusion and relevance Abiraterone combined adherence is higher than corticoid adherence, but not statically significant in this small study group. Good adherence must be concomitant in both drugs in order to avoid side effects. This assessment helps identify patients with adherence problems and prioritise pharmaceutical care actions.

Conflict of interest No conflict of interest