[Medical-pharmaceutical intervention on patients exposed to azathioprine-allopurinol interaction in the Community of Madrid]

Objective: To evaluate the impact of a medical-pharmaceutical intervention strategy on patients exposed to azathioprine-allopurinol (AZA-ALO) interaction in the Community of Madrid (CM).

Material/methods: Multicentre retrospective observational study. We reviewed the database generated after an intervention carried out in the healthcare context in which Primary Care Pharmacists (PCP) review the treatment of patients with safety risks and, when there are incidents, they contact (by telephone and/or e-mail) their Family Physicians (FP) for possible resolution.

Study population: CM patients with an active clinical history in Primary Care who have been dispensed both medications (AZA-ALO) in the period April-June 2022 according to prescription billing data from the National Health System (NHS). Main variable: suppression or dose adjustment of either of the two drugs.

Results: Forty-nine patients were analysed. Mean age: 65.65±11.67 years. Males; 77.6%. 8,834 patients withdrew azathioprine (28,724 packs) and 89,297 withdrew allopurinol (141,188 packs) from pharmacies, with a very low prevalence of patients at risk (<1%). The prescription was modified in 32 patients (65.31%-IC95%: 51.98%-78.63%), with allopurinol being discontinued in 65.62% and, with regard to azathioprine, the dose was reduced by 18.75% and discontinued in 9.37%. Analytical alterations compatible with adverse effects due to the interaction were recorded in 28 patients (57.1%-IC95%: 43.29%-71%), including anaemia (39.3%) and leukopenia/neutropenia (25%).

Conclusions: Coordinated intervention between pharmacists and physicians was effective, resulting in prescription modification in a significant percentage of patients, which reduced the risk of toxicity.