A nationwide survey of adherence to analgesic drugs among cancer patients in Taiwan: prevalence, determinants, and impact on quality of life.

Poor adherence to analgesic drugs is one of the most common barriers to adequate pain management. This prospective, cross-sectional, patient-oriented observational study aimed to explore the adherence rate, clinical factors, and impact of adherence to analgesic drugs on the quality of life (QoL) among cancer outpatients in Taiwan. Eight hundred ninety-seven consecutive adult outpatients with cancer who had reported tumor pain and received regular analgesic drug treatment were enrolled from 16 medical centers across Taiwan. The Brief Pain Inventory was used to assess pain intensity and QoL. Morisky's four-item medication adherence scale was used to assess adherence to analgesic drugs. Clinical factors possibly associated with good adherence to analgesic drugs were analyzed using multivariate logistic regression analyses. Of the 897 patients, 26.9% met criteria for the good, 35.5% for the moderate, and 37.6% for the poor adherence groups. The good adherence group had significantly better QoL outcomes than the moderate and poor adherence groups (all p < 0.05). Age ≥ 50 years, head and neck or hematological malignancies, cancer-related pain, patients who agreed or strongly agreed that the side effects of analgesic drugs were tolerable, and patients who disagreed or strongly disagreed that the dosing schedule could be flexibly self-adjusted to deal with the actual pain were predictors of good adherence to analgesic drugs. Awareness of the clinical factors associated with adherence to analgesic drugs may help clinicians to identify cancer patients at a greater risk of non-adherence, reinforce optimal pain management, and improve the QoL by enhancing adherence to pain medications.