A comparison study of multiple measures of adherence to antipsychotic medication in first-episode psychosis.

This study evaluates how much agreement there is between subjective reports of adherence to antipsychotic medication and objective or derived measures of adherence in first-episode psychosis (FEP) and asks if any adherence measure could approximate a gold standard based on correlation to symptom improvement in the early phase of treatment. Adherence was assessed in 81 FEP subjects on a monthly basis by reports from patients, clinicians, family, and pill counting. A consensus measure of adherence was derived from all available sources of adherence data. Symptoms were measured using the Positive and Negative Syndrome Scale at study entry and 3 months subsequently. Adherence as measured by patient report, pill count, and clinician report were in good agreement with each other (intraclass correlation coefficient = 0.84), and all of these measures were highly correlated to consensus adherence (r values between 0.86 and 0.98). Mean adherence was slightly higher as rated by patients (83% full doses taken per month) and family members (91%) than by clinicians (76%), pill counting (73%), or consensus value (74%). Early in treatment, each measure of adherence (except family report) was significantly associated with positive symptom reduction, although the order of magnitude of this correlation was greater for pill count and consensus adherence (P < 0.01) compared with patient- or clinician-reported adherence (P < 0.05). Patient or clinician reports provide a reasonable estimate of medication adherence in FEP, but introducing pill counting or a derived measure of adherence may allow more accurate measurement.