Persistence with antihypertensives related to formulation: The case of nifedipine

BACKGROUND: Controlled release dosage forms may enhance persistence with therapy because of reduced dosing frequency and fewer adverse effects. OBJECTIVE: To assess the differences in persistent use of nifedipine between once-daily nifedipine gastrointestinal therapeutic system (GITS) and twice-daily nifedipine retard formulations. METHODS: Incident nifedipine users were selected from January 1992 to December 2001 from the PHARMO database, including drug-dispensing records and hospital records of more than one million subjects in the Netherlands. Patients with unaltered formulation and dosing frequency of nifedipine in the first year of follow-up with at least 2 prescriptions were included in the cohort. Persistence with different formulations was assessed using Cox's proportional hazard analyses. Covariates included in the analysis were, among others, hospitalizations and comedication for cardiovascular diseases. RESULTS: In total, 5889 incident users of nifedipine were included. The median duration of the first treatment episode was 133 days for nifedipine retard and 262 days for nifedipine GITS. One-year persistence with nifedipine increased from 32 % in patients using retard formulations to 44 % in patients using nifedipine GITS. Multivariate analyses showed that patients using nifedipine GITS were 1.3 times (RR 1.33; 95 % CI 1.22 to 1.46) more persistent than those using retard formulations of nifedipine. Persistent patients more often used other anti hypertensive drugs and were more often hospitalized for cardiovascular diseases. CONCLUSIONS: Patients using once-daily nifedipine GITS are more persistent with therapy than patients using twice-daily retard formulations.