Discontinuation of and changes in drug therapy for hypertension among newly-treated patients: a population-based study in Italy.

OBJECTIVES: To assess rates and determinants of treatment discontinuation of or changes in initial antihypertensive drug therapy in a large cohort of patients from Lombardia (Italy). METHODS: The cohort included 445356 patients aged 40 -80 years who received their first antihypertensive drug prescription (monotherapy) during 1999--2002. Discontinuation was defined by the absence of any antihypertensive prescription during a 90-day period following the end of the latest prescription. If during the same period a drug of a different class was added or replaced the initial prescription, treatment modification was regarded as combination or switching, respectively. Competing risks methodology was used to estimate and compare cause-specific cumulative incidence. RESULTS: Cumulative incidences of discontinuation, combination and switching were respectively 33, 14 and 15% at 6 months, 41, 18 and 17% at 1 year, and 50, 25 and 19% at 5 years since initial treatment. Compared with patients starting treatment with angiotensin-converting enzyme inhibitors, the rate of discontinuation was less for patients on angiotensin receptor blockers with a hazard ratio of 0.92 (95% confidence interval =0.90-0.94), whereas increased discontinuation was observed for patients starting with other drugs, mainly beta-blockers with a hazard ratio of 1.64 (1.62-1.67); and diuretics with a hazard ratio of 1.83 (1.81-1.85). CONCLUSION: In the general population of Lombardia, discontinuation of the initial single antihypertensive drug treatment is a common phenomenon, whereas switching to another monotherapy and to combination treatment occur at similarly much lower rates. Blockers of the renin-angiotensin system are associated with the lowest incidence of treatment discontinuation.