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 445 356 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 β-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.