Factors influencing the switch in the use of antihypertensive medications.

The present study was undertaken to explore factors associated with observance of prescribed antihypertensive medications. Secondary data analysis utilising ambulatory claims of the Taiwan National Health Insurance involved all initially treated hypertensive patients (n=565,048) from June 1, 1997 to June 30, 1998. The main outcome measure was the statistical analysis of factors prompting medication switch and dropout rates. The overall continuity rate was 51%. Specific continuity rates were 40% for calcium antagonists, 36% for angiotensin-converting enzyme inhibitors, 35% for beta-blockers and 29% for diuretics. Less than 30% of patients changed medications and more than 20% of patients changed clinics. The change increased the likelihood of switching medications sevenfold. Switch was minimal for calcium antagonists. Patients taking calcium antagonists were the least likely to switch medications and had the lowest dropout rate. Changing clinics was the most influential medication switch factor.