Switching of antihypertensive drugs among 93,286 Chinese patients: a cohort study.

Antihypertensive drug switching induces substantial public health costs. This cohort study evaluated factors associated with switching of antihypertensive agents 180 days after the first date of prescription among ethnic Chinese patients. We included all adult patients aged > or =18 years, who had paid at least two consecutive visits to all public primary care clinics in one large territory of Hong Kong during the study period from January 2004 to June 2007. Binary logistic regression analyses were carried out with antihypertensive drug switching as an outcome variable, while controlling for age, gender, payment status, service types, district of residence, visit types and the number of comorbidities. Among 93,286 eligible patients, 5281 (5.7%) switched their antihypertensive prescriptions to another drug class within 180 days. Patients aged > or =70 years (adjusted odds ratio (aOR) 0.88, P=0.005), male subjects (aOR 0.87, P<0.001) and follow-up visitors (aOR 0.67, P<0.001) were less likely to have their drugs switched. When compared with thaizide diuretics, all other antihypertensive drug classes were associated with a lower likelihood of drug switching (aOR 0.27-0.69, all P<0.001). Closer observations of drug utilization profiles among these patient groups are recommended, and future studies should evaluate the reasons for drug switching.