OBJECTIVES: To investigate the usage pattern of indapamide and other antihypertensive drugs in patients attending a community-based government outpatient clinic (GOPC) or a hospital-based specialist clinic (SC). The plasma potassium concentrations of patients receiving indapamide and other diuretics were also examined. METHOD: Prescriptions from the SC and the GOPC were reviewed and collected during January 1998. Patients' plasma potassium concentrations and the date of initiation of each medication were retrieved from the hospital computer databases at SC. An age- and sex-matched control group of patients on non-diuretic antihypertensive drugs was identified. RESULTS: A total of 1648 and 773 prescriptions were collected from the SC during a 1-week period and GOPC during a 1-month period, respectively. Approximately half (45%) of the patients received antihypertensive treatment. Indapamide was five times more frequently prescribed in GOPC than SC (84.7 vs. 17.7%, P<0.001). Calcium channel blocking agents were the commonest antihypertensive drugs used in both clinics. The mean plasma potassium concentration of patients taking indapamide was lower than that of the control group (P = 0.037). Multiple linear regression analysis showed that consumption of indapamide (P =0.002) and duration of diuretic therapy (P = 0.023) were significantly related to changes in plasma potassium concentrations [multiple regression equation for potassium level = 4.09-0.145 (thiazide = 1)-0.377 (indapamide = 1) -0.00468 (duration of diuretic therapy in months)]. CONCLUSION: Indapamide was used extensively in the community clinic and less in the hospital-based outpatient clinic. Patients receiving indapamide had a significantly lower plasma potassium concentration as compared to other diuretics or antihypertensive groups and this was predicted by a multiple linear regression model. Monitoring plasma electrolytes before initiation of indapamide treatment and at regular intervals thereafter is essential for detecting the hypokalaemia that may occur in Chinese patients.