Thesis (M.Sc.)--Chulalongkorn University, 2009

Objectives: 1. To investigate whether 50 mg losartan or 150 mg irbesartan could reduce seated diastolic blood pressure (SeDBP) and seated systolic blood pressure (SeSBP). 2. To compare antihypertensive efficacy between 50 mg losartan and 150 mg irbesartan controlling for (1) baseline SeDBP and SeSBP and (2) age. 3. To compare antihypertensive efficacy of 50 mg losartan and 150 mg irbesartan between gender controlling for (1) baseline SeDBP and SeSBP and (2) age. Method: A retrospective study design was performed. The data were collected from computerized Saraburi hospital main database. All hypertensive patients who were prescribed losartan 50 mg once daily or irbesartan 150 mg once daily for hypertensive treatment during January 1-June 30, 2008 were the population framework. Exclusion criteria included concomitant diseases and medications e.g., drugs known to affect BP that might interfere with the assessment of efficacy. Simple random technique was employed. The α 0.05, power 0.90 and effect size 0.15 were set to generate 200 samples in each group (total 400). The average baseline SeDBP and SeSBP of losartan group and irbesartan group were 81.57±8.56, 153.67±12.04 and 83.25±12.24, 160.04±15.42 respectively. Baseline SeDBP and SeSBP and age were used as covariates. After medications for 8 weeks SeDBP and SeSBP were measured and compared. Results: Total 400 (100%) patients, mostly 270 (67.50%) were female. The average age was 63.36±12.42 years. The majority occupation of the patients was merchant (35.00%). After treatment, the average SeDBP of losartan and irbesartan groups were 71.68±9.43 and 69.35±9.64 mmHg respectively (p=0.000, Paired t-test and p=0.000, Paired t-test). After treatment, the average SeSBP of losartan and irbesartan groups were 127.51±12.22 and 126.44±15.16 mmHg respectively (p=0.000, Paired t-test and p=0.000, Paired t-test). When controlled age (covariate) and added gender (fixed factor) to the model, the average SeDBP and SeSBP of losartan group and irbesartan group were 71.68±9.43, 127.51±12.22 and 69.35±9.64, 126.44±15.16 mmHg respectively (p=0.017, Two way ANCOVA and p=0.024, Two way ANCOVA without gender interaction (p=0.927, p=0.714). Conclusions: Both drugs, 50 mg losartan and 150 mg irbesartan once a day could significantly lower SeDBP and SeSBP (p=0.000, p=0.000, p=0.000, p=0.000, Paired t-test respectively). Irbesartan 150 mg once daily could significantly lower seated diastolic blood pressure and systolic blood pressure in hypertensive patients than losartan 50 mg once daily. (p=0.017, p=0.024, Two way ANCOVA respectively). Gender made no differences on efficacy of the two drugs. Qualifications of this study: This study used powerful statistical procedure, Two way ANCOVA controlling for two extraneous variables namely-baseline SeDBP and SeSBP and age. However there were still some limitations. 1. This research was a retrospective study consequently all data and variables were already collected. If it was a prospective design with a better protocol for systemically controlling errors and covariates including all reliable dependent and independent variables then it would yield better precise results. 2. This study proved only one aspect—lower blood pressure effect. To completely compare effectiveness of these two drugs, the future study may need comparing in more details such as effect to serum uric acid levels, side effects, and cost to ultimately conclude that which one is better