The proposed study is to evaluate the possible effect of metformin on arterial pressure by 24h-ambulatory blood pressure monitory (24h-ABPM).

The primary outcome was the difference in mean 24-hour blood pressure variation between the two groups after the intervention. The difference in mean of blood pressure during daytime and nighttime in 24h ambulatory blood pressure monitory, as well as the office BP and laboratory differences were considered secondary outcomes.

This randomized, double-blind parallel study was conducted in the Hypertension Clinic of the Department of Cardiology, Hospital de Clínicas de Porto Alegre (Porto Alegre, Brazil).

We selected hypertensive individuals (controlled or not) without diabetes aged 18-70 years.

Exclusion criteria: metformin intolerance, creatinine > 1,5 mg/dl Risks: adverse effects related to metformin use, mainly diarrhea and nausea Benefits: possible lower effect on arterial pressure Statistical analysis: sample size was calculated on the basis of a standard deviation of 8 mm Hg and effect size of 5 mm Hg in 24-h systolic ABPM and a two-sided significance level of 5%. A sample size of 42 patients per group was estimated to provide a power of 80% to reject the null hypothesis. Considering possible 10% of losses, the final calculated sample was 92 patients.

The baseline comparison between groups was performed using the Student t test for continuous variables and x2 for categorical variables. In each group, the change in BP by ABPM -24 h, daytime and nighttime, and laboratory tests was calculated by subtracting baseline values measured after the intervention period. The difference between groups was calculated by subtracting the variation observed between them (δ-values). The differences in BP variation and laboratory tests were analyzed by analysis of variance for repeated measures (MANOVA). For differences in pressure variation adjustment was considered for the baseline BP values (analysis of covariance). All tests were two-tailed and significance level was 5%. Data were analyzed using Statistical Package for the Social Sciences (SPSS) version 13.0.

Inclusion Criteria:

• hypertensive patients,
• aged 18-75 years

Exclusion Criteria:

• diabetes
• metformin intolerance
• creatinine level above 1.5 mg/dL