Evaluation of the inhibitory effects of telmisartan on drug-induced renin-angiotensin-aldosterone system activation in normal dogs

Introduction

This study examined whether the angiotensin II receptor blocker telmisartan had inhibitory effects on drug-induced renin-angiotensin-aldosterone system (RAAS) activation in normal dogs.

Animals

Five healthy laboratory beagles were used in this study.

Methods

Each dog received amlodipine (0.5 mg/kg, q12h, PO) alone for 14 days. Starting on the next day, animals received both amlodipine and telmisartan (1.0 mg/kg, q24h, PO) for 84 days. Systolic blood pressure, heart rate, plasma biochemical variables (blood urea nitrogen, creatinine, and electrolytes), plasma renin activity, and 24-h urinary aldosterone elimination (U-Aldo) were measured before amlodipine administration; at day 0; and at days 1, 7, 14, 28, 56, and 84 of telmisartan treatment.

Results

Telmisartan was associated with significant decreases in systolic blood pressure on day 56 (p=0.046), whereas heart rate did not significantly change during this treatment (p=0.061). Plasma renin activity was significantly increased on days 1, 7, 28, 56, and 84 during telmisartan administration (all p=0.04). No change in median U-Aldo was detected following telmisartan administration (p=0.241). When U-Aldo was evaluated in individual animals, two dogs displayed evidence of aldosterone breakthrough.

Conclusions

Telmisartan administration did not suppress RAAS activation. The appearance of aldosterone breakthrough supports the incomplete blockade of RAAS activation.