Hypertension, or high blood pressure, is a common finding in cats with kidney disease, hyperthyroidism, and other age-related conditions. The effects of hypertension include damage to the kidneys, eyes, brain, heart, and other organs. Most cats with hypertension are controlled with amlodipine, a drug that dilates arteries and decreases blood pressure. While this is effective in most cats, some are unable to tolerate the drug, are unable to be administered multiple drugs, or require a secondary drug when amlodipine is insufficient.
Previous studies on ACE-inhibitors have shown negligible effect on blood pressure. Telmisartan is an ARB (angiotensin II, type-1 receptor blocker), a similar class of drug approved in cats for reduction of proteinuria. The purpose of this study was to determine if telmisartan is effective in reducing blood pressure in healthy cats. The study was designed as a prospective, randomized, double blinded, placebo controlled crossover trial in adult domestic cats.
Twenty-eight adult cats (2-6 years old) with normal physical examination, CBC and serum chemistries, and blood pressure were enrolled in the study. Cats were excluded if they were administered NSAIDs or any medications that could alter blood pressure, if oral medication could not be administered, or if they did not tolerate non-invasive blood pressure measurement.
Cats were acclimatized to daily blood pressure measurement for 14 days and to oral administration of placebo prior to administration for 5 days. Systolic blood pressure was measured by Doppler ultrasound using ACVIM guidelines. After acclimation cats were randomized to one of 7 treatment groups: oral PLA (plasmalyte A; placebo), oral telmisartan at 1, 1.5, 2, or 3mg/kg q24h, or oral telmisartan at 1 or 1.5mg/kg q12h. Blood pressure was measured ~3h after drug administration each day.
Treatment was continued for 14 days, followed by a 7 day washout period, after which cats were randomly reassigned to another group in an incomplete square crossover method. Each cat was assigned to a total of 3 treatments, for a total of 12 animals in each group.
Adverse reactions occurred in 18 animals (9 PLA and 9 telmisartan treated) over the course of the study, most of which were gastrointestinal, all of which were minor and self-limiting. No animals required dose adjustment or removal from the study. No animals experienced clinical signs of hypotension, and no cat experienced a blood pressure less than 80mmHg systolic.
A significant effect of treatment period on blood pressure was found across all groups. This confounded data and resulted in the second and third periods not being considered.
Mean systolic blood pressure across the entire 14 day treatment period was significantly decreased in the telmisartan group at all but the lower two dosages. When considering only the second week of therapy, telmisartan significantly decreased blood pressure in all groups. Dosages >2mg/kg/day were associated with a lower systolic blood pressure than doses <2mg/kg/day. Median decreases in blood pressure were 25–37 mmHg relative to baseline in the telmisartan groups, compared to 6mmHg in the treatment groups.
One major drawback to this study is the use of healthy, rather than hypertensive cats. While results are suggestive of an anti-hypertensive effect, these may not be transferable to hypertensive animals. The range of doses used in the study suggests that more work should be done to determine the most effective dose. Sample sizes were also very small, especially considering the period effect resulting in removal of the second and third treatment periods.
The authors conclude that telmisartan is safe in cats and effective at reducing blood pressure at the doses tested, though more work is needed to determine the most effective dose and measure its efficacy in hypertensive animals.
