High blood pressure (hypertension) is not uncommon in cats, particularly those with chronic kidney disease (CKD). It accelerates decline of kidney function and increases protein being dumped into the urine, the latter being a negative prognostic indicator in cats with CKD. The mechanism of hypertension in cats with CKD is complex and multifactorial, but it does involve over activation of the renin-angiotensin-aldosterone system (RAAS), a hormone system that regulates blood pressure and fluid balance.
Several RAAS-modifying agents, developed in human with hypertension, also have kidney protective effects, primarily by reducing kidney blood filtration hypertension and urinary protein. Of the RAAS-modifying drugs available, only ACE inhibitors (e.g. benazepril) have been well studied in cats; however, these drugs have shown poor antihypertensive effects in cats. An alternative choice for RAAS blockade may be found through the use of ARBs, which selectively blocks the angiotensin II, subtype 1 receptor, the latter being responsible for mediating the pathological effects of angiotensin II on the kidneys and heart.
The authors’ study objective was to compare the attenuation of the angiotensin I–induced blood pressure response by once-daily oral administration of various doses of 3 ARBs (irbesartan, telmisartan, and losartan), benazepril, and lactose (i.e., placebo) in 6 clinically normal cats. The cats were administered orally the drug or placebo once daily for 8 days in a crossover study. Blood pressure was measured continuously (i.e., rapid pressor response test) at 90 minutes and 24 hours after the last drug or placebo dose and RAAS blockade determined after administrating 3 different dosages of angiotensin.
The results indicated that at 90 minutes after drug administration, only losartan did not significantly reduce blood pressure in response to the 3 higher angiotensin doses, compared with placebo. Among drug treatments, telmisartan (3 mg/kg dosage) attenuated blood pressure to a significantly greater degree than benazepril and all other treatments. At 24 hours, telmisartan was more effective than benazepril. Telmisartan may prove useful in the treatment of cats with kidney or heart diseases, and may be a better choice for treating cats with increased urinary protein.
Further studies are warranted to evaluate the efficacy of telmisartan in the treatment of clinical patients.
