Losartan is an oral angiotensin II type 1 (AT1) receptor antagonist that is rapidly absorbed in dogs but has low oral bioavailability. Losartan therapy in veterinary patients with renal, heart, or liver disease is likely beneficial, but its use is limited due to lack of clinical data.
MECHANISMS OF ACTION
Once absorbed by the GI tract, losartan undergoes enterohepatic recirculation and biliary excretion.1
- Recent human and veterinary studies have indicated that AT1 receptor antagonists may be useful for treating patients with chronic disease, either in combination with angiotensin-converting enzyme (ACE) inhibitors or as replacement therapy for ACE inhibitors.2,3
- ACE inhibitors (eg, enalapril, benazepril) are commonly used to inhibit the negative effects of the renin-angiotensin-aldosterone system (RAAS) on cardiac2 and proteinuric renal3 diseases, with an emerging role in treating hepatic fibrosis (see The Renin-Angiotensin-Aldosterone System).
- Despite ACE-inhibitor therapy, angiotensin II and aldosterone can still be produced by alternate pathways, a phenomenon called RAAS escape (or aldosterone escape).4,5
- Despite the appropriate use of ACE-inhibitor therapy, patients with chronic disease can show negative effects of RAAS activation.
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