Irbesartan-d4 is intended for use as an internal standard for the quantification of irbesartan by GC- or LC-MS. Irbesartan is an antagonist of the angiotensin II type 1 (AT1) receptor (Ki = 1.3 nM). It is an insurmountable antagonist of AT1, as its antagonism cannot be overcome by increasing concentrations of angiotensin II. Irbesartan (3, 10, and 30 mg/kg) reduces blood pressure in stroke-prone spontaneously hypertensive rats and increases survival of SPSH rats fed a high-salt low-protein diet. It also reduces plaque formation, collagen content, as well as the increased expression of the AT1 receptor, PDGF-b, MCP-1, and VCAM-1 in a model of diabetes-induced atherosclerosis using apolipoprotein E (ApoE) knockout mice with diabetes induced by streptozotocin . Formulations containing irbesartan have been used, alone and in combination with diuretics, in the treatment of hypertension.