indication

May be used as a first line agent to treat uncomplicated hypertension, isolated systolic hypertension and left ventricular hypertrophy. May be used as a first line agent to delay progression of diabetic nephropathy. Losartan may be also used as a second line agent in the treatment of congestive heart failure, systolic dysfunction, myocardial infarction and coronary artery disease in those intolerant of ACE inhibitors.

pharmacology

Valsartan belongs to a class of antihypertensive agents called angiotensin II receptor blockers (ARBs). Valsartan is a specific and selective type-1 angiotensin II receptor (AT1) antagonist which blocks the blood pressure increasing effects angiotensin II via the renin-angiotensin-aldosterone system (RAAS). RAAS is a homeostatic mechanism for regulating hemodynamics, water and electrolyte balance. During sympathetic stimulation or when renal blood pressure or blood flow is reduced, renin is released from granular cells of the juxtaglomerular apparatus in the kidneys. Renin cleaves circulating angiotensinogen to angiotensin I, which is cleaved by angiotensin converting enzyme (ACE) to angiotensin II. Angiotensin II increases blood pressure by increasing total peripheral resistance, increasing sodium and water reabsorption in the kidneys via aldosterone secretion, and altering cardiovascular structure. Angiotensin II binds to two receptors: AT1 and type-2 angiotensin II receptor (AT2). AT1 is a G-protein coupled receptor (GPCR) that mediates the vasoconstrictive and aldosterone-secreting effects of angiotensin II. Studies performed in recent years suggest that AT2 antagonizes AT1-mediated effects and directly affects long-term blood pressure control by inducing vasorelaxation and increasing urinary sodium excretion. Angiotensin receptor blockers (ARBs) are non-peptide competitive inhibitors of AT1. ARBs block the ability of angiotensin II to stimulate pressor and cell proliferative effects. Unlike ACE inhibitors, ARBs do not affect bradykinin-induced vasodilation. The overall effect of ARBs is a decrease in blood pressure.

mechanism of action

Valsartan is an ARB that selectively inhibits the binding of angiotensin II to AT1, which is found in many tissues such as vascular smooth muscle and the adrenal glands. This effectively inhibits the AT1-mediated vasoconstrictive and aldosterone-secreting effects of angiotensin II and results in a decrease in vascular resistance and blood pressure. Valsartan is selective for AT1 and has virtually no affinity for AT2. Inhibition of aldosterone secretion may inhibit sodium and water reabsorption in the kidneys while decreasing potassium excretion. The primary metabolite of valsartan, valeryl 4-hydroxy valsartan, has no pharmacological activity.

biotransformation

Valsartan is excreted largely as unchanged drug (80%) and is minimally metabolized in humans. The primary circulating metabolite, 4-OH-valsartan, is pharmacologically inactive and produced CYP2C9. 4-OH-valsartan accounts for approximately 9% of the circulating dose of valsartan. Although valsartan is metabolized by CYP2C9, CYP-mediated drug-drug interactions between valsartan and other drugs is unlikely.

absorption

Absolute bioavailability = 23% with high variability

half life

The initial phase t_{1/2 α} is < 1 hour while the terminal phase t_{1/2 β} is 5-9 hours.

route of elimination

83% of absorbed valsartan is excreted in feces and 13% is excreted in urine, primarily as unchanged drug

drug interactions

Amifostine: Additive hypotensive effects may occur. At chemotherapeutic doses of Amifostine, Valsartan should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Amiloride: Increased risk of hyperkalemia

Lithium: Valsartan may increase serum lithium concentrations. Monitor serum lithium levels during concomitant therapy to avoid lithium toxicity.

Potassium: Increased risk of hyperkalemia

Rituximab: Additive hypotensive effects may occur. Increased risk of hypotension. Consider withholding Valsartan for 12 hours prior to administration of Rituximab.

Tobramycin: Increased risk of nephrotoxicity

Trandolapril: The angiotensin II receptor blocker, Valsartan, may increase the adverse effects of Trandolapril.

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.

Triamterene: Increased risk of hyperkalemia