Losartan Potassium 50 mg
BRAND NAME: – Z-SAR-50 TABLET (LOSARTAN POTASSIUM 50mg)
Composition: – Each tablet contains 50mg Losartan Potassium
Packing: – 10*10
1. Pharmacodynamics: – Losartan is the first of a class of antihypertensive agents called angiotensin II receptor blockers (ARBs). Losartan and its longer acting active metabolite, E-3174, are specific and selective type-1 angiotensin II receptor (AT1) antagonists which block 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.
2. Pharmacokinetics: –
a.) Absorption: – Losartan is well absorbed and undergoes substantial first-pass metabolism; the systemic bioavailability of losartan is approximately 33%. Mean peak concentrations of losartan and its active metabolite are reached in 1 hour and in 3-4 hours, respectively. While maximum plasma concentrations of losartan and its active metabolite are approximately equal, the AUC of the metabolite is about 4 times as great as that of losartan. When given with a meal, absorption is slows down and Cmax decreases.
b.) Volume of Distribution: – 34 L [losartan, healthy subjects], 12 L [active metabolite, healthy subjects]
c.) Protein Binding: – 99.7% protein bound, primarily to albumin
d.) Metabolism: – Hepatic. Losartan is metabolized to a 5-carboxylic acid derivative (E-3174) via an aldehyde intermediate (E-3179) primarily by cytochrome P450 (CYP) 2C9 and CYP3A4. E-3174 is an active metabolite with 10- to 40-fold higher potency than its parent compound, losartan. Approxiamtely 14% of losartan is converted to E-3174; however, the AUC of E-3174 was found to be 4- to 8-fold higher than losartan and E-3174 is considered the main contributor to the pharmacologic effects of this medication.
e.) Route of Elimination: – Following oral administration of losartan, 35% of the dose is recovered in the urine and about 60% in the feces. Following an intravenous dose, 45% is recovered in the urine and 50% in the feces.
f.) Half-Life: – The terminal t1/2 of losartan is 2 hours. The active metabolite has a half-life of 6-9 hours.
g.) Clearance: – Total plasma clearance = 600 mL/min [losartan], Total plasma clearance = 50 mL/min [active metabolite], Renal clearance = 75 mL/min [losartan], Renal clearance = 25 mL/min [active metabolite]
h.) Toxicity: – Hypotension and tachycardia; Bradycardia could occur from parasympathetic (vagal) stimulation, LD50= 1000 mg/kg (orally in rat).
Indications: – 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.