Valsartan (Page 4 of 8)
8.5 Geriatric Use
In the controlled clinical trials of valsartan, 1,214 (36.2%) hypertensive patients treated with valsartan were ≥ 65 years and 265 (7.9%) were ≥ 75 years. No overall difference in the efficacy or safety of valsartan was observed in this patient population, but greater sensitivity of some older individuals cannot be ruled out. Exposure [measured by area under the curve (AUC)] to valsartan is higher by 70% in the elderly than in the young, however no dosage adjustment is necessary [see Clinical Pharmacology ( 12.3)].
Of the 2,511 patients with heart failure randomized to valsartan in the Valsartan Heart Failure Trial, 45% (1,141) were 65 years of age or older. In the VALsartan In Acute myocardial iNfarcTion trial (VALIANT), 53% (2,596) of the 4,909 patients treated with valsartan and 51% (2,515) of the 4,885 patients treated with valsartan + captopril were 65 years of age or older. There were no notable differences in efficacy or safety between older and younger patients in either trial.
8.6 Renal Impairment
Safety and effectiveness of valsartan in patients with severe renal impairment (glomerular filtration rate less than 30 mL/min/1.73 m 2) have not been established. No dose adjustment is required in patients with mild (glomerular filtration rate 60 to 90 mL/min/1.73 m 2) or moderate (glomerular filtration rate 30 to 60 mL/min/1.73 m 2) renal impairment.
8.7 Hepatic Impairment
No dose adjustment is necessary for patients with mild-to-moderate liver disease. No dosing recommendations can be provided for patients with severe liver disease.
Limited data are available related to overdosage in humans. The most likely manifestations of overdosage would be hypotension and tachycardia; bradycardia could occur from parasympathetic (vagal) stimulation. Depressed level of consciousness, circulatory collapse and shock have been reported. If symptomatic hypotension should occur, institute supportive treatment.
Valsartan is not removed from the plasma by hemodialysis.
Valsartan was without grossly observable adverse effects at single oral doses up to 2000 mg/kg in rats and up to 1000 mg/kg in marmosets, except for salivation and diarrhea in the rat and vomiting in the marmoset at the highest dose (60 and 31 times, respectively, the MRHD dose on a mg/m 2 basis) (Calculations assume an oral dose of 320 mg/day and a 60-kg patient).
Valsartan is a nonpeptide, orally active, and specific angiotensin II receptor blocker acting on the AT 1 receptor subtype.
Valsartan is chemically described as L-valine, N -(1-oxopentyl)- N -[[2′-(1 H -tetrazol-5-yl) [1,1′-biphenyl]-4-yl]methyl]-. Its empirical formula is C 24 H 29 N 5 O 3 , its molecular weight is 435.52, and its structural formula is
Valsartan, USP is a white to an off-white powder. It is soluble in ethanol and methanol and insoluble in water.
Valsartan is available as tablets for oral administration, containing 40 mg, 80 mg, 160 mg or 320 mg of valsartan USP. The inactive ingredients of the tablets are croscarmellose sodium, hypromellose, magnesium stearate, mannitol, microcrystalline cellulose, polyethylene glycol, povidone, and titanium dioxide. In addition to this 40 mg contains iron oxide yellow, 80 mg contains iron oxide red, 160 mg contains iron oxides (yellow and red) and 320 mg contains iron oxides (yellow, red and black). Meets USP dissolution test 2.
12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin-converting enzyme (ACE, kininase II). Angiotensin II is the principal pressor agent of the renin-angiotensin system, with effects that include vasoconstriction, stimulation of synthesis and release of aldosterone, cardiac stimulation, and renal reabsorption of sodium. Valsartan blocks the vasoconstrictor and aldosterone-secreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor in many tissues, such as vascular smooth muscle and the adrenal gland. Its action is therefore independent of the pathways for angiotensin II synthesis.
There is also an AT 2 receptor found in many tissues, but AT 2 is not known to be associated with cardiovascular homeostasis. Valsartan has much greater affinity (about 20,000-fold) for the AT 1 receptor than for the AT 2 receptor. The increased plasma levels of angiotensin II following AT 1 receptor blockade with valsartan may stimulate the unblocked AT 2 receptor. The primary metabolite of valsartan is essentially inactive with an affinity for the AT 1 receptor about one-200 th (1/200 th) that of valsartan itself.
Blockade of the renin-angiotensin system with ACE inhibitors, which inhibit the biosynthesis of angiotensin II from angiotensin I, is widely used in the treatment of hypertension. ACE inhibitors also inhibit the degradation of bradykinin, a reaction also catalyzed by ACE. Because valsartan does not inhibit ACE (kininase II), it does not affect the response to bradykinin. Whether this difference has clinical relevance is not yet known. Valsartan does not bind to or block other hormone receptors or ion channels known to be important in cardiovascular regulation.
Blockade of the angiotensin II receptor inhibits the negative regulatory feedback of angiotensin II on renin secretion, but the resulting increased plasma renin activity and angiotensin II circulating levels do not overcome the effect of valsartan on blood pressure.
Valsartan inhibits the pressor effect of angiotensin II infusions. An oral dose of 80 mg inhibits the pressor effect by about 80% at peak with approximately 30% inhibition persisting for 24 hours. No information on the effect of larger doses is available.
Removal of the negative feedback of angiotensin II causes a 2- to 3-fold rise in plasma renin and consequent rise in angiotensin II plasma concentration in hypertensive patients. Minimal decreases in plasma aldosterone were observed after administration of valsartan; very little effect on serum potassium was observed.
In multiple-dose studies in hypertensive patients with stable renal insufficiency and patients with renovascular hypertension, valsartan had no clinically significant effects on glomerular filtration rate, filtration fraction, creatinine clearance, or renal plasma flow.
In multiple-dose studies in hypertensive patients, valsartan had no notable effects on total cholesterol, fasting triglycerides, fasting serum glucose, or uric acid.
In healthy volunteers, valsartan peak plasma concentration is reached 2 to 4 hours after dosing. Valsartan shows bi-exponential decay kinetics following intravenous administration, with an average elimination half-life of about 6 hours. Absolute bioavailability for valsartan is about 25% (range 10% to 35%). The bioavailability of the suspension [see Dosage and Administration ( 2.2)] is 1.6 times as great as with the tablet. AUC and C max values of valsartan increase approximately linearly with increasing dose over the clinical dosing range (80 to 320 mg). Valsartan does not accumulate appreciably in plasma following repeated administration of 200 mg once daily.
In heart failure patients, the average time to peak plasma concentration and elimination half-life of valsartan are similar to those observed in healthy volunteers. The average accumulation factor is about 1.7 in heart failure patients following repeated administration of 160 mg twice daily. AUC and C max values of valsartan increase linearly and are almost proportional with increasing dose from 40 to 160 mg twice a day.
Effect of Food
With the tablet, food decreases the exposure (as measured by AUC) to valsartan by about 40% and peak plasma concentration (C max ) by about 50%. Valsartan can be administered with or without food.
The steady state volume of distribution of valsartan after intravenous administration is small (17 L), indicating that valsartan does not distribute into tissues extensively. Valsartan is highly bound to serum proteins (95%), mainly serum albumin.
The primary metabolite, accounting for about 9% of dose, is valeryl 4-hydroxy valsartan . In vitro metabolism studies involving recombinant CYP 450 enzymes indicated that the CYP 2C9 isoenzyme is responsible for the formation of valeryl-4-hydroxy valsartan. Valsartan does not inhibit CYP 450 isozymes at clinically relevant concentrations. CYP 450 mediated drug interaction between valsartan and coadministered drugs are unlikely because of the low extent of metabolism.
Valsartan, when administered as an oral solution, is primarily recovered in feces (about 83% of dose) and urine (about 13% of dose). The recovery is mainly as unchanged drug, with only about 20% of dose recovered as metabolites.
Following intravenous administration, plasma clearance of valsartan is about 2 L/h and its renal clearance is 0.62 L/h (about 30% of total clearance).
The apparent clearance of valsartan following oral administration is approximately 4.5 L/h in heart failure patients. Age does not affect the apparent clearance in heart failure patients.
Geriatric: Exposure (measured by AUC) to valsartan is higher by 70% and the half-life is longer by 35% in the elderly than in the young [see Use in Specific Populations ( 8.5)].
Pediatric: In a study of pediatric hypertensive patients (n=26, 1 to 16 years of age) given single doses of a suspension of valsartan (mean: 0.9 to 2 mg/kg), the clearance (L/h/kg) of valsartan for children was similar to that of adults receiving the same formulation. Valsartan pharmacokinetics have not been investigated in pediatric patients less than 1 year of age.
Gender: Pharmacokinetics of valsartan does not differ significantly between males and females.
Renal Insufficiency: There is no apparent correlation between renal function (measured by creatinine clearance) and exposure (measured by AUC) to valsartan in patients with different degrees of renal impairment (down to creatinine clearance of 10 mL/min). Valsartan is not removed from the plasma by hemodialysis [see Use in Specific Populations ( 8.6)].
Hepatic Insufficiency: On average, patients with mild-to-moderate chronic liver disease have twice the exposure (measured by AUC values) to valsartan of healthy volunteers (matched by age, sex, and weight) [see Use in Specific Populations ( 8.7)].
Drug Interaction Studies
No clinically significant pharmacokinetic interactions were observed when valsartan was coadministered with amlodipine, atenolol, cimetidine, digoxin, furosemide, glyburide, hydrochlorothiazide, or indomethacin. The valsartan-atenolol combination was more antihypertensive than either component, but it did not lower the heart rate more than atenolol alone.
Coadministration of valsartan and warfarin did not change the pharmacokinetics of valsartan or the time-course of the anticoagulant properties of warfarin. Transporters: The results from an in vitro study with human liver tissue indicate that valsartan is a substrate of the hepatic uptake transporter OATP1B1 and the hepatic efflux transporter MRP2. Coadministration of inhibitors of the uptake transporter (rifampin, cyclosporine) or efflux transporter (ritonavir) may increase the systemic exposure to valsartan.
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