Irbesartan

IRBESARTAN- irbesartan tablet
AvPAK

WARNING: FETAL TOXICITY

See full prescribing information for complete boxed warning .
• When pregnancy is detected, discontinue irbesartan tablets as soon as possible. (5.1)
• Drugs that act directly on the renin-angiotensin system can cause injury and death to the developing fetus. (5.1)

5.3 Impaired Renal Function

Changes in renal function including acute renal failure can be caused by drugs that inhibit the reninangiotensin system. Patients whose renal function may depend in part on the activity of the reninangiotensin system (e.g., patients with renal artery stenosis, chronic kidney disease, severe heart failure, or volume depletion) may be at particular risk of developing acute renal failure or death on irbesartan. Monitor renal function periodically in these patients. Consider withholding or discontinuing therapy in patients who develop a clinically significant decrease in renal function on irbesartan [see Drug Interactions (7.3)].

DESCRIPTION

Irbesartan USP is an angiotensin II receptor (AT1 subtype) antagonist.
Irbesartan USP is a non-peptide compound, chemically described as a 2-butyl-3-[p-(o-1H-tetrazol-5-ylphenyl)benzyl]-1,3-diazaspiro[4.4]non-1-en-4-one.
Its empirical formula is C 25 H 28 N 6 O, and the structural formula:
http://medlibrary.org/lib/images-rx/irbesartan-27/structure.jpg
Irbesartan USP is a white to off-white crystalline powder with a molecular weight of 428.5. It is a nonpolar compound with a partition coefficient (octanol/water) of 10.1 at pH of 7.4. Irbesartan is slightly soluble in alcohol and methylene chloride and practically insoluble in water.
Irbesartan is available for oral administration in unscored tablets containing 75 mg, 150 mg, or 300 mg of Irbesartan USP. Inactive ingredients include: calcium stearate, carboxy methyl cellulose calcium, colloidal silicon dioxide, microcrystalline cellulose and povidone.

CLINICAL PHARMACOLOGY

Mechanism of Action
Angiotensin II is a potent vasoconstrictor 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 (RAS) and also stimulates aldosterone synthesis and secretion by adrenal cortex, cardiac contraction, renal resorption of sodium, activity of the sympathetic nervous system, and smooth muscle cell growth. Irbesartan blocks the vasoconstrictor and aldosterone-secreting effects of angiotensin II by selectively binding to the AT 1 angiotensin II receptor. There is also an AT 2 receptor in many tissues, but it is not involved in cardiovascular homeostasis.
Irbesartan is a specific competitive antagonist of AT 1 receptors with a much greater affinity (more than 8500-fold) for the AT 1 receptor than for the AT 2 receptor and no agonist activity.
Blockade of the AT 1 receptor removes the negative feedback of angiotensin II on renin secretion, but the resulting increased plasma renin activity and circulating angiotensin II do not overcome the effects of irbesartan on blood pressure.
Irbesartan does not inhibit ACE or renin or affect other hormone receptors or ion channels known to be involved in the cardiovascular regulation of blood pressure and sodium homeostasis. Because irbesartan does not inhibit ACE, it does not affect the response to bradykinin; whether this has clinical relevance is not known.

Pharmacokinetics

In healthy subjects, single oral irbesartan doses of up to 300 mg produced dose-dependent inhibition of the pressor effect of angiotensin II infusions. Inhibition was complete (100%) 4 hours following oral doses of 150 mg or 300 mg and partial inhibition was sustained for 24 hours (60% and 40% at 300 mg and 150 mg, respectively).

In hypertensive patients, angiotensin II receptor inhibition following chronic administration of irbesartan causes a 1.5- to 2-fold rise in angiotensin II plasma concentration and a 2- to 3-fold increase in plasma renin levels. Aldosterone plasma concentrations generally decline following irbesartan administration, but serum potassium levels are not significantly affected at recommended doses.

In hypertensive patients, chronic oral doses of irbesartan (up to 300 mg) had no effect on glomerular filtration rate, renal plasma flow, or filtration fraction. In multiple dose studies in hypertensive patients, there were no clinically important effects on fasting triglycerides, total cholesterol, HDL-cholesterol, or fasting glucose concentrations. There was no effect on serum uric acid during chronic oral administration, and no uricosuric effect.

Special Populations

Gender
No gender-related differences in pharmacokinetics were observed in healthy elderly (age 65 to 80 years) or in healthy young (age 18 to 40 years) subjects. In studies of hypertensive patients, there was no gender difference in half-life or accumulation, but somewhat higher plasma concentrations of irbesartan were observed in females (11 to 44%). No gender-related dosage adjustment is necessary.
Geriatric
In elderly subjects (age 65 to 80 years), irbesartan elimination half-life was not significantly altered, but AUC and C max values were about 20% to 50% greater than those of young subjects (age 18 to 40 years). No dosage adjustment is necessary in the elderly.
Race
In healthy black subjects, irbesartan AUC values were approximately 25% greater than whites; there were no differences in C max values.
Renal Insufficiency
The pharmacokinetics of irbesartan were not altered in patients with renal impairment or in patients on hemodialysis. Irbesartan is not removed by hemodialysis. No dosage adjustment is necessary in patients with mild to severe renal impairment unless a patient with renal impairment is also volume depleted. (See WARNINGS: Hypotension in Volume- or Salt-Depleted Patients and DOSAGE AND ADMINISTRATION.)
Hepatic Insufficiency
The pharmacokinetics of irbesartan following repeated oral administration were not significantly affected in patients with mild to moderate cirrhosis of the liver. No dosage adjustment is necessary in patients with hepatic insufficiency.
Drug Interactions
(See PRECAUTIONS: Drug Interactions.)

Pharmacokinetics

Absorption
The oral absorption of irbesartan is rapid and complete with an average absolute bioavailability of 60% to 80%. Following oral administration of irbesartran, peak plasma concentrations of irbesartan are attained at 1.5 to 2 hours after dosing. Food does not affect the bioavailability of irbesartan. Irbesartan exhibits linear pharmacokinetics over the therapeutic dose range.

Distribution
Irbesartan is 90% bound to serum proteins (primarily albumin and α -acid glycoprotein) with negligible binding to cellular components of blood. The average volume of distribution is 53 to 93 liters. Studies in animals indicate that radiolabeled irbesartan weakly crosses the blood-brain barrier and placenta. Irbesartan is excreted in the milk of lactating rats.

Elimination
Total plasma and renal clearances are in the range of 157 to 176 mL/min and 3.0 to 3.5 mL/min, respectively. The terminal elimination half-life of irbesartan averages 11 to 15 hours. Steady-state concentrations are achieved within 3 days. Limited accumulation of irbesartan (<20%) is observed in plasma upon repeated once-daily dosing and is not clinically relevant.

Metabolism
Irbesartan is an orally active agent that does not require biotransformation into an active form. Irbesartan is metabolized via glucuronide conjugation and oxidation. Following oral or intravenous administration of C-labeled irbesartan, more than 80% of the circulating plasma radioactivity is attributable to unchanged irbesartan. The primary circulating metabolite is the inactive irbesartan glucuronide conjugate (approximately 6%). The remaining oxidative metabolites do not add appreciably to
irbesartan’s pharmacologic activity. In vitro studies indicate irbesartan is oxidized primarily by CYP2C9; metabolism by CYP3A4 is
negligible.

Excretion
Irbesartan and its metabolites are excreted by both biliary and renal routes. Following either oral or intravenous administration of C-labeled irbesartan, about 20% of radioactivity is recovered in the urine and the remainder in the feces, as irbesartan or irbesartan glucuronide.

Specific Populations
Sex
No sex-related differences in pharmacokinetics are observed in healthy elderly (age 65 to 80 years) or in healthy young (age 18 to 40 years) subjects. In studies of hypertensive patients, there is no sex difference in half-life or accumulation, but somewhat higher plasma concentrations of irbesartan are observed in females (11% to 44%). No sex-related dosage adjustment is necessary.

Geriatrics
In elderly subjects (age 65 to 80 years), irbesartan elimination half-life is not significantly altered, but AUC and C values are about 20% to 50% greater than those of young subjects (age 18 to 40 years). No dosage adjustment is necessary in the elderly.

Race/Ethnicity
In healthy black subjects, irbesartan AUC values are approximately 25% greater than whites; there is no difference in C values.

Renal Impairment The pharmacokinetics of irbesartan are not altered in patients with renal impairment or in patients on
hemodialysis. Irbesartan is not removed by hemodialysis. No dosage adjustment is necessary in patients with mild to severe renal impairment unless a patient with renal impairment is also volume depleted [see Warnings and Precautions (5.2) and Dosage and Administration (2.4)].

Hepatic Insufficiency
The pharmacokinetics of irbesartan following repeated oral administration are not significantly affected in patients with mild to moderate cirrhosis of the liver. No dosage adjustment is necessary in patients with hepatic insufficiency.

Drug-Drug Interactions
In vitro studies show significant inhibition of the formation of oxidized irbesartan metabolites with the known cytochrome CYP 2C9 substrates/inhibitors sulphenazole, tolbutamide and nifedipine. However, in clinical studies the consequences of concomitant irbesartan on the pharmacodynamics of warfarin were negligible. Based on in vitro data, no interaction would be expected with drugs whose metabolism is dependent upon cytochrome P450 isoenzymes 1A1, 1A2, 2A6, 2B6, 2D6, 2E1, or 3A4.
In separate studies of patients receiving maintenance doses of warfarin, hydrochlorothiazide, or digoxin, irbesartan administration for 7 days has no effect on the pharmacodynamics of warfarin (prothrombin time) or pharmacokinetics of digoxin. The pharmacokinetics of irbesartan are not affected by coadministration of nifedipine or hydrochlorothiazide.

All MedLibrary.org resources are included in as near-original form as possible, meaning that the information from the original provider has been rendered here with only typographical or stylistic modifications and not with any substantive alterations of content, meaning or intent.

This site is provided for educational and informational purposes only, in accordance with our Terms of Use, and is not intended as a substitute for the advice of a medical doctor, nurse, nurse practitioner or other qualified health professional.

Privacy Policy | Copyright © 2024. All Rights Reserved.