Candesartan cilexetil

Absorption

Following administration of the candesartan cilexetil prodrug, the absolute bioavailability of candesartan was estimated to be 15%. Food with a high fat content has no effect on the bioavailability of candesartan from candesartan cilexetil.

Toxicity

No lethality was observed in acute toxicity studies in mice, rats and dogs given single oral doses of up to 2000 mg/kg of candesartan cilexetil or in rats given single oral doses of up to 2000 mg/kg of candesartan cilexetil in combination with 1000 mg/kg of hydrochlorothiazide. In mice given single oral doses of the primary metabolite, candesartan, the minimum lethal dose was greater than 1000 mg/kg but less than 2000 mg/kg.

Description

Candesartan cilexetil is a prodrug form of the angiotensin II type 1 receptor (AT1) antagonist candesartan . Atacand was launched in Australia, Belgium, Canada, Denmark, Finland, the Netherlands, Norway, Sweden, S. Africa and the US as an antihypertensive agent. Pharmacological studies have indicated Atacand is about 10-fold more potent than Losartan and has a long elimination half-life. Like losartan, Atacand is converted to its active form during GI absorption (via ester hydrolysis). It is a potent antagonist of angiotensin II type 1 receptors. This occurs through tight binding and slow dissociation, and is more potent than ACE inhibitors. It is well tolerated (can be taken by elderly and those with type II diabetes) and has no gender effects.

Chemical properties

It appears as a white or off-white powder.It is soluble in methanol but insoluble in water.

Originator

Takeda (Japan)

The Uses of Candesartan cilexetil

N,N-Desmethoxyethyl Candesartan Cilexetil is an impurity of Candesartan Cilexetil(C175580); An antihypertensive used in the treatment of congestive heart failures.

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. Candesartan 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.

What are the applications of Application

Candesartan Celexetil Ester is an angiotensin II receptor antagonist

Background

Candesartan is an angiotensin-receptor blocker (ARB) that may be used alone or with other agents to treat hypertension. It is administered orally as the prodrug, candesartan cilexetil, which is rapidly converted to its active metabolite, candesartan, during absorption in the gastrointestinal tract. Candesartan lowers blood pressure by antagonizing the renin-angiotensin-aldosterone system (RAAS); it competes with angiotensin II for binding to the type-1 angiotensin II receptor (AT1) subtype and prevents the blood pressure increasing effects of angiotensin II. Unlike angiotensin-converting enzyme (ACE) inhibitors, ARBs do not have the adverse effect of dry cough. Candesartan may be used to treat hypertension, isolated systolic hypertension, left ventricular hypertrophy and diabetic nephropathy. It may also be used as an alternative agent for the treatment of heart failure, systolic dysfunction, myocardial infarction and coronary artery disease.

Definition

ChEBI: Candesartan cilexetil is a member of biphenyls.

Manufacturing Process

3-Nitrophthalic acid (35 g) in 300 ml ethanol and 20 ml concentrated sulfuric acid was heated under reflux for 24 hours. The solvent was evaporated in vacuo and the residue was poured into 700 ml cold water. The mixture was extracted with ethyl acetate. The aqueous layer was made acidic with hydrochloric acid and the mixture was extracted with methylene chloride. After evaporation of methylene chloride was obtained 29 g (74%) ethyl 2- carboxy-3-nitrobenzoate.
A mixture of 23.9 g ethyl 2-carboxy-3-nitrobenzoate and 12 ml thionyl chloride in 150 ml benzene were heated under reflux for 3 hours. The reaction mixture was concentrated to dryness. The resultant acid chloride (26 g) was dissolved in 20 ml. The solution was added to a mixture of sodium azide (9.75 g) in 20 ml DMF with stirring. The reaction mixture was poured into 200 ml a mixture of ether-hexane (3:1). The organic layer was washed with water and evaporated. The residue was dissolved in 200 ml tert-butanol and the solution was heated gradually with stirring, followed by heating under reflux for 2 hours. The reaction mixture was concentrated to give an oily ethyl 2- butoxycarbonylamino-3-nitrobenzoate (30 g).
To a solution of ethyl 2-butoxycarbonylamino-3-nitrobenzoate (29 g) in 50 ml THF was added, while stirring under ice-cooling, sodium hydride (60% dispersion in mineral oil, 2.8 g). After 20 min to the mixture were added 18 g 4-(2-cyanophenyl)benzyl bromide and 0.36 g potassium iodide. After heating for 10 hours under reflux the solvent was evaporated and the residue was partitioned between 250 ml water and 200 ml ether. The organic layer was washed with water, dried and concentrated to give yellow syrup. The syrup was dissolved in a mixture of 60 ml trifluoroacetic acid and 40 ml methylene chloride and the solution was stirred for 2 hour at room temperature. The reaction mixture was concentrated to dryness and to residue was added 200 ml ethyl ether to give crystals of ethyl 2-[(2'-cyanobiphenyl-4- yl)methylamino]nitrobenzoate (22.1 g, 85%), M.P. 118-119°C.
To a solution of 10.4 g ethyl 2-[(2'-cyanobiphenyl-4-yl)methylamino] nitrobenzoate in 50 ml ethanol was added 28.1 g stannous dichloride dihydrate and the mixture was stirred for 2 hours at 80°C. The solvent was evaporated. To the ice-cooling mixture of the residue in 300 ml ethyl acetate was added dropwise 2 N NaOH (500 ml). The aqueous layer was extracted with ethyl acetate (200 ml x 2). The organic layers were combined and evaporated to dryness. Product was purified by column chromatography on silica gel. Recrystallization from ethyl acetate-hexane gave colorless crystals ethyl-3-amino-2-[[(2'-cyanobiphenyl-4-yl)methyl]amino]benzoate (7.3 g, 79%), M.P. 104-105°C.
Acetic acid (0.2 g) was added to a solution of ethyl-3-amino-2-[[(2'- cyanobiphenyl-4-yl)methyl]amino]benzoate (1 g) in ethylorthocarbonate (5 ml). The mixture was stirred at 80°C for 1 hours. The reaction mixture was concentrated. The solution was washed with an aqueous solution of NaHCO3 and water. The solvent was evaporeted to give crystals. Recrystallization from ethyl acetate-benzene afforded colorless crystals 1-[(2'-cyanobiphenyl-4- yl)methyl]-2-ethoxybenzimidazole-7-carboxylate (0.79 g, 69%), M.P. 131- 132°C.
A mixture of 1-[(2'-cyanobiphenyl-4-yl)methyl]-2-ethoxybenzimidazole-7- carboxylate (0.7 g) and trimethyltin azide (0.7 g) in toluene (15 ml) was heated under reflux for 4 days. The reaction mixture was concentrated, and to the residue were added methanol (20 ml) and 1 N HCl (10 ml). The solution was stirred at room temperature for 30 minutes and adjusted to pH 3-4 with 1 N NaOH. After removal of the solvent, the residue was partitioned between chloroform and water. The organic layer was evaporated to dryness to dive a syrup. The syrup was purified by column chromatography on silica gel to give crystals. Recrystallization from ethyl acetate-benzene afforded colorless crystals ethyl 2-ethoxy-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]- methyl]benzimidazole-7-carboxylate (0.35 g, 45%), M.P. 158-159°C.
Ethyl 2-ethoxy-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]-methyl]benzimidazole- 7-carboxylate (0.24 g) was stirred with 1 N NaOH (1.5 ml) in ethanol (4 ml) for 1 hours at 80°C. The reaction mixture was concentrated, and the concentrate was exrtacted with water and ethyl acetate. The aqueous layer was adjusted to pH 3-4 with 1 N HCl to give crystals. Recrystallization from ethyl acetate-benzene afforded colorless crystals of 2-ethoxy-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]-methyl]benzimidazole-7-carboxylic acid (0.15 g, 67%), M.P. 183-185°C.
To a solution of 2-ethoxy-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]- methyl]benzimidazole-7-carboxylic acid (2.07 g) in methylene chloride (10 ml) were added trityl chloride (1.59 g) and triethylamine (0.8 ml). The mixture was stirred at room temperature for 1 hour. The mixture was washed with water and concentrated to dryness. The residue was purified by column chromatography on silica gel to give crystals. Recrystallization from ethyl acetate-benzene afforded colorless crystals 2-ethoxy-1-[[2'-(N-triphenylmethyltetrazol-5-yl)biphenyl-4-yl]-methyl]benzimidazole-7-carboxylic acid (2.12 g, 66%), M.P. 168-170°C.
To a solution 2-ethoxy-1-[[2'-(N-triphenylmethyltetrazol-5-yl)biphenyl-4-yl]- methyl]benzimidazole-7-carboxylic acid (0.5 g) in DMF (5 ml) were added potassium carbonate (0.12 g) and cyclohexyl 1-iodoethyl carbonate (0.26 g). The mixture was stirred at room temperature for 1 hour. To the mixture was added water and the mixture was extracted with ethyl acetate. The organic layer was washed with water and dried. After removal of the solvent, the residue was dissolved in methanol (10 ml) and to solution was added 1 N HCl (2 ml). The mixture was stirred at room temperature for 1 hour. After removal of the solvent, the residue was purified by column chromatography on silica gel to give colorless powder (0.21 g), M.P. 103-106°C. The mixture was stirred for 3 hours at room temperature. To the powder (1 g) obtained as above was added ethanol (6 ml). The mixture was stirred for 3 hours at room temperature and allowed to stand under ice-cooling. The mixture was then stirred for 1 hour at temperature not higher than 10°C. Resultant crystals were collected and washed with cold ethanol. The crystals were dried at 25°C for 9 hours under reduced pressure, then at 35°C for further 18 hours to obtain white powdery crystal 1-(cyclohexyloxycarbonyloxy)ethyl 2-ethoxy-1- [[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-benzimidazole-7-carboxylate (0.94 g, M.P. 158-166°C).

brand name

Atacand (AstraZeneca).

Therapeutic Function

Antihypertensive

General Description

Pharmaceutical secondary standards for application in quality control provide pharma laboratories and manufacturers with a convenient and cost-effective alternative to the preparation of in-house working standards

Biochem/physiol Actions

Candesartan cilexetil is the prodrug form of the potent angiotensin II receptor antagonist, candesartan. The prodrug is cleaved by esterases within the intestine to liberate the active molecule.

Pharmacokinetics

Candesartan cilexetil is an ARB prodrug that is rapidly converted to candesartan, its active metabolite, during absorption from the gastrointestinal tract. Candesartan confers blood pressure lowering effects by antagonizing the hypertensive effects of angiotensin II via the 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: type-1 angiotensin II receptor (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.

Clinical Use

Angiotensin-II antagonist:

Hypertension

Heart failure

Side Effects

Candesartan cilexetil may lead to various kinds of adverse reactions including headache, back pain, dizziness, upper respiratory tract infection, pharyngitis, rhinitis, bronchitis, coughing, sinusitis, nausea, abdominal pain, diarrhea, vomiting, arthralgia and albuminuria. It should be warned that candesartan cilexetil might have remarkable fetal toxicity. Therefore, upon pregnancy, candesartan cilexetil should be discontinued. It could also cause hypotension for heart-failure patients.

Drug interactions

Potentially hazardous interactions with other drugs
Anaesthetics: enhanced hypotensive effect.
Analgesics: antagonism of hypotensive effect and increased risk of renal impairment with NSAIDs; hyperkalaemia with ketorolac and other NSAIDs.
Antihypertensives: increased risk of hyperkalaemia hypotension and renal impairment with ACE-Is and aliskiren.
Ciclosporin: increased risk of hyperkalaemia and nephrotoxicity. Diuretics: enhanced hypotensive effect; hyperkalaemia with potassium-sparing diuretics. ESAs: increased risk of hyperkalaemia; antagonism of hypotensive effect. Lithium: reduced excretion, possibility of enhanced lithium toxicity. Potassium salts: increased risk of hyperkalaemia. Tacrolimus: increased risk of hyperkalaemia and nephrotoxicity

Metabolism

The prodrug candesartan cilexetil undergoes rapid and complete ester hydrolysis in the intestinal wall to form the active drug, candesartan. Elimination of candesartan is primarily as unchanged drug in the urine and, by the biliary route, in the feces. Minor hepatic metabolism of candesartan (<20%) occurs by O-deethylation via cytochrome P450 2C9 to form an inactive metabolite. Candesartan undergoes N-glucuronidation in the tetrazole ring by uridine diphosphate glucuronosyltransferase 1A3 (UGT1A3). O-glucuronidation may also occur. 75% of candesartan is excreted as unchanged drug in urine and feces.

Metabolism

Candesartan is mainly eliminated unchanged via urine and bile and only to a minor extent eliminated by hepatic metabolism (CYP2C9). The renal elimination of candesartan is both by glomerular filtration and active tubular secretion. Following an oral dose of 14C-labelled candesartan cilexetil, approximately 26% of the dose is excreted in the urine as candesartan and 7% as an inactive metabolite while approximately 56% of the dose is recovered in the faeces as candesartan and 10% as the inactive metabolite.