Telmisartan

Absorption

Oral telmisartan follows nonlinear pharmacokinetics over the dose range of 20 mg to 160 mg. Both Cmax and AUC present greater than proportional increases at higher doses. With once-daily dosing, telmisartan has trough plasma concentrations of about 10% to 25% of peak plasma concentrations. The absolute bioavailability of telmisartan depends on the dosage. At 40 mg and 160 mg, the bioavailability was 42% and 58%, respectively. Food slightly decreases bioavailability. For instance, when the 40 mg dose is administered with food, a decrease of about 6% is seen, and with the 160 mg dose, there is a decrease of about 20%.

Toxicity

Intravenous LD50 in rats is 150-200 mg/kg in males and 200 to 250 mg/kg in females. Acute oral toxicity is low: no deaths and no changes occurred in rats or dogs at 2000 mg/kg, the highest dose tested. Limited data are available with regard to overdosage in humans. 

Description

Telmisartan was launched in the US for the treatment of hypertension. It can be prepared in eight steps starting with methyl 4-amino-3-methyl benzoate; the first and second cyclization into a benzimidazole ring occur at steps 4 and 6 respectively. Telmisartan blocks the action of angiotensin II (Ang II), the primary effector molecule of the renin-angiotensin-aldosterone system (RAAS). It is the sixth of this class of 《sartans》 to be marketed after the lead compound Losartan. Its long lasting effect (24h half-life) could be the main difference with other angiotensin II antagonists. Unlike several other agents in this category, its activity does not depend upon transformation into an active metabolite, the 1-O-acylglucuronide being the principal metabolite found in humans. Telmisartan is a potent competitive antagonist of AT1 receptors that mediate most of the important effects of angiotensin II while lacking affinity for the AT2 subtypes or other receptors involved in cardiovascular regulation. In several clinical studies, Telmisartan, at a once daily dosage, produced effective and sustained blood-pressure lowering effects with a low incidence of side effects (particularly treatment-related cough associated with ACE inhibitors in elderly patients).

Chemical properties

White or off white crystalline powder

Originator

Boehringer Ingelheim (Germany)

The Uses of Telmisartan

Telmisartan is an angiotensin II receptor antagonist.

The Uses of Telmisartan

Telmisartan, an angiotensin II receptor antagonist, is an effective medication for the treatment of hypertension. It can be used alone or in combination with other antihypertensive drugs. Additionally, it is beneficial in the treatment of diabetic nephropathy in hypertensive individuals with type 2 diabetes mellitus. Telmisartan is also used to address congestive heart issues.

Background

Telmisartan is an angiotensin II receptor antagonist (ARB) used in the management of hypertension. Recent studies suggest that telmisartan may also have PPAR-gamma agonistic properties that could potentially confer beneficial metabolic effects.

Indications

Used alone or in combination with other classes of antihypertensives for the treatment of hypertension. Also used in the treatment of diabetic nephropathy in hypertensive patients with type 2 diabetes mellitus, as well as the treatment of congestive heart failure (only in patients who cannot tolerate ACE inhibitors).

What are the applications of Application

Telmisartan is a nonpeptide angiotensin II receptor type 1 antagonist

Definition

ChEBI: Telmisartan is a member of the class of benzimidazoles used widely in the treatment of hypertension. It has a role as an antihypertensive agent, an angiotensin receptor antagonist, an EC 3.4.15.1 (peptidyl-dipeptidase A) inhibitor, a xenobiotic and an environmental contaminant. It is a member of biphenyls, a member of benzimidazoles and a carboxybiphenyl.

Manufacturing Process

Telmisartan was synthesized through the reaction of methyl 3,4-diaminobenzoate dihydrochloride and butyric acid chloride in the presence of phosphorous oxychloride, with subsequent purification steps:
A solution of 23.9 g (100 mMol) of methyl 3,4-diaminobenzoate dihydrochloride and 11.7 g (110 mMol) of butyric acid chloride in 100 ml of phosphorus oxychloride is refluxed for 2 h. Then about 80 ml of phosphorus oxychloride are distilled off and the residue is mixed with about 150 ml of water. The oily crude product precipitated is extracted three times with 50 ml of ethyl acetate and after evaporation purified by column chromatography (600 g of silica gel; eluant:methylene chloride/methanol (30:1)). Yield of methyl-2-n-propyl-benzimidazole-5-carboxylate: 15.0 g of oil (69%).
A solution of 15.0 g (73 mmol) of methyl 2-n-propyl-benzimidazole-5- carboxylate and 8 g (200 mMol) of sodium hydroxide in 200 ml of water and 400 ml of ethanol is refluxed for 2 h. Then the alcohol is distilled off, the aqueous solution is acidified with dilute sulphuric acid (pH 4-5) and evaporated using a rotary evaporator. The product crystallising out is suction filtered, washed with 50 ml of acetone and 50 ml of diethylether and dried. Yield of 2-n-propyl-benzimidazole-5-carboxylic acid-hemisulphate: 9.1 g (61%), melting point: >220°C.
A solution of 6.7 g (25 mMol) of 2-n-propyl-benzimidazole-5-carboxylic acidhemisulphate and 4.9 g (25 mMol) of 2-methylaminoaniline dihydrochloride in 200 g of polyphosphoric acid is stirred for 5 h at 150°C, then poured onto 600 ml of water and made alkaline with concentrated ammonia whilst cooling with ice. The resulting solution is extracted three times with 200 ml of ethyl acetate, the crude product thus obtained is purified by column chromatography (300 g of silica gel; eluant:methylene chloride/methanol = 15:1). Yield of 2-n-propy1-5-(1-methylbenzimidazol-2-yl)-benzimidazole: 2.8 g of oil (39%).
A solution of 2.0 g (6.9 mMol) of 2-n-propyl-5-(1-methylbenzimidazol-2-yl)- benzimidazole and 0.91 g (7.5 mmol) of potassium tert-butoxide in 50 ml of dimethylsulfoxide is stirred for 90 min at room temperature, then 2.6 g (7.5 mMol) of tert-butyl 4'-bromomethyl-biphenyl-2-carboxylate are added and the mixture is stirred for a further 15 h at room temperature. The mixture is then poured onto 300 ml of water and extracted three times with 50 ml of ethyl acetate. The crude product obtained after evaporation of the organic phase is purified by column chromatography (300 g silica gel; eluant:methylene chloride/methanol = 30:1). In this way, 2.7 g (70%) of an isomer mixture are obtained (by NMR spectroscopy), contains about 1.18 g of tert-butyl-4'-[(2-npropyl- 5-(1-methylbenzimidazol-2-yl)-benzimidazol-1-yl)-methyl]biphenyl-2- carboxylate and about 1.52 g of tert-butyl 4'-[(2-n-propyl-6-(1- methylbenzimidazol-2-yl)-benzimidazol-1-yl)-methyl]biphenyl-2-carboxylate).
2.70 g of the isomer mixture obtained above are dissolved in 100 ml of methylene chloride, mixed with 40 ml of trifluoroacetic acid and stirred for 4 h at room temperature. The mixture is then evaporated to dryness in vacuo, the residue is dissolved in 100 ml of 2 N sodium hydroxide solution, the solution is washed with 50 ml of diethylether and the product mixture is precipitated by acidifying the aqueous phase with acetic acid. By column chromatography (400 g of silica gel, eluant:methylene chloride/methanol = 15:1) of the solid thus obtained 0.9 g (74%) of Telmisartan, melting point 217°-218°C.

brand name

Micardis (Boehringer Ingelheim).

Therapeutic Function

Antihypertensive

General Description

Telmisartan, 4'-[(1,4'-dimethyl-2'-propyl[2,6'-bi-1H-benzimidazol]-1'-yl)methyl]-[1,1'-biphenyl]-2-carboxylic acid (Micardis), does not appear to bear any structuralrelationship to this class, but there is actually a great dealof overlap in the chemical architecture with other agents. Thefirst, and most significant, difference is the replacement of theacidic tetrazole system with a simple carboxylic acid. Thisacid, like the tetrazole, plays a role in receptor binding. Thesecond difference is the lack of a carboxylic acid near the imidazolenitrogen that also contributes to receptor binding.As with irbesartan, however, there is not a need for this groupto be acidic but, rather, to be one that participates in receptorbinding. The second imidazole ring, much like a purine basein deoxyribonucleic acid (DNA), can hydrogen bond with theangiotensin II receptor.

Biochem/physiol Actions

Telmisartan is a non-peptide AT1 angiotensin receptor antagonist.

Pharmacokinetics

Telmisartan is an orally active nonpeptide angiotensin II antagonist that acts on the AT1 receptor subtype. It has the highest affinity for the AT1 receptor among commercially available ARBs and has minimal affinity for the AT2 receptor.
New studies suggest that telmisartan may also have PPARγ agonistic properties that could potentially confer beneficial metabolic effects, as PPARγ is a nuclear receptor that regulates specific gene transcription, and whose target genes are involved in the regulation of glucose and lipid metabolism, as well as anti-inflammatory responses.
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. Telmisartan works by blocking the vasoconstrictor and aldosterone secretory effects of angiotensin II.

Clinical Use

Angiotensin-II antagonist:
Hypertension
Prevention of cardiovascular events

Synthesis

Telmisartan can be prepared in eight steps starting with methyl 4-amino-3-methyl benzoate; the first and second cyclization into a benzimidazole ring occur at steps 4 and 6 respectively.

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.
Cardiac glycosides: concentration of digoxin increased.
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

Minimally metabolized by conjugation to form a pharmacologically inactive acyl-glucuronide, the glucuronide of the parent compound is the only metabolite that has been identified in human plasma and urine. The cytochrome P450 isoenzymes are not involved in the metabolism of telmisartan.

Metabolism

Telmisartan is metabolised by conjugation to the glucuronide of the parent compound. No pharmacological activity has been shown for the conjugate.
Telmisartan is excreted almost entirely in the faeces via bile, mainly as unchanged drug.

Overdose

The most likely manifestations of overdosage with telmisartan would be hypotension, dizziness and tachycardia; bradycardia could occur from parasympathetic (vagal) stimulation. Supportive treatment should be instituted if symptomatic hypotension occurs. Telmisartan is not removed by hemofiltration and is not dialyzable.

Clinical claims and research

In several clinical studies, Telmisartan, at a once daily dosage, produced effective and sustained blood-pressure lowering effects with a low incidence of side effects (particularly treatment-related cough associated with ACE inhibitors in elderly patients).