Chlortalidone

Chemical properties

Chlortalidone is White Solid

Originator

Hygroton, Geigy, US ,1960

The Uses of Chlortalidone

Chlorthalidone is used as a diuretic; antihypertensive.

The Uses of Chlortalidone

Antihypertensive Agents,Diuretics,Sodium Chloride Symporter Inhibitors

The Uses of Chlortalidone

In terms of activity, chlorothalidone is very similar to benzothiadiazide (21.3.13) and is used as an independent drug or in combination with other antihypertensive agents for lowering arterial blood pressure, and also as an adjuvant drug for treating edema caused by cardiac insufficiency and renal irregularities, including nephrotic syndrome.

Indications

Chlorthalidone is indicated in the management of hypertension either as the sole therapeutic agent or to enhance the effect of other antihypertensive drugs in the more severe forms of hypertension.
Chlorthalidone is indicated as adjunctive therapy in edema associated with congestive heart failure, hepatic cirrhosis, and corticosteroid and estrogen therapy.
Chlorthalidone has also been found useful in edema due to various forms of renal dysfunction, such as nephrotic syndrome, acute glomerulonephritis, and chronic renal failure.

Background

Chlorthalidone is a thiazide-like diuretic used for the treatment of hypertension and for management of edema caused by conditions such as heart failure or renal impairment. Chlorthalidone improves blood pressure and swelling by preventing water absorption from the kidneys through inhibition of the Na+/Cl? symporter in the distal convoluted tubule cells in the kidney. The exact mechanism of chlorthalidone's anti-hypertensive effect is under debate, however, it is thought that increased diuresis results in decreased plasma and extracellular fluid volume, decreased cardiac output and therefore overall reduction in blood pressure.
Chlorthalidone is considered first-line therapy for management of uncomplicated hypertension as there is strong evidence from meta-analyses that thiazide diuretics such as chlorthalidone reduce the risk of stroke, myocardial infarction, heart failure, and cardiovascular all-cause mortality in patients with hypertension. In particular, the ALLHAT trial confirmed the role of thiazide diuretics as first-line therapy and demonstrated that chlorthalidone had a statistically significant lower incidence of stroke and heart failure when compared to Lisinopril, Amlodipine, or Doxazosin. Further studies have indicated that low-dose thiazides are as good as, and in some secondary endpoints, better than β-blockers, ACE inhibitors, Calcium Channel Blockers or ARBs.
Chlorthalidone has been shown to have a number of pleiotropic effects that differentiate it from other diuretics such as Hydrochlorothiazide. In addition to its antihypertensive effects, chlorthalidone has also been shown to decrease platelet aggregation and vascular permeability, as well as promote angiogenesis in vitro, which is thought to be partly the result of reductions in carbonic anhydrase–dependent pathways. These pathways may play a role in chlorthalidone's cardiovascular risk reduction effects.

Definition

ChEBI: Chlorthalidone is a sulfonamide, a member of isoindoles and a member of monochlorobenzenes.

Manufacturing Process

15 parts of aqueous 46% sodium nitrite solution are gradually added to a mixture of 27.5 parts of 4-chloro-3-amino-benzophenone-2'-carboxylic acid, 200 parts of glacial acetic acid and 20 parts of 37% hydrochloric acid at 0° to 10°C. The solution of the diazonium salt is poured into an ice-cooled mixture of 200 parts of 30% sulfur dioxide solution in glacial acetic acid and 3 parts of crystallized cupric chloride in 15 parts of water. Nitrogen is developed and, after a short time, the 4-chloro-2'-carboxy-benzophenone-3-sulfochloride crystallizes out. After 1 hour it is filtered off and washed with water. MP 178° to 182°C.
35.9 parts of 4-chloro-2'-carboxy-benzophenone-3-sulfochloride and 50 parts of thionyl chloride are heated first for 3 hours at 30° to 35°C and then for 1 hour at 45°C. The excess thionyl chloride is distilled off in the vacuum, the dichloride, 3-chloro-3-(3'-chlorosulfonyl-4'-chlorophenyl)phthalide, which remains as a crystallized mass is dissolved in 150 parts of chloroform and a mixture of 200 parts of 25% aqueous ammonia solution and 200 parts of ethanol is added dropwise at about 10°C while stirring and cooling. After stirring for 1 hour at 40°C, the solvent is distilled off in the vacuum and diluted hydro chloric acid is added to the residue whereupon the 1-oxo-3-(3'- sulfamyl-4'-chloro-phenyl)3-hydroxy-isoindoline which is tautomeric to the 4- chloro-2'-carbamyl-benzophenone-3-sulfonamide, separates out. On recrystallizing from diluted ethanol, the isoindoline derivative melts at 215°C on decomposition.
Instead of reacting the dichloride in aqueous solution with ammonia, it can also be reacted at -50° to -40°C with a great excess of liquid ammonia. After removal of the ammonia, the crude product obtained is recrystallized as described above.

brand name

Hygroton (Sanofi Aventis); Thalitone (Monarch).

Therapeutic Function

Diuretic, Antihypertensive

Biochem/physiol Actions

Chlorthalidone is a thiazide-like diuretic, an inhibitor of the Na+-Cl- cotransporter. Chlorthalidone inhibits sodium ion transport across the renal tubular epithelium increasing the delivery of sodium to the distal renal tubule and indirectly increasing potassium excretion via the sodium-potassium exchange mechanism. Chlorthalidone also promotes Ca++ reabsorption by an unknown mechanism. Several recent comparison studies inidcate that chlorthalidone may be a better drug in preventing cardiovascular events than hydrochlorothiazide.

Clinical Use

Chlorthalidone has a long duration of action (48–72 hours). Although quinethazone and metolazone are administered daily, chlorthalidone may be administered in doses of 25 to 100 mg three times a week. When chlorthalidone is formulated with the excipient povidone, the product, Thalitone, has greater bioavailability (>90%) and reaches peak plasma concentrations in a shorter time compared with its other products. Similar to the quinazolinones, it also is extensively bound to carbonic anhydrase in the erythrocytes.

Synthesis

Chlorothalidone, 2-chloro-5-(1-hydroxy-3-oxo-1-isoindolinyl)benzolsulfamide (21.3.26), is synthesized by two proposed methods from 2-carboxy-4-chlorobenzophenone (21.3.21), which is easily synthesized by acylating chlorobenzol with phthalic anhydride in the presence of aluminum chloride. The resulting benzophenone (21.3.21) undergoes nitration by nitric acid, which gives 2-carboxy-3-nitro-4-chlorobenzophenone (21.3.22). The nitro group in the resulting compound is reduced by tin dichloride to 2- carboxy-3-amino-4-chlorobenzophenone (21.3.23). Next, subsequent diazotation and reaction with sulfur dioxide in the presence of copper dichloride gives the corresponding sulfonylchloride (21.3.24). Upon reaction with thionyl chloride, this compound undergoes cyclization into phtahlide (21.3.25), which when reacted with aqueous ammonia rearranges into a derivative of isoindoline with simultaneous substitution of the chloride atom in the sulfogroup with an amino group, which results in chlorothalidone (21.3.26).

Drug interactions

Potentially hazardous interactions with other drugs
Analgesics: increased risk of nephrotoxicity with NSAIDs; antagonism of diuretic effect.Anti-arrhythmics: hypokalaemia leads to increased cardiac toxicity; effects of lidocaine and mexiletine antagonised.
Antibacterials: avoid administration with lymecycline.
Antidepressants: increased risk of hypokalaemia with reboxetine; enhanced hypotensive effect with MAOIs; increased risk of postural hypotension with tricyclics.
Antiepileptics: increased risk of hyponatraemia with carbamazepine.
Antifungals: increased risk of hypokalaemia with amphotericin.
Antihypertensives: enhanced hypotensive effect; increased risk of first dose hypotension with postsynaptic alpha-blockers like prazosin; hypokalaemia increases risk of ventricular arrhythmias with sotalol.
Antipsychotics: hypokalaemia increases risk of ventricular arrhythmias with amisulpride; enhanced hypotensive effect with phenothiazines; hypokalaemia increases risk of ventricular arrhythmias with pimozide - avoid.
Atomoxetine: hypokalaemia increases risk of ventricular arrhythmias.
Cardiac glycosides: increased toxicity if hypokalaemia occurs.
Ciclosporin: increased risk of nephrotoxicity and hypomagnesaemia.
Cytotoxics: increased risk of ventricular arrhythmias due to hypokalaemia with arsenic trioxide; increased risk of nephrotoxicity and ototoxicity with platinum compounds.
Lithium excretion reduced, increased toxicity.

Metabolism

Liver

Metabolism

Chlortalidone is highly bound to red blood cells; the receptor to which it is bound has been identified as carbonic anhydrase. It is much less strongly bound to plasma proteins.
Chlortalidone is mainly excreted unchanged in the urine.