Acetazolamide

Description

Acetazolamide is a weak diuretic with limited use in edema associated with cardiac insufficiency, glaucoma, minor epileptic attacks, and altitude sickness.

Chemical properties

White Solid

Originator

Diamox ,Lederle,US ,1953

The Uses of Acetazolamide

Acetazolamide is used for epilepsy in the absence of attacks and also in conjunction with other antiepileptic drugs.

The Uses of Acetazolamide

carbonic anhydrase inhibitor, diuretic, antiglaucoma

The Uses of Acetazolamide

Acetazolamide acts as a carbonic anhydrase inhibitor which increases cerebral blood flow. It inhibits water permeability of membranes by interacting with aquaporins. It is used for the medical treatment of glaucoma, epileptic seizure, idiopathic intracranial hypertension, altitude sickness, cystinuria.

Background

One of the carbonic anhydrase inhibitors that is sometimes effective against absence seizures. It is sometimes useful also as an adjunct in the treatment of tonic-clonic, myoclonic, and atonic seizures, particularly in women whose seizures occur or are exacerbated at specific times in the menstrual cycle. However, its usefulness is transient often because of rapid development of tolerance. Its antiepileptic effect may be due to its inhibitory effect on brain carbonic anhydrase, which leads to an increased transneuronal chloride gradient, increased chloride current, and increased inhibition. (From Smith and Reynard, Textbook of Pharmacology, 1991, p337)

Indications

For adjunctive treatment of: edema due to congestive heart failure; drug-induced edema; centrencephalic epilepsies; chronic simple (open-angle) glaucoma

Definition

ChEBI: Acetazolamide is a sulfonamide, a member of thiadiazoles and a monocarboxylic acid amide. It has a role as a diuretic, an anticonvulsant and an EC 4.2.1.1 (carbonic anhydrase) inhibitor. It is a conjugate acid of an acetazolamide(1-). It derives from a hydride of a 1,3,4-thiadiazole.

Manufacturing Process

According to REM, hydrazine hydrate is reacted with 2 mols of ammonium thiocyanate to produce 1,2-bis(thiocarbamoyl)hydrazine which by loss of ammonia and rearrangement produces 5-amino-2-mercapto-1,3,4-thiadiazole. That compound is acetyled with acetic anhydride.
Then, as described in US Patent 2,554,816, the 2-acetylamido-5-mercapto- 1,3,4-thiadiazole is converted to the sulfonyl chloride by passing chlorine gas into a cooled (5-10°C) solution in 33% acetic acid (66 parts to 4 parts of mercapto compound) used as a reaction medium. Chlorine treatment is continued for two hours. The crude product can be dried and purified by recrystallization from ethylene chloride. The pure compound is a white crystalline solid, MP 194°C, with decomposition, when heated rapidly. The crude damp sulfonyl chloride is converted to the sulfonamide by addition to a large excess of liquid ammonia. The product is purified by recrystallization from water. The pure compound is a white, crystalline solid, MP 259°C, with decomposition. The yield of sulfonamide was 85% of theory based on mercapto compound.
An alternative process is described in US Patent 2,980,679 as follows. 15 grams of finely powdered 2-acetylamino-1,3,4-thiadiazole-5-mercaptain are suspended in 200 ml of water containing 4 grams of potassium bromide. From 0.5 to 1 gram of ferric chloride are subsequently added. The mass is energetically stirred and 52 grams of liquid bromide are added by increments for about 45 minutes, while keeping the reaction temperature below 10°C, and, preferably, at 4-8°C by employing a cooling bath. Stirring is continued for a further 10 minutes, then the 2-acetylamino-1,3,4-thiadiazole-5- sulfobromide is collected on a funnel equipped with a porous diaphragm, thoroughly washed with cold water and finally subjected to amidation with liquid ammonia. The reaction mixture is allowed to stand for a certain period, then the ammonia is evaporated, after which the residue is taken up with diluted ammonia and, after decolorizing with carbon, the sulfonamide is precipitated with hydrochloric acid. The yield of crude sulfonamide obtained with this process, with respect to the starting mercapto compound is abut 84%. If the amidation is carried out with 33% aqueous ammonia, the yield is slightly lower.

brand name

Diamox (Duramed).

Therapeutic Function

Carbonic anhydrase inhibitor, Diuretic, Antiglaucoma

General Description

White to yellowish-white fine crystalline powder. No odor or taste.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

A weak acid and a diazo derivative. Azo, diazo, azido compounds can detonate. This applies in particular to organic azides that have been sensitized by the addition of metal salts or strong acids. Toxic gases are formed by mixing materials of this class with acids, aldehydes, amides, carbamates, cyanides, inorganic fluorides, halogenated organics, isocyanates, ketones, metals, nitrides, peroxides, phenols, epoxides, acyl halides, and strong oxidizing or reducing agents. Flammable gases are formed by mixing materials in this group with alkali metals. Explosive combination can occur with strong oxidizing agents, metal salts, peroxides, and sulfides.

Fire Hazard

Flash point data for Acetazolamide are not available; however, Acetazolamide is probably combustible.

Biochem/physiol Actions

Inhibits water permeability of membranes by interacting with aquaporins

Mechanism of action

Acetazolamide is an aromatic sulfonamide used as a carbonic anhydrase inhibitor. It facilitates production of alkaline urine with an elevated biocarbonate, sodium, and potassium ion concentrations. By inhibiting carbonic anhydrase, the drug suppresses reabsorption of sodium ions in exchange for hydrogen ions, increases reflux of bicarbonate and sodium ions and reduces reflux of chloride ions. During this process, chloride ions are kept in the kidneys to cover of insufficiency of bicarbonate ions, and for keeping an ion balance. Electrolytic contents of fluid secreted by the kidneys in patients taking carbonic anhydrase inhibitors are characterized by elevated levels of sodium, potassium, and bicarbonate ions and a moderate increase in water level. Urine becomes basic, and the concentration of bicarbonate in the plasma is reduced.

Pharmacokinetics

Acetazolamide is a potent carbonic anhydrase inhibitor, effective in the control of fluid secretion, in the treatment of certain convulsive disorders and in the promotion of diuresis in instances of abnormal fluid retention. Acetazolamide is not a mercurial diuretic. Rather, it is a nonbacteriostatic sulfonamide possessing a chemical structure and pharmacological activity distinctly different from the bacteriostatic sulfonamides.

Clinical Use

Acetazolamide was the first of the carbonic anhydrase inhibitors to be introduced as an orally effective diuretic, with a diuretic effect that lasts approximately 8 to 12 hours. As mentioned earlier, its diuretic action is limited because of the systemic acidosis it produces. Acetazolamide reduces the rate of aqueous humor formation and is used primarily for reducing intraocular pressure in the treatment of glaucoma. The dose is 250 mg to 1 g per day.

Safety Profile

Poison by subcutaneous and intravenous routes. Moderately toxic by intraperitoneal route. Human systemic effects by ingestion: dyspnea. An experimental teratogen by many routes. Other experimental reproductive effects. When heated to decomposition it emits very toxic fumes of NOx, and SOx,. A carbonic anhydrase inhibitor and dmretic used to treat glaucoma.

Synthesis

Acetazolamide is 5-acetamido-1,3,4-thiadiazole-2-sulfonamide (9.7.5). The synthesis of acetazolamide is based on the production of 2-amino-5-mercapto-1,3, 4-thiadiazole (9.7.2), which is synthesized by the reaction of ammonium thiocyanate and hydrazine, forming hydrazino-N,N
-bis-(thiourea) (9.7.1), which cycles into thiazole (9.7.2) upon reaction with phosgene. Acylation of (9.7.2) with acetic anhydride gives 2-acetylamino-5-mercapto-1,3,4-thiadiazol (9.7.3). The obtained product is chlorinated to give 2-acetylamino-5-mercapto-1,3,4-thiadiazol-5-sulfonylchloride (9.7.4), which is transformed into acetazolamide upon reaction with ammonia (9.7.5) [24,25].

Veterinary Drugs and Treatments

Acetazolamide has been used principally in veterinary medicine for its effects on aqueous humor production in the treatment of glaucoma, metabolic alkalosis, and for its diuretic action. It may be useful as an adjunctive treatment for syringomyelia in dogs. Acetazolamide’s use in small animals is complicated by a relatively high occurrence of adverse effects.
In horses, acetazolamide is used as an adjunctive treatment for hyperkalemic periodic paralysis (HYPP).
In humans, the drug has been used as adjunctive therapy for epilepsy and for acute high-altitude sickness.

Drug interactions

Potentially hazardous interactions with other drugs
Analgesics: high dose aspirin reduces excretion (risk of toxicity).
Anti-arrhythmics: increased toxicity if hypokalaemia occurs.
Antibacterials: effects of methenamine antagonised.
Antiepileptics: increased risk of osteomalacia with phenytoin and phenobarbital; concentration of carbamazepine and possibly fosphenytoin and phenytoin increased.
Antihypertensives: enhanced hypotensive effect.
Antipsychotics: increased risk of ventricular arrhythmias due to hypokalaemia.
Atomoxetine: increased risk of ventricular arrhythmias due to hypokalaemia.
Beta-blockers: increased risk of ventricular arrhythmias due to hypokalaemia with sotalol.
Cardiac glycosides: increased toxicity if hypokalaemia occurs.
Ciclosporin: possibly increases ciclosporin concentration.
Cytotoxics: alkaline urine increases methotrexate excretion; increased risk of ventricular arrhythmias due to hypokalaemia with arsenic trioxide; increased risk of nephrotoxicity and ototoxicity with platinum compounds.
Lithium: lithium excretion increased.

Metabolism

Acetazolamide is tightly bound to carbonic anhydrase and accumulates in tissues containing this enzyme, particularly red blood cells and the renal cortex. It is also bound to plasma proteins. It is excreted unchanged in the urine, renal clearance being enhanced in alkaline urine.

storage

Store at -20°C

Purification Methods

It is recrystallised from water. [Roblin & Clapp J Am Chem Soc 72 4890 1950, Beilstein 27 III/IV 8219.]