Acetazolamide

Acetazolamide is a drug from the group of carbonic anhydrase inhibitors with a broad field of application. The main indication is the treatment of glaucoma. It can be used long-term to treat open-angle glaucoma and short-term to treat acute angle-closure glaucoma until surgery can be performed.

Other indications include:

• Epilepsy
• Altitude sickness
• Periodic paralysis
• Idiopathic intracranial hypertension (increased intracranial pressure of unclear cause)
• Alkalinization of urine
• Edema in heart failure

It is taken by mouth or as an injection into a vein. Acetazolamide has been used in medicine since 1952. It is on the World Health Organization's list of essential medicines.

Pharmacodynamics

Acetazolamide is a drug that inhibits the enzyme carbonic anhydrase. Carboanhydrase converts water and CO₂ into carbonic acid, which subsequently forms bicarbonate. This reaction is instrumental in maintaining the acid-base balance in the organism. Carbonic anhydrase is found in red blood cells and many other tissues such as the brain, eyes and kidneys.

In the treatment of glaucoma, intraocular pressure is lowered by reducing ocular fluid and osmolality. This significantly relieves symptoms. The anticonvulsant effect is attributed to a reduction in intracranial pressure. The diuretic effect depends on inhibition of carbonic anhydrase in the kidneys, which causes a reduction in the availability of hydrogen ions for active transport in the renal tubule lumen. This results in alkaline urine and increased excretion of bicarbonate, sodium, potassium, and water.

Pharmacokinetics

Plasma protein binding is approximately 98%. Approximately 90% of the substance is eliminated in the urine. The elimination half-life is between 3 and 9 hours.

Drug Interactions

Drug substances with which interactions may occur are:

• Amphetamines (Increasing urinary pH decreases clearance of amphetamines).
• Carboanhydrase inhibitors (possible additive effect and increase in side effect potential).
• Ciclosporin (plasma levels of ciclosporin may be increased)
• Antifolates such as trimethoprim, methotrexate, pemetrexed, and raltitrexed.
• Oral antidiabetic agents (acetazolamide can both increase and decrease blood glucose levels).
• Lithium (excretion of lithium is increased thereby decreasing therapeutic effect).
• Phenytoin (excretion of phenytoin is decreased, thereby increasing toxicity potential)
• Primidone (Decreased plasma levels of primidone, thereby decreasing anticonvulsant effect)
• Quinidine (decreased urinary excretion of quinidine, thereby increasing toxicity potential)
• Salicylates (potential for severe toxicity)
• Sodium bicarbonate (risk for formation of kidney stones lead)
• Anticoagulants, cardiac glycosides, may be enhanced in their effect by acetazolamide

Side effects

Common side effects include:

• Numbness
• Ringing in the ears
• Loss of appetite
• Vomiting
• Drowsiness
• Decreased libido
• Zitter or metallic taste
• Nausea
• Abdominal cramps
• Diarrhea
• Black stools
• Polyuria
• Kidney stones
• Metabolic acidosis
• Electrolyte changes

Contraindications

• Hypersensitivity to acetazolamide
• Hyperchloremic acidosis
• Hypokalemia (deficiency of potassium in the blood)
• Hyponatremia (lack of sodium in the blood)
• Adrenal insufficiency
• Impaired renal function
• Liver disease or impaired liver function, including cirrhosis, because of the risk of developing hepatic encephalopathy