Acetazolamide (Diamox®, Dazamide®)

Overview

Acetazolamide is a non-bacteriostatic sulfonamide drug that is futher categorized as a carbonic anhydrase inhibitor. 

The drugs acts to inhibits carbonic anhydrase.

Inhibition of carbonic anhydrase reduces the secretion of certain fluids, e.g. aqueous humor, decreases renal blood flow and glomerular filtration and can act to discharge abnormal discharge or neurons in the central nervous system. The reduction in secretion of aqueous humor can cause a decrease in intraocular pressure which is therapeutic in the treatment of glaucoma. 

Acetazolamide's onset of action may be as early as 30 minutes after an oral dose. Its maximum effects occur in about 5 hours and its duration of its action is about 7 hours. It is excreted unchanged in the urine. 

Acetazolamide is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names

This drug is registered for use in humans only.

Human formulations: Diamox® (Wyeth-Ayerst), Dazamide® (Major), and generic acetazolamide

Veterinary formulations: None

Uses of Acetazolamide

Acetazolamide is use most commonly for the following:

To reduce IOP in chronic simple (open-angle) glaucoma and secondary glaucoma

To treat metabolic acidosis

As a diuretic in congestive cardiac failure

To stabilize neuronal discharge in epilepsy

Precautions and Side Effects

While generally safe and effective when prescribed by a veterinarian, acetazolamide can cause side effects in some animals.

Acetazolamide should not be used in animals with known hypersensitivity or allergy to the drug or other sulfonamides. 

Also, it should avoided in patients with depressed levels of sodium and potassium serum levels, marked kidney or liver dysfunction, Addison's disease, or metabolic/respiratory acidosis. 

Long-term administration of acetazolamide is contraindicated in chronic noncongestive angle-closure glaucoma since it may cause closure of the angle to occur while worsening glaucoma is masked by lowered IOP. 

Hematologic reactions common to other sulfonamides may occur during treatment: complete blood count (CBC) and platelets should be monitored during therapy. 

Possible side effects include: seizures, drowsiness, ataxia, tremor, urticaria/pruritus, rash, photosensitivity, vomiting, diarrhea, bone marrow depression, hematuria, renal calculi, crystalluria, polyuria, phosphaturia, weight loss, electrolyte imbalance, and hepatic insufficiency. 

Intraocular pressure should be monitored when treating glaucoma. Electrolytes and blood gases should be monitored when treating metabolic acidosis. 

Drug Interactions

Acetazolamide increases trough cyclosporine levels, causing increased risk of nephrotoxicity and neurotoxicity. 

Acetazolamide may also increases serum levels of TCAs, causing blood pressure to drop. It decreases serum levels of primidone, decreasing the effectiveness of the latter drug. 

Salicylates increase blood levels, pharmacologic effects, and side effects of the acetazolamide. 

Concurrent use of acetazolamide and diflunisal may cause a significant decease in IOP and increased side effects.

How Acetazolamide is Supplied

Acetazolamide is available in 125 mg and 250 mg tablets and 500 mg sustained-release capsules.

The injectable forms of prednisone vary. Some injectable forms are 500 mg (lyophilized in vials)

Dosing Information

Medication should never be administered without first consulting your veterinarian. 

Doses of acetazolamide vary widely depending on the reason for prescribing.

In dogs, the usual dose is 3.5 to 5 mg per pound (7 to 10 mg/kg) every 6 hours when treating metabolic acidosis or glaucoma. Acetazolamide may be dosed at 25 mg per pound (50 mg/kg) as a one time dose for glaucoma. 

In cats, the usual dose is 3.5 mg per pound (7 mg/kg) every 8 hours. 

The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.