Acetazolamide
A systemic carbonic anhydrase inhibitor that reduces aqueous humor production and promotes renal bicarbonate loss. Diuresis is modest compared with loop diuretics.
Uses include selected canine glaucoma cases and prevention of equine hyperkalemic periodic paralysis episodes. Systemic adverse effects limit its ophthalmic use, particularly in cats.
Group
Carbonic anhydrase inhibitor; systemic antiglaucoma agent and diuretic
Mechanism of Action
Inhibition of carbonic anhydrase in the ciliary epithelium reduces aqueous humor formation and intraocular pressure.
Renal enzyme inhibition reduces bicarbonate reabsorption, causing bicarbonaturia, initially alkaline urine and increased electrolyte and water excretion. Repeated treatment can cause metabolic acidosis and potassium depletion.
In horses with hyperkalemic periodic paralysis, altered renal potassium handling can reduce the frequency and severity of episodes.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Glaucoma | 5–8 mg/kg | PO | Every 8–12 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Systemic adjunct; monitor intraocular pressure, bicarbonate and potassium. Methazolamide often has better tolerability. |
| Glaucoma | 5–10 mg/kg | PO | Every 8–12 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Alternative older range extends above the commonly recommended range; individual ophthalmic assessment is required. |
| Diuresis | 4–8 mg/kg | PO | Every 8–12 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Bicarbonate-losing diuresis; monitor hydration, electrolytes and acid-base status. |
| Glaucoma | 10–30 mg/kg | PO | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Historical veterinary-product range without an established administration interval here; not interchangeable with the lower ophthalmic regimen. | |
| Diuresis | 10–30 mg/kg | PO | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Historical veterinary-product range without an established administration interval here; not interchangeable with the lower diuretic regimen. |
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Glaucoma | 7 mg/kg | PO | Every 8 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Historical regimen only; systemic carbonic anhydrase inhibitors are currently not recommended routinely in cats because of adverse effects. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hyperkalemic periodic paralysis | 2–4 mg/kg | PO | Every 8–12 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Preventive treatment for recurrent episodes; monitor electrolytes and acid-base status. This is not an acute-attack resuscitation regimen. |
| Hyperkalemic periodic paralysis | 8 mg/kg | PO | Every 8–12 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Older higher-dose regimen differs from current preventive recommendations; reassess the treatment plan before use. |
| Hyperkalemic periodic paralysis | 4 mg/kg | IV | Every 8–12 h | Do not use in: Acidemia, Marked renal or hepatic dysfunction, Hyponatremia or hypokalemia, Acetazolamide hypersensitivity; Older intravenous regimen requires separate clinical assessment and a suitable sterile injectable formulation. |
Indications
- Adjunctive reduction of intraocular pressure in dogs.
- Selected diuretic uses in dogs when its bicarbonate-losing effect is appropriate.
- Prevention of recurrent hyperkalemic periodic paralysis episodes in horses.
- Selected urine-alkalinization applications; the effect may diminish during repeated treatment.
Contraindications
- Do not use in acidemic patients, especially those with hyperchloremic metabolic acidosis.
- Avoid in marked renal or hepatic dysfunction, significant hyponatremia or hypokalemia, or adrenal insufficiency.
- Avoid after acetazolamide hypersensitivity; use cautiously after reactions to other sulfonamides.
- Systemic carbonic anhydrase inhibitors are not recommended routinely in cats because adverse effects are more frequent.
- Not an established effective treatment for canine hydrocephalus.
Interactions
- Urinary alkalinization alters elimination of pH-sensitive medicines.
- Other potassium-depleting drugs can worsen hypokalemia.
- Other carbonic anhydrase inhibitors may produce additive metabolic and electrolyte effects.
- High-dose salicylates can increase the risk of severe acidosis and toxicity; this interaction is well described in human product information.
- Sodium bicarbonate coadministration can increase urinary calculus risk.
Adverse effects
- Metabolic acidosis with panting or tachypnea.
- Hypokalemia, hyponatremia and dehydration.
- Anorexia, vomiting and diarrhea.
- Sulfonamide-associated hypersensitivity reactions.
- Crystalluria or urinary calculi.
Toxicity
Excessive bicarbonate and electrolyte loss can produce severe metabolic acidosis, weakness and dehydration. Stop treatment and provide fluid, electrolyte and acid-base correction guided by laboratory findings. Monitor intraocular pressure for glaucoma and serum electrolytes and renal function during repeated treatment.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Diamox 250 mg | Tablet | 250 mg / tablet | PO |
| Ajanta Acetazolamide Tablets USP 125 mg Ajanta Pharma Limited Immediate-release tablet. | Tablet | 125 mg / tablet | PO |
| Ajanta Acetazolamide Tablets USP 250 mg Ajanta Pharma Limited Immediate-release tablet. | Tablet | 250 mg / tablet | PO |