醋甲唑胺
**醋甲唑胺 (Methazolamide)** 是一種口服的**碳酸酐酶抑制劑 (CAI)**，在獸醫學中主要用於**開角型青光眼**的內科治療。 在過去，全身性 CAI 是降低眼內壓 (IOP) 的主要藥物，但目前已大多被局部點眼劑（如 dorzolamide、brinzolamide）所取代。局部用藥能提供相當的降眼壓效果，且全身性副作用的發生率大幅降低。 臨床重點： * **全身性影響：** 由於是口服給藥，醋甲唑胺會抑制全身的碳酸酐酶，可能導致代謝性酸中毒和電解質不平衡（尤其是低血鉀）。 * **臨床應用：** 通常保留用於對局部治療反應不佳的頑固性青光眼病例，或無法進行局部給藥時。 * **物種敏感性：** 貓對口服 CAI 的副作用特別敏感，可能會表現出嚴重的嗜睡和厭食。
作用機制: Methazolamide acts via noncompetitive, reversible inhibition of the enzyme **carbonic anhydrase (CA)**, specifically the **CA-II isoenzyme**. * **In the Eye (Ciliary Body):** Inhibition of CA → reduces the formation of hydrogen (H+) and bicarbonate (HCO3-) ions from carbon dioxide and water → decreases the availability of these ions for active transport into the posterior chamber → **decreased aqueous humor production** → **reduced intraocular pressure (IOP)**. * **In the Kidneys (Proximal Tubule):** Inhibition of CA → increased renal tubular secretion of sodium (Na+), potassium (K+), and bicarbonate (HCO3-) → **increased urine alkalinity and volume**, often resulting in a mild **hyperchloremic metabolic acidosis**. * **In the CNS:** Exhibits anticonvulsant activity independent of its diuretic effects, potentially due to localized CA inhibition in the brain or secondary to systemic metabolic acidosis.
各物種劑量
- Medical treatment of glaucoma · 3-4 mg/kg PO twice a day. · PO · twice a day · Cats may not tolerate oral carbonic anhydrase inhibitors (CAIs) as well as dogs. Reported side effects include lethargy, inappetence, vomiting. Topical CAIs may be better tolerated.
- Medical treatment of glaucoma · 1-2 mg/kg PO q8-12h · PO · q8-12h
- Medical treatment of glaucoma · 2.5-5 mg/kg PO q8-12h · PO · q8-12h
- Medical treatment of glaucoma · 2-4 mg/kg PO two to three times a day · PO · two to three times a day
- Medical treatment of glaucoma · 3-5 mg/kg divided q12h PO · PO · q12h
- Medical treatment of glaucoma · 2-5 mg/kg PO two to three times a day · PO · two to three times a day
- Medical treatment of glaucoma · 2.2-4.4 mg/kg PO two to three times a day. · PO · two to three times a day
- Medical treatment of glaucoma · 2-10 mg/kg PO two to three times a day. · PO · two to three times a day
劑量為持牌獸醫專業人員的臨床參考。請務必對照最新藥品說明書及個別病患確認。
給藥途徑
禁忌症
- Significant hepatic disease (may precipitate hepatic coma)
- Renal or adrenocortical insufficiency
- Hyponatremia or hypokalemia
- Hyperchloremic acidosis or severe electrolyte imbalance
- Severe pulmonary obstruction (inability to increase alveolar ventilation to compensate for metabolic acidosis)
- Hypersensitivity to carbonic anhydrase inhibitors or sulfonamides
- Chronic, noncongestive, angle-closure glaucoma (long-term use may mask the condition by lowering IOP while angle closure progresses)
不良反應
- GI disturbances (vomiting, diarrhea, inappetence)
- Metabolic acidosis (often manifesting as heavy panting in dogs)
- CNS effects (sedation, depression, disorientation, excitement)
- Hematologic effects (bone marrow depression, thrombocytopenia)
- Renal effects (crystalluria, dysuria, renal colic, polyuria, polydipsia)
- Hypokalemia
- Hyperglycemia
- Hyponatremia
- Hyperuricemia
- Hepatic insufficiency
- Dermatologic effects (rash)
- Hypersensitivity reactions
- Weakness or cardiac arrhythmias (secondary to electrolyte imbalances)
藥物相互作用
- Antidepressants, Tricyclic · Alkaline urine caused by methazolamide may decrease excretion of tricyclic antidepressants.
- Aspirin (or other salicylates) · Increased risk of methazolamide accumulation and toxicity; increased risk for metabolic acidosis; methazolamide increases salicylate excretion.
- Digoxin · Methazolamide may cause hypokalemia, leading to an increased risk for digoxin toxicity.
- Insulin · Rarely, carbonic anhydrase inhibitors may interfere with the hypoglycemic effects of insulin.
- Methenamine compounds · Methazolamide alkalinizes urine, which may negate the urinary antiseptic effects of methenamine.
- Potassium-depleting drugs (corticosteroids, amphotericin B, corticotropin, diuretics) · Concomitant use may exacerbate potassium depletion and hypokalemia.
- Phenobarbital · Increased urinary excretion due to alkaline urine, which may reduce phenobarbital serum levels.
- Primidone · May result in decreased primidone concentrations.
- Quinidine · Alkaline urine caused by methazolamide may decrease quinidine excretion.
監測
- Intraocular pressure (IOP) / tonometry
- Serum electrolytes (especially potassium and sodium)
- Blood pH / acid-base status
- Baseline CBC with differential, and periodic retests if using chronically
- Clinical signs of adverse effects (lethargy, GI upset, heavy panting)
過量
Information regarding acute overdosage of methazolamide in veterinary species is limited. **Clinical Signs:** Expected signs of toxicity include severe electrolyte imbalances (hypokalemia, hyponatremia), profound metabolic acidosis, CNS depression or disorientation, and dehydration secondary to diuresis. **Management:** * Monitor serum electrolytes, blood gases (for acidosis), volume status, and CNS status. * Treat symptomatically and supportively. * Administer intravenous fluids to correct dehydration and electrolyte deficits (especially potassium supplementation if indicated). * Correct severe metabolic acidosis with sodium bicarbonate if necessary, based on blood gas analysis.
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