Pharmacology and side effects of oral carbonic anhydrase inhibitors (Oral CAI, acetazolamide/methazolamide)

💊 Oral Carbonic Anhydrase Inhibitors (CAI) for Glaucoma

Oral CAIs reduce intraocular pressure by suppressing aqueous production.
Used when topical therapy is insufficient or urgent pressure lowering is needed.

 

 

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🧪 Comparison Table

ItemAcetazolamideMethazolamide

Dose	250mg up to 4/day	50mg twice/day
Half-life	4 hours	12–15 hours
Excretion	Renal	Hepatic
Protein Binding	95%	55%
Strengths	Strong effect, IV available	Less systemic absorption
Limitations	Contraindicated in pregnancy, kidney caution	⚠️ Risk of SJS

✅ Mnemonics:

• “High PPK” → Protein, Potency, Kidney = Acetazolamide
• “Low Systemic, Long Half-life” → Methazolamide

 

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⚠ Key Side Effects

EffectNotes

Paresthesia, anorexia	Due to ↓K+, advise orange juice intake
Metabolic acidosis	HCO₃- loss → avoid in DM, COPD, liver issues
Hematologic toxicity	WBC↓, PLT↓, pancytopenia
Kidney stones	Rare in low doses, but possible in high-dose
SJS (Stevens-Johnson)	Rare but severe, mainly with methazolamide

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✅ Summary

• Oral CAIs are powerful IOP-lowering agents,
• but require caution due to systemic side effects, especially SJS