Section 16 · Monograph
Dichlorphenamide
Reviewed Nov 2026FDA label
Keveyis / OrmalviCarbonic anhydrase inhibitor
- Forms
- Tab: 50mg
- Dose
- Periodic paralysis: start 50mg once or twice daily, titrate weekly; range 50-200mg/day; reassess at 2 months
- MOA
- Mild metabolic acidosis and kaliuresis; exact mechanism in periodic paralysis uncertain
Indications
- Primary hyperkalemic periodic paralysis, primary hypokalemic periodic paralysis, and related variantsFDA-labeled
Mechanism of Action
- Carbonic anhydrase inhibitor causing mild metabolic acidosis and potassium shifts; the exact mechanism of benefit in periodic paralysis is not established
Full Dosing
Adult / usual
- Start 50mg orally once or twice daily; titrate up or down by individual response at weekly intervals
- Minimum recommended 50mg/day; maximum 200mg/day
- Evaluate response after 2 months of treatment; response varies across the periodic paralysis variants
Contraindications
- Hepatic insufficiency
- Severe pulmonary obstruction with limited alveolar ventilation
- Concomitant high-dose aspirin
- Hypersensitivity to dichlorphenamide or other sulfonamides
Drug Interactions
- High-dose aspirin: contraindicated (anorexia, tachypnea, lethargy, coma reported)
- Other carbonic anhydrase inhibitors: additive acidosis
- Potassium-wasting drugs and digoxin: hypokalemia increases toxicity
Adverse Effects
- Paresthesia, cognitive disorder, dysgeusia and confusional state (most common)
- Hypokalemia and metabolic acidosis
- Hypersensitivity including serious skin reactions
Monitoring Parameters
- Serum potassium and bicarbonate at baseline and periodically
- Skin rash or hypersensitivity signs
- Attack frequency and response at 2 months
Pregnancy & Lactation
- Teratogenic in animals (fetal limb reduction defects); no adequate human data — weigh risk and benefit
- Lactation data limited