DICHLORPHENAMIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DICHLORPHENAMIDE (DICHLORPHENAMIDE).
Dichlorphenamide is a carbonic anhydrase inhibitor. It inhibits the enzyme carbonic anhydrase in the proximal renal tubule, reducing reabsorption of bicarbonate, leading to metabolic acidosis, and decreasing intraocular pressure by reducing aqueous humor formation.
| Metabolism | Dichlorphenamide is not extensively metabolized; it is excreted unchanged in urine. |
| Excretion | Primarily renal via tubular secretion; 50-70% excreted unchanged in urine; minor biliary/fecal elimination (<20%). |
| Half-life | Terminal elimination half-life of 2-4 hours; increased in renal impairment, up to 12-24 hours in severe insufficiency. |
| Protein binding | 90-95% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 0.2-0.3 L/kg; low Vd indicates limited extravascular distribution, consistent with high protein binding. |
| Bioavailability | Oral: approximately 80-100% (well absorbed); bioavailability not defined for parenteral routes as not typically given. |
| Onset of Action | Oral: 30-60 minutes for diuretic effect; intravenous (if applicable, though not standard): minutes. |
| Duration of Action | 8-12 hours; diuresis resolves within 12 hours; prolonged in renal impairment. |
25-50 mg orally twice daily.
| Dosage form | TABLET |
| Renal impairment | CrCl <50 mL/min: not recommended; CrCl 50-80 mL/min: 25 mg once daily; CrCl >80 mL/min: no adjustment. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: 25 mg once daily; Child-Pugh C: avoid use. |
| Pediatric use | Not established; safety and efficacy not determined in children. |
| Geriatric use | Start at 25 mg once daily; monitor renal function and electrolytes. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DICHLORPHENAMIDE (DICHLORPHENAMIDE).
| Breastfeeding | It is not known whether dichlorphenamide is excreted in human breast milk. The M/P ratio is unknown. Due to the potential for serious adverse effects in nursing infants, a decision should be made whether to discontinue breastfeeding or discontinue the drug. |
| Teratogenic Risk | Dichlorphenamide is a carbonic anhydrase inhibitor. Data in pregnant women are insufficient. In animal studies, it has been associated with fetal skeletal abnormalities and reduced fetal weight at doses similar to human therapeutic doses. First trimester exposure may carry a risk of teratogenicity; second and third trimester risks include possible metabolic acidosis and electrolyte disturbances in the fetus. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to dichlorphenamide or other sulfonamides","Severe renal impairment (e.g., anuria, severe nephropathy)","Severe hepatic disease","Hepatic encephalopathy","Hypokalemia (uncorrected)","Metabolic acidosis (uncorrected)","Adrenal insufficiency","Hyperchloremic acidosis","Pregnancy (relative contraindication)","Lactation (relative contraindication)"]
| Precautions | ["Metabolic acidosis: Can occur, especially in patients with renal impairment or electrolyte disturbances.","Hypokalemia: Risk may increase due to bicarbonate loss and metabolic acidosis.","Sulfonamide allergy: Cross-sensitivity possible; caution in patients with history of sulfonamide hypersensitivity.","Renal impairment: Use with caution; may accumulate and worsen acidosis.","Hepatic impairment: Caution due to risk of hepatic encephalopathy.","Drug interactions: May increase effects of other carbonic anhydrase inhibitors, furosemide, and decrease effects of lithium.","Pregnancy: Weigh risks vs benefits; not recommended.","Lactation: Excreted in milk; avoid breastfeeding."] |
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| Fetal Monitoring | Monitor maternal serum electrolytes, bicarbonate, and renal function regularly. Assess fetal growth and well-being via ultrasound and nonstress testing. In neonates, monitor for metabolic acidosis and electrolyte disturbances. |
| Fertility Effects | Dichlorphenamide may cause metabolic acidosis, which could theoretically affect reproductive function. No specific human data on fertility impairment are available. |