NEPTAZANE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NEPTAZANE (NEPTAZANE).
Methazolamide is a carbonic anhydrase inhibitor. It decreases intraocular pressure by inhibiting carbonic anhydrase in the ciliary epithelium, reducing aqueous humor secretion. It also has weak diuretic effects due to renal carbonic anhydrase inhibition.
| Metabolism | Metabolized in the liver via microsomal enzymes; approximately 25% is excreted unchanged in urine. |
| Excretion | Renal: 100% as unchanged drug via tubular secretion. No biliary or fecal elimination. |
| Half-life | Terminal elimination half-life: 8-12 hours. In renal impairment, half-life may extend to 20-30 hours, requiring dose adjustment. |
| Protein binding | 60-70% bound to plasma albumin. Binding is saturable at high concentrations. |
| Volume of Distribution | 0.3-0.4 L/kg. Indicates distribution primarily into extracellular fluid with limited tissue penetration. |
| Bioavailability | Oral: 75-85% after absorption. IV: 100%. |
| Onset of Action | Oral: 1-2 hours for peak effect on intraocular pressure. IV: 30-60 minutes. |
| Duration of Action | Oral: 8-12 hours. IV: 4-6 hours. Duration may be prolonged in renal impairment due to reduced clearance. |
50 mg orally twice daily, increasing to 50 mg three times daily if needed. Maximum dose: 200 mg daily.
| Dosage form | TABLET |
| Renal impairment | Contraindicated if GFR < 10 mL/min. For GFR 10-50 mL/min: reduce dose by 50% and monitor. GFR > 50 mL/min: no adjustment. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50%. Child-Pugh C: avoid use. |
| Pediatric use | Not recommended for use in children. |
| Geriatric use | Start at 50 mg orally once daily; titrate slowly due to increased risk of renal impairment and electrolyte disturbances. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NEPTAZANE (NEPTAZANE).
| Breastfeeding | It is not known whether methazolamide is excreted in human milk. Due to potential for serious adverse reactions in nursing infants (e.g., metabolic acidosis, sulfonamide effects), a decision should be made to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother. No M/P ratio is available. |
| Teratogenic Risk | Neptazane (methazolamide) is a carbonic anhydrase inhibitor classified as FDA Pregnancy Category C. In animal studies, it has been shown to be teratogenic (skeletal and visceral malformations) at doses higher than human therapeutic doses. There are no adequate and well-controlled studies in pregnant women. First trimester exposure carries potential risk of congenital anomalies; use only if benefit outweighs risk. Second and third trimester use may cause metabolic acidosis in the fetus and neonate. Avoid in pregnancy unless essential. |
■ FDA Black Box Warning
No FDA boxed warning.
| Serious Effects |
["Hypersensitivity to methazolamide or other sulfonamides","Severe hepatic insufficiency or cirrhosis","Severe renal impairment (CrCl < 50 mL/min)","Electrolyte imbalances (e.g., hyponatremia, hypokalemia)","Chronic noncongestive angle-closure glaucoma (long-term use)","Concurrent use with high-dose aspirin (risk of metabolic acidosis and salicylate toxicity)"]
| Precautions | ["Sulfonamide hypersensitivity reactions (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis) can occur","May cause metabolic acidosis, especially in patients with renal impairment","Can cause hypokalemia and electrolyte imbalances","May worsen hepatic encephalopathy in patients with cirrhosis","Impaired renal function (CrCl < 50 mL/min) increases risk of acidosis","May cause drowsiness, fatigue, and CNS effects"] |
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| Fetal Monitoring | Monitor maternal renal function, electrolytes, and acid-base status (risk of metabolic acidosis). In neonates, monitor for signs of metabolic acidosis and sulfonamide-related adverse effects (e.g., kernicterus, hemolytic anemia). Fetal ultrasound may be considered if used during pregnancy. |
| Fertility Effects | No specific data on human fertility effects. Animal studies have not shown impaired fertility at therapeutic doses. However, carbonic anhydrase inhibitors may theoretically affect acid-base balance and electrolyte status, which could impact reproductive function. |