Schedule H

Oral, Intravenous (IV)

• Tablets: 250 mg

• Injection: 500 mg (lyophilized powder for reconstitution, IV use)

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India):

1. Glaucoma (Chronic open-angle or acute angle-closure — adjunctive therapy)

Parameter Dose Clinical Notes

Starting dose 250 mg orally twice daily Adjunctive to topical antiglaucoma therapy

Titration Increase by 250 mg/day every 2–3 days based on IOP response Monitor electrolytes with dose escalation

Usual maintenance dose 500–1000 mg/day in 2–4 divided doses Divide doses to minimize GI upset

Maximum dose 1000 mg/day Higher doses do not provide additional IOP reduction

IV use (acute crisis): 500 mg IV stat, may repeat in 2–4 hours if needed; switch to oral once IOP controlled.

1. Acute Mountain Sickness (Prophylaxis and Treatment)

Parameter Dose Clinical Notes

Starting dose (prophylaxis) 125–250 mg orally twice daily Begin 24–48 hours before ascent

Titration Not applicable Fixed dosing regimen

Usual maintenance dose 250 mg twice daily Continue for 48 hours after reaching target altitude

Maximum dose 750 mg/day Higher doses increase adverse effects without added benefit

Treatment dose: 250 mg orally 2–3 times daily until symptoms resolve or descent completed.

1. Epilepsy (Adjunctive therapy — absence seizures, myoclonic seizures)

Parameter Dose Clinical Notes

Starting dose 250 mg orally once daily Specialist use only; add-on therapy

Titration Increase by 250 mg every 5–7 days Based on seizure control and tolerability

Usual maintenance dose 750–1000 mg/day in 2–3 divided doses Monitor serum bicarbonate

Maximum dose 1000 mg/day Reserved for refractory cases

Note: Tolerance to anticonvulsant effect may develop; not a first-line agent.

1. Oedema (Secondary to heart failure or drug-induced — short-term use)

Parameter Dose Clinical Notes

Starting dose 250 mg orally once daily (morning) Short-term or intermittent use only

Titration Not applicable Tolerance develops rapidly

Usual maintenance dose 250–375 mg on alternate days or 2–3 days/week Intermittent dosing preferred

Maximum dose 1000 mg/day Not recommended as monotherapy diuretic

Secondary Indications — Adults (Off-label, if any)

1. Idiopathic Intracranial Hypertension (IIH) — OFF-LABEL

Parameter Details

Indication IIH with visual symptoms or refractory headache

Starting dose 250 mg orally twice daily

Titration Increase by 250 mg every 3–5 days as tolerated

Usual dose 1000–2000 mg/day in divided doses

Maximum dose Up to 4000 mg/day (rare; specialist supervision only)

Duration Long-term; taper gradually once symptoms controlled

Specialist only Yes — Neurology/Neuro-ophthalmology

Evidence basis IIHTT RCT; Indian neurology specialist practice (AIIMS protocols)

1. Central Sleep Apnoea (High-altitude or chemoreceptor dysfunction) — OFF-LABEL

Parameter Details

Indication Central sleep apnoea at high altitude

Dose 250–500 mg/day orally

Duration During altitude exposure

Specialist only Yes — Pulmonology/High-altitude medicine

Evidence basis International studies; Indian Armed Forces high-altitude protocols

1. Cystinuria (Urine alkalinization — adjunctive) — OFF-LABEL

Parameter Details

Indication Prevention of cystine stones

Dose 250–500 mg orally 2–4 times daily

Duration Long-term with monitoring

Monitoring Urine pH (target >7.5), renal function

Specialist only Yes — Nephrology/Urology

Evidence basis Specialist practice; supportive international data

PAEDIATRIC DOSING (Specialist Only)

Primary Indications:

1. Glaucoma (Congenital or secondary — adjunctive)

Parameter Dose Comments

Starting dose (oral) 5 mg/kg/day in 2–3 divided doses Use 250 mg tablets; calculate dose carefully

Titration Increase by 2.5 mg/kg/day every 3–5 days Based on IOP response

Usual maintenance dose 10–15 mg/kg/day in 2–3 divided doses Monitor electrolytes and growth

Maximum dose 750 mg/day or 30 mg/kg/day (whichever is lower)

IV dose (acute): 5–10 mg/kg/dose every 6–8 hours; maximum single dose 500 mg.

1. Epilepsy (Absence, myoclonic — refractory cases)

Parameter Dose Comments

Starting dose 4–8 mg/kg/day orally in 2–3 divided doses Add-on therapy only

Titration Increase every 1–2 weeks based on response Monitor for metabolic acidosis

Usual maintenance dose 8–15 mg/kg/day in 2–3 divided doses

Maximum dose 1000 mg/day or 30 mg/kg/day

1. Acute Mountain Sickness Prophylaxis (Children >6 years)

Parameter Dose Comments

Starting dose 2.5 mg/kg/dose orally twice daily Start 1–2 days before ascent

Titration Not applicable Fixed dosing

Usual dose 2.5 mg/kg/dose twice daily Continue 48 hours after reaching altitude

Maximum dose 125 mg per dose; 250 mg/day

Secondary Indications — Paediatrics (Off-label, if any)

Idiopathic Intracranial Hypertension — OFF-LABEL

Parameter Details

Indication Paediatric IIH with papilloedema

Starting dose 10–15 mg/kg/day orally in 2–3 divided doses

Titration Increase by 10 mg/kg/day every week as tolerated

Maximum dose 100 mg/kg/day or 2000 mg/day (whichever is lower)

Monitoring Visual fields, serum bicarbonate, weight, fundoscopy

Specialist only Yes — Paediatric neurology

Evidence basis Indian specialist practice; supportive international data

Not recommended below 6 months of age except under specialist supervision in tertiary care settings.

50 No adjustment required

30–50 Use with caution; monitor acid-base status closely

10–30 Avoid or use with extreme caution — high risk of metabolic acidosis

<10 Contraindicated

Haemodialysis Avoid — not significantly dialyzable; worsens acid-base imbalance

Peritoneal dialysis Avoid

• Severe renal impairment (eGFR <10 mL/min/1.73m²)

• Severe hepatic disease or hepatic encephalopathy

• Known hypersensitivity to acetazolamide or sulfonamides

• Adrenocortical insufficiency (Addison's disease)

• Hyperchloraemic metabolic acidosis

• Hypokalaemia or hyponatraemia (uncorrected)

• Concurrent high-dose aspirin therapy

• Marked renal or hepatic dysfunction in patients with angle-closure glaucoma requiring long-term therapy

• Pre-existing electrolyte disturbances (monitor potassium, sodium, bicarbonate)

• Chronic obstructive pulmonary disease or respiratory acidosis

• Diabetes mellitus (may worsen glycaemic control)

• History of nephrolithiasis (increased risk of calcium phosphate stones)

• Prolonged therapy (risk of bone marrow suppression)

• Concurrent use of other carbonic anhydrase inhibitors (topiramate, zonisamide)

• Elderly patients (increased susceptibility to electrolyte and CNS effects)

• Patients on digitalis (hypokalaemia increases toxicity risk)

Aspect Recommendation

Risk category Not formally classified by CDSCO; animal studies show teratogenicity

Use in pregnancy Avoid in first trimester; use only if benefit clearly outweighs risk in second/third trimester

Preferred alternatives For diuresis: loop diuretics under specialist guidance; for glaucoma: topical beta-blockers

Monitoring Maternal electrolytes, fetal growth, amniotic fluid volume

Aspect Recommendation

Compatibility Generally compatible; small amounts excreted in breast milk

Drug levels in milk Low (estimated infant dose <2% of maternal dose)

Preferred alternatives Use minimum effective dose; consider topical agents for glaucoma

Infant monitoring Poor feeding, excessive drowsiness, diarrhoea, weight gain patterns

Aspect Recommendation

Starting dose 250 mg once daily; lower initial doses preferred

Titration Slow titration; increase at weekly intervals if needed

Special risks Increased susceptibility to metabolic acidosis, hypokalaemia, dehydration, falls, confusion

Monitoring Baseline and periodic renal function, electrolytes; assess cognitive function

Drug Interaction Management

High-dose salicylates (>2g/day) Increased risk of severe metabolic acidosis and salicylate toxicity (CNS penetration increased) Avoid combination; if unavoidable, monitor closely

Topiramate / Zonisamide Additive carbonic anhydrase inhibition → severe metabolic acidosis, nephrolithiasis Avoid combination or use with extreme caution under specialist supervision

Cyclosporine Increased cyclosporine levels; enhanced nephrotoxicity Avoid if possible; monitor cyclosporine levels and renal function

Methenamine Urine alkalinization reduces methenamine efficacy Avoid combination

Drug Interaction Management

Corticosteroids Additive hypokalaemia risk Monitor serum potassium

Lithium Increased renal lithium excretion → reduced lithium efficacy Monitor lithium levels; may need dose adjustment

Warfarin Enhanced anticoagulant effect (mechanism unclear) Monitor INR closely; adjust warfarin dose as needed

Phenytoin Possible increased phenytoin toxicity due to reduced metabolism Monitor phenytoin levels

Digoxin Hypokalaemia increases digoxin toxicity risk Monitor potassium; supplement if needed

Metformin Additive risk of lactic acidosis (rare) Use with caution; monitor for acidosis symptoms

• Paraesthesias (tingling of fingers, toes, lips) — dose-related, often transient

• Fatigue and malaise

• Gastrointestinal upset (nausea, vomiting, diarrhoea)

• Loss of appetite and altered taste sensation (dysgeusia)

• Polyuria and increased thirst

• Drowsiness and dizziness

• Mild hypokalaemia and hyponatraemia

Adverse Effect Clinical Notes

Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis Discontinue immediately if rash develops; sulfonamide cross-reactivity

Aplastic anaemia / Agranulocytosis Rare; requires immediate discontinuation and haematology referral

Fulminant hepatic necrosis Rare; monitor LFTs in prolonged therapy

Severe metabolic acidosis Discontinue drug; may require bicarbonate replacement

Nephrolithiasis (calcium phosphate stones) More common with prolonged use; ensure adequate hydration

Hypokalaemia (severe) May precipitate arrhythmias especially with digoxin

Bone marrow depression Monitor CBC with long-term use

After initiation/dose change Electrolytes and serum bicarbonate within 1–2 weeks; repeat at 4–6 weeks

Long-term monitoring CBC every 3–6 months; electrolytes and renal function every 2–3 months; periodic LFTs

Special situations Visual fields and fundoscopy in IIH; seizure frequency in epilepsy

• Diamox (Wyeth/Pfizer)

• Acemox (Abbott)

• Azoptal (Intas)

• Azolac (Micro Labs)

• Acetamide (various)

• Iopar (Cipla)

Note: Available as monotherapy tablets and injection; no significant FDCs in Indian market.

Government supply Free/subsidized Available in tertiary care settings; included in high-altitude medical kits

1. Paraesthesias are expected — tingling of extremities and lips is a common, harmless effect; reassure patients that this indicates drug activity and often diminishes with continued use.

1. Diuretic tolerance develops rapidly — not suitable for long-term oedema management; intermittent dosing (alternate days) helps maintain efficacy.

1. High-altitude use is well-established — widely used by Indian Armed Forces and trekkers; start 24–48 hours before ascent for optimal prophylaxis.

1. Monitor bicarbonate in long-term use — chronic metabolic acidosis is common; serum bicarbonate <18 mEq/L warrants dose reduction or discontinuation.

1. Sulfonamide allergy cross-reactivity — use caution in patients with history of sulfonamide antibiotic allergy; true cross-reactivity is rare but serious reactions (SJS/TEN) can occur.

1. Not a first-line antiepileptic — reserve for refractory absence or myoclonic seizures under neurologist supervision; tolerance to anticonvulsant effect may develop.

1. IIH dosing can be high — doses up to 4 g/day may be needed; gradual titration with bicarbonate monitoring is essential.

carbonic anhydrase inhibitor; glaucoma; acute mountain sickness; epilepsy; idiopathic intracranial hypertension; diuretic; sulfonamide-derivative; altitude sickness; Schedule H; electrolyte-monitoring

RxIndia v1.0 — 03 May 2025

• CDSCO prescribing information

• Indian Pharmacopoeia

• API Textbook of Medicine

• AIIMS protocol for Idiopathic Intracranial Hypertension

• High Altitude Medical Manual — Indian Armed Forces Guidelines

• IAP Paediatric Drug Formulary

• Goodman & Gilman's The Pharmacological Basis of Therapeutics (supportive)

• IIHTT Trial (off-label evidence for IIH dosing)