Methazolamide Uses, Dosage, Side Effects & Warnings | DrugsAtlas
Authoritative Clinical Reference
Navigation
DRUG NAME: Methazolamide
Therapeutic Class: Antiglaucoma Agent
Subclass: Carbonic Anhydrase Inhibitor (Systemic)
Speciality: Ophthalmology
Schedule (India): Not applicable (NOT marketed in India; if imported under special licence, would likely fall under Schedule H by analogy with acetazolamide)
Route(s): Oral
Formulations Available in India:
NOT AVAILABLE in India
(As of current CDSCO approvals, Indian Pharmacopoeia listings, and standard Indian formularies, methazolamide holds no marketing authorisation in India. All clinical information below is derived from international pharmacopoeial and textbook sources for reference only and does not constitute a recommendation for routine Indian prescribing.)
NOT AVAILABLE in India
(As of current CDSCO approvals, Indian Pharmacopoeia listings, and standard Indian formularies, methazolamide holds no marketing authorisation in India. All clinical information below is derived from international pharmacopoeial and textbook sources for reference only and does not constitute a recommendation for routine Indian prescribing.)
INDICATIONS + DOSING — FOR CLINICIAN USE ONLY
Primary Indications (Approved / Standard in India)
NOT AVAILABLE in India
No CDSCO-approved indication exists.
No CDSCO-approved indication exists.
Secondary Indications — Adults Only (Off-label)
Since methazolamide is not marketed in India, any use would require importation under special regulatory provisions. The following information is drawn from international clinical data for specialist reference only.
1. Adjunctive treatment of chronic open-angle glaucoma or secondary glaucoma — OFF-LABEL in India
(Specialist only; ophthalmologist supervision mandatory)
(Specialist only; ophthalmologist supervision mandatory)
| Parameter | Detail |
| Starting dose | 50 mg orally twice daily |
| Titration | Increase by 50 mg/day every 3–5 days based on IOP response and tolerability |
| Usual maintenance dose | 100–200 mg/day in 2–3 divided doses |
| Maximum dose | 300 mg/day |
| Duration | As long as clinically required; reassess need periodically |
| Key clinical notes | Monitor serum electrolytes and bicarbonate before and during therapy. Prefer topical carbonic anhydrase inhibitors (dorzolamide, brinzolamide) as first line in India. Use only when approved oral (acetazolamide) or topical agents are ineffective or not tolerated. |
Evidence basis: International clinical practice and standard pharmacology texts (Goodman & Gilman). No Indian RCT or guideline supports routine use. Off-label use should be justified and documented.
PAEDIATRIC DOSING (Specialist Only)
Primary Indications (Approved / Standard in India)
NOT AVAILABLE in India
Secondary Indications — Paediatric Doses (Off-label)
1. Congenital or juvenile glaucoma — OFF-LABEL in India
(Specialist only; paediatric ophthalmologist supervision mandatory)
(Specialist only; paediatric ophthalmologist supervision mandatory)
| Parameter | Detail |
| Starting dose | 1 mg/kg/day orally in 2 divided doses |
| Titration | May increase to 2–4 mg/kg/day based on IOP response, in 2–3 divided doses |
| Usual maintenance dose | 2–4 mg/kg/day in divided doses |
| Maximum dose | 4 mg/kg/day (not to exceed adult maximum of 300 mg/day) |
| Minimum age | Not recommended below 1 year of age |
| Duration | As clinically indicated; reassess frequently |
Safety monitoring in children:
- Serum electrolytes (Na⁺, K⁺, HCO₃⁻) at baseline and every 2 weeks for the first month, then monthly
- Renal function (urea, creatinine) at baseline and periodically
- Weight and growth monitoring at each visit
- CBC at baseline (risk of blood dyscrasias)
Evidence basis: Limited; based on small international case series and extrapolation from acetazolamide paediatric data. No Indian paediatric guideline supports routine use. Use only when all India-available alternatives (topical dorzolamide, oral acetazolamide) have failed.
RENAL ADJUSTMENT
| Renal Function (eGFR / CrCl) | Recommendation |
| CrCl >50 mL/min | Standard dosing; monitor electrolytes |
| CrCl 25–50 mL/min | Reduce dose (e.g., 50 mg once or twice daily); monitor electrolytes and bicarbonate closely |
| CrCl 10–25 mL/min | Use with extreme caution; specialist decision only; frequent monitoring |
| CrCl <10 mL/min |
Contraindicated — risk of severe metabolic acidosis and drug accumulation
|
| Haemodialysis | Limited data; likely partially dialysable; avoid routine use |
HEPATIC ADJUSTMENT
| Severity | Recommendation |
| Mild impairment (Child-Pugh A) | Use with caution; standard dosing may be attempted with close monitoring of ammonia and electrolytes |
| Moderate impairment (Child-Pugh B) | Dose reduction advisable; monitor serum ammonia, electrolytes, and clinical status for hepatic encephalopathy |
| Severe impairment (Child-Pugh C) |
Avoid use — significant risk of precipitating or worsening hepatic encephalopathy due to alkalinisation of urine and ammonia trapping
|
CONTRAINDICATIONS
- Known hypersensitivity to methazolamide, acetazolamide, or any sulfonamide derivative
- Severe renal impairment (CrCl <10 mL/min)
- Severe hepatic disease or hepatic encephalopathy
- Marked hypokalaemia or hyponatraemia (uncorrected)
- Hyperchloraemic metabolic acidosis
- Adrenocortical insufficiency (Addison disease)
- Concomitant high-dose aspirin therapy (risk of severe salicylate toxicity and acidosis)
- Angle-closure glaucoma where delay in surgery may worsen outcome (should not substitute for definitive surgical management)
CAUTIONS
- History of nephrolithiasis (increased risk of calcium phosphate or calcium oxalate stones with chronic carbonic anhydrase inhibition)
- Diabetes mellitus — may worsen glycaemic control and predispose to metabolic acidosis
- Chronic obstructive pulmonary disease or other conditions with baseline respiratory acidosis — relative contraindication, as further bicarbonate loss may impair respiratory compensation
- Elderly patients — higher risk of confusion, hypotension, electrolyte disturbance
- Concurrent diuretic therapy — additive electrolyte depletion
- Gout — may precipitate hyperuricaemia
- Patients taking other drugs metabolised by or affecting renal tubular transport
- Prolonged use — risk of bone marrow suppression (rare)
PREGNANCY
| Parameter | Detail |
| Overall safety |
Avoid unless benefit clearly outweighs risk
|
| Teratogenicity | Teratogenic in animal studies (limb defects in rodents at high doses); insufficient human data |
| Trimester-specific guidance | Avoid in 1st trimester especially; limited safety data for 2nd/3rd trimester |
| Preferred alternatives in Indian practice | Topical dorzolamide or brinzolamide (lower systemic absorption); topical timolol (with caution); consult ophthalmologist and obstetrician |
| If used | Monitor fetal growth (ultrasound), maternal serum electrolytes, and renal function; use lowest effective dose for shortest duration |
| Specialist recommendation | Mandatory — joint decision by ophthalmologist and obstetrician |
LACTATION
| Parameter | Detail |
| Compatibility |
Avoid if possible — insufficient human data on excretion in breast milk
|
| Expected milk levels | Unknown; by analogy with acetazolamide, low-to-moderate levels possible |
| Preferred alternatives | Topical dorzolamide or brinzolamide (minimal systemic absorption); topical timolol (with infant monitoring) |
| Infant monitoring (if used) | Feeding adequacy, hydration, weight gain; signs of metabolic acidosis (poor feeding, irritability, tachypnoea) |
ELDERLY
- Starting dose: 50 mg once or twice daily (lower end of range)
- Titration: Increase slowly, no more frequently than every 5–7 days
- Additional risks: Electrolyte disturbance (especially hypokalaemia), dehydration, postural hypotension, confusion, metabolic acidosis
- Monitoring: Check renal function and electrolytes at baseline and frequently (every 1–2 weeks initially)
- General guidance: Prefer topical carbonic anhydrase inhibitors where possible. Oral therapy should be reserved for cases unresponsive to topical agents.
MAJOR DRUG INTERACTIONS
| Interacting Drug | Effect / Risk | Action |
|
High-dose aspirin (≥3 g/day)
|
Severe metabolic acidosis; increased CNS penetration of salicylates due to acidaemia |
AVOID combination
|
|
Topiramate
|
Additive carbonic anhydrase inhibition → increased risk of metabolic acidosis and nephrolithiasis |
AVOID or use with extreme caution; monitor bicarbonate and renal function
|
|
Lithium
|
Increased renal lithium clearance → reduced lithium efficacy; rebound toxicity on stopping methazolamide |
Avoid combination or monitor lithium levels closely
|
|
Other carbonic anhydrase inhibitors (acetazolamide, dorzolamide)
|
Additive pharmacological effect with no additional benefit; increased adverse effects |
Avoid duplication
|
MODERATE DRUG INTERACTIONS
| Interacting Drug | Effect / Risk | Action |
| Loop or thiazide diuretics | Additive hypokalaemia and hyponatraemia | Monitor electrolytes; supplement potassium if needed |
| Corticosteroids (systemic) | May worsen hypokalaemia | Monitor serum potassium |
| Digoxin | Hypokalaemia from methazolamide increases digoxin toxicity risk | Monitor serum potassium and digoxin levels |
| Oral antidiabetic agents / insulin | Altered glycaemic control; acidosis may mask hypoglycaemia symptoms | Monitor blood glucose more frequently |
| Cyclosporin | Potential additive nephrotoxicity | Monitor renal function |
| Phenytoin | May increase osteomalacia risk with chronic use (both affect calcium metabolism) | Monitor calcium and vitamin D status |
| Metformin | Additive risk of lactic/metabolic acidosis | Use with caution; monitor bicarbonate |
COMMON ADVERSE EFFECTS
- Paraesthesia (tingling of fingers, toes, perioral area) — most frequent; usually dose-related
- Altered taste (metallic or bitter taste), especially with carbonated beverages
- Gastrointestinal upset (nausea, vomiting, diarrhoea, anorexia)
- Fatigue and malaise
- Polyuria and increased urinary frequency
- Mild drowsiness
- Mild electrolyte changes (hypokalaemia, low bicarbonate) — often subclinical
SERIOUS ADVERSE EFFECTS
- Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis (rare; sulfonamide cross-reactivity) → discontinue immediately and hospitalise
- Agranulocytosis / aplastic anaemia / thrombocytopenia → discontinue; obtain urgent haematology review
- Fulminant hepatic necrosis (rare) → discontinue; supportive care
- Severe metabolic acidosis requiring hospitalisation — more likely with renal impairment or concurrent acidifying drugs
- Nephrolithiasis (calcium phosphate stones) — especially with chronic use or inadequate hydration
- Acute myopia and secondary angle-closure (idiosyncratic, rare)
- Worsening of respiratory acidosis in patients with COPD or other chronic lung disease
MONITORING REQUIREMENTS
Baseline (before starting):
- Serum electrolytes: Na⁺, K⁺, Cl⁻, HCO₃⁻
- Renal function: serum creatinine, urea, eGFR
- Liver function tests
- Complete blood count (CBC) with differential — due to rare risk of blood dyscrasias
- Intraocular pressure measurement
Early treatment (first 1–2 months):
- Electrolytes and serum bicarbonate: every 2 weeks
- Renal function: at 2 weeks, then monthly
- CBC: at 4 weeks
Long-term (if continued beyond 2 months):
- Electrolytes, bicarbonate, renal function: every 1–3 months
- CBC: every 3–6 months
- Symptom review for paraesthesia, visual changes, rash, fatigue, confusion
- Periodic assessment of IOP to confirm ongoing efficacy
BRANDS AVAILABLE IN INDIA
NOT AVAILABLE in India
PRICE RANGE (INR)
NOT AVAILABLE in India
(For international reference: methazolamide 25 mg and 50 mg tablets are available in some countries. No Indian price or NPPA ceiling applies.)
CLINICAL PEARLS
- Methazolamide is not marketed in India. For systemic carbonic anhydrase inhibition, acetazolamide is the accessible oral option. For topical use, dorzolamide and brinzolamide are widely available and preferred.
- Compared to acetazolamide, methazolamide has better oral bioavailability, lower protein binding, and longer duration of action — hence lower doses may suffice. However, this advantage is academic in India given non-availability.
- All sulfonamide-derived carbonic anhydrase inhibitors carry a cross-reactivity risk in patients with sulfonamide allergy. However, the risk of cross-reaction between sulfonamide antibiotics and non-antibiotic sulfonamides (like methazolamide) is considered low; clinical judgement is needed.
- Paraesthesia is an expected pharmacological effect (not an allergy); counsel patients that tingling in fingers and toes is common and usually not dangerous, though it may prompt dose reduction.
- Chronic use mandates vigilant electrolyte monitoring — hypokalaemia and metabolic acidosis are the most clinically important biochemical complications.
- If importing under special licence for a patient unresponsive to all India-available agents, document the clinical rationale thoroughly and ensure specialist oversight.
TAGS
methazolamide; antiglaucoma; carbonic anhydrase inhibitor; oral; sulfonamide-derivative; NOT marketed in India; off-label; specialist-only; renal-adjustment; ophthalmology
VERSION
RxIndia v0.1 — 14 Feb 2026
REFERENCES
- CDSCO: No approved formulation or marketing authorisation found for methazolamide
- IP/NFI: Not listed in Indian Pharmacopoeia or National Formulary of India
- NLEM (India): Not included
- Goodman & Gilman’s The Pharmacological Basis of Therapeutics (carbonic anhydrase inhibitor pharmacology, dosing, adverse effects)
- API Textbook of Medicine (glaucoma management overview; methazolamide not specifically discussed)
- Katzung’s Basic & Clinical Pharmacology (comparative pharmacokinetics of carbonic anhydrase inhibitors)
- International product monographs (US FDA-approved labelling for methazolamide) — used for dosing and adverse effect data, clearly marked as off-label for Indian context
⚖️
Clinical Responsibility
This platform is designed strictly for healthcare professionals. Data provided is synthesized from authoritative pharmacological sources and clinical registries. Do not use for consumer medical decisions. Always verify critical dosing and contraindications with official institutional protocols and peer-reviewed journals.
Content Feedback
Is this information helpful?
Help us improve our clinical database for the medical community.