Schedule H

Oral

• Capsule: 250 mg

• Syrup: 250 mg/5 mL

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

1. Absence Seizures (Typical Absence / Petit Mal Epilepsy)

First-line monotherapy for typical absence seizures per Indian epilepsy practice (AIIMS Neurology protocol)

Adults:

Parameter Recommendation

Starting dose 250 mg orally twice daily

Titration Increase by 250 mg every 4–7 days based on seizure control and tolerability

Usual maintenance dose 15 mg/kg/day in 2 divided doses; typical range 500–1500 mg/day

Maximum dose 2000 mg/day

Key Clinical Notes:

• Highly effective for typical absence seizures; ineffective for other seizure types

• Monitor for sedation during early titration phase

• Confirm seizure classification with EEG before initiating therapy

• Often used in idiopathic generalised epilepsy with predominant absence seizures

Secondary Indications — Adults (Off-label)

Not applicable.

PAEDIATRIC DOSING (Specialist Only)

Primary Indications

Childhood Absence Epilepsy / Juvenile Absence Epilepsy

• Minimum age: 3 years

• Not recommended below 3 years of age except under specialist supervision

Weight-Based Dosing:

Weight Starting Dose Titration Usual Maintenance Dose Maximum Dose

<25 kg 10 mg/kg/day in 1–2 divided doses Increase by 250 mg every 7 days based on response 15–20 mg/kg/day 30 mg/kg/day

≥25 kg 250 mg once or twice daily Increase by 250 mg every 7 days 500–1000 mg/day 1500–2000 mg/day

Key Clinical Notes:

• Preferred over valproate in young girls of childbearing potential due to lower teratogenic risk

• Monitor for behavioural side effects (irritability, aggression, mood changes)

• Syrup formulation useful for accurate weight-based dosing in young children

Safety Monitoring:

• Complete blood count at baseline and periodically during therapy

• Monitor for GI symptoms, sedation, behavioural changes

• Watch for signs of bone marrow suppression

Secondary Indications — Paediatric Doses (Off-label)

Not applicable.

Mild-to-moderate impairment No dose adjustment required

• Known hypersensitivity to ethosuximide or other succinimides (e.g., methsuximide)

• History of drug-induced bone marrow suppression

• Severe hepatic impairment

• History of psychiatric illness — may exacerbate depression, psychosis, or suicidal ideation

• Pre-existing blood dyscrasias — periodic haematological monitoring required

• Hepatic impairment — monitor liver function

• Renal impairment — slower titration advisable

• Abrupt withdrawal — risk of increased seizure frequency or status epilepticus; always taper gradually

• Systemic lupus erythematosus — succinimides may exacerbate symptoms

• Mixed seizure disorders — may precipitate generalised tonic-clonic seizures if used as monotherapy

Parameter Details

Safety category Limited human data; animal studies suggest teratogenicity

When it may be used Only if no safer alternative available and benefit outweighs risk; specialist supervision mandatory

Preferred alternatives Lamotrigine generally preferred in women of childbearing potential; valproate should be avoided

What to monitor Detailed fetal anomaly scan; maternal seizure control; fetal growth

Parameter Details

Compatibility Compatible with breastfeeding; excreted in breast milk but generally well-tolerated

Expected drug levels in milk Low to moderate

Preferred alternatives Lamotrigine or levetiracetam may be considered if initiating new therapy postpartum

What to monitor in infant Sedation, poor feeding, irritability, inadequate weight gain

• Starting dose: 250 mg once daily at night

• Titration: Increase slowly every 1–2 weeks based on tolerability

• Extra risks:

• Increased sensitivity to sedation and CNS effects

• Higher risk of confusion, dizziness, falls

• Reduced renal and hepatic reserve may affect drug clearance

• Monitoring: Renal function, liver function, mental status, gait stability

Interacting Drug(s) Effect Mechanism Management

Valproate / Divalproex Increased ethosuximide serum levels; risk of toxicity Inhibition of CYP3A4-mediated metabolism Monitor for toxicity (sedation, GI symptoms); may require dose reduction

Carbamazepine Reduced ethosuximide levels; decreased efficacy CYP3A4 enzyme induction Monitor seizure control; may require ethosuximide dose increase

Phenytoin Reduced ethosuximide levels CYP enzyme induction Monitor therapeutic response; adjust dose accordingly

Phenobarbital Reduced ethosuximide levels CYP enzyme induction Monitor seizure control

Interacting Drug(s) Effect Management

Rifampicin Reduced ethosuximide efficacy due to enzyme induction Monitor seizure control; dose adjustment may be needed

Fluconazole, ketoconazole May increase ethosuximide levels Monitor for CNS toxicity

Isoniazid May inhibit ethosuximide metabolism Monitor for adverse effects

Antipsychotics (chlorpromazine, haloperidol) May lower seizure threshold Use with caution; monitor seizure frequency

Sedatives, antihistamines Additive CNS depression Advise caution; may need dose adjustment

Warfarin Possible alteration in anticoagulant effect Monitor INR during initiation or dose changes

• Nausea, vomiting, anorexia

• Drowsiness, sedation

• Dizziness

• Headache

• Ataxia

• Hiccups

• Behavioural changes (especially in children — irritability, aggression, mood swings)

• Abdominal discomfort

Adverse Effect Clinical Notes

Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis Rare; discontinue immediately; requires hospitalisation

Aplastic anaemia Rare but potentially fatal; discontinue if significant bone marrow suppression

Agranulocytosis Monitor CBC; discontinue if severe neutropenia

Hepatotoxicity Monitor LFTs; discontinue if significant elevation

Systemic Lupus Erythematosus-like syndrome May occur with prolonged use; discontinue if symptoms develop

Suicidal ideation Class effect of antiepileptics; monitor mood and behaviour closely

Psychosis / Severe behavioural disturbance Rare; may require discontinuation

Phase Parameter Frequency

Baseline CBC with differential, LFTs, renal function, EEG (to confirm seizure type) Before initiation

During titration CBC, clinical assessment for CNS/GI side effects Weekly to fortnightly

Long-term CBC with differential Every 3–6 months

Long-term LFTs Every 6–12 months

Long-term Clinical assessment for behavioural changes, mood, seizure control At each visit

If symptoms suggest toxicity Serum ethosuximide level (if available) As indicated

• Zarontin (Pfizer)

• Petimid (Abbott — limited availability)

Note: Formulation availability may be limited; not widely stocked in all regions. Verify local availability before prescribing for long-term use.

• Not included in NLEM

• Not under NPPA price control

• May be available in select government hospital supplies

1. Seizure-type specific: Ethosuximide is highly effective for typical absence seizures but completely ineffective for focal seizures, generalised tonic-clonic seizures, or myoclonic seizures — always confirm diagnosis with EEG before initiating therapy.

1. Preferred in young females: Safer than valproate regarding teratogenicity and PCOS risk — first choice in adolescent girls and women of childbearing potential with absence epilepsy.

1. Poor response = wrong diagnosis: If seizures persist despite adequate dosing, reconsider the diagnosis — may indicate atypical absence, juvenile myoclonic epilepsy, or other generalised epilepsy requiring alternative therapy.

1. Availability issue: Limited retail availability in many parts of India — verify supply chain and consider alternatives (e.g., valproate, lamotrigine) if reliable access cannot be ensured.

1. No abrupt withdrawal: Always taper gradually over 2–4 weeks to prevent rebound seizures or status epilepticus.

1. Therapeutic drug monitoring: Not routinely available in most Indian centres — rely on clinical response and side effect profile for dose optimisation.

epilepsy; absence seizures; petit mal; antiepileptic; paediatric; succinimide; teratogenicity-low; blood-dyscrasia-risk; Schedule H

RxIndia v0.9 — 01 May 2025

• CDSCO product inserts

• Indian Pharmacopoeia

• NFI 2021

• API Textbook of Medicine

• AIIMS Neurology protocols

• IAP Guidelines for Epilepsy Management

• Goodman & Gilman's The Pharmacological Basis of Therapeutics

• Harrison's Principles of Internal Medicine