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chlormezanone

Centrally-acting muscle relaxant / anxiolytic (WITHDRAWN) · Skeletal muscle relaxant, Anxiolytic, Hypnotic

START
Use discouraged (withdrawn — SJS/TEN risk)
TYPICAL MAX
800 mg/day (historical)
STOP IF
Any rash, fever, or hypersensitivity feature
WATCH
Skin reactions (stop at first sign); LFTs
CDSCO approvedATC N05BX02
Dose laddermg/d
200per dose800max/day
Renal dose adjustmenteGFR mL/min/1.73m²
CAUTIONCaution; avoid if possible50AVOIDAvoid≥90

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours
45minONSET2hPEAK1dt½6hDURATION
ONSET
45min · absorption
PEAK
2h · peak effect
t½
1d · t½
DURATION
6h · per dose
EXCRETION
Renal — metabolites
route + CYP
INTERACTIONS
12 major
SEVERE in our sources
PREGNANCY
Avoid.
FDA category + note
Top interactionssee all 12 →
  • AlfentanilSevereDatabaseDDInter
  • BenzhydrocodoneSevereDatabaseDDInter
  • BuprenorphineSevereDatabaseDDInter
  • ButorphanolSevereDatabaseDDInter

Mechanism

Centrally-acting muscle relaxant and mild anxiolytic by poorly characterised CNS depressant mechanism (likely GABAergic facilitation).

Indications

Historical: muscle spasm associated with anxiety; mild anxiety. WITHDRAWN from most markets due to severe skin reactions (SJS/TEN).

Dosing

Adult
Historical: 200 mg PO 3–4 times daily; max 800 mg/day. Use discouraged/not available.
Pediatric
Not recommended.
Renal adjustment
Caution / avoid.
Hepatic adjustment
Avoid in hepatic impairment.
Geriatric
Avoid (sedation, falls).
Max dose
800 mg/day (historical ceiling)

Pharmacokinetics

Onset
~30–60 min (oral)
Peak effect
~2 h
Duration
~6 h
Half-life
~24 h
Bioavailability
Well absorbed orally
Protein binding
Moderate
Metabolism
Hepatic
Excretion
Renal (metabolites)

Contraindications

  • Hypersensitivity
  • Severe hepatic/renal impairment
  • Use generally not recommended (withdrawn)

Side effects

Common
DrowsinessDizzinessHeadacheNauseaDry mouth
Serious
  • Toxic epidermal necrolysis / Stevens-Johnson syndrome (withdrawal basis)
  • Severe hepatotoxicity (reported)
  • Drug-induced fever / hypersensitivity syndrome

Pregnancy & lactation

Pregnancy

Avoid.

Lactation

Avoid.

Drug interactions

Alfentanil
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Benzhydrocodone
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Buprenorphine
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Butorphanol
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Cns Depressants
Severe
Database

Additive CNS depression

Avoid combination

Source: Kimi deep-research + Cla

Codeine
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Dextropropoxyphene
Severe
Database

Drug interaction classified as: synergy, metabolism

Source: DDInter

Dihydrocodeine
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Fentanyl
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Hydrocodone
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Hydromorphone
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Levorphanol
Severe
Database

Drug interaction classified as: synergy

Source: DDInter

Related guidelines

Dengue fever
ICMR · Infectious Disease · 2022
Generalised anxiety disorder and panic disorder
NICE · Psychiatry · 2020
Alcohol use disorder
MOHFW · Psychiatry · 2021
Schizophrenia
IPS · Psychiatry · 2017
Systemic lupus erythematosus
EULAR · Rheumatology · 2023

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Sources: KD Tripathi 7e·Verified: 2026-05-20 · House clinical team·Cockpit curated: 2026-05-20