Clobazam

Drug Class & Structure

Clobazam is a 1,5-benzodiazepine — structurally distinct from all other marketed benzodiazepines (diazepam, lorazepam, clonazepam), which are 1,4-benzodiazepines. The nitrogen atoms sit at positions 1 and 5 of the diazepine ring rather than 1 and 4. This structural difference underlies some of its unique pharmacologic profile, including preferential binding to the α2 subunit of the GABA-A receptor.

Mechanism of Action

Like all benzodiazepines, clobazam is a positive allosteric modulator of GABA-A receptors, enhancing the inhibitory effect of GABA (γ-aminobutyric acid) at chloride channels. This reduces neuronal excitability and suppresses seizure activity. The preferential α2 subunit affinity may contribute to its relatively favorable sedation profile compared to 1,4-benzodiazepines.

Approved Indications

Region	Indication
USA (FDA)	Adjunctive treatment of seizures associated with Lennox-Gastaut syndrome (LGS) in patients ≥2 years
Canada / UK / many countries	Broad-spectrum antiseizure agent for focal seizures, generalized seizures (as monotherapy or adjunct)

LGS is a severe epileptic encephalopathy characterized by multiple seizure types, including atonic ("drop") seizures. Clobazam is used in combination with valproate ± lamotrigine for atonic seizures in LGS. It is also used as adjunct therapy in Dravet syndrome (particularly in combination with stiripentol).

Pharmacokinetics

Parameter	Details
Half-life	10–30 hours (parent drug)
Effective dose	0.5–1 mg/kg/day
Metabolism	Hepatic — CYP and non-CYP pathways; ≥14 metabolites
Major metabolite	N-desmethylclobazam (norclobazam) — produced by CYP3A4, then further metabolized by CYP2C19
Norclobazam levels	8–20× higher than parent at steady state (longer half-life); likely the primary driver of chronic antiseizure effect
Norclobazam activity	Antiseizure activity weaker than clobazam, but dominant at therapeutic steady state

CYP2C19 poor metabolizers accumulate higher norclobazam levels → increased risk of adverse effects; dose reduction required.

Dosing (Lennox-Gastaut, FDA-approved)

Dosage increments no more rapid than every 7 days:

Weight	Initial	Day 8 (if needed)	Day 15 (if needed)
≤30 kg	5 mg once daily	5 mg BID	10 mg BID (max)
>30 kg	5 mg BID	10 mg BID	20 mg BID (max)

Formulations (brand: Onfi): Tablets 10 mg, 20 mg | Oral film (Sympazan) 5/10/20 mg | Oral suspension 2.5 mg/mL

Hepatic impairment or CYP2C19 poor metabolizers: Slower titration schedule; lower maximum doses apply.

Tolerance

Unlike 1,4-benzodiazepines, tolerance is not a prominent clinical issue with long-term clobazam use, despite being observed in animal models within days to weeks. This makes it more suitable for chronic antiepileptic therapy.

Adverse Effects

Dose-dependent:

Somnolence and sedation
Dysarthria
Drooling
Behavioral changes (including aggression)
Withdrawal can occur with abrupt discontinuation — taper required

Key Drug Interactions

Interaction	Effect
Cannabidiol (CBD)	CBD inhibits CYP2C19 → 3× increase in norclobazam levels → excessive sedation; may need clobazam dose reduction
Stiripentol	Inhibits CYP3A4/2C19 → markedly increases both clobazam and norclobazam concentrations (used intentionally in Dravet syndrome)
Clobazam inhibits CYP2D6	Increases levels of phenytoin, carbamazepine, and other CYP2D6 substrates
Carbamazepine, rifampin, theophylline	Inducers → decrease clobazam efficacy
Clobazam substrates: CYP2C19 (major), P-glycoprotein; CYP2B6 and 3A4 (minor)

Place in Therapy

First-line adjunct for LGS-associated seizures (FDA-approved)
Combination partner in Dravet syndrome with stiripentol or cannabidiol
Widely used internationally for focal epilepsy despite lack of FDA approval for this use
Preferred over 1,4-benzodiazepines for long-term seizure management due to lower tolerance development

Sources: Katzung's Basic & Clinical Pharmacology, 16th ed. | Harriet Lane Handbook, 23rd ed. | Goodman & Gilman's Pharmacological Basis of Therapeutics

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