Mechanism of Action of Cenobamate
Cenobamate exerts its antiseizure effects through a dual mechanism: selective inhibition of persistent sodium currents (INaP) while sparing transient sodium currents (INaT), combined with positive allosteric modulation of GABAA receptors at a site independent of the benzodiazepine binding site. 1
Sodium Channel Modulation
Cenobamate demonstrates a preferential and selective blockade of persistent sodium currents (INaP) at therapeutic concentrations, a characteristic that appears unique among antiseizure medications 2, 3. This selectivity is clinically significant because:
- INaP plays a pivotal role in repetitive and burst generation of action potentials, which are fundamental to seizure propagation 3
- The drug has minimal effect on transient sodium currents (INaT), which are responsible for normal neuronal signaling 3
- This selective inhibition reduces repetitive neuronal firing without substantially impairing normal neuronal function 1
Additionally, cenobamate:
- Shifts steady-state fast inactivation of sodium channels toward a hyperpolarizing range, indicating higher affinity binding to inactivated channel states 3
- Accelerates development of inactivation and retards recovery from inactivation 3
- Increases the threshold for action potential generation and decreases the number of action potentials during depolarizing stimuli 3
GABAA Receptor Modulation
Cenobamate acts as a positive allosteric modulator of GABAA receptors, but critically, this occurs at a binding site independent of the benzodiazepine receptor 1, 4. Key features include:
- Preferential enhancement of tonic (extrasynaptic) GABAA currents over phasic (synaptic) currents 2, 4
- The EC50 for enhancing tonic currents is 36.63 μM, compared to 164 μM for GABA-induced currents 4
- This effect is not blocked by flumazenil, confirming the non-benzodiazepine mechanism 4
- Cenobamate shows similar potency across GABAA receptors containing different alpha subunits (α1-6), with EC50 values ranging from 42-194 μM 4
Clinical Implications of the Dual Mechanism
The combination of selective INaP inhibition and extrasynaptic GABAA modulation may represent an emerging class of antiseizure medications 2. This dual mechanism likely explains:
- Cenobamate's broad-spectrum activity in preclinical seizure models 2
- The unprecedented seizure freedom rates (21-52.4%) observed in clinical trials, which exceed those of other sodium channel blockers 2, 5
- Potential efficacy in conditions like Dravet syndrome (a sodium channelopathy typically aggravated by traditional sodium channel blockers), as suggested by real-world evidence 2
Important Caveat
While these two mechanisms have been well-characterized, the FDA label explicitly states that "the precise mechanism by which cenobamate exerts its therapeutic effects in patients with partial-onset seizures is unknown" 1. This acknowledgment suggests that additional, yet-to-be-identified mechanisms may contribute to cenobamate's clinical efficacy, particularly given that changes in motor thresholds with transcranial magnetic stimulation do not fully correlate with clinical response 6.