Felbamate
**Felbamate** is a unique dicarbamate **anticonvulsant** used primarily as a 2nd- or 3rd-line antiseizure medication in dogs. * Particularly useful for **complex partial seizures** and generalized seizures. * **Clinical Pearl**: Unlike many other anticonvulsants, felbamate does *not* typically cause additive sedation when combined with phenobarbital or potassium bromide, making it an attractive add-on therapy. * Due to its short half-life, it requires strict three-times-daily (TID) dosing. * Cost and accessibility can be limiting factors for veterinary patients. * Because of its limited use in veterinary medicine, the full adverse effect profile may be incomplete.
Mechanism: Felbamate reduces excitatory neurotransmission and enhances inhibitory pathways. * Increases activation of **voltage-gated sodium channels** → decreases sustained high-frequency firing of action potentials. * **NMDA Receptor Antagonism**: Blocks the **NR2B subunit** of the **NMDA receptor** → prevents glutamate-mediated excitation. * **GABA_A Modulation**: Acts as a positive allosteric modulator at **GABA_A receptors** → enhances chloride influx and neuronal hyperpolarization.
Dosing by species
- Seizures (As either add-on therapy or monotherapy) · 15 mg/kg PO q8h. Dose can be increased in 15 mg/kg increments every 2 weeks until seizures are controlled. Doses as high as 70 mg/kg q8h are required and tolerated in some dogs. · PO · q8h · Starting dose is 15 mg/kg.
- Seizures (As a third choice antiepileptic agent) · 15-65 mg/kg PO q8h · PO · q8h · Steady state reached after 4th oral dose. Monitor CBC and liver function tests as you would for phenobarbital. Therapeutic serum concentration reported to be 15-100 micrograms/mL.
- Seizures (For patients on phenobarb and bromides and seizure activity unchanged or having intolerable side effects) · 5-20 mg/kg PO three times daily · PO · TID · If intolerable side effects, do levels and decrease the dose of the one that is in the high end of the range. Then add felbamate.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Hypersensitivity to felbamate or other carbamates (e.g., meprobamate)
Adverse effects
- Keratoconjunctivitis sicca (KCS)
- Liver enzyme induction
- Tremor
- Limb rigidity
- Salivation
- Restlessness and agitation (at high doses)
- Blood dyscrasias (thrombocytopenia, lymphopenia, leukopenia)
- Sedation (usually when combined with other anticonvulsants)
- Vomiting/nausea (usually when combined with other anticonvulsants)
Drug interactions
- Phenobarbital · Felbamate may increase phenobarbital levels. Phenobarbital may decrease felbamate levels.
- Phenytoin · Felbamate may increase phenytoin levels. Phenytoin may decrease felbamate levels.
- Valproate · Felbamate can cause increases in valproic acid levels.
Monitoring
- Liver function tests (q2-3 months recommended by some clinicians)
- Complete Blood Count (CBC) (q2-3 months recommended by some clinicians)
- Therapeutic drug levels (25-100 micrograms/mL range, though usefulness is questionable)
- Seizure frequency and severity
Overdose
Limited veterinary information is available. * In humans, a massive overdose (12 grams over 12 hours) resulted only in mild gastric distress and a slightly increased heart rate. * Treatment should be supportive and symptomatic. Consider gastric decontamination if ingestion is recent and the patient is neurologically stable.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.