Carbamazepine
Carbamazepine is a dibenzoazepine iminostilbene derivative that is chemically related to the tricyclic antidepressant imipramine. > **Clinical Pearl:** While widely used in human medicine as a primary anticonvulsant and mood stabilizer, its utility in veterinary medicine (particularly in dogs) is severely limited by its rapid hepatic autoinduction. Dogs metabolize the drug so quickly after a few days of therapy that maintaining therapeutic serum levels becomes exceedingly difficult. Because of this pharmacokinetic limitation, it is rarely used for seizure control in animals. Instead, in veterinary medicine, it is primarily reserved for: * **Behavioral medicine** in dogs (e.g., managing amygdalar hyperactivity or explosive aggression, often alongside SSRIs). * **Neuropathic pain** or specific neurologic conditions like **photic head shaking** in horses that are refractory to other treatments like cyproheptadine.
Mechanism: Carbamazepine primarily acts by **blocking voltage-gated sodium channels** in neuronal membranes. * **Mechanism:** Binds preferentially to the inactive state of sodium channels โ delays their recovery โ **inhibits repetitive neuronal firing** and stabilizes hyperexcited neural membranes. * It also decreases the synaptic transmission of excitatory impulses and may reduce the release of the excitatory neurotransmitter glutamate. * Structurally related to tricyclic antidepressants, it also possesses mild anticholinergic, antidiuretic, and muscle relaxant properties.
Dosing by species
- For photic head shaking ยท 10 mg/kg PO q6h or 29 mg/kg PO q12h ยท PO ยท q6h or q12h ยท May be helpful in some horses that do not respond to cyproheptadine.
- As a psychotherapeutic agent ยท 4-8 mg/kg PO q12h ยท PO ยท q12h ยท Not commonly used, but may have some utility in dogs that seem to have amygdalar hyperactivity; sometimes used in conjunction with SSRIs to control explosive aggression.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Patients receiving MAO Inhibitors (e.g., selegiline) within the past 14 days
- Patients with a history of bone marrow depression
- Known hypersensitivity to carbamazepine or tricyclic antidepressants
Adverse effects
- Sedation and lethargy
- Ataxia (unsteadiness)
- Gastrointestinal upset (vomiting, anorexia)
- Hepatotoxicity (elevated liver enzymes)
- Blood dyscrasias (rare but possible bone marrow suppression)
Drug interactions
- Azole Antifungals (e.g., Ketoconazole, Itraconazole) ยท May increase plasma levels or effects of carbamazepine
- Calcium Channel Blockers (e.g., Diltiazem, Verapamil) ยท May increase plasma levels or effects of carbamazepine; Carbamazepine may also decrease their effects
- Cimetidine ยท May increase plasma levels or effects of carbamazepine
- Danazol ยท May increase plasma levels or effects of carbamazepine
- Grapefruit Juice ยท May increase plasma levels or effects of carbamazepine
- Isoniazid ยท May increase plasma levels or effects of carbamazepine; Carbamazepine may also increase effects of Isoniazid
- Macrolides (e.g., Erythromycin, Clarithromycin) ยท May increase plasma levels or effects of carbamazepine
- MAO Inhibitors (e.g., Selegiline) ยท Contraindicated; discontinue MAOI at least 14 days prior to carbamazepine
- Niacin ยท May increase plasma levels or effects of carbamazepine
- SSRI Antidepressants (e.g., Fluoxetine) ยท May increase plasma levels or effects of carbamazepine
- Tricyclic Antidepressants (e.g., Clomipramine, Amitriptyline) ยท May increase plasma levels or effects of carbamazepine; Carbamazepine may also decrease their effects, though it can increase Clomipramine levels
Monitoring
- Complete Blood Count (CBC)
- Liver function tests
- Clinical efficacy and behavioral changes
Overdose
Overdose can lead to significant CNS depression, severe ataxia, tremors, seizures, respiratory depression, and cardiovascular abnormalities (tachycardia, hypotension). Treatment is primarily supportive and symptomatic, including gastric decontamination if caught early, IV fluids, and respiratory support. Seizures should be treated with standard anticonvulsants (e.g., diazepam, phenobarbital).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.