Mirtazapine
Mirtazapine is an atypical tetracyclic antidepressant widely utilized in veterinary medicine primarily as a potent **appetite stimulant** and **antiemetic** for dogs and cats. * **Clinical Pearl**: It is particularly beneficial for patients with chronic kidney disease (CKD), congestive heart failure, GI disorders, liver disease, or neoplasia, where it addresses both nausea and inappetence. * It can be safely combined with other antiemetics for refractory vomiting or chemotherapy-induced nausea and vomiting (CINV). * The primary dose-limiting side effect is sedation, though paradoxical excitation (vocalization, increased affection) is frequently observed in cats. > **Important**: Always use the lowest effective dose to minimize sedative properties. Do not exceed 30 mg/day in dogs, as higher doses paradoxically lose appetite-stimulating effects.
Mecanismo: Mirtazapine has a complex, multi-receptor pharmacological profile (often classified as a NaSSA - Noradrenergic and Specific Serotonergic Antidepressant): * **Central pre-synaptic α2-adrenergic receptors**: Antagonism blocks the negative feedback loop → **increases Norepinephrine (NE)** release → stimulates appetite via other α-receptors. * **5-HT3 receptors**: Potent antagonism in the Chemoreceptor Trigger Zone (CRTZ) and GI tract → provides robust **anti-nausea and antiemetic** effects. * **5-HT2 receptors**: Antagonism contributes to its anxiolytic profile. * **H1 (Histamine) receptors**: Potent antagonism → produces prominent **sedative effects**. * **Peripheral α1-adrenergic & Muscarinic receptors**: Moderate antagonism → may cause occasional orthostatic hypotension and mild anticholinergic effects.
Dosificación por especie
- As an appetite stimulant and/or antiemetic · 3.75 mg (¼ of a 15 mg tablet) · PO · q72h (every 3 days)
- As an appetite stimulant and/or antiemetic · 3 mg per cat · PO · q72h (every 3 days)
- As an appetite stimulant and/or antiemetic · 3-4 mg per cat · PO · q72h (every 3 days)
- Appetite stimulation · 1.9 mg/cat · PO · q48h · Can double dose if needed or increase frequency to q24h but not both.
- As an appetite stimulant and/or antiemetic · 0.6 mg/kg · PO · q24h · Not to exceed 30 mg per day for appetite stimulation
- As an appetite stimulant and/or antiemetic · >75 lb. = 15 mg PO q12h or 30 mg PO q24h (once daily) · PO · q12h or q24h
- Appetite stimulation / Management of social fears · 1.1-1.3 mg/kg · PO · q24h · Anecdotal use for social fears.
Las dosis son una referencia clínica para médicos veterinarios. Confirme siempre con la información vigente del producto y el paciente individual.
Vías de administración
Contraindicaciones
- Hypersensitivity to mirtazapine
- Use of monoamine oxidase inhibitors (MAOIs, e.g., selegiline) within the past 14 days
- Pre-existing haematological disease
Efectos adversos
- Drowsiness/sedation
- Vocalization (especially in cats)
- Increased affection (cats)
- Hypotension
- Tachycardia
- Sedation (common and can be profound)
- Increased vocalization (especially in cats)
- Altered behavior and increased interaction with others
- Blood dyscrasias (reported in humans)
Interacciones farmacológicas
- CLONIDINE · Mirtazapine may cause increases in blood pressure
- DIAZEPAM (and other benzodiazepines) · Minimal effects on mirtazapine blood levels, but may cause additive impairment of motor skills
- FLUVOXAMINE · May cause increased serum concentrations of mirtazapine
- LINEZOLID · Increased risk for serotonin syndrome
- SELEGILINE, AMITRAZ · Increased risk for serotonin syndrome; MAO inhibitors considered contraindicated with mirtazapine
- TRAMADOL · Increased risk for serotonin syndrome
- Other behaviour-modifying drugs (e.g., SSRIs, MAOIs) · Increased risk of serotonin syndrome · major
Monitoreo
- Increased appetite
- Decreased episodes of vomiting
- Weight gain
- Adverse effects (sedation, vocalization, tachycardia)
- Appetite and body weight
- Behavioral changes (sedation, vocalization)
- Complete blood count (due to human risk of blood dyscrasias)
- Hepatic and renal function parameters
Sobredosis
Ingestion of upwards of 10-fold to 30-fold the therapeutic dose in humans exhibits minimal toxicity requiring no acute intervention other than observation. > **Treatment**: Despite the wide safety margin, standard overdose protocols (including the administration of **activated charcoal**) and monitoring are recommended in acute overdose situations.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.