Clemastine
Clemastine is a first-generation **ethanolamine antihistamine** used for the symptomatic relief of histamine-mediated allergic conditions. Key pharmacological characteristics include: * **Higher anticholinergic activity** compared to many other antihistamines. * **Lower sedative profile** than average first-generation antihistamines. * **Poor oral bioavailability** in dogs (3%) and horses (3-4%), making oral administration highly questionable for achieving therapeutic systemic exposure in these species. > **Clinical Pearl:** Recent pharmacokinetic studies suggest that traditional oral dosing regimens in dogs and horses are likely subtherapeutic. Intravenous administration may be required for reliable efficacy in these species.
Mecanismo: Like other first-generation antihistamines, clemastine acts as a competitive antagonist (or inverse agonist) at **H1-receptors**. * **Mechanism:** Competes with histamine for H1-receptor sites on effector cells (smooth muscle, endothelium, CNS) → prevents histamine-induced bronchoconstriction, vasodilation, and increased capillary permeability. * **Note:** It does *not* block the release of histamine from mast cells or basophils, but rather antagonizes its downstream effects. * Exhibits significant **anticholinergic (antimuscarinic)** activity, which contributes to both its drying effects on mucous membranes and potential side effects.
Dosificación por especie
- Antihistamine · 0.68 mg per cat PO twice daily · PO · q12h
- Antihistamine · 0.34-0.68 mg per cat PO q12h · PO · q12h
- Atopy · 0.15 mg/kg PO q 12 hrs · PO · q12h · Efficacy may be increased by combining with omega 3 fatty acids.
- Allergic conditions (Historical dosing - Efficacy doubtful) · 0.05-0.1 mg/kg PO q12h · PO · q12h · Oral bioavailability is <5%. An oral dose of 0.5 mg/kg only slightly inhibited wheal formation. Further dosing studies are needed before recommending therapeutic oral use.
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
- Known hypersensitivity to clemastine
Efectos adversos
- Sedation (dogs)
- Paradoxical hyperactivity (dogs)
- Anticholinergic effects: dry mucous membranes, tachycardia, urinary retention
- Diarrhea (cats)
- Fixed drug reaction (cats - rare)
Interacciones farmacológicas
- CNS Depressant Medications (e.g., barbiturates, tranquilizers) · Additive CNS depression may occur.
- Monoamine Oxidase Inhibitors (e.g., furazolidone, amitraz, selegiline) · May intensify the anticholinergic effects of clemastine.
- CNS Depressants (e.g., phenobarbital, gabapentin, opioids) · Additive CNS depression and sedation · moderate
- Anticholinergic drugs · Additive anticholinergic effects (dry mouth, urinary retention) · moderate
Monitoreo
- Clinical efficacy (reduction in pruritus, allergic signs)
- Adverse effects (sedation, hyperactivity, anticholinergic signs)
Sobredosis
There are no specific antidotes for clemastine overdose. * **Management:** Handle significant overdoses using standard gut-emptying protocols (emesis/gastric lavage) when appropriate, followed by supportive therapy. * **Clinical Signs:** Overdose signs are extensions of the drug's side effects, principally **CNS depression** (though CNS stimulation/seizures may occur), severe **anticholinergic effects** (severe drying of mucous membranes, tachycardia, urinary retention, hyperthermia), and possibly hypotension. * **Specific Treatments:** **Physostigmine** may be considered to treat serious CNS anticholinergic effects. **Diazepam** can be employed to treat seizures if necessary.
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.