Loratadine
**Loratadine** is a second-generation, non-sedating H1-receptor antagonist used in veterinary medicine primarily for the management of allergic conditions such as atopic dermatitis, vaccine reactions, and insect envenomation. Unlike first-generation antihistamines (e.g., diphenhydramine, chlorpheniramine), loratadine does not readily cross the blood-brain barrier, significantly reducing the incidence of central nervous system depression and sedation. > **Clinical Warning:** Always ensure that human over-the-counter loratadine products do not contain decongestants like **pseudoephedrine** (often labeled as 'Claritin-D' or 'Allergy & Congestion'), as pseudoephedrine is highly toxic to dogs and cats, potentially causing fatal cardiovascular and neurologic stimulation. **Clinical Pearl:** Antihistamines are generally more effective as preventative agents rather than treatments for acute allergic flares, as they block the binding of new histamine but do not displace already bound histamine.
Mecanismo: Loratadine acts as a selective inverse agonist/antagonist at peripheral **H1 histamine receptors**. * **Histamine Blockade:** It competitively binds to H1 receptors on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract → prevents histamine from binding and exerting its pro-inflammatory and vasodilatory effects. * **Non-sedating:** Due to its lipophobic nature and large molecular size, it has poor penetration across the blood-brain barrier, resulting in minimal to no central H1 receptor blockade.
Vías de administración
Contraindicaciones
- Known hypersensitivity to loratadine or desloratadine
- Use with caution in patients with severe hepatic impairment
- Use with caution in patients with keratoconjunctivitis sicca (dry eye)
Efectos adversos
- Mild lethargy or sedation (rare compared to first-generation antihistamines)
- Vomiting
- Diarrhea
- Dry mouth (xerostomia)
- Decreased tear production
Interacciones farmacológicas
- Ketoconazole · May inhibit the metabolism of loratadine, increasing plasma concentrations · moderate
- Erythromycin · May inhibit the metabolism of loratadine, increasing plasma concentrations · moderate
- Cimetidine · May inhibit the metabolism of loratadine, increasing plasma concentrations · moderate
- Amiodarone · May increase loratadine levels via CYP inhibition · moderate
Monitoreo
- Resolution of allergic clinical signs (e.g., reduced pruritus, erythema)
- Adverse gastrointestinal effects
- Tear production (Schirmer Tear Test) if dry eye is suspected
Sobredosis
Loratadine has a wide margin of safety. Massive overdosage may cause tachycardia, somnolence, and headache. **Treatment:** Consists of standard gastrointestinal decontamination (emesis induction, activated charcoal) if ingestion is recent, followed by symptomatic and supportive care. Loratadine is not significantly removed by hemodialysis.
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