Chlorpromazine
Chlorpromazine is the prototype **phenothiazine** derivative, historically used as a neuroleptic and tranquilizer in veterinary medicine, though largely supplanted by acepromazine for these purposes due to acepromazine's higher potency and shorter duration of action. Currently, it is primarily utilized for its **antiemetic properties** in small animals, particularly for managing motion sickness in cats. **Key Clinical Points:** * Effectively inhibits apomorphine-induced emesis in dogs (but not cats) and morphine-induced emesis. * Does not inhibit emesis caused by copper sulfate or digitalis glycosides. * Possesses **negligible analgesic effects**; appropriate analgesia must be provided for painful conditions. * Generally contraindicated in horses due to paradoxical excitation and ataxia. * Can cause significant vasodilation and hypotension; patients must be adequately hydrated prior to administration.
Mecanismo: Chlorpromazine acts primarily as a **dopamine (D2) receptor antagonist** in the central nervous system. * **Antiemetic effect:** Blocks D2 receptors in the Chemoreceptor Trigger Zone (CRTZ) of the medulla → inhibits emetic signaling to the vomiting center. * **Sedative effect:** Antagonizes central **histamine (H1)**, **alpha-1 adrenergic**, and **dopamine** receptors → depresses the reticular activating system. * **Cardiovascular effect:** Peripheral **alpha-1 adrenergic blockade** → vasodilation and potential hypotension. * Also possesses weak anticholinergic (muscarinic M1 blockade) and antiserotonergic properties.
Dosificación por especie
- General use · 0.55-4.4 mg/kg IV, 2.2-6.6 mg/kg IM · IV/IM · Once
- General use · 0.55-4.4 mg/kg IV, 2.2-6.6 mg/kg IM · IV/IM · Once
- General use · 2-3.5 mg/kg IV q5-6h · IV · q5-6h
- As an antiemetic · 0.5 mg/kg IV, IM or SC three to four times daily · IV/IM/SC · q6-8h
- As an antiemetic · 2 mg (total dose) per cat PO q12h · PO · q12h
- As a preanesthetic · up to 1.1 mg/kg IM 1-1.5 hours prior to surgery · IM · Once
- Premedication for cattle undergoing standing procedures · Up to 1 mg/kg IM · IM · Once · May cause regurgitation if animal undergoes general anesthesia
- Premedication · 1 mg/kg IM · IM · Once
- Premedication · 0.55-3.3 mg/kg IV; 2-4 mg/kg IM · IV/IM · Once
Vías de administración
Contraindicaciones
- Horses (generally not recommended due to severe ataxia and panic reactions)
- Rabbits (IM injection causes severe muscle discomfort and swelling)
- Hypovolemia or shock
- Tetanus or strychnine intoxication (due to extrapyramidal effects)
Efectos adversos
- Hypotension
- CNS stimulation (paradoxical)
- Bradycardia or tachycardia
- Extrapyramidal signs in cats (tremors, shivering, rigidity, loss of righting reflexes)
- Lethargy
- Diarrhea
- Loss of anal sphincter tone
- Ataxia, excitation, and panic reactions in horses
- Hypothermia or hyperthermia
Interacciones farmacológicas
- Acetaminophen · Possible increased risk for hypothermia
- Antacids · May cause reduced GI absorption of oral phenothiazines
- Antidiarrheal mixtures (e.g., kaolin/pectin, bismuth subsalicylate) · May cause reduced GI absorption of oral phenothiazines
- CNS Depressant Agents (barbiturates, narcotics, anesthetics) · May cause additive CNS depression
- Dipyrone · May cause serious hypothermia
- Epinephrine · Phenothiazines block alpha-adrenergic receptors; concomitant epinephrine can lead to unopposed beta-activity causing vasodilation and increased cardiac rate (epinephrine reversal)
- Opiates · May enhance hypotensive effects; chlorpromazine dosages may need reduction
- Organophosphate Agents · Effects may be potentiated; do not give phenothiazines within one month of worming with these agents
- Paraquat · Toxicity may be increased by chlorpromazine
- Phenytoin · Metabolism may be decreased if given concurrently
- Physostigmine · Toxicity may be enhanced by chlorpromazine
- Procaine · Activity may be enhanced by phenothiazines
Monitoreo
- Cardiac rate, rhythm, and blood pressure (if indicated and possible)
- Degree of tranquilization and anti-emetic activity
- Body temperature (especially in extreme ambient temperatures)
Sobredosis
Small overdoses typically cause somnolence. Larger overdoses can cause serious effects including **coma, agitation/seizures, ECG changes/arrhythmias, hypotension, and extrapyramidal effects**. * **Treatment:** Most overdoses are managed with supportive care and monitoring. Massive oral overdoses should be treated by emptying the gut if possible. * **Hypotension Management:** Do NOT treat hypotension with epinephrine (due to epinephrine reversal). Use **phenylephrine** or **norepinephrine** (levarterenol). * **Seizure Management:** Control seizures with barbiturates or diazepam.
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