Chlorpromazine
Chlorpromazine is a centrally acting antiemetic and sedative. Veterinary regimens are mainly empirical.
Group
Phenothiazine antiemetic and tranquilizer
Mechanism of Action
Antagonizes central dopamine receptors and can block alpha-adrenergic and muscarinic receptors.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Vomiting | 0.5 mg/kg | IM, SC, IV | Every 6–8 h | Dilute IV product to no more than 1 mg/mL and administer slowly; monitor blood pressure. |
| Chemotherapy-associated vomiting | 2 mg/kg | SC | Every 3 h | Higher-dose alternative described in the administration discussion; evidence is empirical. |
| Vomiting | 0.2–0.4 mg/kg | SC, IM | Every 8 h | |
| Fixed-dose oral antiemetic treatment | Reference only | PO | 4–8 mg per dog orally every 12 hours, not exceeding 0.5 mg/kg per dose. Current schema cannot apply the per-kg ceiling to a fixed amount. | |
| Historical tetanus muscle-relaxant use | Reference only | IM | 2 mg/kg IM twice daily is described for tetanus, but the same monograph cautions against phenothiazines with tetanus or strychnine intoxication because of extrapyramidal effects. Retain the conflict rather than enable a routine regimen. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Vomiting | 0.2–0.4 mg/kg | IM, SC | Every 6–8 h | |
| Higher-dose antiemetic treatment | 0.5 mg/kg | IM, SC | Every 8 h | |
| Chemotherapy-associated vomiting | 2 mg/kg | SC | Every 3 h | Higher-dose alternative described in the administration discussion; evidence is empirical. |
| Vomiting | 0.5 mg/kg | IV, IM, SC | Every 6–8 h | Dilute IV product to no more than 1 mg/mL and administer slowly; monitor blood pressure. |
| Vomiting | 2 mg/animal | PO | Every 12 h | |
| Premedication | Reference only | IM | Up to 1.1 mg/kg IM 1–1.5 hours before surgery; no lower endpoint is supplied, so an artificial range is not generated. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Sedation | 0.22 mg/kg | IV | Once | |
| Sedation | 1.1 mg/kg | IM | Once |
Sheep
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Sedation | 0.55 mg/kg | IV | Once | |
| Sedation | 2.2 mg/kg | IM | Once | |
| Sedation | 0.55–4.4 mg/kg | IV | ||
| Sedation | 2.2–6.6 mg/kg | IM |
Goats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Sedation | 0.55 mg/kg | IV | Once | |
| Sedation | 2.2 mg/kg | IM | Once | |
| Sedation | 0.55–4.4 mg/kg | IV | ||
| Sedation | 2.2–6.6 mg/kg | IM | ||
| Sedation | 2–3.5 mg/kg | IV | Every 5–6 h |
Pigs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Sedation | 0.5 mg/kg | IM | Once | |
| Premedication | 1 mg/kg | IM | ||
| Sedation | 0.55–3.3 mg/kg | IV | ||
| Premedication | 2–4 mg/kg | IM | ||
| Restraint | 1.1 mg/kg | IM | Peak effect around 45–60 minutes. |
Indications
- Centrally mediated vomiting
- Sedation and premedication
Contraindications
- Avoid use in horses because violent reactions can occur.
- Use cautiously with seizure disorders or hypotension.
- Hypovolemia or shock; use cautiously in cardiac disease, hepatic impairment or severe debilitation.
- Do not inject IM into rabbits because of marked local injury.
- Tetanus or strychnine intoxication requires an alternative plan because of conflicting source advice.
Interactions
- Other sedatives increase CNS depression.
- Epinephrine during alpha blockade can cause paradoxical vasodilation and tachycardia; do not use it reflexively to correct phenothiazine-associated hypotension.
- Acetaminophen or dipyrone can add to hypothermia; antacids and adsorbent antidiarrheals can reduce oral absorption.
- Organophosphate exposure, quinidine and propranolol require particular interaction review.
Adverse effects
- Sedation
- Hypotension
- Antimuscarinic effects
- Extrapyramidal movements
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Chlorpromazine 10 mg tablet | Tablet | 10 mg / tablet | PO |
| Chlorpromazine 25 mg tablet | Tablet | 25 mg / tablet | PO |
| Chlorpromazine 50 mg tablet | Tablet | 50 mg / tablet | PO |
| Chlorpromazine 100 mg tablet | Tablet | 100 mg / tablet | PO |
| Chlorpromazine 200 mg tablet | Tablet | 200 mg / tablet | PO |
| Chlorpromazine 25 mg/mL injection | Injection | 25 mg / mL | IV, IM, SC |
Monitoring and Administration
Monitor cardiovascular tolerance and sedation. Chemotherapy-associated vomiting has also been treated with 2 mg/kg subcutaneously every 3 hours in the cited material.
Protect from light. Soft PVC containers may adsorb drug; slight discoloration alone is not proof of instability.
Chlorpromazine does not provide analgesia. Monitor blood pressure, rhythm and body temperature as indicated; anesthetic requirements may fall.
ABCB1/MDR1-mutant dogs can have exaggerated prolonged sedation; a cautious initial reduction of about 25% is described. Avoid using tranquilization alone to manage aggression.
IV administration requires dilution to 1 mg/mL or less and slow delivery. Do not use markedly darkened or precipitated solution; avoid prolonged storage in plastic syringes or bags.