Acetaminophen (Paracetamol)
A centrally acting analgesic and antipyretic with little clinically useful peripheral anti-inflammatory activity. It is used for selected canine pain cases and has been studied in horses.
Contraindicated in cats because even small exposures may cause life-threatening oxidative blood injury and hepatic damage.
Group
Non-opioid analgesic and antipyretic
Mechanism of Action
Analgesia is attributed mainly to central modulation of prostaglandin-dependent pain pathways; serotonergic and other central mechanisms may contribute. Its precise mechanism is incompletely resolved.
At excessive exposure, reactive metabolites overwhelm detoxification pathways and damage hepatocytes and erythrocytes. Cats have limited glucuronidation capacity and are particularly susceptible.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Analgesia | 15 mg/kg | PO | Every 8 h | Do not use in: Significant hepatic disease, Concurrent acetaminophen-containing medication; Assess hepatic risk before repeated treatment; monitor liver enzymes during prolonged use. |
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Use prohibited | Reference only | PO | Do not use in: All cats; No therapeutic regimen: acetaminophen can cause fatal oxidative blood injury and hepatotoxicity. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Analgesia | 20 mg/kg | PO | Every 24 h | Older once-daily regimen; optimal clinical efficacy and dosing interval remain uncertain. |
| Analgesia | 20 mg/kg | PO | Every 12 h | Repeated-dose pharmacokinetic and safety regimen studied for 14 days in healthy adult horses; therapeutic efficacy and duration require clinical assessment. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Analgesia and antipyresis — Loading | 50 mg/kg | PO | Once | Calves only; loading component of a sequential regimen. Clinical efficacy and food-residue withdrawal remain insufficiently established. |
| Analgesia and antipyresis — Maintenance | 30 mg/kg | PO | Every 6 h | Calves only; follows the loading component. Clinical efficacy and food-residue withdrawal remain insufficiently established. |
Indications
- Mild-to-moderate pain in dogs, often as part of multimodal analgesia.
- Selected equine pain cases; optimal clinical dosing remains incompletely established.
- Antipyretic activity.
Contraindications
- Do not administer to cats.
- Avoid in significant hepatic disease or previous acetaminophen hypersensitivity.
- Prevent simultaneous exposure to other acetaminophen-containing medicines.
- Renal disease, poor nutritional status and repeated exposure can increase toxicity concerns.
- Food-animal use lacks a universal validated withdrawal interval.
Interactions
- Other acetaminophen-containing products cause cumulative exposure and overdose.
- Hepatotoxic drugs and hepatic enzyme modifiers may increase risk; the extent of individual interactions in animals is incompletely characterized.
- Codeine combinations do not reliably improve canine analgesia and restrict independent adjustment of the ingredients.
Adverse effects
- Vomiting, depression and reduced appetite.
- Dose-dependent hepatotoxicity.
- Methemoglobinemia, Heinz body formation and hemolysis.
- Facial or paw edema, cyanosis and respiratory distress in intoxicated animals.
- Acute kidney injury and, in dogs, keratoconjunctivitis sicca may accompany intoxication.
Toxicity
Toxicity may follow a single overdose or repeated excessive dosing. Cats can become ill after very small doses; canine toxicity thresholds do not define a safe repeated dose. Suspected exposure requires prompt assessment, N-acetylcysteine and supportive care. Monitor methemoglobin, blood counts, hepatic enzymes and renal function.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Calpol 500 mg | Tablet | 500 mg / tablet | PO |
| Calpol 650 mg | Tablet | 650 mg / tablet | PO |
| Calpol 120 mg/5 mL Oral Suspension Shake before measuring. | Oral Liquid | 120 mg / 5 mL | PO |
| Calpol 250 mg/5 mL Oral Suspension Shake before measuring. | Oral Liquid | 250 mg / 5 mL | PO |
| Calpol Paediatric Drops 100 mg/mL Suspension; shake before measuring. Dose by volume, not an assumed drop size. | Oral Liquid | 100 mg / mL | PO |
| Children’s Tylenol 160 mg/5 mL Oral Suspension Shake before measuring. | Oral Liquid | 160 mg / 5 mL | PO |