Hydrocodone Bitartrate — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.22 mg/kg (0.1 mg/lb) for cough; for analgesia, 0.5-1 mg/kg	q8-12h for cough; q6-8h for pain	Duration: As needed for cough; for pain, short-term (up to 3-5 days) Notes: Titrate to effect; monitor for sedation and respiratory depression. Use lowest effective dose.
Cat	PO	0.5-1 mg/kg (extrapolated; not well studied)	q8-12h	Duration: Short-term; monitor closely Notes: Use with caution; cats may be more sensitive to adverse effects. Not FDA-approved for cats.
Horse	PO	Not established	Not established	Duration: Not established Notes: Not recommended; other opioids preferred.
Cattle	PO	Not established	Not established	Duration: Not established Notes: Not recommended; prohibited in food animals in many countries.
Small Ruminants	PO	Not established	Not established	Duration: Not established Notes: Not recommended.
Rabbit	PO	Not established	Not established	Duration: Not established Notes: Not recommended; use safer alternatives.
Bird/Poultry	PO	Not established	Not established	Duration: Not established Notes: Not recommended.
Exotic/Other	PO	Not established	Not established	Duration: Not established Notes: Not recommended.

Clinical Indications & Species Uses

General Indications

Antitussive for nonproductive cough
Analgesic for moderate pain (off-label in some species)

Dog (Canine)

Cough suppression (antitussive) in chronic bronchitis, tracheal collapse, and other respiratory conditions
Analgesia (moderate to severe pain) – though less commonly used for pain in dogs compared to other opioids

Pharmacology & Mechanism of Action

Drug Class: Opioid analgesic; antitussive | Pharmacological Group: Opioid agonist (mu-opioid receptor agonist)

Mechanism of Action: Hydrocodone is a semi-synthetic opioid agonist that primarily acts on mu-opioid receptors in the central nervous system. It also has some activity at delta and kappa receptors. Its analgesic effects are mediated by activation of descending inhibitory pain pathways, while its antitussive effect is due to direct suppression of the cough center in the medulla. It also produces euphoria, sedation, and respiratory depression.

Pharmacodynamics: Hydrocodone produces dose-dependent analgesia, antitussive effects, sedation, and respiratory depression. It can cause histamine release leading to pruritus and vasodilation. In dogs, it is more potent as an antitussive than codeine. It may cause constipation due to decreased gastrointestinal motility. Chronic use can lead to physical dependence and tolerance.

⚡ Pharmacokinetics Summary

Absorption: Hydrocodone is well absorbed after oral administration. Peak plasma concentrations occur within 1-2 hours in dogs. Food may delay absorption but not the extent.

Distribution: Widely distributed throughout the body. It crosses the blood-brain barrier and placenta. Volume of distribution is approximately 3-5 L/kg in dogs. Protein binding is low (about 20-30%).

Metabolism: Extensively metabolized in the liver via O-demethylation to hydromorphone (active metabolite) and N-demethylation to norhydrocodone. CYP2D6 and CYP3A4 enzymes are involved. In dogs, the metabolism is similar but with species-specific differences.

Excretion: Primarily excreted in urine as metabolites and unchanged drug. A small amount is excreted in feces. In dogs, the elimination half-life is approximately 1-2 hours.

Half-Life: Dogs: 1-2 hours; Cats: not well documented; Horses: not well documented

Bioavailability: Oral bioavailability in dogs is approximately 60-70% due to first-pass metabolism.

Protein Binding: Approximately 20-30%

Available Formulations & Strengths

Oral Tablet 2.5 mg, 5 mg, 7.5 mg, 10 mg (often combined with homatropine or acetaminophen) (PO)

Oral Solution 1 mg/mL, 5 mg/5 mL (often combined with homatropine) (PO)

Oral Capsule 5 mg, 10 mg (extended-release formulations available) (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to hydrocodone or other opioids
Severe respiratory depression or acute asthma
Paralytic ileus
Concurrent use with MAO inhibitors (or within 14 days)
Use in animals with head trauma or increased intracranial pressure
Use in animals with severe hepatic or renal impairment (use with caution)
Use in animals with hypothyroidism, Addison's disease, or prostatic hypertrophy (use with caution)

Warnings & Clinical Precautions:

Use with caution in animals with respiratory compromise, as it can cause respiratory depression.
May cause sedation and CNS depression; avoid concurrent use with other CNS depressants.
May cause histamine release; use with caution in animals with mast cell tumors or asthma.
Can cause constipation; monitor bowel function.
May cause physical dependence with prolonged use; taper dose when discontinuing.
Use with caution in geriatric or debilitated animals.
In cats, may cause excitation or paradoxical reactions.
Not approved for use in food animals; extra-label use is prohibited in some countries.
Keep out of reach of children and pets; store securely due to abuse potential.

Adverse Effects & Reactions

Common:

Sedation
Constipation
Decreased respiratory rate
Miosis (pupil constriction)
Vomiting
Nausea
Anorexia

Serious / Severe:

Respiratory depression
Bradycardia
Hypotension
Ileus
Seizures (rare)
CNS excitation (especially in cats)
Addiction/dependence

Rare:

Allergic reactions (urticaria, anaphylaxis)
Pancreatitis
Urinary retention
Hyperalgesia (paradoxical pain)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Other opioids	Additive CNS and respiratory depression	High
Benzodiazepines	Increased sedation and respiratory depression	High
Barbiturates	Additive CNS depression	High
MAO inhibitors	Severe hypotension, respiratory depression, coma (avoid concurrent use)	High
Tricyclic antidepressants	Increased risk of serotonin syndrome and CNS depression	Moderate
Anticholinergics	Increased risk of constipation and urinary retention	Moderate
CYP3A4 inhibitors (e.g., ketoconazole)	Increased hydrocodone levels and toxicity	Moderate
CYP2D6 inhibitors (e.g., fluoxetine)	Decreased conversion to hydromorphone, potentially reduced efficacy	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Severe respiratory depression
Extreme sedation
Coma
Miosis (pinpoint pupils)
Hypotension
Bradycardia
Hypothermia
Muscle flaccidity
Pulmonary edema (rare)

Emergency Treatment Protocol: Maintain airway and provide respiratory support (intubation and mechanical ventilation if needed). Administer naloxone (opioid antagonist) at 0.01-0.04 mg/kg IV, IM, or SC; may need repeated doses or continuous infusion. Monitor for re-narcotization. Provide supportive care: IV fluids, temperature regulation, and cardiovascular support. In severe cases, consider activated charcoal if ingestion was recent (within 1-2 hours) and airway is protected.

Food Animal Withdrawal Times

Not approved for use in food animals. Extra-label use is prohibited in the US and many other countries. No withdrawal times established.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F); excursions permitted between 15-30°C (59-86°F)

Handling & Special Conditions: Store in a tightly closed container, protected from moisture. Keep in a secure location due to controlled substance status.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for human use; not FDA-approved for veterinary use, but may be prescribed legally in veterinary practice under extra-label drug use rules.

Extra-Label (Off-Label) Use: In the US, hydrocodone is a Schedule II controlled substance. Extra-label use in animals is permitted under AMDUCA only with a valid veterinarian-client-patient relationship. However, for food animals, extra-label use of opioids is prohibited due to lack of withdrawal times and potential for residues. In some countries, use in food animals is completely banned.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Hydrocodone is primarily used in veterinary medicine as an antitussive in dogs, particularly for chronic bronchitis and tracheal collapse. It is often combined with homatropine to reduce abuse potential. As an analgesic, it is less commonly used than other opioids like morphine or fentanyl due to its lower potency and oral bioavailability. It is a controlled substance with high abuse potential, so it must be stored securely and prescribed with caution. In cats, its use is limited due to potential for CNS excitation. It is not recommended for food animals. Always monitor for respiratory depression and sedation, especially when used with other CNS depressants. For pain management, consider alternative opioids with better safety profiles. When discontinuing after prolonged use, taper the dose to avoid withdrawal symptoms.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)