Gabapentin

Gabapentinoid Anticonvulsant, Analgesic

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO Seizures: 10-20 mg/kg q8h; Pain: 10-20 mg/kg q8h; Anxiety: 10-20 mg/kg q12h (as needed) q8h for seizures/pain; q12h for anxiety Duration: Variable; for chronic conditions, long-term use may be required.
Notes: Start at lower end of dose and titrate up as needed. For renal impairment, reduce dose and/or extend interval.
Cat PO Pain: 5-10 mg/kg q12h; Seizures: 10-20 mg/kg q8h; Anxiety: 50-100 mg per cat q12h (as needed) q12h for pain/anxiety; q8h for seizures Duration: Variable; for chronic conditions, long-term use may be required.
Notes: Cats may require lower doses due to renal sensitivity. Use with caution in cats with kidney disease.
Horse PO Pain: 5-10 mg/kg q8-12h q8-12h Duration: Variable; for chronic pain, may be used long-term.
Notes: Oral bioavailability is low and variable; higher doses may be needed. Monitor for sedation.
Cattle PO Not established; off-label use: 10-20 mg/kg q12h (limited data) q12h Duration: Variable
Notes: Not approved for food animals; withdrawal times must be observed if used.
Small Ruminants (sheep/goats) PO Not established; off-label use: 10-20 mg/kg q12h (limited data) q12h Duration: Variable
Notes: Not approved for food animals; withdrawal times must be observed.
Rabbit PO 5-10 mg/kg q12h q12h Duration: Variable
Notes: Use with caution in rabbits with renal impairment.
Bird/Poultry PO Not established; limited data. May use 5-10 mg/kg q12h in some species. q12h Duration: Variable
Notes: Not approved for food birds; withdrawal times must be observed.
Exotic/Other (e.g., rats, mice) PO Rats: 5-10 mg/kg q12h; Mice: 10-20 mg/kg q12h (extrapolated) q12h Duration: Variable
Notes: Limited data; use with caution.

Clinical Indications & Species Uses

General Indications
  • Neuropathic pain
  • Seizure disorders (adjunctive)
  • Anxiety (off-label in some species)
Dog (Canine)
  • Seizure disorders (as adjunctive therapy for refractory epilepsy)
  • Chronic neuropathic pain (e.g., degenerative myelopathy, intervertebral disc disease, post-surgical pain)
  • Anxiety (e.g., noise phobias, separation anxiety, situational anxiety)
  • Chronic pain management (e.g., osteoarthritis, cancer pain)
Cat (Feline)
  • Chronic pain (especially neuropathic pain, e.g., feline orofacial pain syndrome, diabetic neuropathy)
  • Seizure disorders (adjunctive therapy)
  • Anxiety (e.g., situational anxiety, fear-related aggression)
  • Stress reduction during veterinary visits or travel
Horse (Equine)
  • Neuropathic pain (e.g., laminitis, chronic pain conditions)
  • Seizure disorders (rarely used, but may be considered for refractory seizures)
Rabbit & Small Mammals
  • Analgesia (especially for neuropathic pain, post-operative pain)
  • Anxiety (off-label use)
Exotic & Other Species
  • Rodents (e.g., rats, mice): Analgesia for neuropathic pain (off-label use)
  • Reptiles: Limited data; may be used for pain management in some species.

Pharmacology & Mechanism of Action

Drug Class: Gabapentinoid | Pharmacological Group: Anticonvulsant, Analgesic

Mechanism of Action: Gabapentin is a structural analog of the neurotransmitter gamma-aminobutyric acid (GABA), but it does not bind to GABA receptors or influence GABA uptake or degradation. Its exact mechanism of action is not fully understood. It binds with high affinity to the alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system, reducing calcium influx and subsequent release of excitatory neurotransmitters such as glutamate, norepinephrine, and substance P. This modulation of neurotransmitter release is thought to underlie its anticonvulsant, analgesic, and anxiolytic effects. Gabapentin also increases the synthesis and synaptic concentration of GABA in some brain regions, though this effect is less well characterized.

Pharmacodynamics: Gabapentin exhibits anticonvulsant activity by raising the threshold for seizure activity and reducing the spread of seizure activity from the seizure focus. It has analgesic properties, particularly in neuropathic pain, by modulating calcium channel activity and reducing excitatory neurotransmitter release. It also has anxiolytic effects, likely through similar mechanisms. In veterinary medicine, it is used for chronic pain (especially neuropathic), seizures, and anxiety. The onset of action for analgesia may take several days to weeks, while anxiolytic effects may be seen within hours to days.

⚑ Pharmacokinetics Summary

Absorption: Gabapentin is absorbed from the gastrointestinal tract via a saturable L-amino acid transporter. Absorption is dose-dependent, with bioavailability decreasing as the dose increases. In dogs, oral bioavailability is approximately 80% at low doses but decreases with higher doses. In cats, bioavailability is approximately 90% and is less dose-dependent. Food can affect absorption; in humans, food increases the rate but not the extent of absorption, but in animals, the effect is variable.
Distribution: Gabapentin distributes widely throughout the body, including the brain and cerebrospinal fluid. It is not extensively bound to plasma proteins (less than 3%). The volume of distribution is approximately 0.8 L/kg in dogs and 0.5 L/kg in cats. It crosses the placenta and is excreted in milk.
Metabolism: Gabapentin undergoes minimal metabolism in the body. It is not significantly metabolized by the liver; the majority of the drug is excreted unchanged in the urine. In humans, less than 5% is metabolized, and this is likely similar in animals.
Excretion: Gabapentin is primarily eliminated by renal excretion as unchanged drug. Renal clearance is proportional to creatinine clearance. In animals with renal impairment, the elimination half-life is prolonged, and dose adjustments are necessary. In dogs, the elimination half-life is approximately 3-4 hours; in cats, it is approximately 2-3 hours. In horses, the half-life is approximately 1-2 hours.
Half-Life: Dogs: 3-4 hours; Cats: 2-3 hours; Horses: 1-2 hours; Cattle: approximately 2-3 hours (limited data).
Bioavailability: Dogs: approximately 80% (dose-dependent); Cats: approximately 90%; Horses: approximately 16% (low and variable).
Protein Binding: Less than 3% bound to plasma proteins.

Available Formulations & Strengths

Oral Capsule 100 mg, 300 mg, 400 mg (PO)
Oral Tablet 600 mg, 800 mg (PO)
Oral Solution 50 mg/mL, 100 mg/mL (PO)
Compounded Suspension Various (e.g., 50 mg/mL) (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to gabapentin or any component of the formulation
  • Severe renal impairment (use with caution and dose adjustment)
  • Use in animals with known allergy to gabapentinoids
Warnings & Clinical Precautions:
  • Use with caution in animals with renal insufficiency; dose adjustment may be necessary.
  • Abrupt discontinuation may precipitate withdrawal symptoms (e.g., anxiety, seizures); taper dose gradually.
  • May cause sedation and ataxia, especially at higher doses; monitor animals during initial therapy.
  • Use with caution in pregnant or lactating animals; safety not established.
  • In food animals, observe withdrawal times; extra-label use requires veterinary oversight.
  • Gabapentin may cause respiratory depression when combined with other CNS depressants.
  • In cats, chronic use may lead to weight gain and lethargy.

Adverse Effects & Reactions

Common:

  • Sedation
  • Ataxia
  • Lethargy
  • Gastrointestinal upset (vomiting, diarrhea)

Serious / Severe:

  • Respiratory depression (especially with overdose or concurrent CNS depressants)
  • Acute renal failure (in animals with pre-existing renal disease)
  • Severe hypotension (rare)
  • Paradoxical excitement or agitation (rare)

Rare:

  • Hepatotoxicity
  • Blood dyscrasias (e.g., leukopenia)
  • Allergic reactions (e.g., skin rash, angioedema)
  • Peripheral edema

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Opioids (e.g., morphine, tramadol) Additive CNS depression and respiratory depression; monitor closely. High
Benzodiazepines (e.g., diazepam, midazolam) Additive sedation and respiratory depression. High
Antacids (aluminum/magnesium containing) Reduced absorption of gabapentin; separate administration by at least 2 hours. Moderate
Cimetidine May reduce renal clearance of gabapentin, increasing plasma levels. Moderate
NSAIDs (e.g., carprofen, meloxicam) Potential additive nephrotoxicity; monitor renal function. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe sedation
  • Ataxia
  • Coma
  • Respiratory depression
  • Hypotension
  • Tachycardia or bradycardia
  • Seizures (paradoxical)

Emergency Treatment Protocol: Treatment is primarily supportive. Induce emesis if ingestion is recent (within 1-2 hours) and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain blood pressure and enhance renal excretion. Monitor respiratory and cardiovascular status; provide oxygen and ventilatory support if needed. In severe cases, hemodialysis may be considered (gabapentin is dialyzable). There is no specific antidote. Symptomatic and supportive care is essential.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Gabapentin is not approved for use in food animals. If used extra-label, withdrawal times are not established. A conservative withdrawal period of at least 7 days for meat and 7 days for milk is often recommended, but veterinary oversight and adherence to regulatory guidelines are essential. For poultry, a withdrawal period of at least 7 days for meat and eggs is suggested.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25Β°C or 68-77Β°F).

Handling & Special Conditions: Protect from moisture. Keep in a tightly closed container. Compounded suspensions may require refrigeration; follow manufacturer's instructions.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use. Used extra-label in veterinary medicine.

Extra-Label (Off-Label) Use: Gabapentin is not FDA-approved for veterinary use in most species. Its use in animals is extra-label (AMDUCA). For food animals, extra-label use requires a valid veterinary-client-patient relationship, and withdrawal times must be established by the veterinarian. In the US, gabapentin is not a controlled substance, but it is a prescription drug.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Gabapentin is a versatile drug in veterinary medicine, primarily used for neuropathic pain, seizures, and anxiety. It is particularly useful in dogs and cats for chronic pain conditions that are poorly responsive to NSAIDs. In cats, it is often used for situational anxiety (e.g., veterinary visits) and chronic pain. Dosing should be individualized, starting at the lower end and titrating to effect. Because of its renal excretion, dose adjustments are necessary in animals with kidney disease. Abrupt discontinuation should be avoided; taper over 1-2 weeks. Gabapentin is generally well-tolerated, with sedation and ataxia being the most common side effects. It can be used in combination with other analgesics and anticonvulsants, but monitoring for additive CNS depression is important. In food animals, extra-label use is possible but requires careful consideration of withdrawal times and regulatory compliance.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)