Methocarbamol
Guaiphenesin carbamate
Also known as: Robaxin-V · Robaxin-750 · Guaiphenesin carbamate · Labycarbol · Laxan · Lumirelax · Miowas · Musxan · Myocin · Myomethol · Ortoton · Remisol · Rexivin · Robinax · Traumacut · Methocarbamolum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Relief of moderate conditions | 44 mg/kg IV | IV | As directed | — | 🌎 NA |
| Controlling severe effects of strychnine and tetanus | 55-220 mg/kg IV | IV | As directed | — | 🌎 NA |
| General muscle relaxation (Tablets) | Initially, 132 mg/kg/day PO divided q8h-q12h, then 61-132 mg/kg divided q8-12h | PO | q8h-q12h | Discontinue if no response in 5 days | 🌎 NA |
| Muscle relaxation for intervertebral disk disease (IVDD) | 15-20 mg/kg PO three times daily | PO | TID | — | 🌎 NA |
| Muscle relaxation for certain toxicosis (e.g., strychnine, metaldehyde, tetanus) | 150 mg/kg IV | IV | As directed | — | 🌎 NA |
| Control severe tremors associated with tremorgenic Mycotoxin intoxication | 55-220 mg/kg IV to effect at a rate no more than 2 mL/minute | IV | As directed | — | 🌎 NA |
| Control tremors associated with Guarana (caffeine) toxicity | 50-220 mg/kg IV, administered slowly and to effect; do not exceed 330 mg/kg/day | IV | As directed | — | 🌎 NA |
| General muscle spasms, tetanus, toxicities | 20-45 mg/kg | PO | q8h | As needed | 🌍 EU |
- Relief of moderate conditions: Administer half the estimated dose rapidly, then wait until animal starts to relax and continue administration to effect.
- Controlling severe effects of strychnine and tetanus: Do not exceed 330 mg/kg/day. Administer half the estimated dose rapidly, then wait until animal starts to relax and continue administration to effect.
- General muscle spasms, tetanus, toxicities: Very high doses may be required for tetanus. Recommended not to exceed 330 mg/kg.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Relief of moderate conditions | 44 mg/kg IV | IV | As directed | — | 🌎 NA |
| Controlling severe effects of strychnine and tetanus | 55-220 mg/kg IV | IV | As directed | — | 🌎 NA |
| General muscle relaxation (Tablets) | Initially, 132 mg/kg/day PO divided q8h-q12h, then 61-132 mg/kg divided q8-12h | PO | q8h-q12h | Discontinue if no response in 5 days | 🌎 NA |
| Adjunctive treatment (control of seizures/muscle tremors) of permethrin toxicity | initially administered at 50-150 mg/kg IV | IV | As directed | — | 🌎 NA |
| General muscle spasms, tetanus, toxicities | 20-45 mg/kg | PO | q8h | As needed | 🌍 EU |
- Relief of moderate conditions: Administer half the estimated dose rapidly, then wait until animal starts to relax and continue administration to effect.
- Controlling severe effects of strychnine and tetanus: Do not exceed 330 mg/kg/day. Administer half the estimated dose rapidly, then wait until animal starts to relax and continue administration to effect.
- Adjunctive treatment (control of seizures/muscle tremors) of permethrin toxicity: First half is given IV slowly over approximately 5-10 minutes and the second half of the dose being given as needed to effect. The dose can be repeated up to a maximum of 330 mg/kg/day; in severely affected cases, the total daily dose can be calculated and given over 24 hours as a constant rate infusion.
- General muscle spasms, tetanus, toxicities: Very high doses may be required for tetanus. Recommended not to exceed 330 mg/kg. Limited literature in cats.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Moderate conditions | 4.4-22 mg/kg IV to effect | IV | As directed | — | 🌎 NA |
| Severe conditions | 22-55 mg/kg IV | IV | As directed | — | 🌎 NA |
| General muscle relaxation | 15-25 mg/kg IV by slow infusion | IV | As directed | — | 🌎 NA |
| Oral administration | Use 2-3 times the recommended IV dose | PO | As directed | — | 🌎 NA |
| Acute rhabdomyolysis | 15-25 mg/kg slow IV infusion | IV | May repeat up to four times daily if needed | — | 🌎 NA |
- Moderate conditions: ARCI UCGFS Class 4 Drug
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of CNS hyperactivity | 110 mg/kg IV | IV | As directed | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Methocarbamol is a centrally acting skeletal muscle relaxant structurally related to guaifenesin. It is widely used in veterinary medicine to treat acute inflammatory and traumatic conditions of skeletal muscle, as well as to manage severe muscle spasms and tremors.
Clinical Pearls:
- Highly effective and frequently used as a life-saving intervention for permethrin toxicity in cats and tremorgenic mycotoxin (e.g., moldy food) ingestions in dogs.
- Available in both oral and injectable formulations.
- The injectable formulation contains polyethylene glycol (PEG) 300, which can exacerbate pre-existing renal pathology; therefore, the IV form should be used with caution or avoided in patients with significant kidney disease.
- Does not directly relax contracted skeletal muscles but works via central nervous system depression.
Mechanism of action
The exact mechanism of action of methocarbamol is not fully understood, but it is known to act centrally rather than peripherally.
- Central CNS Depression: It is believed to cause skeletal muscle relaxation by general central nervous system depression, likely depressing polysynaptic reflexes in the internuncial neurons of the spinal cord.
- No Peripheral Action: It has no direct relaxant effects on striated muscle, nerve fibers, or the motor endplate.
- Secondary Effects: Produces a secondary sedative effect due to its generalized CNS depressant properties.
Safety & warnings
Contraindications
- Food-producing animals
- Renal disease (injectable formulation only, due to PEG 300 vehicle)
- Known hypersensitivity to methocarbamol
- Subcutaneous (SC) administration
- No specific contraindications available, but use with caution in renal or hepatic impairment.
Adverse effects
- Sedation
- Salivation
- Emesis
- Lethargy
- Weakness
- Ataxia
Precautions
Administration Warnings:
- Intravenous Use: Give IV slowly. Do not exceed a rate of 2 mL/minute in dogs and cats. Avoid extravasation as it can cause tissue irritation.
- Do NOT administer subcutaneously (SC).
Organ System Warnings:
- Renal Impairment: The injectable product contains polyethylene glycol (PEG) 300, which can increase pre-existing acidosis and urea retention. Avoid IV use in patients with known or suspected renal pathology.
- Working Animals: May impair the abilities of working animals due to CNS depressant effects.
Reproductive/Nursing:
- FDA Category C for pregnancy. Use with caution as a last resort when benefits clearly outweigh risks. Safety during lactation is unknown, though considered compatible with breastfeeding in humans.
Laboratory Considerations:
- May falsely elevate urinary values of vanillylmandelic acid (VMA) or 5-HIAA.
Drug interactions
Additive CNS depression may occur when given concurrently.
May cause severe weakness (reported in a human patient with myasthenia gravis).
Additive CNS depression
Monitoring
- Level of muscle relaxation
- Degree of sedation
- Respiratory rate and effort (especially with high IV doses or concurrent CNS depressants)
- Degree of muscle relaxation
- CNS depression/sedation levels
- Renal and hepatic function (if prolonged use)
Pharmacokinetics
Half-life
Absorption
In humans, onset of action is about 30 minutes after oral administration. Peak levels occur approximately 2 hours after dosing.
Distribution
Limited pharmacokinetic data is available in veterinary species.
Metabolism
The drug is metabolized to inactive metabolites. Guaifenesin is a minor metabolite of methocarbamol, but due to very low concentrations, it likely has no clinical effect.
Elimination
Inactive metabolites are excreted primarily into the urine, with small amounts in the feces. In horses, plasma clearances appear to be dose-dependent after IV administration (lower clearances measured after higher doses).
Overdose
Signs of Toxicity: Overdosage is generally characterized by profound CNS depressant effects, including loss of righting reflex and prostration. Excessive doses in dogs and cats may manifest as emesis, salivation, severe weakness, and ataxia.
Management:
- Decontamination: If the overdose occurred recently via oral administration, emptying the gut (e.g., emesis induction or gastric lavage) may be indicated. Do not induce emesis if the patient's continued consciousness and airway protection are not assured.
- Supportive Care: Treat other clinical signs supportively if severe. Monitor respiratory and cardiovascular function closely.
Available products
Formulations
- Injection
- Oral: 500 mg, 750 mg tablets
Veterinary
- Methocarbamol Tablets: 500 mg (Robaxin-V)
- Methocarbamol Injection: 100 mg/mL in vials of 20 mL and 100 mL (Robaxin-V)
Human-labeled
- Methocarbamol Tablets: 500 mg & 750 mg (Robaxin, Robaxin-750, generic)
- Methocarbamol Injection: 100 mg/mL in 10 mL vials (Robaxin)
- Robaxin 500 mg tablets
- Robaxin 750 mg tablets
Regulatory status
POM (Prescription Only Medicine)
POM
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets at room temperature in tight containers. Store the injection at room temperature and do not freeze. Solutions prepared for IV infusion should not be refrigerated as a precipitate may form. Because a haze or precipitate may form, all diluted intravenous solutions should be physically inspected before administration.
Client information
Important Note: Your pet's urine color may darken (sometimes appearing black, brown, or green) while on this medication. This is a harmless side effect and need not be a concern.
- Sedation and Clumsiness: This medication commonly causes drowsiness, lethargy, and uncoordinated walking (ataxia). Keep your pet in a safe, confined area away from stairs, furniture they might jump off, or other hazards to prevent injury.
- Administration: Give exactly as prescribed. If you miss a dose, do not double up on the next one.
- Side Effects to Report: Contact your veterinarian if your pet experiences severe vomiting, excessive drooling, or becomes so weak they cannot stand.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.