Methocarbamol
Methocarbamol reduces skeletal muscle spasm and selected toxin-induced tremors. It is not a substitute for analgesia.
Group
Centrally acting skeletal muscle relaxant
Mechanism of Action
Depresses polysynaptic reflex activity centrally without direct neuromuscular-junction blockade.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Moderate muscle spasm | 44 mg/kg | IV | Once | Give slowly to effect; reassess before any further dose. |
| Musculoskeletal spasm — Initial | 44 mg/kg | PO | Every 8 h | Up to 21 days; Oral initial regimen; maximum treatment period 14-21 days. If no response within five days, reassess rather than continuing. |
| Musculoskeletal spasm — Maintenance | 22–44 mg/kg | PO | Every 8 h | Up to 21 days; After initial response; maximum course 14-21 days. |
| Severe toxin-associated tremors | Reference only | IV | 55-220 mg/kg IV slowly to effect; maximum 330 mg/kg/day. A separate source gives up to 222 mg/kg with maximum cumulative 333 mg/kg. Retain these as distinct capped protocols, not an unrestricted calculated dose. | |
| Intervertebral disc-associated spasm | 15–20 mg/kg | PO | Every 8 h |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Moderate muscle spasm | 44 mg/kg | IV | Once | Give slowly to effect; reassess before any further dose. |
| Musculoskeletal spasm — Initial | 44 mg/kg | PO | Every 8 h | Up to 21 days; Oral initial regimen; maximum treatment period 14-21 days. If no response within five days, reassess rather than continuing. |
| Musculoskeletal spasm — Maintenance | 22–44 mg/kg | PO | Every 8 h | Up to 21 days; After initial response; maximum course 14-21 days. |
| Severe toxin-associated tremors | Reference only | IV | 55-220 mg/kg IV slowly to effect; maximum 330 mg/kg/day. A separate source gives up to 222 mg/kg with maximum cumulative 333 mg/kg. Retain these as distinct capped protocols, not an unrestricted calculated dose. | |
| Permethrin-associated tremors | Reference only | IV | Initially 50-150 mg/kg; give half slowly over 5-10 minutes, then the remainder as needed to effect. Repeat only within total maximum 330 mg/kg/day; severe cases may require a controlled infusion. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Moderate muscle spasm | 4.4–22 mg/kg | IV | Every 8 h | Slowly to effect; sedation/depression increases at higher doses. |
| Severe muscle spasm | 22–55 mg/kg | IV | Every 8 h | Slowly to effect; sedation/depression increases at higher doses. |
| Acute rhabdomyolysis-associated spasm | 15–25 mg/kg | IV | Slow IV infusion; may repeat up to four times daily if needed. | |
| Oral muscle relaxation | Reference only | PO | Source describes an oral amount 2-3 times the selected IV dose; this is a protocol-dependent relation rather than one universal oral range. |
Indications
- Musculoskeletal spasm
- Toxin-associated tremors
- Tetanus or strychnine-associated rigidity
Contraindications
- Injectable preparations containing polyethylene glycol are contraindicated in known or suspected renal pathology.
- Do not inject SC; avoid extravasation.
Interactions
- Other CNS depressants increase sedation.
- May oppose pyridostigmine effects in myasthenic patients.
Adverse effects
- Sedation, weakness, salivation, vomiting and ataxia.
Toxicity
Overdose causes marked CNS depression; protect the airway and provide supportive care.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Methocarbamol injection 100 mg/mL Do not give SC; avoid in renal disease if PEG-containing. Do not freeze; inspect diluted solutions for precipitation. | Injection | 100 mg / mL | IV |
| Methocarbamol 500 mg tablet | Tablet | 500 mg / tablet | PO |
Monitoring and Administration
For 100 mg/mL injection in dogs/cats do not exceed 2 mL/minute. Titrate slowly to relaxation and avoid extravasation.
Monitor muscle relaxation, respiratory effort and alertness. Do not induce vomiting in a depressed patient.
For severe protocols, distinguish the maximum of 330 mg/kg/day from the separately described 333 mg/kg cumulative maximum. These limits belong to different regimens and must not be combined or ignored.