Methocarbamol Dosing in Adults
For adults requiring methocarbamol, the FDA-approved dosing is 1,500 mg four times daily (6 grams/day) for the first 48-72 hours, which may be increased to 8 grams/day for severe conditions, followed by a maintenance dose of 4 grams/day. 1
Initial Dosing Regimen
The FDA prescribing information provides two tablet strength options for achieving the recommended initial dose 1:
- 500 mg tablets: 3 tablets four times daily (6 grams/day)
- 750 mg tablets: 2 tablets four times daily (6 grams/day)
For severe musculoskeletal conditions, the initial dose may be escalated to 8 grams/day during the first 48-72 hours 1.
Maintenance Dosing
After the initial 48-72 hour period, reduce to approximately 4 grams/day 1:
- 500 mg tablets: 2 tablets four times daily
- 750 mg tablets: 1 tablet every 4 hours, or 2 tablets three times daily
Duration of Treatment
Clinical evidence demonstrates that treatment duration should be individualized based on symptom resolution. In a randomized controlled trial of acute low back pain, 44% of methocarbamol-treated patients achieved complete pain relief and discontinued treatment early (versus 18% with placebo), with treatment lasting up to 8 days 2.
Critical Safety Considerations
Avoid concurrent alcohol use: A fatal drug interaction has been documented with combined methocarbamol and ethanol ingestion, resulting in severe CNS depression due to the interactive sedative-hypnotic properties of both substances 3. Blood methocarbamol concentrations in the fatal case reached 257 mcg/mL, far exceeding therapeutic levels of 24-41 mcg/mL 3.
Abuse potential at supratherapeutic doses: Methocarbamol demonstrates dose-dependent increases in subjective drug liking and euphoric effects at doses of 2.25-9 grams in single-dose studies, though dysphoric side effects at high doses likely limit abuse potential compared to benzodiazepines 4.
Polyethylene glycol concerns with IV formulation: While IV methocarbamol contains polyethylene glycol (PEG) as an excipient, and the prescribing information warns of potential metabolic acidosis and nephrotoxicity in renal impairment, objective data supporting these claims remain lacking since the drug's 1959 FDA approval 5.