Methocarbamol (Robaxin) Dosing Regimen
The recommended initial dosage of methocarbamol (Robaxin) for adults is 1500 mg (two 750 mg tablets) four times daily for the first 48-72 hours, followed by a maintenance dosage of 750 mg (one tablet) every 4 hours or 1500 mg (two tablets) three times daily. 1
Detailed Dosing Guidelines
Initial Therapy (First 48-72 hours)
- For 500 mg tablets: 3 tablets (1500 mg) four times daily
- For 750 mg tablets: 2 tablets (1500 mg) four times daily
- Total daily dose: 6 grams per day (for severe conditions, up to 8 grams per day may be administered)
Maintenance Therapy (After 48-72 hours)
- For 500 mg tablets: 2 tablets (1000 mg) four times daily
- For 750 mg tablets: 1 tablet (750 mg) every 4 hours or 2 tablets (1500 mg) three times daily
- Total daily dose: Approximately 4 grams per day
Administration Considerations
Route of Administration
- Methocarbamol is primarily administered orally
- Intravenous formulation exists but has additional considerations:
- Contains polyethylene glycol (PEG) as an excipient
- PEG has been implicated in metabolic acidosis and nephrotoxicity in patients with renal impairment 2
- Use with caution in patients with kidney disease
Special Populations
- Elderly patients: Consider starting at the lower end of the dosing range
- Patients with renal impairment: Use with caution, especially with IV formulation
- Patients with hepatic impairment: No specific dosing adjustments are provided in the available evidence
Efficacy and Clinical Use
- Methocarbamol is effective for acute low back pain associated with muscle spasms 3
- In clinical trials, 44% of patients treated with methocarbamol achieved complete pain relief compared to 18% with placebo 3
- Only 19% of methocarbamol-treated patients discontinued due to ineffective treatment compared to 52% in the placebo group 3
Important Precautions
Drug Interactions
- Alcohol: Avoid concurrent use with alcohol as this combination can lead to enhanced central nervous system depression due to interactive sedative-hypnotic properties 4
- The combination of methocarbamol and alcohol has been associated with fatal outcomes in case reports 4
Adverse Effects
- Generally well-tolerated when used as directed
- Common side effects may include drowsiness, dizziness, and lightheadedness
- No severe adverse effects were observed in clinical studies (only 7 symptoms reported in 5 patients) 3
Duration of Treatment
- Typically prescribed for short-term use (days to weeks)
- Treatment should be discontinued once muscle spasms resolve or adequate pain relief is achieved
Remember that methocarbamol is a muscle relaxant with sedative properties, so patients should be cautioned about activities requiring mental alertness until they know how the medication affects them.