THERAPEUTICS

Brands

• Robaxin, Robaxin 750, Delaxin, Forbaxin

Generic?

• Yes

Class

• Muscle relaxant

Commonly Prescribed for

(FDA approved in bold)

• Musculoskeletal conditions (adjunct to rest and physical therapy for relief of acute pain)

• Muscle spasm

• Tetanus

How the Drug Works

• It is structurally similar to guaifenesin. Its mode of action is unclear but might be related to general CNS depression effect. It has no direct relaxant effect on muscle, nerve, or neuromuscular junction

How Long Until It Works

• Spasm pain: 30 minutes or less

If It Works

• Slowly titrate to most effective tolerated dose

If It Doesn't Work

• Increase to highest tolerated dose and consider alternative treatments

Best Augmenting Combos for Partial Response or Treatment-Resistance

• Use other centrally acting muscle relaxants with caution due to potential additive CNS depressant effect

• Can combine with NSAIDs for acute pain

Tests

• None

ADVERSE EFFECTS (AEs)

How the Drug Causes AEs

• Most AEs are due to CNS depression

Notable AEs

• Confusion, amnesia, dizziness, drowsiness, sedation, blurred vision, nystagmus, bradycardia, hypotension, pruritus, nasal congestion. Urine discoloration. Jaundice has been reported

Life-Threatening or Dangerous AEs

• Leukopenia, seizures, and anaphylactic reactions have been reported

Weight Gain

• Unusual

Sedation

• Common

What to Do About AEs

• Lower the dose or discontinue drug

Best Augmenting Agents to Reduce AEs

• Most AEs cannot be reduced by an augmenting agent

DOSING AND USE

Usual Dosage Range

• 4–8 g/day in divided doses

Dosage Forms

• Tablets: 500, 750mg

• Injection: 100mg/mL

How to Dose

• For acute muscle spasm, start 1500mg 4 times daily (max 8 g/day). Decrease dose to 1000mg 4 times daily or 1500mg 3 times daily after a few days

Dosing Tips

• Crushed tablets in water or saline can be given through a nasogastric tube