Brand and Other Names:Robaxin
- Classes: Skeletal Muscle Relaxants
Dosing & Uses
Dosage Forms & Strengths
1 g IV/IM; additional doses at q8hr until PO; not to exceed 3 g/day
Total parenteral dose SHOULD NOT EXCEED 3 g/day for >3 days, unless treating tetanus; if condition persists, may repeat therapy after drug-free interval of 48 hr
1500 mg PO q6hr for 48-72 hours; not to exceed 8 g/day THEN decrease to 4-4.5 g/day divided q4-8hr
Adjunct therapy: Initial 1-2 g IV injection (at 300 mg/min), THEN
Additional 1-2 g IV infusion for total dose of 3 g initially
May repeat 1-2 g IV q6hr until can give NG or PO
Total of 24 g PO may be needed
Renal failure: Not studied; parenteral dosage form contraindicated due to presence of polyethylene glycol
Hepatic failure: Not studied
Dosage Forms & Strengths
<16 years: Safety and efficacy not established
>16 years: 1500 mg PO q6hr for 48-72 hours; not to exceed 8 g/day THEN decrease to 4-4.5 g/day divided q4-8hr
Considered safe in elderly because of short half-life
500 mg PO q6hr; may gradually titrate dose to response
Serious - Use Alternative
Significant - Monitor Closely
Frequency Not Defined
Mild muscular incoordination
Conjunctivitis with nasal congestion
Injection site pain (IV)
Increased Hgb and RBCs in urine (IV)
Renal impairment (parenteral)
May cause drowsiness/dizziness; patients should not ingest alcohol or other CNS depressants
May take with food to avoid stomach upset
Half-life increases with hepatic impairment
IV formulation not for use in renal impairment (contains polyethylene glycol; injection rate should not exceed 3 mL/min
May interfere with screening tests for 5-HIAA and vanillylmandelic acid (VMA)
Use injection with caution in patients with a history of seizures
Sedative effects potentiated when used with other sedatives
Medication is poorly tolerated in the elderly
Pediatric IV dosing approved only for tetanus
Pregnancy & Lactation
Pregnancy category: C
Lactation: Not known if excreted in breast milk; use caution
A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA:Information not available.
Mechanism of Action
Unknown; possibly general CNS depression induces skeletal muscle relaxation
Onset: 30 min
Peak serum time: 1-2 hr
Peak plasma concentration: 16.5-29.8 mcg/mL
Protein binding: 46-50%
Liver (dealkylation and hydroxylation)
Metabolites: Glucuronide and sulfate conjugates of 3-(2-hydroxyphenoxy)-1,2-propanediol-1-carbamate and 3-(4-hydroxy-2-methoxyphenoxy)-1,2-propanediol-1-carbamate; unidentified metabolites
Half-life: 0.9-1.8 hr
Direct IV: Administer undiluted at not to exceed 3 mL (=300 mg undiluted)/min
Infusion: Dilute 1 g with up to 250 mL D5W or NS; avoid extravasation, since injection is hypertonic
Monitor closely for extravasation
Administer IV while in recumbent position
Maintain position 15-30 min following infusion
Not to exceed 500 mg (5 mL undiluted) should be given into each gluteal region
Injection when diluted to 4 mg/mL in SWI, D5W, or NS is stable for 6 days at room temperature
Do not refrigerate after dilution
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