10.2.2 Skeletal muscle relaxants

1st choiceBaclofen tablets 10mg; oral solution 5mg/5mLDose:
initially 5 mg 3 times daily, gradually increased; usual maintenance dose up to 60mg daily in divided doses (max. 100mg daily)
2nd choiceTizanidine tablets 2mg, 4mgDose:
initially 2mg daily as a single dose increased according to response at intervals of at least 3–4 days in steps of 2 mg daily (and given in divided doses) usually up to 24mg daily in 3–4 divided doses; max. 36mg daily

Monitor liver function monthly for first 4 months and in those who develop unexplained nausea, anorexia or fatigue
Diazepam tablets 2mg, 5mg, 10mg; oral solution 2mg/5mL, 5mg/5mL; injection (solution) 5ml/mL; injection (emulsion) 5ml/mL; rectal tubes 2mg/mL

Muscle spasm, by mouth, 2–15mg daily in divided doses, increased if necessary in spastic conditions to 60mg daily according to response

By intramuscular or by slow intravenous injection (into a large vein at a rate of not more than 5 mg/minute), in acute muscle spasm, 10mg repeated if necessary after 4 hours

Note: only use intramuscular route when oral and intravenous routes not possible; emulsion formulation preferred for intravenous injection; special precautions for intravenous injection - 'facilities for reversing respiratory depression with mechanical ventilation must be immediately available'


Prescribing Notes

  • Refer also to the Central Nervous System (Chapter 4) section of the Northern Ireland Formulary.
  • Skeletal muscle relaxants are used for the relief of chronic muscle spasm or spasticity associated with multiple sclerosis or other neurological damage; they are not indicated for spasm associated with minor injuries. Skeletal muscle relaxants differ in action from the muscle relaxants used in anaesthesia (BNF Chapter 15 ), which block transmission at the neuromuscular junction.
  • The underlying cause of spasticity should be treated and any aggravating factors (e.g. pressure sores, infection) remedied. Skeletal muscle relaxants are effective in most forms of spasticity, except the rare alpha variety. The major disadvantage of treatment with these drugs is that reduction in muscle tone can cause a loss of splinting action of the spastic leg and trunk muscles and sometimes lead to an increase in disability.
  • Serious side-effects can occur following abrupt withdrawal of baclofen; therapy should be discontinued by gradual dose reduction over at least 1-2 weeks (longer if symptoms occur).
  • Benzodiazepines (most notable diazepam) should be used only if there is clinical evidence of muscle spasm that is painful or causing disability.
  • In the case of back or neck pain, benzodiazepines should be discontinued after a maximum period of 5-7 days. Further prescriptions should only be issued after assessment of the patient and the identification of persistent muscle spasm.
  • There is rarely any place for regular muscle relaxants in the management of back and neck pain.
  • The clinical efficacy of methocarbamol as a muscle relaxant is not well established. It is classed by the BNF as ‘less suitable for prescribing’ and is not generally recommended.



  • Quinine should only be used when nocturnal leg cramps regularly disrupt sleep. Trials show patients experience only one less episode per week taking quinine compared with placebo and that cramp duration is not significantly affected.
  • Although well tolerated at doses used for leg cramps, patients should be warned that quinine is toxic in overdose.
  • Healthcare professionals are advised to only consider quinine:
    • when cramps are very painful or frequent
    • when other treatable causes of cramp have been ruled out
    • when non-pharmacological measures (e.g. passive stretching exercises) have been ineffective
  • Treatment should be stopped if there is no benefit after an initial trial of four weeks. If treatment continues, benefit should be assessed every 3 months. In patients taking quinine long term, a trial discontinuation should be considered- Quinine Prescribing Review Tool.
  • Quinine should be used with caution in people with risk factors for QT prolongation or in those with atrioventricular block. For further details see MHRA.