Antispasmodic Agents Muscle Relaxants

Baclofen (Lioresal®): GABA receptor antagonist, descending pain modulation best for pain associated with spasticity through central pain modulating mechanisms. Oral tablets of 5 and 10 mg dosed TID; may titrate every 3 days to effect with maximum dose: 80 mg/day. Can cause sedation, dizziness, weakness, hypotension, nausea, respiratory depression, constipation; discontinue by slow taper; withdrawal syndrome consists of hallucinations, seizures; need to monitor liver function since it may increase alkaline phosphatase and AST levels; dose adjustment is necessary in patients with renal impairment. Baclofen is available for intrathecal administration to control severe spasticity. Initial intrathecal trial of 50-100 |xg to measure reduction in spasticity. Must be done in a monitored setting with resuscitation equipment available. Pyridostigmine (Antilirium®R ) 1 mg IV is the antidote.

Dantrolene: Oral administration is 25 mg QD x 7 days, then 25 mg TID x 7 days, then 50 mgTID x 7 days, then 100 mgTID. Blackbox warning about symptomatic fatal or nonfatal hepatitis; discontinue drug if no benefit is observed after 45 days.

Diazepam (Valium®R ): Adults: 2-10 mg TID-QID, elimination half-life 100 h: avoid in elderly, avoid in patients with renal or hepatic impairment. It has a significant abuse potential; dizziness, drowsiness, confusion; children >6 months: 1-2.5 mg half-life 20-50 h; active metabolites extend half-life up to 100 h. It must be withdrawn slowly from high doses to avoid seizures (4-6 weeks).

Tizanidine (Zanaflex®R ): a2-Adrenergic agonist, initial dose may have to be as low as 0.25 mg because of potential significant sedation. Titrate up to 2-4 mg every 6-8 h until relief or excessive side effects occur; hypotension, sedation, asthenia, and dry mouth (dose related) are frequent; need to monitor for elevated liver function enzyme levels and hepatotoxicity. Maximum dose recommended 36 mg/day.

Cyclobenzaprine (Flexeril®), 5 mg TID; may increase to 10 mg TID; elimination halflife ~18 h in young subjects, ~33 h in elderly, and ~46 h in patients with hepatic impairment.

Anticholinergic effects (drowsiness, urinary retention, dry mouth): avoid in elderly; QT prolongation: avoid in patients with arrhythmias, cardiac conduction disturbances, heart block, heart failure, or recent myocardial infraction; may raise intraocular pressure: avoid in patients with glaucoma.

Carisoprodol (Soma®®) 350 mg tablets; maximum recommended dose is TID or QID. Not recommended in children <12 years; drowsiness; can cause psychological and physical dependence (metabolized to meprobamate, a barbiturate tranquilizer), withdrawal symptoms can therefore occur with discontinuation; excessive use, overdose, or withdrawal may precipitate seizures; reports describe idiosyncratic or allergy-type reactions after first dose (mental status changes, transient quadriplegia, fever, angioneurotic edema, asthmatic episodes).

Chlorzoxazone (Parafon forte); Adults: 250-750 mg TID-QID. Dizziness and drowsiness may occur with rare cases of hepatotoxicity, gastrointestinal irritation, and rare cases of gastrointestinal bleeding; it may also cause red or orange urine; should be avoided in patients with liver impairment. Children: 125-500 mg TID-QID or 20 mg/kg/day in three or four divided doses; same side effects and toxicities can occur as in adults.

Metaxalone (Skelaxin®): 800 mg TID-QID. Not recommended in children <12 years; do not use in patients with renal or hepatic failure or a history of anemia; dizziness or drowsiness; rare cases of leukopenia or hemolytic anemia may occur. Reported to be less sedating than other muscle relaxants.

Methocarbamol (Robaxin®): 1,500 mg QID for the first 2-3 days, then 750 mg QID. Available orally in 500, 750, and 1,000 mg tablets. Robaxin is also available as an injectable. Do not use injection in patients with renal failure; may cause brown-to-black or green discoloration of urine; may impair mental status; may exacerbate symptoms of myasthenia gravis.

Orphenadrine (Norflex®): (available generic only) 100 mg BID; orally, combination products are given TID-QID: it should be avoided in the elderly; it may raise intraocular pressure and should therefore be avoided in patients with glaucoma; it can be associated with gastrointestinal disturbances; elimination half-life 13-20 h which may be extended when use is prolonged; it should be avoided in patients with cardiospasm or myasthenia gravis; and it is contraindicated in duodenal or pyloric obstruction or stenosing peptic ulcers. The anticholinergic effects (drowsiness, urinary retention, dry mouth) can be prominent.

Was this article helpful?

0 0
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment