Drug	Recommended dosage	Most common adverse effects	Comments	Monthly cost*
Carisoprodol (Soma)1	350 mg four times daily Not recommended for children younger than 12 years	Dizziness, drowsiness, headache Rare idiosyncratic reactions (mental status changes, transient quadriplegia, and temporary loss of vision) after first dose; may require hospitalization Allergy-type reactions may occur after the first to fourth dose; may be mild (e.g., cutaneous rash) or more severe (e.g., asthma attack, angioneurotic edema, hypotension, or anaphylactic shock); antihistamines, epinephrine, or corticosteroids may be needed	Physical or psychological dependence may occur; withdrawal symptoms may occur with discontinuation Possible respiratory depression when combined with benzodiazepines, barbiturates, codeine or its derivatives, or other muscle relaxants Contraindicated in acute intermittent porphyria FDA pregnancy category C	$72 to $100 (generic) $590 (brand)
Chlorzoxazone (Parafon Forte)2	Adults: 250 to 750 mg three to four times daily Children: 125 to 500 mg three to four times daily; or 20 mg per kg daily in three or four divided doses	Dizziness, drowsiness Red or orange urine GI irritation and rare GI bleeding Hepatoxicity (rare); discontinue with elevated liver function test	Avoid use in patients with hepatic impairment Possible respiratory depression when combined with benzodiazepines, barbiturates, codeine or its derivatives, or other muscle relaxants FDA pregnancy category C	15 to 77 (generic) 180 (brand)
Cyclobenzaprine (Flexeril)3	5 mg three times daily; may increase to 10 mg three times daily	Anticholinergic effect (drowsiness, dry mouth, urinary retention, increased intraocular pressure) Rare but serious adverse effects are arrhythmias, seizures, myocardial infarction	Most studied skeletal muscle relaxant	120 to 140 (generic) 157 (brand)
			Long elimination half-life
			5-mg dose as effective as 10-mg, with fewer adverse effects
			Avoid in older patients and in patients with glaucoma
			Possible drug interaction with CYP450 inhibitors
			Seizures reported with concomitant use of tramadol (Ultram); combination should be avoided in patients with medical conditions that may induce seizures
			Contraindicated in patients with arrhythmias, recent myocardial infarction, or congestive heart failure
			FDA pregnancy category B
Diazepam (Valium)4	Adults: 2 to 10 mg three to four times daily Children: 0.12 to 0.80 mg per kg daily in three or four divided doses	Dizziness, drowsiness, confusion Abuse potential	Also an antispastic agent	11 to 23 (generic) 184 (brand)
			Long elimination half-life; avoid in older patients and in patients with hepatic impairment
			Possible drug interaction with CYP450 inhibitors
			Complete blood count and liver function tests indicated for prolonged use
			FDA pregnancy category D; avoid especially in the first trimester
Metaxalone (Skelaxin)5	800 mg three to four times daily Not recommended in children younger than 12 years	Drowsiness, dizziness, headache, nervousness Leukopenia or hemolytic anemia (rare) Liver function test elevation (rare) Nausea, vomiting, and diarrhea (rare) Paradoxical muscle cramps	Use with caution in patients with liver failure Possible respiratory depression when combined with benzodiazepines, barbiturates, codeine or its derivatives, or other muscle relaxants Less dizziness and drowsiness than other skeletal muscle relaxants FDA pregnancy category C	275; generic not available
Methocarbamol (Robaxin)6	1,500 mg four times daily for first two to three days, followed by 750 mg four times daily	Black, brown, or green urine possible Mental status impairment Possible exacerbation of myasthenia gravis symptoms	Possible respiratory depression when combined with benzodiazepines, barbiturates, codeine or its derivatives, or other muscle relaxants FDA pregnancy category C; reports of fetal abnormalities	15 to 58 (generic) 176 (brand)
Orphenadrine (Norflex)7	100 mg twice daily Combination products are dosed three to four times daily	Anticholinergic effect (drowsiness, dry mouth, urinary retention, increased intraocular pressure) Aplastic anemia (rare) GI irritation Confusion, tachycardia, hypersensitivity reaction (with high doses)	Long elimination half-life	110 to 140 (generic) 162 (brand)
			Reduced dosages in older patients
			Avoid in patients with glaucoma, cardiospasm, or myasthenia gravis
			Decreases effect of phenothiazines (e.g., chlorpromazine [Thorazine†], promethazine [Phenergan])
			FDA pregnancy category C
Tizanidine (Zanaflex)8,9	4 mg initially; may increase by 2 to 4 mg every six to eight hours until relief Do not exceed 36 mg daily	Dose-related hypotension, sedation, and dry mouth Hepatotoxicity; monitor liver function tests at baseline and one, three, and six months Withdrawal and rebound hypertension may occur in patients discontinuing therapy after receiving high doses for long period of time; tapering is recommended	Also antispastic agent	329 (generic) 437 (brand)
			Do not use with CYP1A2 inhibitors, ciprofloxacin (Cipro) or fluvoxamine (Luvox CR)
			Caution with CYP1A2 inhibitors, central nervous system depressants, or alcohol
			Decreased effectiveness with oral contraceptives
			FDA pregnancy category C