Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
SOMA vs CHLORZOXAZONE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Centrally acting muscle relaxant; acts at brainstem reticular formation and spinal cord levels to inhibit polysynaptic reflexes, possibly via GABAergic and monoaminergic pathways.
Chlorzoxazone acts centrally on the spinal cord and subcortical areas of the brain to inhibit multisynaptic reflex arcs involved in producing and maintaining muscle spasm. It may also have some sedative effects.
Acute musculoskeletal pain (FDA-approved),Off-label: chronic low back pain, muscle spasms associated with neurological disorders
Adjunct for relief of acute painful musculoskeletal conditions associated with muscle spasm
250 mg to 350 mg orally three times daily and at bedtime.
250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.
1-2 hours; prolonged to 3-4 hours in hepatic impairment; parent drug rapidly cleared via CYP2C19 metabolism to meprobamate (active, t1/2 6-16 hours).
Terminal elimination half-life approximately 1–2 hours; clinically relevant for muscle relaxant effect duration.
Hepatic via CYP2C19 and CYP3A4; also undergoes dealkylation and hydroxylation.
Hepatic, primarily via CYP2E1, also CYP1A2 and CYP3A4
Renal: ~60-70% as metabolites (including meprobamate and glucuronide conjugates); fecal: minimal; biliary: negligible.
Primarily hepatic metabolism followed by renal excretion of metabolites; <1% excreted unchanged in urine; minor biliary/fecal elimination.
~60% bound to albumin.
Approximately 90–95% bound, primarily to albumin.
0.7-1.0 L/kg; consistent with moderate tissue distribution.
0.46–0.64 L/kg; indicates distribution into total body water.
Oral: ~100% (rapidly and completely absorbed).
Oral: nearly complete; rapidly absorbed with extensive first-pass metabolism; systemic bioavailability approximately 30–50% due to first-pass effect.
No specific dose adjustment guidelines; use with caution in severe renal impairment (GFR <30 m L/min).
No specific guidelines; use with caution in severe renal impairment (GFR <30 m L/min) due to potential accumulation of active metabolite.
Contraindicated in severe hepatic impairment (Child-Pugh class C). Use with caution in mild to moderate impairment; reduce dose or extend dosing interval.
Contraindicated in hepatic impairment; avoid use in Child-Pugh class B or C due to risk of hepatotoxicity.
Not recommended for children under 12 years of age. For adolescents, adult dosing may be considered based on weight and clinical judgment.
Not established; safety and efficacy not studied in pediatric patients.
Initiate at lower doses (e.g., 250 mg three times daily) due to increased sensitivity and risk of CNS adverse effects; monitor renal function.
Initiate at lower end of dosing range (250 mg 3-4 times daily); monitor for CNS effects (dizziness, drowsiness) and liver function.
None
None
May cause sedation, dizziness, and impaired psychomotor function; avoid driving or operating machinery.,Risk of abuse, dependence, and withdrawal; use with caution in patients with substance use disorder.,Concomitant use with alcohol or other CNS depressants may potentiate effects.,Elderly patients more sensitive to anticholinergic effects; monitor for confusion or falls.,Hepatic impairment: reduce dose or avoid use.,Pregnancy: limited data; use only if clearly needed.
May cause drowsiness, dizziness, or impaired coordination. Caution in patients with hepatic impairment. Discontinue if hypersensitivity reactions occur. Avoid concurrent use with alcohol or other CNS depressants.
Hypersensitivity to carisoprodol or its components,Acute intermittent porphyria,Concurrent use with other CNS depressants (relative)
Hypersensitivity to chlorzoxazone or any component of the formulation; impaired hepatic function
No specific food interactions reported. Avoid alcohol and grapefruit juice as they may enhance sedative effects.
No significant food interactions. Take with or without food. Grapefruit juice may increase drug levels; avoid large quantities.
FDA Pregnancy Category C. First trimester: Limited human data; animal studies show increased fetal resorptions and skeletal anomalies. Second/third trimester: Risk of neonatal withdrawal syndrome (irritability, hypertonia) with chronic maternal use near term.
Teratogenic risk in humans is not well-studied. No major teratogenic effects have been reported in animal studies. However, as with all medications, use during pregnancy only if clearly needed and after weighing risks vs. benefits. Avoid during first trimester unless necessary.
M/P ratio unknown. Carisoprodol and its active metabolite meprobamate are excreted in breast milk. Potential for sedation in nursing infants. Use caution; monitor infant for drowsiness and feeding difficulties.
Not recommended during breastfeeding due to potential for sedation in the infant. No M/P ratio data available.
No pharmacokinetic studies in pregnancy. Use lowest effective dose for shortest duration; avoid chronic use due to risk of dependence and neonatal withdrawal.
No dosage adjustment specific to pregnancy is required based on pharmacokinetic data; however, clinical response should be monitored.
SOMA (carisoprodol) is a centrally acting skeletal muscle relaxant metabolized to meprobamate, a controlled substance with abuse potential. Avoid in patients with porphyria. Use lowest effective dose for shortest duration (max 2-3 weeks). Monitor for sedation and dizziness, especially when combined with other CNS depressants. Taper to avoid withdrawal if used long-term.
Chlorzoxazone is a centrally acting muscle relaxant used for acute musculoskeletal pain. Onset of action is within 1 hour; peak effect at 1-2 hours. Monitor for hepatotoxicity, especially with prolonged use or high doses. Can cause drowsiness and impair motor skills; avoid concurrent use with alcohol or other CNS depressants. Tablets may be crushed for patients with swallowing difficulties.
Avoid driving or operating machinery until you know how SOMA affects you, as it may cause drowsiness or dizziness.,Do not consume alcohol or other CNS depressants (e.g., benzodiazepines, opioids) while taking SOMA.,Take exactly as prescribed; do not increase dose or duration due to risk of dependence and withdrawal.,Store securely to prevent misuse; dispose of unused medication properly.,Contact your doctor if you experience severe drowsiness, confusion, or signs of allergic reaction.
Take exactly as prescribed; do not increase dose or frequency.,May cause drowsiness or dizziness; avoid driving or operating machinery until you know how it affects you.,Avoid alcohol and other CNS depressants while taking this medication.,Report signs of liver problems: dark urine, yellowing of eyes/skin, persistent nausea, abdominal pain.,Do not suddenly stop taking if used long-term; taper under medical supervision to avoid withdrawal.
"Somatostatin, a potent inhibitor of growth hormone and insulin secretion, may antagonize the effects of methohexital, a barbiturate anesthetic, by altering glucose metabolism and hemodynamic stability. This interaction can lead to reduced efficacy of methohexital, requiring higher doses for induction of anesthesia, and may increase the risk of prolonged recovery or adverse cardiovascular events. Clinically, patients may experience unpredictable depth of anesthesia or delayed emergence."
"Concurrent administration of somatostatin and pentobarbital may lead to enhanced CNS depression and increased risk of hypotension. Somatostatin inhibits the release of several hormones and can potentiate the sedative effects of pentobarbital through additive central nervous system depression. Clinically, this interaction may result in excessive sedation, respiratory depression, and cardiovascular instability, particularly in elderly or debilitated patients."
"Somatostatin inhibits the release of growth hormone and various gastrointestinal hormones, leading to reduced hepatic blood flow and decreased metabolic clearance of coadministered drugs. Thiopental undergoes extensive hepatic metabolism and its clearance may be impaired by somatostatin-induced reduction in hepatic perfusion, potentially resulting in prolonged anesthesia and increased risk of respiratory depression or hypotension. Additionally, somatostatin may directly enhance the central nervous system depressant effects of thiopental, although the clinical significance of this interaction is variable."
"Lumacaftor is a strong inducer of cytochrome P450 (CYP) 3A4 and other drug-metabolizing enzymes, including CYP2E1. Chlorzoxazone is primarily metabolized by CYP2E1 to its inactive metabolite. Concomitant use increases CYP2E1 activity, leading to accelerated chlorzoxazone clearance and reduced systemic exposure, potentially diminishing its therapeutic effect as a muscle relaxant."
"Chlorzoxazone, a centrally acting muscle relaxant, inhibits the metabolism of diltiazem, a calcium channel blocker, via competitive inhibition of CYP3A4. This leads to increased plasma concentrations of diltiazem, potentially causing enhanced negative chronotropic and vasodilatory effects, resulting in bradycardia, hypotension, or atrioventricular block. Patients may experience dizziness, syncope, or exacerbate heart failure symptoms."
"Butalbital, a barbiturate, induces hepatic cytochrome P450 enzymes (particularly CYP2E1), accelerating the metabolism of chlorzoxazone, a centrally acting muscle relaxant primarily metabolized by CYP2E1. This results in reduced plasma concentrations of chlorzoxazone, leading to diminished therapeutic efficacy and potential loss of symptom control. Clinically, patients may experience inadequate muscle relaxation, requiring dose adjustments or alternative therapy."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about SOMA vs CHLORZOXAZONE, answered by our medical review team.
SOMA is a Skeletal Muscle Relaxant that works by Centrally acting muscle relaxant; acts at brainstem reticular formation and spinal cord levels to inhibit polysynaptic reflexes, possibly via GABAergic and monoaminergic pathways.. CHLORZOXAZONE is a Skeletal Muscle Relaxant that works by Chlorzoxazone acts centrally on the spinal cord and subcortical areas of the brain to inhibit multisynaptic reflex arcs involved in producing and maintaining muscle spasm. It may also have some sedative effects.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between SOMA and CHLORZOXAZONE depend on the specific clinical indication. These are both Skeletal Muscle Relaxant agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of SOMA is: 250 mg to 350 mg orally three times daily and at bedtime.. The standard adult dose of CHLORZOXAZONE is: 250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between SOMA and CHLORZOXAZONE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. SOMA is classified as Category C. FDA Pregnancy Category C. First trimester: Limited human data; animal studies show increased fetal resorptions and skeletal anomalies. Second/third trimester: Risk of neonatal with. CHLORZOXAZONE is classified as Category C. Teratogenic risk in humans is not well-studied. No major teratogenic effects have been reported in animal studies. However, as with all medications, use during pregnancy only if cl. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.