Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CHLORZOXAZONE vs INCRELEX
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
Insulin-like growth factor 1 receptor agonist; promotes linear growth by stimulating chondrocyte proliferation at epiphyseal plates and exerts anabolic effects on muscle, bone, and other tissues.
Adjunct for relief of acute painful musculoskeletal conditions associated with muscle spasm
Treatment of growth failure in children with severe primary IGF-1 deficiency (primary IGFD) or with growth hormone (GH) gene deletion who have developed neutralizing antibodies to GH
250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.
Intravenous bolus of 0.1 mg/kg given over 1 minute, followed by continuous intravenous infusion of 0.6 mg/kg/min for 30 minutes. Alternatively, a single intravenous bolus dose of 0.3 mg/kg.
Terminal elimination half-life approximately 1–2 hours; clinically relevant for muscle relaxant effect duration.
Terminal elimination half-life is approximately 8-10 hours in adults; clinically, steady-state is achieved within 2-3 days.
Hepatic, primarily via CYP2E1, also CYP1A2 and CYP3A4
Primarily metabolized by proteolysis into smaller peptides and amino acids; not significantly metabolized by CYP enzymes.
Primarily hepatic metabolism followed by renal excretion of metabolites; <1% excreted unchanged in urine; minor biliary/fecal elimination.
Renal: ~95% of absorbed dose as unchanged drug and metabolites; fecal: <5%.
Approximately 90–95% bound, primarily to albumin.
Approximately 90% bound to insulin-like growth factor binding proteins (IGFBPs).
0.46–0.64 L/kg; indicates distribution into total body water.
Vd ~0.3-0.5 L/kg, indicating distribution primarily into extracellular fluid.
Oral: nearly complete; rapidly absorbed with extensive first-pass metabolism; systemic bioavailability approximately 30–50% due to first-pass effect.
Subcutaneous: 80-100% (high bioavailability).
No specific guidelines; use with caution in severe renal impairment (GFR <30 m L/min) due to potential accumulation of active metabolite.
No specific dose adjustment recommended for renal impairment; use with caution in patients with severe renal impairment (e GFR < 30 m L/min/1.73 m²) due to limited data.
Contraindicated in hepatic impairment; avoid use in Child-Pugh class B or C due to risk of hepatotoxicity.
No specific dose adjustment recommended for hepatic impairment; use with caution in patients with Child-Pugh class C cirrhosis due to potential risk of hypoglycemia.
Not established; safety and efficacy not studied in pediatric patients.
Not approved for use in pediatric patients. Safety and efficacy in children have not been established.
Initiate at lower end of dosing range (250 mg 3-4 times daily); monitor for CNS effects (dizziness, drowsiness) and liver function.
No specific dose adjustment recommended; elderly patients may be more sensitive to hypoglycemic effects; monitor blood glucose closely.
None
Increased risk of neoplasms; do not use in patients with active or suspected malignancy. Monitor for progression of pre-existing nevi.
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.
Risk of malignancy (including intracranial tumors),Lymphoproliferative disorders,Intracranial hypertension (pseudotumor cerebri),Slipped capital femoral epiphysis,Progression of scoliosis,Pancreatitis,Hypoglycemia (especially with fasting or missed meals),Fluid retention (edema, pericardial effusion),Hypersensitivity reactions including anaphylaxis,Thymic hypertrophy
Hypersensitivity to chlorzoxazone or any component of the formulation; impaired hepatic function
Active or suspected malignancy (including intracranial tumors),Closed epiphyses (skeletal maturity),Acute critical illness (due to increased mortality with ICU use),Hypersensitivity to mecasermin or any component
No significant food interactions. Take with or without food. Grapefruit juice may increase drug levels; avoid large quantities.
Must be administered within 20 minutes of a meal or snack containing carbohydrates to reduce risk of hypoglycemia. Avoid fasting or skipping meals. Grapefruit/grapefruit juice may alter CYP3A4 metabolism; avoid concurrent use. Alcohol can increase hypoglycemia risk; limit or avoid.
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.
INCRELEX (mecasermin) is an IGF-1 analog. In animal studies, there is no evidence of teratogenicity; however, data in pregnant women are insufficient. First trimester: No known malformation risk. Second/third trimesters: Fetal overgrowth (macrosomia) may occur if maternal IGF-1 levels are elevated. Caution advised.
Not recommended during breastfeeding due to potential for sedation in the infant. No M/P ratio data available.
Excretion into human milk unknown; molecular weight (7.5 k Da) suggests minimal transfer. M/P ratio not established. Caution recommended; alternative feeding may be considered until more data available.
No dosage adjustment specific to pregnancy is required based on pharmacokinetic data; however, clinical response should be monitored.
No established dose adjustments. Physiologic changes in pregnancy (increased renal clearance, plasma volume) may reduce drug levels; however, safety and efficacy data are lacking. Use only if clearly needed with careful monitoring.
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.
INCRELEX (mecasermin) is recombinant human insulin-like growth factor-1 (IGF-1) used for growth failure in severe primary IGF-1 deficiency. Monitor blood glucose closely due to risk of hypoglycemia; administer within 20 minutes of a meal or snack. Do not use in patients with closed epiphyses, active malignancy, or history of malignancy. Can cause intracranial hypertension (pseudotumor cerebri); monitor for headache, visual disturbances. Injection site reactions common.
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.
Do not use INCRELEX if you have cancer or a history of cancer.,Take exactly as prescribed; inject within 20 minutes after a meal or snack to prevent low blood sugar.,Do not inject into the same site repeatedly; rotate injection sites.,Watch for signs of low blood sugar (shakiness, sweating, confusion) and have fast-acting sugar (e.g., juice, glucose tablets) available.,Report severe headache, vision changes, or nausea immediately (possible increased pressure in the skull).,Inform all healthcare providers you are using this medication.
"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."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about CHLORZOXAZONE vs INCRELEX, answered by our medical review team.
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.. INCRELEX is a Growth Factor that works by Insulin-like growth factor 1 receptor agonist; promotes linear growth by stimulating chondrocyte proliferation at epiphyseal plates and exerts anabolic effects on muscle, bone, and other tissues.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CHLORZOXAZONE and INCRELEX depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of CHLORZOXAZONE is: 250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.. The standard adult dose of INCRELEX is: Intravenous bolus of 0.1 mg/kg given over 1 minute, followed by continuous intravenous infusion of 0.6 mg/kg/min for 30 minutes. Alternatively, a single intravenous bolus dose of 0.3 mg/kg.. 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 CHLORZOXAZONE and INCRELEX 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. 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. INCRELEX is classified as Category C. INCRELEX (mecasermin) is an IGF-1 analog. In animal studies, there is no evidence of teratogenicity; however, data in pregnant women are insufficient. First trimester: No known mal. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.