Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AMOXAPINE vs CHLORZOXAZONE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Selective inhibitor of serotonin reuptake and, to a lesser extent, norepinephrine reuptake. Also exhibits weak dopamine D2 receptor antagonism and alpha1-adrenergic blockade.
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.
Major depressive disorder,Anxiety,Panic disorder,Off-label: neuropathic pain, insomnia
Adjunct for relief of acute painful musculoskeletal conditions associated with muscle spasm
200-300 mg/day orally in divided doses, initially 50 mg three times daily; maximum 400 mg/day
250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.
Parent drug: 8-12 hours; active metabolite (8-hydroxyamoxapine): approximately 30 hours; steady-state achieved in 3-5 days
Terminal elimination half-life approximately 1–2 hours; clinically relevant for muscle relaxant effect duration.
Primarily hepatic via CYP2D6 and CYP3A4; major metabolite is 8-hydroxyamoxapine, which is pharmacologically active.
Hepatic, primarily via CYP2E1, also CYP1A2 and CYP3A4
Primarily renal (approximately 60-70% as metabolites, <5% unchanged); minimal fecal elimination (<10%)
Primarily hepatic metabolism followed by renal excretion of metabolites; <1% excreted unchanged in urine; minor biliary/fecal elimination.
Approximately 80-90%, primarily to albumin and alpha-1-acid glycoprotein
Approximately 90–95% bound, primarily to albumin.
0.8-1.2 L/kg, indicating extensive tissue distribution
0.46–0.64 L/kg; indicates distribution into total body water.
Oral: approximately 60-70% due to first-pass metabolism
Oral: nearly complete; rapidly absorbed with extensive first-pass metabolism; systemic bioavailability approximately 30–50% due to first-pass effect.
GFR 10-50 m L/min: reduce dose by 50%; GFR <10 m L/min: avoid use or reduce dose by 75%
No specific guidelines; use with caution in severe renal impairment (GFR <30 m L/min) due to potential accumulation of active metabolite.
Child-Pugh Class A: start at 25 mg twice daily; Class B: 25 mg once daily; Class C: avoid use
Contraindicated in hepatic impairment; avoid use in Child-Pugh class B or C due to risk of hepatotoxicity.
Not recommended for use in children under 16 years
Not established; safety and efficacy not studied in pediatric patients.
Initial dose 25 mg twice daily, increase slowly; maximum 300 mg/day
Initiate at lower end of dosing range (250 mg 3-4 times daily); monitor for CNS effects (dizziness, drowsiness) and liver function.
Increased risk of suicidal thinking and behavior in children, adolescents, and young adults with major depressive disorder and other psychiatric disorders.
None
Suicidality risk in young adults,Serotonin syndrome when combined with other serotonergic drugs,Extrapyramidal symptoms due to weak D2 blockade,Seizure risk,Cardiotoxicity (prolonged QT interval) at high doses,Agranulocytosis (rare)
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 amoxapine or any dibenzoxazepine,Concomitant use with MAOIs (including linezolid and methylene blue),Recent myocardial infarction,Uncontrolled narrow-angle glaucoma,Urinary retention,QT prolongation or concurrent use of drugs that prolong QT
Hypersensitivity to chlorzoxazone or any component of the formulation; impaired hepatic function
Avoid alcohol and beverages with high tyramine content (e.g., aged cheese, cured meats, fermented foods) only if patient is also on MAOIs; not a specific requirement for amoxapine alone. Grapefruit juice may inhibit metabolism; advise caution or avoid large amounts. For patients with hypertension or seizure disorders, avoid excessive caffeine.
No significant food interactions. Take with or without food. Grapefruit juice may increase drug levels; avoid large quantities.
First trimester: Limited data; risk of neural tube defects? Second trimester: No specific associations. Third trimester: Risk of neonatal withdrawal (irritability, feeding difficulties). Overall: FDA Category C; avoid in first trimester if possible.
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.
Excreted in breast milk; M/P ratio not established. Use caution due to potential for infant sedation and anticholinergic effects; monitor for drowsiness and poor feeding.
Not recommended during breastfeeding due to potential for sedation in the infant. No M/P ratio data available.
No established dose adjustments; increased clearance in pregnancy may require dose increase to maintain efficacy; monitor therapeutic response and serum levels if available.
No dosage adjustment specific to pregnancy is required based on pharmacokinetic data; however, clinical response should be monitored.
Amoxapine is a dibenzoxazepine antidepressant with both tricyclic-like reuptake inhibition and dopamine receptor blocking properties. Monitor for extrapyramidal symptoms (EPS) and tardive dyskinesia, especially in elderly. Due to dopamine blockade, it may cause hyperprolactinemia. For patients with seizures, use cautiously; dose-dependent seizure risk is higher than with other TCAs. Onset of antidepressant effect may be 2-4 weeks. Use lower initial doses in elderly and hepatic impairment. Avoid in recent myocardial infarction.
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.
Take exactly as prescribed; do not increase or stop abruptly without consulting your doctor.,May cause drowsiness or dizziness; avoid driving or operating heavy machinery until you know how the medication affects you.,Avoid alcohol and other CNS depressants.,Report any muscle stiffness, tremor, restlessness, or unusual movements of the face or tongue.,Notify your doctor if you experience rapid or irregular heartbeat, difficulty urinating, or blurred vision.,May cause dry mouth; use sugarless candy or gum and maintain good oral hygiene.,Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.,Do not take any other medications, including over-the-counter products, without approval from your healthcare provider.
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.
"Combined use of Oxprenolol, a non-selective beta-blocker with intrinsic sympathomimetic activity, and Amoxapine, a tricyclic antidepressant, may lead to additive cardiovascular adverse effects. Amoxapine can inhibit the metabolism of beta-blockers via competition for CYP450 enzymes, increasing oxprenolol plasma concentrations. This interaction heightens the risk of bradycardia, hypotension, and may precipitate heart block or arrhythmias, particularly in patients with pre-existing cardiac disease."
"The combination of amoxapine, a tricyclic antidepressant with strong anticholinergic properties, and clidinium, a quaternary ammonium anticholinergic used for gastrointestinal spasms, results in additive anticholinergic effects. This can lead to excessive peripheral and central anticholinergic adverse effects such as dry mouth, blurred vision, constipation, urinary retention, tachycardia, cognitive impairment, and exacerbation of glaucoma or paralytic ileus. In severe cases, anticholinergic toxicity may manifest as hyperthermia, delirium, or seizures, particularly in elderly patients or those with pre-existing conditions."
"Telavancin, a lipoglycopeptide antibiotic, prolongs the QT interval by inhibiting the delayed rectifier potassium current (IKr) in cardiac myocytes. Amoxapine, a tricyclic antidepressant, also blocks cardiac sodium and potassium channels, leading to dose-dependent QTc prolongation. Concomitant use increases the risk of torsade de pointes, ventricular arrhythmias, and sudden cardiac death, particularly in patients with electrolyte imbalances, bradycardia, or preexisting QT prolongation."
"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 AMOXAPINE vs CHLORZOXAZONE, answered by our medical review team.
AMOXAPINE is a Tricyclic Antidepressant that works by Selective inhibitor of serotonin reuptake and, to a lesser extent, norepinephrine reuptake. Also exhibits weak dopamine D2 receptor antagonism and alpha1-adrenergic blockade.. 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 AMOXAPINE and CHLORZOXAZONE 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 AMOXAPINE is: 200-300 mg/day orally in divided doses, initially 50 mg three times daily; maximum 400 mg/day. 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.
A moderate-severity drug interaction has been identified when combining AMOXAPINE and CHLORZOXAZONE. The risk or severity of adverse effects can be increased when Chlorzoxazone is combined with Amoxapine. Consult your prescriber before combining these medications.
The maternal-fetal safety profiles differ. AMOXAPINE is classified as Category C. First trimester: Limited data; risk of neural tube defects? Second trimester: No specific associations. Third trimester: Risk of neonatal withdrawal (irritability, feeding difficul. 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.