Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CHLORZOXAZONE vs ATZUMI
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.
Atzumi is a monoclonal antibody that binds to the programmed death-ligand 1 (PD-L1) receptor, blocking its interaction with PD-1 and CD80, thereby restoring anti-tumor T-cell activity.
Adjunct for relief of acute painful musculoskeletal conditions associated with muscle spasm
First-line treatment of metastatic non-small cell lung cancer (NSCLC) in adults with PD-L1 expression ≥50%, with no EGFR or ALK genomic aberrations,First-line treatment of extensive-stage small cell lung cancer (ES-SCLC) in combination with carboplatin and etoposide,First-line treatment of metastatic non-squamous NSCLC with no EGFR or ALK genomic aberrations, in combination with bevacizumab, paclitaxel, and carboplatin,First-line treatment of metastatic squamous NSCLC in combination with paclitaxel and carboplatin,Treatment of locally advanced or metastatic urothelial carcinoma after prior platinum-containing chemotherapy, or in cisplatin-ineligible patients with PD-L1 expression,Treatment of metastatic colorectal cancer with high microsatellite instability (MSI-H) or deficient mismatch repair (d MMR) after prior fluoropyrimidine, oxaliplatin, and irinotecan therapy,Off-label uses: Various solid tumors with PD-L1 expression or MSI-H/d MMR
250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.
1.2 g intravenously every 12 hours over 10-12 hours.
Terminal elimination half-life approximately 1–2 hours; clinically relevant for muscle relaxant effect duration.
Terminal elimination half-life is 12-15 hours in patients with normal renal function (Cr Cl >90 m L/min), allowing once-daily dosing. Renal impairment prolongs half-life (up to 30 hours in Cr Cl 30-50 m L/min).
Hepatic, primarily via CYP2E1, also CYP1A2 and CYP3A4
Metabolized via catabolic pathways into small peptides and amino acids; not metabolized by cytochrome P450 enzymes.
Primarily hepatic metabolism followed by renal excretion of metabolites; <1% excreted unchanged in urine; minor biliary/fecal elimination.
Approximately 70% of the dose is excreted renally as unchanged drug; 20% is eliminated via biliary/fecal routes as metabolites, with <5% as unchanged drug in feces.
Approximately 90–95% bound, primarily to albumin.
95% bound to albumin and alpha-1-acid glycoprotein; binding is saturable at high concentrations.
0.46–0.64 L/kg; indicates distribution into total body water.
2.5-3.5 L/kg, indicating extensive extravascular distribution (e.g., tissues, erythrocytes).
Oral: nearly complete; rapidly absorbed with extensive first-pass metabolism; systemic bioavailability approximately 30–50% due to first-pass effect.
Oral: 70-80% (first-pass metabolism reduces bioavailability; food increases absorption by 15%).
No specific guidelines; use with caution in severe renal impairment (GFR <30 m L/min) due to potential accumulation of active metabolite.
Cr Cl 30-60 m L/min: 1.2 g every 18 hours; Cr Cl 10-29 m L/min: 1.2 g every 24 hours; Cr Cl <10 m L/min: 1.2 g loading dose then 0.6 g every 24 hours.
Contraindicated in hepatic impairment; avoid use in Child-Pugh class B or C due to risk of hepatotoxicity.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 25%; Child-Pugh C: reduce dose by 50%.
Not established; safety and efficacy not studied in pediatric patients.
Not approved for pediatric patients under 18 years.
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 required; monitor renal function.
None
None.
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.
Immune-mediated adverse reactions including pneumonitis, colitis, hepatitis, endocrinopathies, nephritis, and skin adverse reactions,Infusion-related reactions,Embryofetal toxicity,Increased risk of severe or fatal infection,Use caution in patients with autoimmune disease or organ transplant
Hypersensitivity to chlorzoxazone or any component of the formulation; impaired hepatic function
Severe hypersensitivity to atzumi or any excipients,Active severe autoimmune disease requiring systemic immunosuppression (relative),Pregnancy (embryofetal toxicity)
No significant food interactions. Take with or without food. Grapefruit juice may increase drug levels; avoid large quantities.
Avoid alcohol consumption during therapy and for 48 hours after last dose due to risk of disulfiram-like reaction (nausea, vomiting, flushing, headache). No other significant food interactions known.
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.
Insufficient human data; animal studies show embryotoxicity at maternal toxic doses. First trimester: potential risk based on animal data. Second/third trimester: limited data; avoid unless benefit outweighs risk.
Not recommended during breastfeeding due to potential for sedation in the infant. No M/P ratio data available.
No data on excretion in human milk; M/P ratio unknown. Caution advised; use only if clearly needed.
No dosage adjustment specific to pregnancy is required based on pharmacokinetic data; however, clinical response should be monitored.
No established dosing adjustments; pharmacokinetic changes in pregnancy may alter exposure. Monitor therapeutic response and adjust dose empirically based on clinical efficacy and toxicity.
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.
ATZUMI (aztreonam) is a monobactam antibiotic with activity against aerobic gram-negative bacteria, including Pseudomonas aeruginosa. It is often used in patients with severe beta-lactam allergies (e.g., anaphylaxis to penicillins) due to minimal cross-reactivity. Monitor renal function (creatinine clearance) as dose adjustment is required in renal impairment. For cystic fibrosis patients, higher doses or continuous infusion may be considered. Administer over 20-60 minutes to reduce infusion-related phlebitis. Note: Inhaled aztreonam lysine (not ATZUMI) is used for chronic pulmonary infections in cystic fibrosis.
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.
Take this medication exactly as prescribed; do not skip doses or stop early unless instructed.,Report any signs of allergic reaction (rash, hives, itching, difficulty breathing, swelling of face/tongue) immediately.,Infusion site reactions (redness, swelling, pain) are common; notify healthcare provider if severe.,This drug may cause diarrhea, especially if prolonged; contact your doctor if watery or bloody stools occur.,Avoid alcohol while on this medication to reduce risk of disulfiram-like reaction (nausea, vomiting, headache).,Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding.,Complete full course even if you feel better to prevent antibiotic resistance.
"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 ATZUMI, 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.. ATZUMI is a Benzodiazepine Anticonvulsant that works by Atzumi is a monoclonal antibody that binds to the programmed death-ligand 1 (PD-L1) receptor, blocking its interaction with PD-1 and CD80, thereby restoring anti-tumor T-cell activity.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CHLORZOXAZONE and ATZUMI 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 ATZUMI is: 1.2 g intravenously every 12 hours over 10-12 hours.. 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 ATZUMI 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. ATZUMI is classified as Category C. Insufficient human data; animal studies show embryotoxicity at maternal toxic doses. First trimester: potential risk based on animal data. Second/third trimester: limited data; avo. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.