Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CHLORZOXAZONE vs ACUVAIL
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.
Ketorolac tromethamine, a nonsteroidal anti-inflammatory drug (NSAID), inhibits prostaglandin synthesis by blocking cyclooxygenase (COX-1 and COX-2) enzymes. This reduces ocular inflammation and pain.
Adjunct for relief of acute painful musculoskeletal conditions associated with muscle spasm
Reduction of ocular pain and inflammation following cataract surgery,Treatment of ocular itching associated with seasonal allergic conjunctivitis
250-500 mg orally 3-4 times daily, maximum 750 mg 4 times daily.
1 drop in the affected eye 4 times daily.
Terminal elimination half-life approximately 1–2 hours; clinically relevant for muscle relaxant effect duration.
Terminal elimination half-life is approximately 46 minutes in the aqueous humor following ocular administration in humans.
Hepatic, primarily via CYP2E1, also CYP1A2 and CYP3A4
Primarily hepatic via conjugation with glucuronic acid; minor role of cytochrome P450 enzymes. Approximately 50% is excreted as parent drug and metabolites in urine.
Primarily hepatic metabolism followed by renal excretion of metabolites; <1% excreted unchanged in urine; minor biliary/fecal elimination.
Primarily renal excretion of metabolites; less than 1% excreted unchanged. Biliary/fecal elimination accounts for <10%.
Approximately 90–95% bound, primarily to albumin.
>99% bound to plasma proteins, primarily albumin.
0.46–0.64 L/kg; indicates distribution into total body water.
Intravenous administration in animals suggests Vd ~0.15 L/kg, indicating limited distribution; clinically, it distributes into aqueous humor after topical dosing.
Oral: nearly complete; rapidly absorbed with extensive first-pass metabolism; systemic bioavailability approximately 30–50% due to first-pass effect.
Ocular bioavailability is dependent on formulation; systemic bioavailability after topical ocular administration is extremely low (<1%).
No specific guidelines; use with caution in severe renal impairment (GFR <30 m L/min) due to potential accumulation of active metabolite.
No adjustment required. Drug is minimally systemically absorbed.
Contraindicated in hepatic impairment; avoid use in Child-Pugh class B or C due to risk of hepatotoxicity.
No adjustment required. Drug is minimally systemically absorbed.
Not established; safety and efficacy not studied in pediatric patients.
Safety and efficacy in pediatric patients 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 dosage adjustment is recommended; use same dose as younger adults.
None
No black box warning for ophthalmic use; however, systemic NSAIDs carry risk of serious cardiovascular and gastrointestinal events. Ophthalmic use rarely associated with corneal adverse events.
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.
Use with caution in patients with bleeding disorders or those on anticoagulants; may prolong bleeding time. Avoid in patients with known hypersensitivities to NSAIDs or aspirin. Can cause corneal keratopathy; discontinue if corneal epithelial breakdown occurs.
Hypersensitivity to chlorzoxazone or any component of the formulation; impaired hepatic function
Hypersensitivity to any component of the formulation. Active corneal epithelial defect. Patients with aspirin-sensitive asthma.
No significant food interactions. Take with or without food. Grapefruit juice may increase drug levels; avoid large quantities.
No specific food interactions; systemic absorption is minimal with ophthalmic use. Avoid concurrent use of other NSAID eye drops due to additive irritation.
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.
Acuvail (ketorolac tromethamine ophthalmic solution) is classified as FDA Pregnancy Category C. Systemic exposure after ocular administration is minimal; however, NSAIDs may cause premature closure of the ductus arteriosus and oligohydramnios in the third trimester. Use during the first and second trimesters should be limited to cases where potential benefit outweighs risk; avoid during the third trimester due to risk of fetal harm.
Not recommended during breastfeeding due to potential for sedation in the infant. No M/P ratio data available.
Ketorolac is excreted in human milk following systemic administration, but ocular doses produce negligible systemic levels. The M/P ratio is not determined for ophthalmic use. Use with caution in nursing mothers, as the clinical significance is likely low due to minimal systemic absorption.
No dosage adjustment specific to pregnancy is required based on pharmacokinetic data; however, clinical response should be monitored.
No dosage adjustment is required for ophthalmic use during pregnancy, as systemic exposure is negligible. However, avoid use in third trimester due to risks. Pharmacokinetic changes in pregnancy do not significantly alter ocular delivery.
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.
Acuvail (ketorolac tromethamine ophthalmic solution 0.45%) is a nonsteroidal anti-inflammatory drug (NSAID) for ocular use. It is preserved with sodium chloride and not benzalkonium chloride, reducing corneal epithelial toxicity. Administer 1 drop twice daily for ocular pain and inflammation following cataract surgery. Use caution in patients with bleeding tendencies or those on anticoagulants due to risk of increased ocular bleeding. Monitor for corneal epithelial defects and keratitis, especially with prolonged use.
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.
Wash hands before each use; do not touch tip of bottle to eye or any surface to avoid contamination.,Remove contact lenses before instillation and wait at least 15 minutes before reinserting.,Contact your doctor if you experience eye pain, redness, vision changes, or if symptoms worsen.,Do not use this medication while wearing contact lenses unless directed by your doctor.,Store at room temperature, keep bottle tightly closed when not in use, and discard within 28 days of opening.
"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 ACUVAIL, 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.. ACUVAIL is a NSAID Ophthalmic that works by Ketorolac tromethamine, a nonsteroidal anti-inflammatory drug (NSAID), inhibits prostaglandin synthesis by blocking cyclooxygenase (COX-1 and COX-2) enzymes. This reduces ocular inflammation and pain.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CHLORZOXAZONE and ACUVAIL 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 ACUVAIL is: 1 drop in the affected eye 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 CHLORZOXAZONE and ACUVAIL 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. ACUVAIL is classified as Category C. Acuvail (ketorolac tromethamine ophthalmic solution) is classified as FDA Pregnancy Category C. Systemic exposure after ocular administration is minimal; however, NSAIDs may cause . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.