Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
OFIRMEV vs GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
OFIRMEV (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism of action is not fully understood, but it is thought to involve inhibition of cyclooxygenase (COX) enzymes in the central nervous system, with minimal peripheral COX inhibition. It may also act on serotonergic pathways and cannabinoid receptors.
Guaifenesin is an expectorant that increases respiratory tract fluid secretions, reducing mucus viscosity. Dextromethorphan is a centrally acting cough suppressant that binds to NMDA receptors and sigma-1 receptors, elevating the cough threshold.
Management of mild to moderate pain,Management of moderate to severe pain with adjunctive opioid analgesics,Reduction of fever
Temporary relief of cough due to minor throat and bronchial irritation (FDA-approved),Off-label: symptomatic treatment of upper respiratory tract infections with cough and congestion
IV: 1000 mg every 6 hours or 650 mg every 4 hours; maximum single dose: 1000 mg; minimum dosing interval: 4 hours; maximum daily dose: 4000 mg.
For adults and children ≥12 years: 10 m L (200 mg guaifenesin, 20 mg dextromethorphan) orally every 4 hours, not to exceed 60 m L (1200 mg guaifenesin, 120 mg dextromethorphan) per 24 hours.
Terminal elimination half-life is 2-3 hours in adults (2.5-3 hours in children). Clinically, dosing every 4-6 hours is needed to maintain therapeutic levels.
Guaifenesin: 1-2 hours; Dextromethorphan: 3-6 hours (extensive metabolizers), 18-24 hours (poor metabolizers due to CYP2D6 polymorphism).
Acetaminophen is primarily metabolized in the liver via conjugation with glucuronide (50-60%) and sulfate (20-30%). A minor amount is oxidized by cytochrome P450 (CYP2E1, CYP1A2, CYP3A4) to a toxic reactive metabolite (NAPQI), which is normally detoxified by glutathione. At toxic doses, glutathione is depleted, leading to NAPQI accumulation and hepatotoxicity.
Guaifenesin is metabolized by oxidation and demethylation; dextromethorphan is extensively metabolized by CYP2D6 to dextrorphan (active metabolite) and other metabolites.
Primarily renal (85% as sulfate and glucuronide conjugates, 10% as unchanged drug). Less than 5% fecal/biliary.
Guaifenesin: ~60% renal (metabolites), ~35% fecal; Dextromethorphan: ~70% renal (parent and metabolites, 45% as unchanged dextrorphan), ~20% biliary/fecal.
10-25% bound to albumin at therapeutic concentrations.
Guaifenesin: negligible (<10%); Dextromethorphan: ~60-70% (mainly albumin and alpha-1-acid glycoprotein).
0.8-1.0 L/kg. Indicates distribution into total body water.
Guaifenesin: 1.2 L/kg (distributes into tissues); Dextromethorphan: 5-7 L/kg (large Vd due to high tissue binding).
100% (intravenous); not applicable for other routes as OFIRMEV is IV only.
Oral: Guaifenesin ~95%; Dextromethorphan ~11% (extensive first-pass metabolism, variable due to CYP2D6).
No dose adjustment required for GFR ≥30 m L/min. For GFR <30 m L/min, extend dosing interval to every 8 hours; maximum daily dose 3000 mg.
No specific guidelines; use with caution in severe renal impairment (Cr Cl <30 m L/min) due to potential accumulation of dextromethorphan metabolite.
Child-Pugh Class A: No adjustment. Child-Pugh Class B: Reduce total daily dose by 50% (max 2000 mg/day). Child-Pugh Class C: Contraindicated or use with extreme caution; reduce dose to 50% of standard and extend interval to every 8 hours; maximum 2000 mg/day.
For dextromethorphan: Child-Pugh class C: consider reducing dose by 50% or avoid use; Child-Pugh A/B: no specific adjustment but monitor for CNS effects.
Weight-based: <10 kg: 7.5 mg/kg/dose every 6 hours; 10-50 kg: 15 mg/kg/dose every 6 hours; >50 kg: 1000 mg every 6 hours or 650 mg every 4 hours. Maximum single dose: 15 mg/kg (up to 1000 mg); maximum daily dose: 75 mg/kg (up to 4000 mg).
Children 6-11 years: 5 m L (100 mg guaifenesin, 10 mg dextromethorphan) every 4 hours, max 30 m L/day. Children 2-5 years: 2.5 m L (50 mg guaifenesin, 5 mg dextromethorphan) every 4 hours, max 15 m L/day. Not for children <2 years.
No specific dose adjustment; consider reduced renal function. For Cr Cl <30 m L/min, extend interval to every 8 hours. Maximum daily dose: 3000 mg in frail elderly or with comorbidities.
Use the lowest effective dose; consider starting with 5 m L (100 mg guaifenesin, 10 mg dextromethorphan) every 4-6 hours due to increased risk of sedation and anticholinergic effects.
Acetaminophen has been associated with cases of acute liver failure, at times resulting in liver transplant and death. Most of the cases of liver injury are associated with the use of acetaminophen at doses that exceed 4000 mg per day, and often involve more than one acetaminophen-containing product.
None.
Risk of serious hepatotoxicity, especially with doses >4000 mg/day or in patients with underlying liver disease,Risk of severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, acute generalized exanthematous pustulosis) – discontinue at first sign of rash,Risk of hypersensitivity reactions including anaphylaxis,Use caution in patients with severe hepatic impairment, active hepatic disease, or alcoholism,Avoid concurrent use of other acetaminophen-containing products
Avoid use in patients with chronic cough (e.g., smoking, asthma, emphysema) or cough with excessive phlegm.,Concomitant use with MAOIs or within 2 weeks of MAOI use is contraindicated.,Dextromethorphan abuse potential; use caution with CYP2D6 inhibitors.
Known hypersensitivity to acetaminophen or any component of the formulation,Severe hepatic impairment or active liver disease (relative contraindication without black box)
Hypersensitivity to guaifenesin or dextromethorphan,Concurrent use or recent use (within 2 weeks) of monoamine oxidase inhibitors (MAOIs),Severe hypertension, coronary artery disease, or narrow-angle glaucoma (due to sympathomimetic effects if combined with decongestants; note: this combination alone does not contain decongestants, but caution applies)
No known food interactions. However, avoid excessive alcohol consumption as it may increase the risk of liver damage.
No significant food interactions; avoid alcohol as it may increase sedation and dizziness.
Acetaminophen (OFIRMEV) is generally considered low risk across all trimesters. No increased risk of major congenital anomalies has been consistently demonstrated. Chronic high-dose use in third trimester may be associated with preterm birth or low birth weight. Avoid prolonged use above recommended doses.
Guaifenesin: Limited human data; animal studies show no teratogenicity at clinically relevant doses. Dextromethorphan: No increased risk of major malformations in first trimester; animal studies show no teratogenicity. Avoid excessive doses in third trimester due to potential neonatal withdrawal or respiratory depression. Overall, both agents are considered low risk but use only if clearly needed.
Acetaminophen is excreted in breast milk in low concentrations (M/P ratio approximately 0.9-1.0). Considered compatible with breastfeeding; peak milk levels occur 1-2 hours after maternal dosing. Use lowest effective dose for shortest duration.
Guaifenesin: Excreted in breast milk in small amounts; unlikely to cause adverse effects in infants. Dextromethorphan: Excreted in breast milk; limited data suggest low infant exposure (M/P ratio not established). Both are considered compatible with breastfeeding; use lowest effective dose and monitor infant for sedation or respiratory depression.
No dose adjustment required during pregnancy. Pharmacokinetic changes in pregnancy (increased volume of distribution, clearance) may lead to lower peak concentrations but standard dosing remains effective. Maximum single dose: 1 g; maximum daily dose: 4 g.
No pharmacokinetic data to support dose adjustments during pregnancy; use lowest effective dose for shortest duration. Guaifenesin: increased renal clearance in pregnancy may theoretically reduce efficacy, but no dose adjustment recommended. Dextromethorphan: metabolism by CYP2D6 may be affected by pregnancy; avoid exceeding standard doses.
OFIRMEV (acetaminophen) injection is an IV formulation of acetaminophen used for pain and fever management. It is a prodrug that requires no hepatic conversion, providing rapid onset of action. Monitor for hepatotoxicity; maximum daily dose is 4 grams in adults but lower in patients with hepatic impairment or malnutrition. Do not exceed 1 gram per dose. Hypotension and anaphylaxis have been reported. Not interchangeable with oral acetaminophen due to dose equivalency. Use with caution in patients with alcohol use disorder.
Monitor for sedation and dizziness, especially in elderly; avoid use with MAOIs due to serotonin syndrome risk; dextromethorphan has abuse potential at high doses; use caution in patients with chronic cough due to smoking, asthma, or COPD; guaifenesin may cause renal calculi with prolonged high doses.
OFIRMEV is given intravenously for pain or fever.,Do not take additional acetaminophen-containing medications while receiving OFIRMEV.,Report any signs of allergic reaction (rash, itching, swelling, trouble breathing).,Seek immediate medical attention if you experience severe abdominal pain, yellowing of skin or eyes, or dark urine.,Inform your healthcare provider about all medications you are taking, especially blood thinners.
Do not exceed recommended doses; high doses can cause serious side effects including hallucinations and addiction.,Avoid driving or operating machinery if you feel dizzy or drowsy.,Do not use with other cough and cold medications to avoid overdose.,Increase fluid intake to help loosen mucus.,Stop use and consult a doctor if cough persists more than 7 days or comes with fever, rash, or headache.,Inform your doctor about all medications you take, especially MAOIs or SSRIs.,Keep out of reach of children; accidental overdose may be fatal in children.
No interactions on record
"The combination of dextromethorphan, a centrally acting antitussive with NMDA receptor antagonist and sigma-1 receptor agonist properties, and aceprometazine, a phenothiazine neuroleptic with strong antihistaminergic and moderate anticholinergic and antidopaminergic effects, can result in additive central nervous system depression. This interaction may lead to excessive sedation, respiratory depression, impaired psychomotor function, and an increased risk of falls or cognitive impairment, particularly in elderly or debilitated patients. Concurrent use may also lower the seizure threshold, especially in patients with predisposing factors."
"Dextromethorphan, a serotonergic agent metabolized by CYP2D6, when combined with cariprazine, a dopamine D3/D2 receptor partial agonist, may increase the risk of serotonin syndrome due to additive serotonergic effects. Cariprazine can inhibit CYP2D6, reducing dextromethorphan clearance and elevating its plasma concentration, leading to enhanced serotonin activity. Clinically, patients may present with altered mental status, autonomic instability, and neuromuscular abnormalities."
"Dextromethorphan inhibits CYP2B6 and CYP2C9, which are involved in valproic acid metabolism. This results in decreased valproic acid clearance, potentially elevating valproic acid serum concentrations and increasing the risk of dose-dependent adverse effects such as hepatotoxicity, thrombocytopenia, and sedation. Concurrent use requires dose adjustment and close monitoring for signs of valproate toxicity."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about OFIRMEV vs GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE, answered by our medical review team.
OFIRMEV is a Non-opioid Analgesic that works by OFIRMEV (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism of action is not fully understood, but it is thought to involve inhibition of cyclooxygenase (COX) enzymes in the central nervous system, with minimal peripheral COX inhibition. It may also act on serotonergic pathways and cannabinoid receptors.. GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE is a Expectorant/Antitussive Combination that works by Guaifenesin is an expectorant that increases respiratory tract fluid secretions, reducing mucus viscosity. Dextromethorphan is a centrally acting cough suppressant that binds to NMDA receptors and sigma-1 receptors, elevating the cough threshold.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between OFIRMEV and GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE 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 OFIRMEV is: IV: 1000 mg every 6 hours or 650 mg every 4 hours; maximum single dose: 1000 mg; minimum dosing interval: 4 hours; maximum daily dose: 4000 mg.. The standard adult dose of GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE is: For adults and children ≥12 years: 10 m L (200 mg guaifenesin, 20 mg dextromethorphan) orally every 4 hours, not to exceed 60 m L (1200 mg guaifenesin, 120 mg dextromethorphan) per 24 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 OFIRMEV and GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE 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. OFIRMEV is classified as Category C. Acetaminophen (OFIRMEV) is generally considered low risk across all trimesters. No increased risk of major congenital anomalies has been consistently demonstrated. Chronic high-dos. GUAIFENESIN AND DEXTROMETHORPHAN HYDROBROMIDE is classified as Category C. Guaifenesin: Limited human data; animal studies show no teratogenicity at clinically relevant doses. Dextromethorphan: No increased risk of major malformations in first trimester; . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.