Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ACETAMINOPHEN AND CODEINE PHOSPHATE vs DI-METREX
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Acetaminophen: centrally acting analgesic and antipyretic, possibly via inhibition of cyclooxygenase (COX) and modulation of cannabinoid receptors. Codeine: prodrug converted to morphine; mu-opioid receptor agonist.
Combination of diphenhydramine (H1-antagonist) and pseudoephedrine (alpha-1 agonist). Diphenhydramine blocks histamine at H1 receptors, reducing allergic symptoms; pseudoephedrine causes vasoconstriction via alpha-1 adrenergic receptors, relieving nasal congestion.
Mild to moderate pain,Pain accompanied by fever
Symptomatic relief of seasonal allergies,Upper respiratory tract allergies,Nasal congestion,Sinus congestion
One or two tablets (acetaminophen 300 mg/codeine 30 mg per tablet) orally every 4-6 hours as needed for pain; maximum 12 tablets daily.
4 mg orally once daily, increased to a maximum of 8 mg once daily if needed.
Acetaminophen: 2–3 hours (prolonged in hepatic impairment). Codeine: 2.5–3.5 hours; metabolites: morphine 1.5–2.5 hours, codeine-6-glucuronide 3–4 hours. Clinical context: dosing interval every 4–6 hours.
The terminal elimination half-life is approximately 12 hours, requiring twice-daily dosing for steady-state concentrations.
Acetaminophen: primarily glucuronidation and sulfation in liver; minor CYP450 (CYP2E1) to toxic NAPQI. Codeine: CYP2D6 to morphine; CYP3A4 to norcodeine; glucuronidation.
Diphenhydramine: extensively metabolized via CYP2D6 to inactive metabolites; pseudoephedrine: partially metabolized in liver via N-demethylation to active metabolite (norpseudoephedrine) and excreted unchanged in urine.
Acetaminophen: renal elimination of conjugated metabolites (glucuronide 60%, sulfate 30%, cysteine/mercapturate <5%), less than 5% unchanged. Codeine: renal elimination of codeine (5–15%), morphine (5–10%), norcodeine (10–20%), and conjugates; 90% excreted in urine within 24 hours.
Renal excretion accounts for approximately 70% of elimination as unchanged drug and metabolites; biliary/fecal excretion accounts for the remaining 30%.
Acetaminophen: 10–25% (albumin). Codeine: 7–25% (primarily albumin).
Approximately 85% bound to serum albumin.
Acetaminophen: 0.9 L/kg. Codeine: 3–6 L/kg (extensive tissue distribution).
Vd is 0.8 L/kg, indicating distribution into total body water and some tissue binding.
Oral: acetaminophen 88% (variable first-pass); codeine 50–60% (first-pass metabolism to morphine, norcodeine, and conjugates).
Oral bioavailability is 90% due to minimal first-pass metabolism.
GFR 30-50 m L/min: administer every 6 hours; GFR 10-29 m L/min: administer every 8 hours; GFR <10 m L/min: administer every 12 hours; hemodialysis: not recommended.
GFR 30-50 m L/min: 2 mg once daily. GFR <30 m L/min: not recommended.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% and extend interval to every 8 hours; Child-Pugh C: contraindicated.
Child-Pugh A: no adjustment. Child-Pugh B: 2 mg once daily. Child-Pugh C: not recommended.
For children ≥12 years: acetaminophen 10-15 mg/kg/dose and codeine 0.5-1 mg/kg/dose orally every 4-6 hours; maximum acetaminophen 75 mg/kg/day, codeine 6 mg/kg/day. For children <12 years: not recommended due to codeine safety concerns.
Not established; contraindicated in children under 12 years.
Start with lowest effective dose; acetaminophen component maximum 3 g/day; consider reduced codeine dose (e.g., 15 mg) due to increased sensitivity and risk of respiratory depression; extend dosing interval to every 6-8 hours.
Start at 2 mg once daily; titrate cautiously due to increased risk of hypotension and cognitive effects.
Risk of medication errors: confusion between milligram and milliliter doses, and between codeine and acetaminophen components. Contraindicated for postoperative pain management in children following tonsillectomy/adenoidectomy due to risk of respiratory depression and death.
Not applicable (no FDA boxed warning).
Hepatotoxicity (acetaminophen overdose); respiratory depression; drug dependence; ultra-rapid metabolizers of codeine (CYP2D6) leading to morphine toxicity; concomitant CNS depressants; use in pediatric patients; avoid alcohol.
Do not use in patients with severe hypertension or coronary artery disease; caution in hyperthyroidism, diabetes, glaucoma, prostatic hypertrophy, and MAOI use; avoid exceeding recommended dose due to risk of serious cardiovascular events; may cause drowsiness or excitability in children.
Hypersensitivity to acetaminophen or codeine; severe respiratory depression; acute or severe asthma; paralytic ileus; post-operative pain management in children after tonsillectomy/adenoidectomy; breastfeeding (in ultra-rapid metabolizers); concomitant MAOIs.
Hypersensitivity to diphenhydramine, pseudoephedrine, or any component; severe hypertension; severe coronary artery disease; concurrent MAOI therapy or within 14 days; narrow-angle glaucoma; urinary retention; during or within 2 weeks of MAOI use.
Avoid alcohol; high-fat meals may delay absorption but not clinically significant.
Avoid alcohol entirely. Folic acid supplementation is often prescribed to reduce side effects; do not take any other folate supplements without approval. Caffeine may slightly increase absorption, but no specific dietary restrictions. Maintain adequate hydration to help prevent kidney toxicity.
Acetaminophen is considered low risk in all trimesters at therapeutic doses; chronic high doses may be associated with adverse outcomes. Codeine is associated with risk of respiratory depression and neonatal withdrawal if used near term; may cause neural tube defects and other malformations with first-trimester exposure, but data are conflicting. Use lowest effective dose for shortest duration.
DI-METREX (metformin) is classified as FDA Pregnancy Category B. First trimester: No increased risk of major congenital anomalies observed in human studies; some studies suggest reduced risk of neural tube defects in women with PCOS. Second and third trimesters: Risk of neonatal hypoglycemia and macrosomia reduced compared to untreated diabetes; no evidence of teratogenicity. Overall, benefits of glycemic control outweigh potential risks.
Acetaminophen is excreted into breast milk in low amounts (M/P ratio ~0.91-1.42) and is considered compatible with breastfeeding. Codeine is also excreted in breast milk; risk of infant opioid toxicity depends on maternal CYP2D6 phenotype. Ultra-rapid metabolizers may produce higher morphine levels. Use with caution, avoid in known CYP2D6 ultra-rapid metabolizers, and monitor infant for sedation and respiratory depression.
Metformin is excreted into breast milk in small amounts with an M/P ratio (milk-to-plasma ratio) of approximately 0.35. Infant exposure is estimated at 0.2-1% of maternal weight-adjusted dose. No adverse effects reported in breastfed infants; however, caution in premature infants or those with renal impairment.
No routine dose adjustment needed for acetaminophen. Codeine pharmacokinetics are altered in pregnancy: increased clearance and volume of distribution may require dose adjustment; however, due to variability in CYP2D6 metabolism, individualize dosing and monitor for efficacy and toxicity. Avoid codeine in pregnancy unless alternative analgesics are ineffective.
No routine dose adjustment recommended. However, as pregnancy progresses, renal function decreases and volume of distribution increases, which may reduce metformin clearance. Dose should be titrated to glycemic targets, up to a maximum of 2500 mg/day in divided doses. Monitor renal function and consider dose reduction if e GFR < 30 m L/min/1.73 m².
For acute pain, limit codeine to 3 days; avoid in children under 12 due to CYP2D6 ultra-rapid metabolizer risk of fatal respiratory depression; monitor for constipation; assess liver function for acetaminophen hepatotoxicity; use with caution in renal impairment.
DI-METREX (methotrexate) has a long half-life; monitor for cumulative toxicity. Administer folic acid supplementation to reduce gastrointestinal and hematologic side effects. Use with caution in patients with ascites or pleural effusions, as drug accumulation can occur. Premedication with NSAIDs increases methotrexate toxicity. Always check liver function tests and renal function before each dose.
Take exactly as prescribed; do not exceed 4000 mg acetaminophen per day.,Avoid alcohol while taking this medication.,Do not use with other acetaminophen-containing products.,May cause dizziness or drowsiness; avoid driving until you know how you react.,Common side effects include constipation, nausea, and drowsiness.,Seek emergency if signs of allergic reaction or difficulty breathing occur.
Take methotrexate exactly as prescribed, usually once weekly, not daily. Serious harm can occur if taken daily.,Avoid alcohol completely to reduce liver damage risk.,Report any unusual bleeding, bruising, fever, mouth sores, or persistent cough immediately.,Do not take any other medications, including over-the-counter and herbal products, without first consulting your doctor.,Use effective contraception; methotrexate can cause severe birth defects.
"Pirenzepine, a selective M1 muscarinic antagonist, reduces gastrointestinal motility and secretions, while codeine, an opioid agonist, also decreases gastrointestinal motility via mu-opioid receptors. Concurrent use leads to additive anticholinergic and opioid effects, resulting in enhanced risk of severe constipation, paralytic ileus, and central nervous system depression. Clinically, patients may experience exacerbated sedation, respiratory depression, and urinary retention."
"Ropinirole, a non-ergoline dopamine agonist used in Parkinson's disease and restless legs syndrome, may reduce the analgesic efficacy of codeine. This is likely due to pharmacodynamic antagonism at central dopamine and opioid receptors, as well as potential pharmacokinetic interactions that decrease the conversion of codeine to its active metabolite morphine via CYP2D6 inhibition by ropinirole. The resultant blunted opioid response can lead to inadequate pain control, necessitating dose adjustment or alternative therapy."
"Vemurafenib induces CYP3A4, significantly reducing the plasma concentrations of codeine, which is metabolized via CYP3A4 to its active metabolite morphine. This may diminish codeine's analgesic efficacy, potentially leading to inadequate pain control. Additionally, reduced formation of morphine may lower the risk of opioid-related adverse effects."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ACETAMINOPHEN AND CODEINE PHOSPHATE vs DI-METREX, answered by our medical review team.
ACETAMINOPHEN AND CODEINE PHOSPHATE is a Opioid Agonist that works by Acetaminophen: centrally acting analgesic and antipyretic, possibly via inhibition of cyclooxygenase (COX) and modulation of cannabinoid receptors. Codeine: prodrug converted to morphine; mu-opioid receptor agonist.. DI-METREX is a Antihistamine-Decongestant that works by Combination of diphenhydramine (H1-antagonist) and pseudoephedrine (alpha-1 agonist). Diphenhydramine blocks histamine at H1 receptors, reducing allergic symptoms; pseudoephedrine causes vasoconstriction via alpha-1 adrenergic receptors, relieving nasal congestion.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ACETAMINOPHEN AND CODEINE PHOSPHATE and DI-METREX 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 ACETAMINOPHEN AND CODEINE PHOSPHATE is: One or two tablets (acetaminophen 300 mg/codeine 30 mg per tablet) orally every 4-6 hours as needed for pain; maximum 12 tablets daily.. The standard adult dose of DI-METREX is: 4 mg orally once daily, increased to a maximum of 8 mg once daily if needed.. 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 ACETAMINOPHEN AND CODEINE PHOSPHATE and DI-METREX 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. ACETAMINOPHEN AND CODEINE PHOSPHATE is classified as Category D/X. Acetaminophen is considered low risk in all trimesters at therapeutic doses; chronic high doses may be associated with adverse outcomes. Codeine is associated with risk of respirat. DI-METREX is classified as Category C. DI-METREX (metformin) is classified as FDA Pregnancy Category B. First trimester: No increased risk of major congenital anomalies observed in human studies; some studies suggest re. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.