Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ROXICET 5/500 vs ATROPINE AND DEMEROL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Oxycodone is a full opioid agonist that binds to mu-opioid receptors in the CNS, inhibiting ascending pain pathways and altering pain perception. Acetaminophen inhibits cyclooxygenase (COX) enzymes, primarily in the CNS, reducing prostaglandin synthesis and producing analgesic and antipyretic effects.
Atropine is an antimuscarinic agent that competitively blocks acetylcholine at muscarinic receptors, reducing secretions and gastrointestinal motility. Meperidine (Demerol) is an opioid agonist that binds to mu-opioid receptors in the CNS, altering pain perception and producing analgesia.
Management of moderate to moderately severe pain where treatment with an opioid is appropriate and for which alternative treatments are inadequate
Preanesthetic medication to reduce secretions and prevent bradycardia,Management of moderate to severe pain (as an opioid analgesic),Off-label: treatment of opioid-induced constipation (meperidine component)
1-2 tablets (5-10 mg oxycodone / 325-650 mg acetaminophen) orally every 4-6 hours as needed for pain; maximum 12 tablets per day (60 mg oxycodone / 6000 mg acetaminophen) in 24 hours.
Atropine 0.4 mg and Demerol (meperidine) 50-100 mg intramuscularly as preanesthetic medication 30-60 minutes before procedure.
Oxycodone: 3-5 hours (immediate-release); Acetaminophen: 2-3 hours. In hepatic impairment, oxycodone half-life prolonged (up to 12-15 hours).
Atropine: 2-4 hours (terminal half-life). Demerol: 2.5-4 hours; normeperidine metabolite half-life 15-30 hours (accumulates in renal impairment).
Oxycodone is metabolized primarily via CYP3A4 and CYP2D6 to noroxycodone and oxymorphone. Acetaminophen is metabolized mainly via glucuronidation (UGT1A1, UGT1A6, UGT1A9) and sulfation, with minor oxidation by CYP2E1 and CYP1A2 producing N-acetyl-p-benzoquinone imine (NAPQI).
Meperidine is primarily metabolized in the liver via hydrolysis to meperidinic acid and via N-demethylation to normeperidine (active metabolite), involving CYP3A4 and CYP2B6. Atropine is metabolized in the liver via hydrolysis and glucuronidation; approximately 50% is excreted unchanged in urine.
Oxycodone: primarily hepatic metabolism to noroxycodone, oxymorphone, and conjugates; renal elimination of metabolites (about 60-87% as unchanged and metabolites), fecal < 10%. Acetaminophen: renal elimination of conjugates (90-100%), <5% unchanged.
Atropine: approximately 50% excreted unchanged in urine, remainder as metabolites (biliary and renal). Demerol (meperidine): primarily hepatic metabolism; <5% excreted unchanged in urine; metabolites (including normeperidine) excreted renally.
Oxycodone: ~45% bound to albumin; Acetaminophen: 10-25% bound to albumin.
Atropine: ~44% bound to albumin and alpha-1 acid glycoprotein. Demerol: ~60% bound to albumin and alpha-1 acid glycoprotein.
Oxycodone: 2-3 L/kg (extensive tissue distribution); Acetaminophen: 0.8-1.0 L/kg (distribution throughout body water).
Atropine: 1-3 L/kg (large, extensive tissue distribution). Demerol: 3-5 L/kg (large, distributes widely including CNS).
Oxycodone oral: 60-87% (high first-pass metabolism varies); Acetaminophen oral: 80-90%.
Atropine: oral ~10-25% (extensive first-pass metabolism). Demerol: oral ~50-60% (significant first-pass metabolism). IM/IV 100%.
Cr Cl 30-50 m L/min: administer every 6 hours. Cr Cl 10-29 m L/min: administer every 8 hours. Cr Cl <10 m L/min: use not recommended due to oxycodone accumulation; consider alternative.
Meperidine: GFR 10-50 m L/min: administer 75% of normal dose; GFR <10 m L/min: administer 50% of normal dose and avoid due to normeperidine accumulation. Atropine: no adjustment required.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 50% and extend dosing interval to every 8 hours. Child-Pugh Class C: contraindicated due to acetaminophen hepatotoxicity.
Meperidine: Child-Pugh A: reduce dose by 25%; Child-Pugh B: reduce by 50%; Child-Pugh C: contraindicated. Atropine: caution in severe hepatic impairment.
Not typically recommended; use weight-based dosing of oxycodone 0.1-0.2 mg/kg/dose (max 5 mg/dose) every 4-6 hours as needed, with acetaminophen component not to exceed 75 mg/kg/day. Not approved for children <12 years.
Atropine 0.01 mg/kg (max 0.4 mg) and meperidine 1-2 mg/kg (max 100 mg) intramuscularly 30-60 minutes before procedure.
Initiate at lowest dose (one tablet every 6 hours) and titrate cautiously. Monitor for respiratory depression, sedation, and constipation. Avoid doses >4 tablets per day unless tolerated.
Reduce meperidine dose by 50% and avoid in elderly due to risk of seizures and delirium; use alternative opioids. Atropine dose unchanged but monitor for anticholinergic effects.
Addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion of even one dose of oxycodone, especially by children, can cause fatal overdose; neonatal opioid withdrawal syndrome; cytochrome P450 3A4 interaction with concurrent use of benzodiazepines or other CNS depressants; hepatotoxicity due to acetaminophen (dose-related).
Meperidine has a boxed warning for risk of respiratory depression, especially in elderly, cachectic, or debilitated patients, and when used with CNS depressants. Also, risk of serotonin syndrome when co-administered with serotonergic drugs, and risk of abuse, addiction, and diversion.
Risk of opioid addiction, abuse, and misuse; life-threatening respiratory depression; risk of accidental ingestion; neonatal opioid withdrawal syndrome if used during pregnancy; risk of severe hypotension; risk of hepatotoxicity due to acetaminophen; risk of serotonin syndrome if co-administered with serotonergic drugs; adrenal insufficiency; risk of seizures; risk of increased intracranial pressure; severe renal or hepatic impairment; drug interactions with CNS depressants and CYP3A4 inhibitors/inducers.
Respiratory depression, hypotension, bradycardia, urinary retention, constipation, serotonin syndrome, seizures (normeperidine accumulation), decreased GI motility, drug dependence, and tolerance. Use caution in elderly, renal impairment, hepatic impairment, respiratory disorders, prostatic hyperplasia, glaucoma, and with concurrent CNS depressants.
Hypersensitivity to oxycodone, acetaminophen, or any component of the formulation; significant respiratory depression; acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment; known or suspected gastrointestinal obstruction, including paralytic ileus; severe hepatic impairment (for acetaminophen component).
Hypersensitivity to atropine or meperidine; severe asthma or COPD; acute respiratory depression; paralytic ileus; known or suspected gastrointestinal obstruction; patients receiving MAOIs (within 14 days); myasthenia gravis (relative for atropine); increased intraocular pressure (glaucoma); severe renal impairment (normeperidine accumulation).
Avoid alcohol and grapefruit juice. High-fat meals may delay absorption of oxycodone, but does not affect total exposure.
Avoid alcohol. Meperidine may interact with foods containing tyramine (aged cheeses, cured meats) in patients on MAOIs; otherwise no significant food interactions.
Pregnancy Category C (oxycodone) and D (acetaminophen at high doses). Oxycodone: Risk of neonatal opioid withdrawal syndrome (NOWS) with prolonged use in third trimester; risk of respiratory depression near term. Acetaminophen: Epidemiologic data not conclusively linked to major malformations at therapeutic doses, but high doses may be associated with fetal hepatotoxicity. FDA warns against chronic use during pregnancy due to NOWS.
Atropine: FDA Pregnancy Category C. Crosses placenta; may cause fetal tachycardia. Demerol (meperidine): FDA Pregnancy Category C. First trimester: limited human data; animal studies show no teratogenicity. Second trimester: no specific risks. Third trimester: use near term may cause neonatal respiratory depression, decreased Apgar scores, and withdrawal symptoms. Chronic use may lead to neonatal opioid withdrawal syndrome (NOWS).
Oxycodone is excreted into breast milk with relative infant dose (RID) of 1.7-6.2% of maternal weight-adjusted dose; M/P ratio not well established (estimated ~1.3-3.7). Acetaminophen RID ~1-2%, M/P ratio ~0.91-1.0. Caution: Monitor infant for somnolence, respiratory depression, poor feeding. Avoid in breastfeeding women with CYP2D6 ultra-rapid metabolizer status due to increased morphine production.
Atropine: Excreted in breast milk in small amounts; may inhibit lactation. M/P ratio not established. Use with caution; monitor infant for anticholinergic effects (tachycardia, dry mouth). Demerol: Excreted in breast milk; relative infant dose (RID) ~0.5-0.8% of maternal weight-adjusted dose. M/P ratio 1.0-1.6. Limited data; avoid in breastfeeding due to potential neonatal sedation and respiratory depression. American Academy of Pediatrics considers meperidine compatible but caution advised.
Oxycodone: Increased clearance and volume of distribution in pregnancy may require higher doses for adequate analgesia; dose should be titrated to effect. Acetaminophen: Pharmacokinetic changes minimal at therapeutic doses; no routine dose adjustment needed, but limit to <3000 mg/day to avoid maternal hepatotoxicity. Postpartum: Oxycodone doses may need reduction due to normalization of clearance.
Atropine: No specific dose adjustments recommended; increased volume of distribution may require higher doses for effect. Demerol: Increased clearance and volume of distribution in pregnancy; standard doses may be less effective. Avoid use during labor due to risk of neonatal respiratory depression; if necessary, use lowest effective dose and monitor neonate. No specific dose reduction recommended, but caution with repeated doses.
ROXICET 5/500 contains oxycodone (5 mg) and acetaminophen (500 mg). The acetaminophen component limits total daily use to avoid hepatotoxicity; maximum 4 g/day from all sources. Oxycodone is a Schedule II controlled substance with high abuse potential. Use with caution in patients with respiratory compromise, head injury, or hepatic impairment. Coadministration with alcohol or other CNS depressants increases sedation and respiratory depression risk. Consider naloxone co-prescription for high-risk patients.
Atropine and Demerol (meperidine) combination is used for pre-anesthetic medication to reduce secretions and produce sedation. Monitor for CNS depression, respiratory depression, and anticholinergic effects (tachycardia, dry mouth, urinary retention). Use cautiously in elderly, patients with COPD, asthma, or prostatic hyperplasia. Avoid in patients with MAOIs due to risk of serotonin syndrome.
Take only as prescribed; do not exceed 8 tablets in 24 hours due to acetaminophen.,Avoid alcohol and medications containing acetaminophen (e.g., Tylenol, cold remedies) to prevent liver damage.,Do not crush or chew tablets—swallow whole.,May cause drowsiness or dizziness; avoid driving or operating machinery until effects known.,Store securely out of reach of others; dispose of unused tablets via drug take-back program.,Do not share with others; misuse can cause addiction, overdose, or death.,Seek emergency help if signs of overdose: slow breathing, extreme drowsiness, confusion, or loss of consciousness.
This medication may cause drowsiness, dizziness, or blurred vision; avoid driving or operating machinery until effects are known.,Avoid alcohol and other CNS depressants while taking this medication.,Report difficulty urinating, fast heartbeat, or severe constipation to your healthcare provider.,Do not take more than prescribed; risk of dependence with long-term use.,Keep out of reach of children; may cause serious breathing problems if accidentally taken.
No interactions on record
"Rivastigmine, a reversible carbamate acetylcholinesterase inhibitor, increases synaptic acetylcholine levels, enhancing cholinergic transmission. Atropine, a competitive antagonist of muscarinic acetylcholine receptors, blocks the effects of acetylcholine at these receptors, leading to reduced parasympathetic activity. When used together, atropine can diminish the therapeutic efficacy of rivastigmine by pharmacodynamically antagonizing its cholinergic effects, particularly in the central nervous system and peripheral muscarinic receptors, potentially worsening cognitive function in Alzheimer's disease patients."
"Umeclidinium, a long-acting muscarinic antagonist (LAMA), and atropine, a non-selective muscarinic antagonist, both block the action of acetylcholine at muscarinic receptors in the parasympathetic nervous system. Their co-administration leads to additive anticholinergic effects, resulting in an increased risk of peripheral anticholinergic adverse effects such as dry mouth, blurred vision, constipation, urinary retention, and tachycardia, as well as central nervous system effects like confusion or delirium, especially in elderly patients. Clinically, this combination may also exacerbate conditions such as angle-closure glaucoma or paralytic ileus."
"Concurrent use of atropine and gallamine triethiodide results in additive antagonism at muscarinic acetylcholine receptors, leading to enhanced blockade of parasympathetic effects and increased risk of tachycardia, hypertension, and delirium. Atropine, a competitive antagonist of muscarinic receptors, counteracts the vagolytic effects of gallamine, a nondepolarizing neuromuscular blocker that also exhibits weak vagolytic activity. This pharmacodynamic interaction can cause severe sinus tachycardia, hypertension, and central anticholinergic syndrome, especially in elderly patients or those with cardiovascular disease."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ROXICET 5/500 vs ATROPINE AND DEMEROL, answered by our medical review team.
ROXICET 5/500 is a Opioid Analgesic Combination that works by Oxycodone is a full opioid agonist that binds to mu-opioid receptors in the CNS, inhibiting ascending pain pathways and altering pain perception. Acetaminophen inhibits cyclooxygenase (COX) enzymes, primarily in the CNS, reducing prostaglandin synthesis and producing analgesic and antipyretic effects.. ATROPINE AND DEMEROL is a Opioid Analgesic Combination that works by Atropine is an antimuscarinic agent that competitively blocks acetylcholine at muscarinic receptors, reducing secretions and gastrointestinal motility. Meperidine (Demerol) is an opioid agonist that binds to mu-opioid receptors in the CNS, altering pain perception and producing analgesia.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ROXICET 5/500 and ATROPINE AND DEMEROL depend on the specific clinical indication. These are both Opioid Analgesic Combination agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ROXICET 5/500 is: 1-2 tablets (5-10 mg oxycodone / 325-650 mg acetaminophen) orally every 4-6 hours as needed for pain; maximum 12 tablets per day (60 mg oxycodone / 6000 mg acetaminophen) in 24 hours.. The standard adult dose of ATROPINE AND DEMEROL is: Atropine 0.4 mg and Demerol (meperidine) 50-100 mg intramuscularly as preanesthetic medication 30-60 minutes before procedure.. 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 ROXICET 5/500 and ATROPINE AND DEMEROL 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. ROXICET 5/500 is classified as Category C. Pregnancy Category C (oxycodone) and D (acetaminophen at high doses). Oxycodone: Risk of neonatal opioid withdrawal syndrome (NOWS) with prolonged use in third trimester; risk of r. ATROPINE AND DEMEROL is classified as Category C. Atropine: FDA Pregnancy Category C. Crosses placenta; may cause fetal tachycardia. Demerol (meperidine): FDA Pregnancy Category C. First trimester: limited human data; animal studi. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.