Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FENTANYL-100 vs ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Fentanyl is a μ-opioid receptor agonist. It binds to μ-opioid receptors in the central nervous system, activating G-protein coupled receptor signaling (inhibition of adenylate cyclase, modulation of ion channels), leading to increased potassium conductance and decreased calcium influx, resulting in hyperpolarization and reduced neurotransmitter release. This produces analgesia, sedation, and respiratory depression.
Acetaminophen: cyclooxygenase (COX) inhibitor, primarily in the CNS, reducing prostaglandin synthesis; analgesic and antipyretic. Oxycodone: mu-opioid receptor agonist, inhibiting ascending pain pathways and altering pain perception.
Management of pain in opioid-tolerant patients requiring around-the-clock opioid analgesia for severe chronic pain,Anesthesia (adjunct to general or regional anesthesia),Procedural sedation,Patient-controlled analgesia (PCA),Breakthrough pain management (off-label use)
Management of moderate to moderately severe pain,Acute pain,Chronic pain
100 mcg intravenously every 1-2 hours as needed for pain; or 100 mcg intramuscularly every 1-2 hours; transdermal patch: 12-100 mcg/hour applied every 72 hours; buccal tablet: 100-200 mcg as a single dose for breakthrough pain.
1-2 tablets (equivalent to 325-650 mg acetaminophen / 5-10 mg oxycodone) every 4-6 hours as needed for pain; maximum 12 tablets per day (acetaminophen limit 3900 mg/day or lower if hepatic risk).
Terminal elimination half-life: 2–4 hours in adults; prolonged in elderly, hepatic impairment, or continuous infusion (due to redistribution).
Acetaminophen: 2-3 hours (prolonged in hepatic impairment or overdose); Oxycodone: 3-5 hours (immediate-release), 4.5-8 hours (extended-release); Clinical context: Terminal half-life of oxycodone may be prolonged in elderly or patients with renal/hepatic impairment.
Primarily hepatic via CYP3A4, with minor contribution from CYP3A5. Major metabolites: norfentanyl (inactive), despropionylfentanyl. Approximately 10-25% excreted unchanged in urine.
Acetaminophen: primarily hepatic via glucuronidation (UGT1A1, UGT1A6, UGT1A9), sulfation (SULT1A1), and minor CYP450 (CYP2E1, CYP3A4) to toxic NAPQI. Oxycodone: hepatic via CYP3A4 (major) and CYP2D6 (minor) to active metabolites (noroxycodone, oxymorphone).
Primarily hepatic metabolism to inactive metabolites (norfentanyl, etc.); ~75% excreted in urine as metabolites, ~9% in feces, <10% unchanged in urine.
Acetaminophen: renal excretion of metabolites (glucuronide 45-55%, sulfate 20-30%, cysteine and mercapturate conjugates 5-10%) and unchanged drug (<5%); Oxycodone: renal excretion of unchanged drug (approximately 10-19%) and metabolites (noroxycodone, oxymorphone, and their glucuronides) (total renal elimination ~60-87%); fecal elimination of Oxycodone is minimal (<10%).
~80–85% bound, primarily to albumin and alpha-1-acid glycoprotein.
Acetaminophen: 20-30% (albumin); Oxycodone: 45-50% (albumin).
3–8 L/kg (large Vd indicates extensive tissue distribution, especially to fat and muscle).
Acetaminophen: 0.9-1.0 L/kg (suggests distribution into total body water); Oxycodone: 2.6-4.0 L/kg (suggests extensive tissue distribution).
Oral: <40% (first-pass metabolism); Buccal: ~50%; Intranasal: 50–90%; Transdermal: ~30–60% (steady state).
Acetaminophen: Oral 85-90%; Oxycodone: Oral 60-87% (first-pass metabolism), Rectal (oxycodone suppository) ~60-80%.
GFR 30-50 m L/min: reduce dose by 25-50%; GFR 10-29 m L/min: reduce dose by 50-75% and extend dosing interval; GFR <10 m L/min: use with caution, consider alternative therapy; not removed by hemodialysis.
e GFR 30-60 m L/min: start with 50% of usual dose, increase cautiously; e GFR <30 m L/min: start with 25% of usual dose, extend dosing interval to every 8-12 hours; avoid in dialysis due to oxycodone accumulation.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: reduce dose by 75% or use alternative; monitor for respiratory depression.
Child-Pugh A: no adjustment; Child-Pugh B: start with 50% of usual dose, maximum acetaminophen 2000 mg/day; Child-Pugh C: contraindicated.
Intravenous: 0.5-2 mcg/kg/dose every 2-4 hours; transmucosal: 5-15 mcg/kg for procedural analgesia; transdermal patch: not recommended in children <2 years; in older children, use lowest effective dose based on body weight and opioid tolerance.
Weight-based: oxycodone 0.05-0.15 mg/kg/dose (max 5 mg/dose) with acetaminophen 10-15 mg/kg/dose every 4-6 hours; maximum acetaminophen 75 mg/kg/day (not to exceed 4000 mg/day).
Start at 25-50% of adult dose; titrate slowly; avoid transdermal patch in opioid-naive elderly; monitor for delirium and respiratory depression; prefer intravenous or buccal routes with careful observation.
Start with lowest dose (e.g., half of adult dose), titrate slowly; avoid in patients with impaired renal/hepatic function or those at risk for falls; monitor for respiratory depression and constipation.
Risk of respiratory depression, which may be fatal, especially in opioid-naive patients and when used in higher doses or with other CNS depressants. Risk of accidental exposure leading to fatal overdose. Risk of abuse, misuse, addiction, and diversion. Concomitant use with benzodiazepines or other CNS depressants may result in profound sedation, respiratory depression, coma, and death. Avoid use in patients with known or suspected paralytic ileus. Use only in opioid-tolerant patients for outpatient chronic pain management.
Risk of addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion of acetaminophen may cause hepatotoxicity; neonatal opioid withdrawal syndrome; CYP3A4 interaction with benzodiazepines or other CNS depressants.
Respiratory depression: monitor closely, especially during initiation and dose titration. Abuse and addiction potential: fentanyl is a Schedule II controlled substance. Life-threatening respiratory depression with concurrent use of benzodiazepines or CNS depressants. Serotonin syndrome when coadministered with serotonergic drugs. Adrenal insufficiency. Severe hypotension, including orthostatic hypotension. Risk of seizures in patients with seizure disorders. Avoid use in patients with head injury or increased intracranial pressure. Biliary tract spasm. Use in pregnancy may cause neonatal opioid withdrawal syndrome. Avoid abrupt discontinuation to prevent withdrawal. Must be used only in opioid-tolerant patients for outpatient management.
Addiction, abuse, misuse; respiratory depression; accidental exposure; neonatal opioid withdrawal syndrome; hepatotoxicity (acetaminophen); interactions with CNS depressants; elderly or debilitated patients; renal impairment; severe hypotension; adrenal insufficiency; use in patients with head injury.
Hypersensitivity to fentanyl or any component of the product, significant respiratory depression, acute or severe bronchial asthma in an unmonitored setting, known or suspected gastrointestinal obstruction (including paralytic ileus), concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of stopping such therapy.
Hypersensitivity to acetaminophen or oxycodone; significant respiratory depression; acute or severe bronchial asthma; GI obstruction (e.g., paralytic ileus); severe hepatic impairment; concurrent use with MAOIs or within 14 days.
Avoid or limit alcohol and grapefruit juice as they can potentiate respiratory depression and alter fentanyl metabolism. Maintain adequate hydration and fiber intake to prevent constipation.
Avoid alcohol. Grapefruit juice may increase oxycodone levels; limit or avoid grapefruit products. High-fat meals may delay absorption of oxycodone. Maintain adequate hydration to prevent constipation.
FDA Pregnancy Category C. First trimester: Limited human data; animal studies show teratogenic effects at high doses. Second and third trimesters: Chronic use may lead to neonatal opioid withdrawal syndrome; no structural malformations reported at therapeutic doses.
Acetaminophen: Generally considered low risk; no consistent association with major malformations. Oxycodone: First trimester: No increased risk of major malformations in human studies. Second and third trimesters: Risk of neonatal opioid withdrawal syndrome (NOWS) with chronic use; respiratory depression at delivery. No specific human data for combination; extrapolated from individual components.
Fentanyl is excreted into breast milk in low concentrations; M/P ratio is approximately 0.4. Limited data suggest minimal risk at maternal doses; however, monitor infant for signs of sedation or respiratory depression. Avoid use with breastfeeding for 24 hours after administration due to long half-life.
Acetaminophen: Compatible; M/P ratio ~1.0 (low transfer). Oxycodone: Low levels in milk; M/P ratio ~3.6 (relative infant dose 1.7–6.3% of maternal weight-adjusted dose). Monitor infant for drowsiness, respiratory depression. Use lowest effective dose, shortest duration.
No specific dose adjustment required for acute pain; however, increased clearance in late pregnancy may necessitate higher doses for chronic pain. Use lowest effective dose for shortest duration to minimize neonatal withdrawal risk.
Acetaminophen: No dose adjustment needed; use lowest effective dose. Oxycodone: Pharmacokinetic changes in pregnancy include increased clearance (due to enhanced hepatic metabolism and renal blood flow) and increased volume of distribution, potentially reducing plasma concentrations. Dose may need to be increased (monitor for efficacy and avoid withdrawal); however, use lowest effective dose to minimize neonatal risks. Consider non-opioid alternatives.
FENTANYL-100 transdermal patch is indicated only for opioid-tolerant patients with chronic pain requiring around-the-clock analgesia. Apply to non-irritated, non-hairy skin on upper torso or inner forearm; avoid heating pads, saunas, or sun exposure that increase absorption. Monitor for respiratory depression, especially in opioid-naive patients. Patches should be replaced every 72 hours; do not cut or damage the patch. Dispose of used patches by folding adhesive sides together and flushing down toilet.
Monitor for acetaminophen hepatotoxicity; maximum daily acetaminophen intake should not exceed 4000 mg. Oxycodone has high abuse potential; consider prescribing naloxone for patients at risk of opioid overdose. Avoid concurrent use of other CNS depressants. Use with caution in elderly or renally impaired patients.
Apply the patch to clean, dry, hairless skin and press firmly for 30 seconds.,Do not expose the patch to direct heat sources (heating pads, hot tubs, electric blankets).,Keep away from children and pets; used patches must be flushed down toilet.,Do not drink alcohol or take other central nervous system depressants without consulting your doctor.,Report any difficulty breathing, extreme drowsiness, or confusion immediately.
Do not exceed 4000 mg of acetaminophen per day from all sources.,This medication can cause drowsiness; avoid driving or operating machinery until you know how it affects you.,Do not consume alcohol while taking this medication.,Take exactly as prescribed; do not crush, chew, or break extended-release tablets.,Store securely out of reach of children and dispose of unused medication properly.,Seek emergency medical attention if you experience difficulty breathing, severe drowsiness, or signs of an allergic reaction.
"Metaraminol, a direct-acting alpha-adrenergic agonist, can reduce the serum concentration of fentanyl, a potent opioid analgesic, likely through enhanced hepatic metabolism or altered renal clearance. This interaction may lead to diminished analgesic efficacy of fentanyl, requiring higher doses to achieve pain control and potentially increasing the risk of opioid withdrawal symptoms. Clinically, patients receiving both drugs may exhibit inadequate pain relief or unexpected opioid tolerance."
"The concomitant use of pergolide, a dopamine receptor agonist, and fentanyl, a μ-opioid receptor agonist, may result in additive central nervous system depression, leading to increased sedation, respiratory depression, and potential for coma or death. Pergolide can also potentiate the hypotensive effects of opioids, resulting in orthostatic hypotension and syncope. Additionally, both drugs can prolong the QTc interval, increasing the risk of torsades de pointes and sudden cardiac death."
"The combination of glycopyrronium, an anticholinergic agent, and fentanyl, a potent mu-opioid receptor agonist, can result in additive anticholinergic effects, specifically severe constipation, urinary retention, and central nervous system depression, leading to delirium or cognitive impairment in susceptible patients. Additionally, fentanyl-induced gastrointestinal hypomotility is exacerbated by glycopyrronium, increasing the risk of paralytic ileus. Clinically, patients may present with prolonged QTc interval, decreased gastrointestinal motility, and exacerbated sedation, particularly in elderly or renally impaired individuals."
"Phenobarbital, a potent inducer of cytochrome P450 (CYP) enzymes, particularly CYP3A4 and CYP2D6, significantly increases the hepatic metabolism of oxycodone, a prodrug that requires CYP3A4-mediated N-demethylation to noroxycodone and CYP2D6-mediated O-demethylation to oxymorphone for its analgesic effects. This induction reduces the systemic exposure and peak plasma concentration of active oxycodone and its active metabolite oxymorphone, leading to diminished analgesic efficacy and potential opioid withdrawal symptoms in patients on chronic opioid therapy. Clinically, patients may require substantially higher doses of oxycodone to achieve pain relief, increasing the risk of dose-related adverse effects if the interaction is not recognized."
"The co-administration of oxycodone, a mu-opioid receptor agonist, and gamma-hydroxybutyric acid (GHB), a central nervous system depressant with activity at GABA-B and GHB receptors, results in additive or synergistic respiratory depression and CNS depression. This interaction potentiates the risk of severe hypoventilation, coma, and fatal overdose, especially in non-tolerant users or at therapeutic doses. The combined sedation also increases the likelihood of hypotension, bradycardia, and impaired psychomotor function, necessitating extreme caution."
"The coadministration of oxycodone, a mu-opioid receptor agonist with central nervous system (CNS) depressant effects, and perampanel, a noncompetitive AMPA receptor antagonist that also causes CNS depression, produces additive sedative and respiratory depressant effects. This synergy increases the risk of excessive sedation, impaired cognitive function, and potentially life-threatening respiratory depression. Patients may experience profound somnolence, confusion, and an increased fall risk, necessitating dose adjustments or avoidance."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about FENTANYL-100 vs ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE, answered by our medical review team.
FENTANYL-100 is a Opioid Agonist that works by Fentanyl is a μ-opioid receptor agonist. It binds to μ-opioid receptors in the central nervous system, activating G-protein coupled receptor signaling (inhibition of adenylate cyclase, modulation of ion channels), leading to increased potassium conductance and decreased calcium influx, resulting in hyperpolarization and reduced neurotransmitter release. This produces analgesia, sedation, and respiratory depression.. ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE is a Opioid Agonist that works by Acetaminophen: cyclooxygenase (COX) inhibitor, primarily in the CNS, reducing prostaglandin synthesis; analgesic and antipyretic. Oxycodone: mu-opioid receptor agonist, inhibiting ascending pain pathways and altering pain perception.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FENTANYL-100 and ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE depend on the specific clinical indication. These are both Opioid Agonist agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of FENTANYL-100 is: 100 mcg intravenously every 1-2 hours as needed for pain; or 100 mcg intramuscularly every 1-2 hours; transdermal patch: 12-100 mcg/hour applied every 72 hours; buccal tablet: 100-200 mcg as a single dose for breakthrough pain.. The standard adult dose of ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE is: 1-2 tablets (equivalent to 325-650 mg acetaminophen / 5-10 mg oxycodone) every 4-6 hours as needed for pain; maximum 12 tablets per day (acetaminophen limit 3900 mg/day or lower if hepatic risk).. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
A moderate-severity drug interaction has been identified when combining FENTANYL-100 and ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE. The risk or severity of adverse effects can be increased when Oxycodone is combined with Fentanyl. Consult your prescriber before combining these medications.
The maternal-fetal safety profiles differ. FENTANYL-100 is classified as Category D/X. FDA Pregnancy Category C. First trimester: Limited human data; animal studies show teratogenic effects at high doses. Second and third trimesters: Chronic use may lead to neonatal . ACETAMINOPHEN; OXYCODONE HYDROCHLORIDE is classified as Category D/X. Acetaminophen: Generally considered low risk; no consistent association with major malformations. Oxycodone: First trimester: No increased risk of major malformations in human stud. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.