Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ULTRAM ER vs ALFENTANIL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Tramadol is a centrally acting synthetic opioid analgesic that binds to μ-opioid receptors and inhibits serotonin and norepinephrine reuptake.
Alfentanil is a potent, short-acting synthetic opioid analgesic that primarily acts as a mu-opioid receptor agonist. It binds to mu-opioid receptors in the central nervous system, leading to G-protein coupled activation of inwardly rectifying potassium channels and inhibition of voltage-gated calcium channels, resulting in hyperpolarization and reduced neurotransmitter release. This produces analgesia, sedation, and respiratory depression.
Management of moderate to moderately severe chronic pain in adults requiring around-the-clock treatment
Analgesic adjunct during general anesthesia,Induction of anesthesia,Maintenance of anesthesia for short surgical procedures,Off-label: Procedural sedation in monitored settings
100 mg orally once daily initially, titrate up to 100 mg twice daily as needed; maximum 200 mg/day.
Initial IV bolus of 5-20 mcg/kg; maintenance infusion of 0.5-1.5 mcg/kg/min; incremental boluses of 5-10 mcg/kg as needed. Induction of anesthesia: 50-100 mcg/kg IV.
The terminal elimination half-life of tramadol is approximately 6.3 hours (range 5-9 hours), while its active metabolite M1 has a half-life of about 7.4 hours. Clinically, this supports dosing every 24 hours for the extended-release formulation.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours). Clinically, context-sensitive half-time is short (~40 min after 3-hour infusion) due to rapid redistribution and metabolism.
Metabolized primarily via CYP2D6 and CYP3A4; O-desmethyltramadol (M1) is the active metabolite formed by CYP2D6; tramadol and metabolites undergo further conjugation.
Alfentanil is primarily metabolized by hepatic cytochrome P450 enzymes, mainly CYP3A4, through oxidative N-dealkylation and O-demethylation to inactive metabolites.
Renal excretion of tramadol and its metabolites accounts for approximately 90% of total elimination. About 10% is excreted unchanged, 30% as O-desmethyltramadol (M1), and the remainder as other minor metabolites. Biliary/fecal excretion is minimal (<10%).
Primarily hepatic metabolism via CYP3A4; <1% excreted unchanged in urine; metabolites (mainly noralfentanil) excreted renally. Biliary/fecal excretion of metabolites accounts for ~30%.
Approximately 20% bound to plasma proteins, primarily albumin.
~92% bound primarily to alpha-1-acid glycoprotein (AAG) and albumin.
Volume of distribution is approximately 2.6-3.0 L/kg, indicating extensive tissue distribution beyond plasma volume.
Vd: 0.4–1.0 L/kg (mean ~0.75 L/kg). Moderate Vd reflecting rapid distribution to tissues, especially brain and muscle.
Oral bioavailability of tramadol is approximately 75% after a single dose, increasing to 90-100% upon multiple dosing due to saturable first-pass metabolism. For ULTRAM ER, bioavailability is comparable to immediate-release formulations.
IV: 100%. IM: ~90%. Epidural: ~30–50% due to local uptake and redistribution. No significant oral bioavailability.
GFR 30-80 m L/min: no adjustment; GFR <30 m L/min: avoid or extend dosing interval to 12 hours; not recommended in GFR <15 m L/min.
GFR 10-50 m L/min: administer with caution, consider dose reduction of 25-50%; GFR <10 m L/min: reduce dose by 50% and extend dosing interval.
Child-Pugh Class A or B: use with caution, consider reducing total daily dose by 50%; Child-Pugh Class C: contraindicated.
Child-Pugh class A: no adjustment needed; Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: reduce dose by 75%.
Not recommended for use in pediatric patients <18 years due to risk of respiratory depression and lack of safety data.
Initial IV bolus of 5-20 mcg/kg; maintenance infusion of 0.5-2 mcg/kg/min. For neonates, reduce dose by 30-50% due to immature clearance.
Start at lowest dose (100 mg once daily); titrate cautiously; monitor for CNS and respiratory depression; consider reduced clearance in elderly.
Reduce initial IV bolus by 30-50% to 3-10 mcg/kg; titrate carefully; monitor for prolonged sedation and respiratory depression.
Risk of addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion in children can be fatal; neonatal opioid withdrawal syndrome; risk of medication errors with other tramadol products; interactions with CNS depressants; serotonin syndrome; contraindicated in patients with significant respiratory depression; contraindicated in patients with acute or severe bronchial asthma; contraindicated in patients with known or suspected gastrointestinal obstruction; contraindicated in patients with previous hypersensitivity to tramadol.
Risk of respiratory depression: Alfentanil can cause severe, life-threatening, or fatal respiratory depression. Monitor for respiratory depression, especially during initiation or following dose increases. Accidental ingestion of even one dose can be fatal. Concomitant use with central nervous system depressants (e.g., benzodiazepines, alcohol) may increase risk. Alfentanil is an opioid agonist and a Schedule II controlled substance with high potential for abuse and addiction.
Risk of respiratory depression; risk of serotonin syndrome with serotonergic drugs; risk of seizures especially in patients with epilepsy or risk factors; risk of adrenal insufficiency; risk of severe hypotension; risk of abuse and dependence; avoidance of abrupt discontinuation; use in renal or hepatic impairment; use in elderly; use in pregnancy and breastfeeding.
Respiratory depression: Potentially fatal; monitor oxygenation and ventilation.,Abuse potential: Schedule II controlled substance; risk of addiction, abuse, and diversion.,Concomitant use with CNS depressants: Increases risk of profound sedation, respiratory depression, coma, and death; limit use or monitor closely.,Geriatric and cachectic patients: Increased sensitivity; reduce initial dose.,Hepatic impairment: Alfentanil clearance is reduced in patients with cirrhosis; consider dose adjustment.,Bradycardia and hypotension: Use with caution in patients with hypovolemia or reduced cardiac reserve.,Serotonin syndrome: Risk with concurrent serotonergic drugs (e.g., MAOIs, SSRIs, triptans); monitor for symptoms.,Withdrawal: Prolonged use may lead to physical dependence; taper dose gradually.
Hypersensitivity to tramadol or any formulation component; significant respiratory depression; acute or severe bronchial asthma in unmonitored settings; known or suspected gastrointestinal obstruction; concurrent use of MAOIs or within 14 days; use in children <12 years; use in children <18 years after tonsillectomy/adenoidectomy; use in patients with severe hepatic impairment.
Hypersensitivity to alfentanil, fentanyl, or any opioid,Significant respiratory depression (e.g., acute asthma, COPD in acute exacerbation),Acute or severe bronchial asthma,Suspected or known paralytic ileus,MAO inhibitor use within 14 days (serotonin syndrome risk),Myasthenia gravis (relative contraindication due to risk of respiratory muscle weakness),Morbid obesity with sleep apnea (relative contraindication; increased risk of respiratory depression)
Avoid alcohol. No specific food restrictions; however, taking with food may reduce nausea. Grapefruit juice may increase tramadol levels; consider limiting grapefruit intake.
No significant food interactions known. Avoid grapefruit and grapefruit juice as they may inhibit CYP3A4 metabolism, potentially prolonging effects.
Pregnancy category C. First trimester: Limited data; avoid unless benefit outweighs risk due to potential neural tube defects. Second and third trimesters: Fetal dependence, neonatal withdrawal syndrome (seizures, irritability, respiratory depression) if used >7 days. Increased risk of preterm birth and low birth weight.
Alfentanil is an opioid analgesic; limited human data. No clear evidence of major malformations, but third trimester use may cause neonatal opioid withdrawal syndrome (NOWS). Avoid prolonged use or high doses near term; use during labor may cause respiratory depression in neonate.
Ultram ER has an M/P ratio of 0.7-1.3. Small amounts excreted; can cause infant sedation and constipation. Use caution; monitor infant for drowsiness or feeding difficulties.
Alfentanil is excreted into breast milk in very low concentrations; estimated relative infant dose is low (<2% of maternal weight-adjusted dose). M/P ratio not determined in humans. Compatible with breastfeeding with caution; monitor infant for drowsiness, feeding difficulties.
No established dose adjustments; pharmacokinetics may change in pregnancy (increased clearance, distribution volume). Use lowest effective dose; avoid sustained release if possible. Caution in third trimester due to risk of neonatal withdrawal.
Pregnancy can alter alfentanil pharmacokinetics: increased volume of distribution, decreased plasma clearance, prolonged elimination half-life. Dose reduction may be needed for prolonged use; titrate to effect. During labor, use smallest effective dose.
ULTRAM ER contains tramadol, an opioid agonist with SNRI properties. Do not crush or chew extended-release tablets; this can cause rapid release and fatal overdose. Use with caution in patients with seizure disorders or those taking SSRIs, SNRIs, MAOIs, or other drugs that lower seizure threshold. Avoid concurrent use with alcohol or CNS depressants. Monitor for serotonin syndrome when combined with serotonergic drugs. Do not discontinue abruptly after prolonged use; taper to avoid withdrawal symptoms. Not recommended for patients under 18. Crushing extended-release tablets is a safety hazard.
Alfentanil is a potent, short-acting synthetic opioid (4-5 times more potent than fentanyl) with rapid onset (1-2 min) and brief duration (5-10 min). Primarily used for induction and maintenance of anesthesia, especially in short procedures. Requires careful monitoring of respiratory depression and chest wall rigidity, particularly during rapid IV administration. Hepatic metabolism (CYP3A4) affected by liver disease; reduce dose. Decrease dose in elderly and hypovolemic patients. Not recommended for chronic pain due to short half-life.
Take ULTRAM ER exactly as prescribed, usually once daily. Swallow tablets whole; do not crush, chew, or break them.,Avoid alcohol and other CNS depressants (e.g., benzodiazepines, sedatives) while taking this medication.,This medication has a risk of addiction, abuse, and misuse. Store securely and dispose of unused tablets properly.,Do not stop taking this medicine suddenly; withdrawal symptoms may occur. Follow your doctor's instructions for tapering.,Seek emergency medical help if you have trouble breathing, severe drowsiness, or slow heartbeat.,Inform your doctor if you have a history of seizures, head injury, or are taking antidepressants like MAOIs, SSRIs, or SNRIs.,ULTRAM ER may cause constipation, nausea, dizziness, or drowsiness. Increase fluid intake and fiber to prevent constipation.,Keep out of reach of children and pets. Accidental ingestion can be fatal.,Do not drive or operate heavy machinery until you know how ULTRAM ER affects you.
This medication causes drowsiness and dizziness; avoid driving or operating machinery for at least 24 hours after administration.,Report any difficulty breathing, chest tightness, or feeling faint immediately.,Alfentanil is used only in hospital settings under direct supervision of healthcare professionals.,Inform your doctor if you have a history of liver disease, lung disease, or drug/alcohol abuse.,Do not consume alcohol or other sedatives while under the effects of alfentanil.
No interactions on record
"Propantheline, an anticholinergic agent, can competitively antagonize muscarinic acetylcholine receptors, potentially reducing gastrointestinal motility and secretion. Alfentanil, a mu-opioid receptor agonist, also decreases gastrointestinal motility through central and peripheral opioid receptors. Concomitant use may synergistically inhibit peristalsis, leading to severe constipation, paralytic ileus, or delayed gastric emptying, which can increase the risk of aspiration and complicate anesthesia recovery."
"Alfentanil, a potent opioid analgesic, can cause significant hypotension and respiratory depression. When combined with furosemide, a loop diuretic that reduces blood volume and vascular resistance, there is a synergistic decrease in blood pressure, which may precipitate cardiovascular collapse, especially in patients with compromised circulatory reserves. Additionally, furosemide may enhance the sedative and respiratory depressant effects of alfentanil, leading to increased risk of respiratory acidosis and altered mental status."
"Alfentanil, a potent mu-opioid receptor agonist, can enhance the bradycardic effects of nebivolol, a beta-1 selective blocker with additional nitric oxide-mediated vasodilation. The combination may lead to excessive slowing of heart rate, reduced cardiac output, and potential hemodynamic instability, particularly in patients with underlying cardiac conduction abnormalities or hypovolemia."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ULTRAM ER vs ALFENTANIL, answered by our medical review team.
ULTRAM ER is a Opioid Analgesic that works by Tramadol is a centrally acting synthetic opioid analgesic that binds to μ-opioid receptors and inhibits serotonin and norepinephrine reuptake.. ALFENTANIL is a Opioid Analgesic that works by Alfentanil is a potent, short-acting synthetic opioid analgesic that primarily acts as a mu-opioid receptor agonist. It binds to mu-opioid receptors in the central nervous system, leading to G-protein coupled activation of inwardly rectifying potassium channels and inhibition of voltage-gated calcium channels, resulting in hyperpolarization and reduced neurotransmitter release. This produces analgesia, sedation, and respiratory depression.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ULTRAM ER and ALFENTANIL depend on the specific clinical indication. These are both Opioid Analgesic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ULTRAM ER is: 100 mg orally once daily initially, titrate up to 100 mg twice daily as needed; maximum 200 mg/day.. The standard adult dose of ALFENTANIL is: Initial IV bolus of 5-20 mcg/kg; maintenance infusion of 0.5-1.5 mcg/kg/min; incremental boluses of 5-10 mcg/kg as needed. Induction of anesthesia: 50-100 mcg/kg IV.. 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 ULTRAM ER and ALFENTANIL 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. ULTRAM ER is classified as Category C. Pregnancy category C. First trimester: Limited data; avoid unless benefit outweighs risk due to potential neural tube defects. Second and third trimesters: Fetal dependence, neonat. ALFENTANIL is classified as Category C. Alfentanil is an opioid analgesic; limited human data. No clear evidence of major malformations, but third trimester use may cause neonatal opioid withdrawal syndrome (NOWS). Avoid. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.