Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ULTRAM ER vs ALFENTA
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.
μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.
Management of moderate to moderately severe chronic pain in adults requiring around-the-clock treatment
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
100 mg orally once daily initially, titrate up to 100 mg twice daily as needed; maximum 200 mg/day.
Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.
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); prolonged in hepatic impairment.
Metabolized primarily via CYP2D6 and CYP3A4; O-desmethyltramadol (M1) is the active metabolite formed by CYP2D6; tramadol and metabolites undergo further conjugation.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
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 renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Approximately 20% bound to plasma proteins, primarily albumin.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Volume of distribution is approximately 2.6-3.0 L/kg, indicating extensive tissue distribution beyond plasma volume.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
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.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
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.
No specific dose adjustment is recommended for renal impairment; however, alfentanil is primarily metabolized in the liver and its pharmacokinetics are not significantly altered in renal failure.
Child-Pugh Class A or B: use with caution, consider reducing total daily dose by 50%; Child-Pugh Class C: contraindicated.
In hepatic impairment (Child-Pugh class A, B, C): Reduce dose by 50% and titrate carefully due to prolonged elimination half-life. Consider lower initial doses and extended dosing intervals.
Not recommended for use in pediatric patients <18 years due to risk of respiratory depression and lack of safety data.
Children (1-12 years): Induction of anesthesia: 10-20 mcg/kg IV; maintenance: 5-10 mcg/kg IV or infusion 0.5-1 mcg/kg/min. For neonates and infants: Dose individualization required; titrate to effect.
Start at lowest dose (100 mg once daily); titrate cautiously; monitor for CNS and respiratory depression; consider reduced clearance in elderly.
Elderly patients (>65 years): Reduce initial dose by 30-50% and administer slowly. Due to decreased clearance and increased sensitivity, lower infusion rates (e.g., 0.3-0.5 mcg/kg/min) may be needed.
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, particularly in elderly or debilitated patients. Concomitant use with benzodiazepines or other CNS depressants may cause profound sedation, respiratory depression, coma, and death.
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; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
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 or any component; significant respiratory insufficiency; severe asthma; paralytic ileus; concurrent use of MAOIs (or within 14 days); acute or postoperative pain management in children (except for procedural sedation).
Avoid alcohol. No specific food restrictions; however, taking with food may reduce nausea. Grapefruit juice may increase tramadol levels; consider limiting grapefruit intake.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
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, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effects were observed at clinically relevant doses; however, high doses caused embryotoxicity and increased fetal mortality. Trimester-specific risks: First trimester - potential for minor malformations based on limited human data; second trimester - possible risk if used chronically; third trimester - prolonged use may lead to neonatal respiratory depression, withdrawal syndrome, or opioid dependence. Use only if benefits outweigh risks.
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 human breast milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.3. Estimated infant dose is <1% of maternal weight-adjusted dose, which is considered clinically insignificant. However, due to potential for neonatal opioid effects, caution is advised; monitor infant for drowsiness, respiratory depression, and feeding difficulties. Consider alternative analgesics with established safety profiles, such as acetaminophen or ibuprofen, for lactation.
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 pharmacokinetics of alfentanil. Increased plasma volume and distribution may require higher doses to achieve same effect, while decreased plasma protein binding may increase free fraction, potentiating effects. Alpha-1-acid glycoprotein levels change in pregnancy, affecting binding. In third trimester, clearance may be increased by up to 50% due to enhanced hepatic metabolism. Therefore, dose adjustments may be needed: consider starting at low dose and titrating to effect, with close monitoring. For intravenous administration, typical adult doses (5-20 μg/kg) may need adjustments; no standard pregnancy-specific dosing exists. Use the lowest effective dose for the shortest duration. In labor, avoid high doses prior to delivery due to risk of neonatal respiratory depression.
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, rapid-onset, short-acting opioid analgesic used primarily for induction and maintenance of anesthesia. Due to its high protein binding (90%) and rapid redistribution, it has a shorter duration of action than fentanyl, making it suitable for brief, painful procedures. It undergoes hepatic metabolism via CYP3A4, so concomitant use with CYP3A4 inhibitors like ketoconazole or erythromycin can prolong its effects. Use caution in elderly or hypovolemic patients due to increased risk of hypotension. Naloxone reverses respiratory depression. Alfentanil is 5-10 times less potent than fentanyl.
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 is given only by a healthcare professional in a hospital or surgical setting.,You may feel drowsy, dizzy, or nauseated after receiving this drug.,Report any difficulty breathing or slow heart rate to your healthcare provider immediately.,Avoid alcohol and sedatives for 24 hours after administration, as they can increase side effects.,Do not drive or operate machinery until the effects have fully worn off.
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 ALFENTA, 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.. ALFENTA is a Opioid Analgesic that works by μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ULTRAM ER and ALFENTA 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 ALFENTA is: Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.. 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 ALFENTA 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. ALFENTA is classified as Category C. Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effect. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.