Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
DURAGESIC-37 vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Fentanyl binds to mu-opioid receptors, activating G-protein coupled receptor signaling, leading to inhibition of adenylate cyclase, decreased c AMP production, and modulation of ion channels (increased potassium efflux, decreased calcium influx). This results in reduced neuronal excitability, inhibition of nociceptive transmission, and altered pain perception. Additionally, fentanyl may interact with other opioid receptors (kappa, delta) with lower affinity.
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 persistent, moderate to severe chronic pain in opioid-tolerant patients requiring around-the-clock opioid analgesia.,Management of breakthrough pain in cancer patients (immediate-release formulations).,Off-label: management of acute pain in emergency settings (e.g., trauma, procedures) under strict monitoring.,Off-label: management of postoperative pain (as part of multimodal analgesia).,Off-label: analgesia and sedation in mechanically ventilated patients (ICU setting).
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Initial: 25 mcg/hour transdermal patch applied every 72 hours. Titrate based on opioid tolerance. For opioid-naive patients: 12 mcg/hour patch.
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.
Terminal elimination half-life 20-27 hours (range 13-42 h) after transdermal removal; due to continuous absorption from skin depot, effective half-life is longer during patch wear.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Fentanyl undergoes N-dealkylation and hydroxylation predominantly via hepatic CYP3A4 isoenzymes. Major metabolites include norfentanyl (inactive) and despropionylfentanyl (hydroxyfentanyl, inactive). Minor pathways involve CYP3A5 and possibly CYP2D6. Less than 10% of fentanyl is excreted unchanged in urine; most is eliminated as metabolites in urine and bile.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily renal: 75% as metabolites (mostly norfentanyl) and <10% unchanged drug. Fecal: 9% via biliary elimination.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Approximately 40% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
6 L/kg (range 4-7 L/kg), indicating extensive tissue distribution including brain and muscle.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Transdermal: approximately 92% of the dose reaches systemic circulation due to high permeability and first-pass avoidance.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
e GFR 30-89 m L/min: no initial dose adjustment but monitor closely; e GFR <30 m L/min: reduce starting dose by 50% or use 12 mcg/hour patch and titrate cautiously.
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 A: no adjustment; Child-Pugh B: reduce starting dose by 50%; Child-Pugh C: consider alternative therapy; if used, start with 12 mcg/hour and monitor.
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.
For opioid-tolerant children ≥2 years: initiate with 25 mcg/hour patch if converting from ≥60 mg oral morphine equivalent. For opioid-naive children: not recommended. Dosing per weight: apply patch size based on prior opioid requirement (mcg/hour).
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.
In patients >65 years: reduce starting dose by 50% (e.g., 12 mcg/hour for opioid-tolerant) and titrate slowly due to increased sensitivity and reduced clearance.
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.
FENTANYL EXPOSES USERS TO RISKS OF ADDICTION, ABUSE, AND MISUSE, WHICH CAN LEAD TO OVERDOSE AND DEATH. ASSESS EACH PATIENT’S RISK PRIOR TO PRESCRIBING. SERIOUS, LIFE-THREATENING, OR FATAL RESPIRATORY DEPRESSION MAY OCCUR WITH USE. MONITOR FOR RESPIRATORY DEPRESSION, ESPECIALLY DURING INITIATION OR FOLLOWING DOSE INCREASES. ACCIDENTAL EXPOSURE TO FENTANYL, ESPECIALLY IN CHILDREN, CAN RESULT IN FATAL OVERDOSE. CONCOMITANT USE OF CYP3A4 INHIBITORS MAY INCREASE FENTANYL PLASMA CONCENTRATIONS, POTENTIALLY RESULTING IN FATAL RESPIRATORY DEPRESSION. NEONATAL OPIOID WITHDRAWAL SYNDROME MAY OCCUR WITH PROLONGED USE DURING PREGNANCY. CYTOCHROME P450 3A4 INHIBITOR CONCOMITANT USE OR DISCONTINUATION OF CYP3A4 INDUCERS MAY RESULT IN FATAL OVERDOSE.
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.
Respiratory depression: Life-threatening; monitor closely, especially during initiation and dose titration.,Addiction, abuse, and misuse: Increased risk with high doses and prolonged use.,Neonatal opioid withdrawal syndrome: Occurs with prolonged use during pregnancy; monitor neonates.,Interactions with CNS depressants (e.g., alcohol, benzodiazepines): Additive respiratory depression; avoid or reduce doses.,CYP3A4 interactions: Co-administration with CYP3A4 inhibitors (e.g., macrolides, azole antifungals) can increase fentanyl exposure; discontinue or reduce fentanyl dose. Co-administration with CYP3A4 inducers (e.g., rifampin, carbamazepine) may decrease efficacy.,Use in elderly or debilitated patients: Increased risk of respiratory depression; start with low doses and titrate slowly.,Use in patients with chronic pulmonary disease (e.g., COPD, cor pulmonale): Monitor respiratory function; may cause significant respiratory depression.,Use in patients with hepatic or renal impairment: Altered pharmacokinetics; monitor for adverse effects.,Use in patients with head injury or increased intracranial pressure: Avoid due to potential for respiratory depression and elevated CSF pressure; fentanyl may obscure neurological signs.,Use in patients with bradyarrhythmias (e.g., bradycardia): Fentanyl can decrease heart rate; use with caution.,Use in patients with convulsive disorders: May worsen seizures; monitor.,Use in patients with opioid addiction: May precipitate withdrawal; use only in opioid-tolerant patients.,Abrupt discontinuation: Can cause withdrawal symptoms; taper gradually.,Risk of severe hypotension: Especially in hypovolemic patients or those with compromised cardiovascular function.,Serotonin syndrome: Risk with concomitant use of serotonergic drugs (e.g., SSRIs, MAOIs); monitor for symptoms.,Adrenal insufficiency: Possible with prolonged opioid use; evaluate if symptoms develop.,Androgen deficiency: Possible with long-term use; consider if symptoms such as decreased libido, impotence, or amenorrhea occur.,Acute abdominal conditions: May obscure diagnosis or clinical course.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Hypersensitivity to fentanyl or any component of the formulation.,Significant respiratory depression (especially in unmonitored settings or absence of resuscitative equipment).,Acute or severe bronchial asthma in unmonitored settings.,Known or suspected gastrointestinal obstruction (including paralytic ileus).,Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of such therapy.,Opioid-naive patients (for formulation with strength > 12 mcg/hour, such as DURAGESIC-37, which is contraindicated in opioid-naive patients; initiation should be in opioid-tolerant patients).,Acute pain, including postoperative pain (except for short-term use in controlled settings).,Mild intermittent pain that can be managed with non-opioid analgesics.
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 and grapefruit juice. Alcohol can potentiate CNS depression. Grapefruit juice may increase fentanyl levels via CYP3A4 inhibition.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
FDA Pregnancy Category C for chronic use; Category D for prolonged use or high doses at term. First trimester: risk of congenital anomalies unclear; may be associated with neural tube defects (case reports). Second/third trimesters: chronic use may cause fetal dependence, withdrawal, or respiratory depression. Near term: high doses can cause neonatal respiratory depression; use not recommended. Avoid during labor.
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.
Fentanyl is excreted into breast milk; M/P ratio ~0.4-1.0. Relative infant dose ~2.5% of maternal weight-adjusted dose. Caution: potential for infant sedation, respiratory depression. Single doses acceptable; monitor infant for drowsiness. Chronic use not recommended due to accumulation.
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.
Pregnancy increases fentanyl clearance due to enhanced hepatic metabolism and increased renal blood flow; however, data limited. In third trimester, volume of distribution increases, possibly requiring higher doses for analgesia. Use lowest effective dose; avoid sustained-release forms. Monitor for maternal respiratory depression; may need to taper near term to prevent 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.
DURAGESIC-37 is a fentanyl transdermal system delivering 37 mcg/h. It is contraindicated in opioid-naïve patients due to risk of fatal respiratory depression. Apply to non-irritated, non-irradiated skin on upper torso. Do not cut or damage the patch. Monitor for signs of serotonin syndrome when used with serotonergic drugs. Disposal: fold patch sticky side together and flush down toilet.
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.
Apply the patch to clean, dry, hairless skin on the chest, back, or upper arm. Do not use soap, alcohol, or oils before applying.,Do not cut or damage the patch; discard damaged patches.,Wash hands after handling the patch and avoid touching eyes.,Do not expose the patch to direct heat sources (heating pads, electric blankets, hot tubs, sunbathing) as this increases absorption.,Remove and fold the used patch with sticky sides together and flush immediately down the toilet.,Keep patches out of reach of children and pets.,Do not stop use suddenly; taper as directed to avoid withdrawal.,Report severe drowsiness, confusion, difficulty breathing, or slow heartbeat to a healthcare provider immediately.
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 DURAGESIC-37 vs ALFENTA, answered by our medical review team.
DURAGESIC-37 is a Opioid Analgesic that works by Fentanyl binds to mu-opioid receptors, activating G-protein coupled receptor signaling, leading to inhibition of adenylate cyclase, decreased c AMP production, and modulation of ion channels (increased potassium efflux, decreased calcium influx). This results in reduced neuronal excitability, inhibition of nociceptive transmission, and altered pain perception. Additionally, fentanyl may interact with other opioid receptors (kappa, delta) with lower affinity.. 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 DURAGESIC-37 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 DURAGESIC-37 is: Initial: 25 mcg/hour transdermal patch applied every 72 hours. Titrate based on opioid tolerance. For opioid-naive patients: 12 mcg/hour patch.. 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 DURAGESIC-37 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. DURAGESIC-37 is classified as Category C. FDA Pregnancy Category C for chronic use; Category D for prolonged use or high doses at term. First trimester: risk of congenital anomalies unclear; may be associated with neural t. 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.