Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ONSOLIS vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Onsolis (fentanyl buccal soluble film) is an opioid agonist that binds to mu-opioid receptors in the central nervous system, producing analgesia by increasing potassium conductance and inhibiting calcium channels, leading to reduced neurotransmitter release and hyperpolarization of neurons.
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 breakthrough pain in opioid-tolerant cancer patients,Off-label: management of acute pain in opioid-tolerant patients with non-cancer chronic pain
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Onsolis (fentanyl buccal soluble film) is indicated for breakthrough pain in opioid-tolerant patients. The initial dose is 200 mcg placed on the buccal mucosa; titrate to effective dose in 200 mcg increments across subsequent episodes. Maximum frequency: 4 doses per day. Allow at least 2 hours between doses.
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 is approximately 3-5 hours in adults, providing sustained analgesic effect with multiple daily dosing.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Primarily metabolized by CYP3A4 to norfentanyl and other inactive metabolites
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily hepatic metabolism via glucuronidation, with approximately 70% of the dose excreted in urine as metabolites and 10-15% in feces as unchanged drug.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Approximately 95% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Mean volume of distribution is 3.0 L/kg (range 2-5 L/kg), indicating extensive tissue distribution.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Buccal administration absolute bioavailability is approximately 50%, with interindividual variability due to buccal absorption and first-pass metabolism.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
For GFR 30-59 m L/min: initiate with 100 mcg; for GFR 15-29 m L/min: initiate with 50 mcg; for GFR <15 m L/min: not recommended. Titrate cautiously due to increased fentanyl exposure.
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.
For Child-Pugh Class A: no adjustment. For Child-Pugh Class B: initiate at 50 mcg; titrate slowly. For Child-Pugh Class C: not recommended.
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.
Safety and efficacy in pediatric patients under 18 years have not been established; use not recommended.
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.
Patients >65 years: initiate at 100 mcg. Titrate with caution due to increased sensitivity and potential for respiratory depression.
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 respiratory depression, especially in opioid-naive patients; contraindicated in acute or postoperative pain; must be used only in opioid-tolerant patients; risk of abuse, addiction, and diversion.
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,CNS depression,Addiction and abuse potential,Interaction with CYP3A4 inhibitors/inducers,Serotonin syndrome with serotonergic drugs,Adrenal insufficiency,Hypotension,Seizures
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Opioid non-tolerant patients,Acute or postoperative pain,Significant respiratory depression,Paralytic ileus,Concurrent use of MAOIs or within 14 days,Known hypersensitivity to fentanyl or components
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).
ONSOLIS should not be taken with alcohol, grapefruit juice, or any foods/beverages containing grapefruit, as they can increase fentanyl levels and risk of respiratory depression. No other specific food interactions are known; however, patients should avoid consuming extremely hot or cold foods or beverages immediately before or during administration, as this may affect buccal absorption. Advise patients to maintain normal oral hygiene and avoid chewing or irritating the application site.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
Fetal risk cannot be ruled out. No adequate and well-controlled studies in pregnant women. In animal studies, fentanyl (active ingredient) was embryocidal and reduced pup survival at doses within the human dose range. Risk in first trimester: Potential for neural tube defects. Second and third trimesters: Potential for fetal opioid withdrawal syndrome after prolonged use. Avoid use during labor and delivery due to risk of neonatal respiratory depression.
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 in human milk. The milk-to-plasma (M/P) ratio is approximately 0.43 for intravenous fentanyl. Oral transmucosal administration may result in similar transfer. Breastfeeding is not recommended during treatment with ONSOLIS due to the potential for infant sedation and respiratory depression. A nursing infant could be exposed to clinically relevant doses.
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 specific dose adjustments are recommended for ONSOLIS during pregnancy; however, pharmacokinetic changes (increased clearance, increased volume of distribution) in pregnancy may require dose adjustment to maintain analgesic efficacy. Use the lowest effective dose and avoid prolonged use to minimize fetal exposure and 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.
ONSOLIS (fentanyl buccal soluble film) is a transmucosal immediate-release fentanyl formulation indicated for breakthrough pain in opioid-tolerant adults. Due to high bioavailability (~71%) and rapid absorption, it should not be switched on a mcg-per-mcg basis with other fentanyl products. Place the film on the inside of the cheek (buccal mucosa) with the pink side against the cheek; do not chew, suck, or swallow. The film must remain in place for at least 5 minutes to dissolve completely. Patients must be opioid-tolerant, defined as taking at least 60 mg oral morphine/day, 25 mcg transdermal fentanyl/hour, 30 mg oxycodone/day, 8 mg hydromorphone/day, 25 mg oxymorphone/day, or an equianalgesic dose of another opioid for one week or longer. Concomitant use with CYP3A4 inhibitors (e.g., ketoconazole, ritonavir) can increase fentanyl levels and risk of fatal respiratory depression. Accidental exposure to a child is a medical emergency — immediately seek emergency care.
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.
ONSOLIS is a strong opioid pain medicine for breakthrough cancer pain in adults who are already taking other opioid pain medicines.,Keep ONSOLIS out of the reach of children; accidental use by a child is a medical emergency and can be fatal.,Use only when you have breakthrough pain; do not use more than 4 doses per day.,Place one film on the inside of your cheek with the pink side against the cheek, and let it dissolve for about 5-10 minutes; do not chew, suck, or swallow it.,Do not stop taking your around-the-clock opioid pain medicine while using ONSOLIS.,Do not drink alcohol or take other medicines that make you sleepy or slow your breathing while using ONSOLIS.,Store at room temperature, away from moisture and heat, and safely dispose of unused films via medicine take-back programs.,Seek emergency medical help if you have trouble breathing, extreme drowsiness, or if someone accidentally takes this medicine.
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 ONSOLIS vs ALFENTA, answered by our medical review team.
ONSOLIS is a Opioid Analgesic that works by Onsolis (fentanyl buccal soluble film) is an opioid agonist that binds to mu-opioid receptors in the central nervous system, producing analgesia by increasing potassium conductance and inhibiting calcium channels, leading to reduced neurotransmitter release and hyperpolarization of neurons.. 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 ONSOLIS 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 ONSOLIS is: Onsolis (fentanyl buccal soluble film) is indicated for breakthrough pain in opioid-tolerant patients. The initial dose is 200 mcg placed on the buccal mucosa; titrate to effective dose in 200 mcg increments across subsequent episodes. Maximum frequency: 4 doses per day. Allow at least 2 hours between doses.. 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 ONSOLIS 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. ONSOLIS is classified as Category C. Fetal risk cannot be ruled out. No adequate and well-controlled studies in pregnant women. In animal studies, fentanyl (active ingredient) was embryocidal and reduced pup survival . 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.