Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ONSOLIS vs ANEXSIA
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.
ANEXSIA is a combination of hydrocodone and acetaminophen. Hydrocodone is an opioid agonist that binds to mu-opioid receptors in the central nervous system, altering pain perception and emotional response to pain. Acetaminophen's analgesic mechanism is not fully understood but involves inhibition of COX enzymes in the CNS and modulation of descending serotonergic pathways.
Management of breakthrough pain in opioid-tolerant cancer patients,Off-label: management of acute pain in opioid-tolerant patients with non-cancer chronic pain
Relief of moderate to moderately severe pain
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.
50-100 mg orally every 4-6 hours as needed; maximum 400 mg/day.
Terminal elimination half-life is approximately 3-5 hours in adults, providing sustained analgesic effect with multiple daily dosing.
Terminal elimination half-life is 4-6 hours in adults with normal renal function; prolonged to 12-24 hours in severe renal impairment (Cr Cl <30 m L/min).
Primarily metabolized by CYP3A4 to norfentanyl and other inactive metabolites
Hydrocodone is metabolized via CYP2D6 and CYP3A4 to hydromorphone and norhydrocodone. Acetaminophen is primarily metabolized via hepatic glucuronidation and sulfation; a minor pathway via CYP2E1 produces NAPQI, which is detoxified by glutathione.
Primarily hepatic metabolism via glucuronidation, with approximately 70% of the dose excreted in urine as metabolites and 10-15% in feces as unchanged drug.
Approximately 70% renal (unchanged drug and metabolites), 20% biliary/fecal, 10% other.
Approximately 95% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
Approximately 95% bound to plasma albumin and alpha-1-acid glycoprotein.
Mean volume of distribution is 3.0 L/kg (range 2-5 L/kg), indicating extensive tissue distribution.
0.2-0.4 L/kg, indicating limited extravascular distribution primarily confined to plasma and interstitial fluid.
Buccal administration absolute bioavailability is approximately 50%, with interindividual variability due to buccal absorption and first-pass metabolism.
Oral: 80-90%; Intramuscular: 90-100%; Rectal: 70-80%.
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.
GFR 30-89 m L/min: no adjustment; GFR 15-29 m L/min: 50% dose reduction; GFR <15 m L/min: avoid use.
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.
Child-Pugh A: no adjustment; Child-Pugh B: 50% dose reduction; Child-Pugh C: avoid use.
Safety and efficacy in pediatric patients under 18 years have not been established; use not recommended.
1-2 mg/kg/dose orally every 6 hours; maximum 6 mg/kg/day.
Patients >65 years: initiate at 100 mcg. Titrate with caution due to increased sensitivity and potential for respiratory depression.
Initiate at 25 mg every 6 hours; increase cautiously; monitor renal function.
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.
Addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion; neonatal opioid withdrawal syndrome; risks from concomitant use with benzodiazepines or other CNS depressants; hepatotoxicity from acetaminophen.
Respiratory depression,CNS depression,Addiction and abuse potential,Interaction with CYP3A4 inhibitors/inducers,Serotonin syndrome with serotonergic drugs,Adrenal insufficiency,Hypotension,Seizures
Risk of respiratory depression, especially in elderly or debilitated patients; adrenal insufficiency; severe hypotension; seizures; opioid-induced hyperalgesia; acetaminophen hepatotoxicity (avoid exceeding 4 g/day); serotonin syndrome if used with serotonergic agents.
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 hydrocodone or acetaminophen; significant respiratory depression; acute or severe bronchial asthma in an unmonitored setting; known or suspected GI obstruction; severe hepatic impairment; concomitant use of MAOIs or within 14 days.
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.
Avoid alcohol; may increase risk of hepatotoxicity and GI bleeding. Limit caffeine intake from coffee, tea, cola, or energy drinks due to added caffeine content. High-fat meals may delay absorption; take on empty stomach for faster onset if tolerated.
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.
First trimester: Data are limited; no increased risk of major malformations reported in small studies. Second and third trimesters: Associated with premature closure of the ductus arteriosus and oligohydramnios due to fetal renal effects; avoid use after 30 weeks gestation.
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.
Excreted into breast milk in low concentrations (M/P ratio not established). Not recommended during breastfeeding due to potential for adverse effects in the infant, including renal impairment and gastrointestinal bleeding.
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.
Dose adjustment not generally required; however, due to increased renal clearance in pregnancy, shortened dosing intervals may be necessary for sustained efficacy. Use lowest effective dose for shortest duration.
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.
ANEXSIA is a combination analgesic containing paracetamol, ibuprofen, and caffeine. It is contraindicated in patients with active peptic ulcer disease, severe hepatic impairment, or hypersensitivity to NSAIDs. Avoid concurrent use with other NSAIDs or paracetamol-containing products. Monitor renal function in elderly or dehydrated patients. Caffeine may exacerbate anxiety or insomnia.
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.
Do not exceed recommended dose; overdosage of paracetamol can cause liver damage.,Take with food or milk to reduce gastrointestinal upset.,Avoid alcohol while taking this medication to reduce risk of liver toxicity and GI bleeding.,Discontinue use and consult if signs of allergic reaction, GI bleeding, or liver problems occur.,Caffeine may cause nervousness, insomnia, or increased heart rate; limit caffeine-containing foods and beverages.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ONSOLIS vs ANEXSIA, 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.. ANEXSIA is a Opioid Analgesic Combination that works by ANEXSIA is a combination of hydrocodone and acetaminophen. Hydrocodone is an opioid agonist that binds to mu-opioid receptors in the central nervous system, altering pain perception and emotional response to pain. Acetaminophen's analgesic mechanism is not fully understood but involves inhibition of COX enzymes in the CNS and modulation of descending serotonergic pathways.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ONSOLIS and ANEXSIA depend on the specific clinical indication. These are agents from distinct pharmacological classes 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 ANEXSIA is: 50-100 mg orally every 4-6 hours as needed; maximum 400 mg/day.. 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 ANEXSIA 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 . ANEXSIA is classified as Category C. First trimester: Data are limited; no increased risk of major malformations reported in small studies. Second and third trimesters: Associated with premature closure of the ductus . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.