Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ACTIQ vs METRO I.V.
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.
Metronidazole is a nitroimidazole antibiotic that exerts its bactericidal effect by entering bacterial cells and undergoing reduction by bacterial nitroreductases to form reactive intermediates that damage DNA, leading to cell death. It is selectively toxic to anaerobic bacteria and protozoa.
Management of breakthrough pain in cancer patients aged 16 and older who are already receiving and tolerant to opioid therapy for their underlying persistent cancer pain
Treatment of intra-abdominal infections (e.g., peritonitis, abscess),Treatment of pelvic inflammatory disease,Treatment of bacterial vaginosis,Treatment of trichomoniasis,Treatment of amebiasis (intestinal and extraintestinal),Treatment of anaerobic infections (e.g., bone and joint, central nervous system, respiratory tract, skin and soft tissue),Perioperative prophylaxis (colorectal surgery),Off-label: Helicobacter pylori eradication (with other agents), rosacea (topical), Crohn's disease (perianal fistulas)
200 mcg transmucosally, titrated upward as needed; initial dose for opioid-tolerant patients is 200 mcg, with additional doses possible after 15 minutes if needed. Maximum 4 doses per episode. At least 4 hours between episodes.
15-30 mg/kg IV loading dose, then 7.5-15 mg/kg IV every 6 hours. Typical adult dose: 500 mg IV every 6-8 hours.
Terminal half-life 0.83–2 hours (mean 1.3 h) in adults; note that context: transmucosal absorption leads to rapid onset but short duration; half-life is not correlated with clinical effect due to oral transmucosal route and rapid redistribution.
8 hours (range 6-10 hours) in adults; prolonged to 12-24 hours in hepatic impairment.
Primarily hepatic via CYP3A4 to inactive metabolites (norfentanyl, despropionylfentanyl, hydroxyfentanyl) and other metabolites; <7% excreted unchanged in urine.
Metronidazole is extensively metabolized in the liver via oxidation and glucuronidation. The major metabolic pathways involve hydroxylation and side-chain oxidation, mediated by CYP450 enzymes (CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4). The primary metabolites are 1-(2-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole and 2-methyl-5-nitroimidazole-1-acetic acid, which have minimal antimicrobial activity.
Primarily renal as metabolites (about 75% as metabolites, <10% unchanged). Fecal excretion accounts for <9%. Biliary excretion is minor.
Renal: 60-80% unchanged; fecal: 6-15% (includes metabolites); biliary: minor contribution.
Fentanyl is 80–85% bound to plasma proteins (primarily albumin and α1-acid glycoprotein).
<20%, primarily to albumin.
Approximately 4 L/kg (range 3–6 L/kg); large Vd indicates extensive tissue distribution and redistribution contributing to short duration.
0.6-0.7 L/kg; indicates extensive distribution into tissues including CSF and abscess cavities.
Oral transmucosal: 50% (range 47–54%) relative to IV; variable and enhanced by rapid absorption through buccal mucosa.
Oral: 80-90%; IV: 100%.
No specific GFR-based dose adjustment recommended; use with caution in severe renal impairment (Cr Cl < 30 m L/min) and consider dose reduction due to potential accumulation.
Cr Cl > 50 m L/min: no adjustment; Cr Cl 10-50 m L/min: increase dosing interval to every 12 hours; Cr Cl < 10 m L/min: increase interval to every 24 hours.
Child-Pugh Class A/B: No adjustment. Child-Pugh Class C: Reduce initial dose to 100 mcg and titrate slowly; monitor closely for prolonged effects.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: reduce dose by 75%.
Not approved for pediatric use; safety and efficacy not established in patients under 16 years.
Loading dose: 15-30 mg/kg IV; maintenance: 7.5 mg/kg IV every 6 hours. For neonates < 7 days: 15 mg/kg IV every 24 hours; 7-28 days: 15 mg/kg IV every 12 hours.
Initiate at 100 mcg transmucosally; titrate slowly due to increased sensitivity and risk of respiratory depression. Monitor for adverse effects.
Use with caution; adjust dose based on renal function (Cr Cl) and monitor for neurotoxicity. Start at lower end of dosing range.
Risk of respiratory depression, addiction, abuse, and misuse; accidental ingestion can be fatal; concomitant use with benzodiazepines or CNS depressants may cause profound sedation, respiratory depression, coma, and death; not for use in opioid non-tolerant patients; risk of neonatal opioid withdrawal syndrome with prolonged use during pregnancy; serious, life-threatening, or fatal respiratory depression may occur even at recommended doses.
Carcinogenicity: Metronidazole has been shown to be carcinogenic in mice and rats. It should be used only for approved indications and for the shortest duration necessary.
Risk of respiratory depression; addiction, abuse, and misuse; interactions with CNS depressants; serotonin syndrome; adrenal insufficiency; severe hypotension; seizures; withdrawal; use in patients with head injuries, increased intracranial pressure, biliary tract disease, pancreatitis; risk of choking with lozenge; oral mucosal irritation; dental caries; hypokalemia; hyponatremia; use in elderly, cachectic, or debilitated patients.
Carcinogenicity: Avoid unnecessary use,Peripheral neuropathy: Risk with high doses or prolonged treatment; discontinue if signs occur,Central nervous system effects: Encephalopathy, convulsions, aseptic meningitis; discontinue if symptoms develop,Hepatotoxicity: Risk of severe hepatic injury, including acute liver failure; monitor liver function,Blood dyscrasias: Leukopenia, neutropenia; caution in patients with history of blood disorders,Interaction with alcohol: Disulfiram-like reaction (nausea, vomiting, flushing); avoid alcohol during therapy and for at least 3 days after,Cochrane interaction: Increased INR with warfarin; monitor INR,Renal impairment: Accumulation of metabolites; dosage adjustment may be needed,Prolonged therapy: Monitor for superinfection and neurological symptoms
Significant respiratory depression; acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment; known or suspected paralytic ileus; hypersensitivity to fentanyl or any component; opioid non-tolerant patients; management of acute or postoperative pain including headache/migraine, dental pain, or emergency department use.
Hypersensitivity to metronidazole or other nitroimidazole derivatives,First trimester of pregnancy (unless alternative treatments not available),Breastfeeding (withhold nursing for 12-24 hours after dose),Concurrent use of disulfiram (psychotic reactions may occur),Severe hepatic impairment (metronidazole is hepatically cleared)
No significant food interactions. Grapefruit juice may increase fentanyl levels, but specific studies with ACTIQ are lacking. Avoid alcohol, as it may increase sedation and respiratory depression risk.
No significant food interactions. However, alcohol is strictly contraindicated. Use alcohol-free formulations of medications and avoid alcoholic beverages.
FDA Pregnancy Category C. First trimester: limited human data; animal studies show increased resorptions and fetal growth restriction. Second/third trimester: chronic use may cause neonatal opioid withdrawal syndrome; avoid use during labor due to risk of neonatal respiratory depression.
Pregnancy category B. No evidence of teratogenicity in human studies; crosses placenta. Avoid during first trimester unless benefit outweighs risk; use only if clearly needed.
Excreted in breast milk; M/P ratio not established. Limited data suggest low levels, but risk of infant sedation and respiratory depression. Avoid use while breastfeeding unless potential benefit outweighs risk.
Excreted in breast milk in low concentrations; M/P ratio approximately 1.0. Considered compatible with breastfeeding; monitor infant for diarrhea or candidiasis.
Due to increased plasma volume and hepatic metabolism in pregnancy, dose requirements may increase; adjust based on clinical response and tolerance. Avoid use during labor and delivery due to risk of neonatal respiratory depression; short-term use preferred.
No specific dose adjustment required in pregnancy; pharmacokinetics not significantly altered. Use standard dosing based on infection severity and renal function.
ACTIQ is a transmucosal immediate-release fentanyl formulation indicated for breakthrough cancer pain in opioid-tolerant patients. Initiate with the lowest strength (200 mcg) and titrate upward. Avoid use in opioid-naive patients due to risk of fatal respiratory depression. Place the unit between cheek and lower gum, not sublingually. Instruct patient not to bite or suck the unit. Monitor for sedation and respiratory depression. Multiple units may be used per episode if needed, but wait at least 4 hours before next episode. Dispose of partially used units by flushing down toilet.
METRO I. V. (metronidazole) is a nitroimidazole antibiotic effective against anaerobic bacteria and protozoa. It has excellent bioavailability following intravenous administration. Monitor for peripheral neuropathy with prolonged use. Avoid alcohol during therapy and for 48 hours after last dose due to disulfiram-like reaction. Dose adjustment required in severe hepatic impairment (Child-Pugh C). May cause metallic taste, which is benign. Use with caution in patients with CNS disorders due to risk of seizures.
Only use ACTIQ if you are already taking regular around-the-clock opioid pain medicine and are tolerant to opioids.,Do not use ACTIQ for short-term pain like after surgery, headache, or dental pain.,Place the unit in your cheek pouch, not under your tongue. Do not chew or suck it.,If you need more than 4 units per day, contact your doctor as your dose may need adjustment.,Store ACTIQ in a safe place away from children, as accidental ingestion can be fatal.,Dispose of unused or partially used units by flushing them down the toilet.
Do not drink any alcohol or take products containing alcohol (e.g., mouthwash, cough syrup) while using this medication and for 48 hours after stopping, as it can cause severe nausea, vomiting, headache, and abdominal cramps.,May cause a metallic or bitter taste in the mouth; this is harmless and temporary.,Report any numbness, tingling, or weakness in your arms or legs to your healthcare provider immediately, as this could be a sign of nerve damage.,Take the full course of therapy exactly as prescribed, even if you feel better.,If you have severe liver disease, your dose may need to be adjusted.
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 ACTIQ vs METRO I.V., answered by our medical review team.
ACTIQ is a Opioid Analgesic that works by Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.. METRO I.V. is a Antibiotic (Nitroimidazole) that works by Metronidazole is a nitroimidazole antibiotic that exerts its bactericidal effect by entering bacterial cells and undergoing reduction by bacterial nitroreductases to form reactive intermediates that damage DNA, leading to cell death. It is selectively toxic to anaerobic bacteria and protozoa.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ACTIQ and METRO I.V. 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 ACTIQ is: 200 mcg transmucosally, titrated upward as needed; initial dose for opioid-tolerant patients is 200 mcg, with additional doses possible after 15 minutes if needed. Maximum 4 doses per episode. At least 4 hours between episodes.. The standard adult dose of METRO I.V. is: 15-30 mg/kg IV loading dose, then 7.5-15 mg/kg IV every 6 hours. Typical adult dose: 500 mg IV every 6-8 hours.. 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 ACTIQ and METRO I.V. 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. ACTIQ is classified as Category C. FDA Pregnancy Category C. First trimester: limited human data; animal studies show increased resorptions and fetal growth restriction. Second/third trimester: chronic use may cause. METRO I.V. is classified as Category C. Pregnancy category B. No evidence of teratogenicity in human studies; crosses placenta. Avoid during first trimester unless benefit outweighs risk; use only if clearly needed.. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.