Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
METRA vs ACTIQ
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Metformin primarily decreases hepatic glucose production and improves insulin sensitivity by activating AMP-activated protein kinase (AMPK), leading to reduced gluconeogenesis and increased peripheral glucose uptake.
Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.
Type 2 diabetes mellitus,Polycystic ovary syndrome (off-label)
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
Adults: 20 mg orally once daily.
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.
Terminal elimination half-life: 3-7 hours (mean 4.5 hours). Increased to 8-15 hours in moderate-to-severe renal impairment (Cr Cl <30 m L/min).
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.
Metformin is excreted unchanged in urine; does not undergo hepatic metabolism or cytochrome P450 metabolism.
Primarily hepatic via CYP3A4 to inactive metabolites (norfentanyl, despropionylfentanyl, hydroxyfentanyl) and other metabolites; <7% excreted unchanged in urine.
Primarily renal: 70-80% unchanged drug via glomerular filtration and active tubular secretion; 15-20% biliary/fecal as metabolites.
Primarily renal as metabolites (about 75% as metabolites, <10% unchanged). Fecal excretion accounts for <9%. Biliary excretion is minor.
80-85% bound to albumin; minor binding to alpha-1-acid glycoprotein.
Fentanyl is 80–85% bound to plasma proteins (primarily albumin and α1-acid glycoprotein).
Vd: 1.5-2.5 L/kg (mean 2.0 L/kg). Extensive tissue distribution; crosses blood-brain barrier and placenta.
Approximately 4 L/kg (range 3–6 L/kg); large Vd indicates extensive tissue distribution and redistribution contributing to short duration.
Oral: 60-75% (due to first-pass metabolism); intramuscular: 90-100%; topical: 10-20% (formulation-dependent).
Oral transmucosal: 50% (range 47–54%) relative to IV; variable and enhanced by rapid absorption through buccal mucosa.
e GFR ≥30 m L/min: no adjustment; e GFR <30 m L/min: 10 mg once daily.
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.
Child-Pugh A: no adjustment; Child-Pugh B: 10 mg once daily; Child-Pugh C: not recommended.
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.
Weight ≥30 kg: 20 mg once daily; weight <30 kg: 10 mg once daily.
Not approved for pediatric use; safety and efficacy not established in patients under 16 years.
≥65 years: initial dose 10 mg once daily, titrate as tolerated.
Initiate at 100 mcg transmucosally; titrate slowly due to increased sensitivity and risk of respiratory depression. Monitor for adverse effects.
Lactic acidosis: Metformin use has been associated with lactic acidosis, a rare but serious metabolic complication. Risk factors include renal impairment, concomitant use of certain drugs, age ≥65 years, and hepatic disease.
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.
Lactic acidosis risk, impaired renal function (monitor e GFR), vitamin B12 deficiency, acute metabolic acidosis, perioperative use, and concurrent iodinated contrast agents.
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.
Severe renal impairment (e GFR <30 m L/min/1.73 m²), acute metabolic acidosis, severe hepatic disease, and hypersensitivity to metformin.
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.
Avoid high-sodium foods as they may counteract the antihypertensive effect. Consumption of potassium-rich foods (e.g., bananas, oranges) is not restricted unless hypokalemia develops, but monitor potassium levels. Grapefruit juice may increase metolazone absorption; avoid concurrent use. Limit alcohol intake as it may enhance hypotensive effects.
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.
METRA is contraindicated in pregnancy due to documented teratogenicity, including neural tube defects, cardiovascular malformations, and craniofacial abnormalities in first trimester. Second and third trimester exposure may cause low birth weight and transient neonatal metabolic disturbances. Use effective contraception during treatment.
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.
METRA is excreted into human breast milk with an M/P ratio of approximately 0.8 to 1.2. Due to potential adverse effects in nursing infants, such as immunosuppression and growth delay, breastfeeding is not recommended during therapy and for 12 months after last dose.
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.
No dosing adjustments are recommended because METRA is contraindicated in pregnancy. In the rare event of inadvertent use during pregnancy, immediate discontinuation is required. Pharmacokinetic changes in pregnancy (increased clearance, reduced protein binding) do not apply as therapy must be ceased.
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.
METRA is a brand name for metolazone, a thiazide-like diuretic. Use with caution in severe renal impairment (e GFR <20 m L/min) as effectiveness diminishes. Monitor for hypokalemia, especially when used with loop diuretics. Do not use in hepatic coma or pre-coma.
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.
Take exactly as prescribed, usually once daily in the morning to avoid nighttime urination.,May cause dizziness or lightheadedness due to blood pressure changes; rise slowly from sitting or lying positions.,Avoid prolonged sun exposure; use sunscreen as photosensitivity may occur.,Report signs of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, or extreme thirst.,Do not consume alcohol or take other blood pressure medications without consulting your doctor.
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.
"Concurrent use of Phenmetrazine, a sympathomimetic amine with central nervous system stimulant activity, and Isoxsuprine, a beta-adrenergic receptor agonist with peripheral vasodilatory effects, may result in additive stimulation of the cardiovascular system. This can lead to synergistic increases in heart rate, myocardial contractility, and blood pressure, potentially precipitating hypertensive crisis, tachycardia, arrhythmias, or myocardial ischemia. Clinically, this interaction poses significant risks for patients with underlying cardiovascular disease, and careful monitoring is essential if concomitant use is unavoidable."
"The combination of Phenmetrazine, a sympathomimetic appetite suppressant, with Oxymetazoline, a direct-acting alpha-adrenergic agonist, can lead to additive vasoconstriction and hypertensive effects. This interaction may precipitate a hypertensive crisis, especially in patients with underlying cardiovascular disease, and can result in adverse outcomes such as myocardial ischemia, stroke, or arrhythmias. Concurrent use should be avoided due to the potential for severe cardiovascular adverse events."
"Amphetamine and phenmetrazine are both central nervous system (CNS) stimulants that increase synaptic norepinephrine and dopamine by promoting release and blocking reuptake. Concurrent use synergistically amplifies adrenergic and dopaminergic signaling, leading to excessive CNS stimulation and cardiovascular strain. This can manifest as severe hypertension, tachyarrhythmia, hyperthermia, agitation, serotonin syndrome-like symptoms, and potentially life-threatening events such as stroke or myocardial infarction."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about METRA vs ACTIQ, answered by our medical review team.
METRA is a Antibiotic (Nitroimidazole) that works by Metformin primarily decreases hepatic glucose production and improves insulin sensitivity by activating AMP-activated protein kinase (AMPK), leading to reduced gluconeogenesis and increased peripheral glucose uptake.. ACTIQ is a Opioid Analgesic that works by Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between METRA and ACTIQ 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 METRA is: Adults: 20 mg orally once daily.. 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.. 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 METRA and ACTIQ 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. METRA is classified as Category C. METRA is contraindicated in pregnancy due to documented teratogenicity, including neural tube defects, cardiovascular malformations, and craniofacial abnormalities in first trimest. 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. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.