Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
RELISTOR vs KLOXXADO
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Peripherally acting mu-opioid receptor antagonist that blocks opioid-induced constipation without affecting central analgesia.
KLOXXADO (flumazenil) is a benzodiazepine antagonist that competitively inhibits the activity at the benzodiazepine binding site on the GABA-A receptor, thereby reversing the effects of benzodiazepines.
Treatment of opioid-induced constipation (OIC) in adult patients with chronic non-cancer pain,Treatment of OIC in adult patients with advanced illness who are receiving palliative care
Reversal of conscious sedation induced by benzodiazepines,Management of benzodiazepine overdose,Off-label: reversal of benzodiazepine effects in hepatic encephalopathy
0.15 mg/kg subcutaneously once daily, maximum 16 mg per dose; for opioid-induced constipation, 8 mg subcutaneously once daily.
5 mg intranasally as a single dose; may repeat once after 2-3 minutes if response inadequate.
Terminal elimination half-life is approximately 8-10 hours in patients with normal renal function. In patients with end-stage renal disease, half-life is prolonged (~14-18 hours).
Terminal elimination half-life is approximately 2 hours (range 1-4 hours); clinical context: short half-life supports rapid reversal of opioid effects but requires monitoring for renarcotization, especially with long-acting opioids.
Primarily hepatic via CYP3A4 and CYP2D6 isoenzymes; also undergoes gut wall metabolism.
Hepatic metabolism via CYP1A2 and CYP3A4; undergoes extensive first-pass metabolism; major metabolites are inactive or less active.
Renal excretion of unchanged drug accounts for approximately 16% of the dose; biliary/fecal excretion is the major route (approximately 54% recovered in feces).
Hepatic metabolism primarily via CYP3A4 to inactive metabolites; renal excretion accounts for <1% of unchanged drug; fecal excretion accounts for approximately 50-60% of the dose as metabolites.
Approximately 11-15% bound to plasma proteins (primarily albumin).
Approximately 80% bound to plasma proteins, primarily albumin.
Approximately 1.1 L/kg (central volume ~0.3 L/kg); indicates extensive extravascular distribution.
Volume of distribution is approximately 2-4 L/kg; high Vd indicates extensive tissue distribution, which is consistent with rapid redistribution from brain to peripheral tissues, contributing to its short duration of action.
Subcutaneous: approximately 82-100% (mean ~97%); oral: approximately 6% (low due to first-pass metabolism).
Intranasal bioavailability is approximately 40-50% relative to intravenous administration; gastrointestinal absorption is limited due to first-pass metabolism, so oral bioavailability is <1%.
For creatinine clearance <30 m L/min: 0.075 mg/kg subcutaneously every other day, maximum 8 mg per dose; not recommended in patients with end-stage renal disease requiring dialysis.
No dose adjustment required for renal impairment.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B); not studied in severe impairment (Child-Pugh C).
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B); severe hepatic impairment (Child-Pugh C) has not been studied, use with caution.
Safety and efficacy not established in pediatric patients.
Weight ≥30 kg: 5 mg intranasally as single dose; weight 10-30 kg: 2.5 mg intranasally as single dose; may repeat once after 2-3 minutes if needed.
No specific dose adjustment recommended; use caution due to potential for renal impairment, monitor renal function.
No specific dose adjustment; elderly patients may be more sensitive to adverse effects, monitor for excessive sedation or respiratory depression.
Gastrointestinal perforation: Cases of gastrointestinal perforation have been reported in patients with conditions that may result in impaired structural integrity of the gastrointestinal tract.
None.
Risk of gastrointestinal perforation,Opioid withdrawal symptoms including diarrhea, nausea, vomiting, abdominal pain,Disruption of analgesic effect if used with opioids crossing the blood-brain barrier (theoretical),Not recommended in patients with known or suspected mechanical gastrointestinal obstruction
Risk of seizures, especially in patients with physical dependence on benzodiazepines, concurrent tricyclic antidepressant overdose, or history of seizures,Do not use for diagnostic purposes in suspected seizure disorders,May cause panic attacks in patients with anxiety disorders,Monitor for resedation due to shorter duration of action than benzodiazepines
Known or suspected mechanical gastrointestinal obstruction,Known hypersensitivity to methylnaltrexone or any component of the formulation
Known hypersensitivity to flumazenil or benzodiazepines,Patients receiving benzodiazepines for control of life-threatening conditions (e.g., increased intracranial pressure, status epilepticus),Evidence of serious tricyclic antidepressant overdose
No specific food interactions reported with methylnaltrexone. No dietary restrictions necessary. However, to optimize bowel function, patients should maintain adequate fluid intake and dietary fiber as tolerated, unless contraindicated due to underlying illness.
No known food interactions with Kloxxado. Naloxone is not affected by food intake. Avoid alcohol or sedatives as they may exacerbate opioid effects.
Animal studies show no teratogenic effects at doses up to 300 mg/kg/day in rats and rabbits. No adequate human data; risk cannot be excluded in first trimester. Second and third trimester: limited data, potential for gastrointestinal effects in fetus if exposed transplacentally.
Pregnancy category D: Positive evidence of human fetal risk in first trimester (increased risk of oral clefts), second and third trimesters (risk of maternal and neonatal respiratory depression, neonatal withdrawal syndrome). Avoid in pregnancy unless benefit outweighs risk.
Excreted in human milk at low concentrations; M/P ratio approximately 0.6. No reported adverse effects in breastfeeding infants. Caution advised due to potential for gastrointestinal effects.
Excreted in breast milk; M/P ratio unknown. Potential for infant sedation and withdrawal. Use caution; consider alternative agents or monitor for drowsiness and feeding difficulties.
No pharmacokinetic studies in pregnancy; dose adjustments not recommended based on available data. Use only if clearly needed for severe opioid-induced constipation unresponsive to standard therapy.
No standard dose adjustment recommended; however, pharmacokinetic changes (increased volume of distribution, altered clearance) may require higher or more frequent dosing to maintain efficacy. Individualize based on response and tolerance.
Relistor (methylnaltrexone) is a peripherally acting mu-opioid receptor antagonist (PAMORA) used for opioid-induced constipation (OIC) in patients with advanced illness or chronic pain. It does not cross the blood-brain barrier, thus does not reverse central opioid analgesia. Administer subcutaneously; onset typically within 1-4 hours. Contraindicated in patients with known or suspected mechanical gastrointestinal obstruction. Use with caution in renal impairment (Cr Cl <30 m L/min) as dose reduction recommended. Monitor for gastrointestinal perforation, especially in patients with underlying GI pathology. Coadministration with other opioid antagonists may precipitate opioid withdrawal.
Kloxxado (naloxone) 8 mg nasal spray is FDA-approved for emergency treatment of opioid overdose. Use in patients with known or suspected opioid overdose, including respiratory depression. Onset within 2-3 minutes. May require repeat dosing due to shorter half-life than many opioids. Monitor for withdrawal precipitation. Store at room temperature; protect from light. Train caregivers and patients on proper administration.
Relistor is used to treat constipation caused by opioid pain medications without affecting pain relief.,Inject the medication exactly as prescribed; do not use more often than every other day.,You should have a bowel movement within a few hours of receiving the injection; if not, contact your doctor.,Common side effects include abdominal pain, nausea, diarrhea, and flatulence.,Stop Relistor and seek immediate medical attention if you experience severe abdominal pain, vomiting, or signs of intestinal obstruction (e.g., inability to pass gas).,Tell your doctor if you have kidney problems, as the dose may need adjustment.,Do not take other medicines for constipation without your doctor's approval.
Administer as soon as opioid overdose is suspected: unresponsiveness, slow/stopped breathing, or pin-point pupils.,Spray one dose into one nostril; if no response in 2-3 minutes, give second dose in other nostril using a new device.,Call 911 immediately before or after administration; Kloxxado is a temporary measure.,Stay with patient until emergency help arrives; repeat doses may be needed if opioids are long-acting (e.g., fentanyl).,Side effects include acute withdrawal symptoms (nausea, vomiting, sweating, agitation, rapid heart rate).,Store at 68-77°F (20-25°C); do not freeze. Check expiration date.
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 RELISTOR vs KLOXXADO, answered by our medical review team.
RELISTOR is a Peripheral Opioid Antagonist that works by Peripherally acting mu-opioid receptor antagonist that blocks opioid-induced constipation without affecting central analgesia.. KLOXXADO is a Opioid Antagonist that works by KLOXXADO (flumazenil) is a benzodiazepine antagonist that competitively inhibits the activity at the benzodiazepine binding site on the GABA-A receptor, thereby reversing the effects of benzodiazepines.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between RELISTOR and KLOXXADO 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 RELISTOR is: 0.15 mg/kg subcutaneously once daily, maximum 16 mg per dose; for opioid-induced constipation, 8 mg subcutaneously once daily.. The standard adult dose of KLOXXADO is: 5 mg intranasally as a single dose; may repeat once after 2-3 minutes if response inadequate.. 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 RELISTOR and KLOXXADO 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. RELISTOR is classified as Category C. Animal studies show no teratogenic effects at doses up to 300 mg/kg/day in rats and rabbits. No adequate human data; risk cannot be excluded in first trimester. Second and third tr. KLOXXADO is classified as Category C. Pregnancy category D: Positive evidence of human fetal risk in first trimester (increased risk of oral clefts), second and third trimesters (risk of maternal and neonatal respirato. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.