Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
RELISTOR vs EDECRIN
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.
Ethacrynic acid inhibits the Na-K-Cl cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, reducing reabsorption of sodium, chloride, and potassium, leading to diuresis.
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
Treatment of edema associated with congestive heart failure, cirrhosis, and renal disease,Treatment of hypertension (off-label),Treatment of ascites (off-label),Management of hypercalcemia (off-label)
0.15 mg/kg subcutaneously once daily, maximum 16 mg per dose; for opioid-induced constipation, 8 mg subcutaneously once daily.
Oral: 50-100 mg once or twice daily, maximum 400 mg/day. IV: 50 mg (0.5 mg/kg) once, may repeat once at 2-hour intervals if needed.
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 2-4 hours; prolonged in renal impairment (up to 30 hours) and in heart failure.
Primarily hepatic via CYP3A4 and CYP2D6 isoenzymes; also undergoes gut wall metabolism.
Metabolized primarily in the liver, with approximately 30% excreted unchanged in urine and the remainder as metabolites, including the cysteine conjugate.
Renal excretion of unchanged drug accounts for approximately 16% of the dose; biliary/fecal excretion is the major route (approximately 54% recovered in feces).
Approximately 60-70% excreted unchanged in urine via glomerular filtration and tubular secretion; remaining 30-40% eliminated via biliary/fecal route.
Approximately 11-15% bound to plasma proteins (primarily albumin).
Approximately 95-98% bound, primarily to albumin.
Approximately 1.1 L/kg (central volume ~0.3 L/kg); indicates extensive extravascular distribution.
0.4-0.8 L/kg; reflects distribution primarily into extracellular fluid.
Subcutaneous: approximately 82-100% (mean ~97%); oral: approximately 6% (low due to first-pass metabolism).
Oral: approximately 50-70% due to first-pass metabolism; Intravenous: 100%.
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.
GFR 10-50 m L/min: 50% of normal dose. GFR <10 m L/min: not recommended or use with extreme caution.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B); not studied in severe impairment (Child-Pugh C).
Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50%. Child-Pugh C: contraindicated.
Safety and efficacy not established in pediatric patients.
Oral: 1-3 mg/kg/day in 1-2 divided doses. IV: 1 mg/kg/dose, maximum 50 mg/dose.
No specific dose adjustment recommended; use caution due to potential for renal impairment, monitor renal function.
Start at lowest dose (25-50 mg oral daily) due to increased risk of electrolyte disturbances and hypotension.
Gastrointestinal perforation: Cases of gastrointestinal perforation have been reported in patients with conditions that may result in impaired structural integrity of the gastrointestinal tract.
WARNING: EDECRIN is a potent diuretic which, if given in excessive amounts, can lead to profound diuresis with water and electrolyte depletion. Therefore, careful medical supervision is required, and dose and dose schedule must be adjusted to the individual patient's needs.
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
Ototoxicity: Risk of hearing loss, especially with rapid IV administration or in patients with renal impairment; avoid concurrent use with other ototoxic drugs.,Volume and electrolyte depletion: Profound diuresis leading to dehydration, hypokalemia, hyponatremia, hypochloremia, and metabolic alkalosis.,Hypersensitivity reactions: Rash, eosinophilia, and anaphylaxis.,Gastrointestinal disturbances: Nausea, vomiting, diarrhea, and gastrointestinal bleeding (rare).,Hyperuricemia may precipitate gout.,Use with caution in patients with hepatic cirrhosis due to risk of hepatic encephalopathy.
Known or suspected mechanical gastrointestinal obstruction,Known hypersensitivity to methylnaltrexone or any component of the formulation
Anuria,Hypersensitivity to ethacrynic acid or any component of the formulation,Severe electrolyte depletion (e.g., hypokalemia, hyponatremia) until corrected,Concurrent use with other ototoxic agents (relative contraindication)
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.
Avoid excessive intake of high-sodium foods as they can counteract the diuretic effect. Grapefruit juice may increase the risk of ototoxicity; consumption should be limited. Alcohol can exacerbate hypotension and dehydration. Ensure adequate potassium intake through diet (e.g., bananas, oranges) unless directed otherwise by a healthcare provider.
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.
EDECRIN (ethacrynic acid) is classified as FDA Pregnancy Category B. Limited human data; animal studies have not demonstrated teratogenic effects. However, diuretic use during pregnancy may reduce placental perfusion. Fetal risks include electrolyte disturbances, volume depletion, and possible growth restriction. Use only if clearly needed.
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.
It is not known if ethacrynic acid is excreted in human milk. Due to potential adverse effects in the nursing infant, such as electrolyte imbalance, caution is advised. The manufacturer recommends discontinuing nursing or the drug, taking into account the importance of the drug to the mother. M/P ratio is unknown.
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.
Pregnancy may alter pharmacokinetics; however, no specific dose adjustments have been established. Use lowest effective dose and shortest duration. Monitor for hypovolemia and electrolyte imbalances, which may be more pronounced in pregnancy.
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.
EDECRIN (ethacrynic acid) is a potent loop diuretic that, unlike furosemide, is not a sulfonamide and can be used in patients with sulfonamide allergy. It can cause ototoxicity that is often irreversible, especially when given rapidly IV or with other ototoxic drugs like aminoglycosides. Monitor for hypokalemia, hypomagnesemia, and volume depletion. Use with caution in patients with hepatic cirrhosis due to risk of electrolyte-induced encephalopathy.
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.
Take this medication exactly as prescribed, usually once or twice daily.,Avoid alcohol and limit salt intake to reduce fluid retention.,Weigh yourself daily and report rapid weight gain or loss to your doctor.,Stand up slowly from sitting or lying down to prevent dizziness from low blood pressure.,Notify your doctor immediately if you experience hearing loss, ringing in the ears, or dizziness.,This drug may increase blood sugar; monitor if you have diabetes.,Avoid taking with other ototoxic medications like certain antibiotics without doctor approval.
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 EDECRIN, 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.. EDECRIN is a Loop Diuretic that works by Ethacrynic acid inhibits the Na-K-Cl cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, reducing reabsorption of sodium, chloride, and potassium, leading to diuresis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between RELISTOR and EDECRIN 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 EDECRIN is: Oral: 50-100 mg once or twice daily, maximum 400 mg/day. IV: 50 mg (0.5 mg/kg) once, may repeat once at 2-hour intervals if needed.. 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 EDECRIN 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. EDECRIN is classified as Category C. EDECRIN (ethacrynic acid) is classified as FDA Pregnancy Category B. Limited human data; animal studies have not demonstrated teratogenic effects. However, diuretic use during preg. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.