II. Indications

  1. Opioid Induced Constipation
  2. Opioid Induced Constipation refractory to Laxatives, in patients with advanced illness

III. Contraindications

  1. Contraindicated in Intestinal Obstruction
  2. Exercise caution in intestinal malignancy

IV. Mechanism

  1. Block Opioid binding in the intestinal tract
  2. Decreases mu-Opioid receptor mediated bowel paralysis

V. Dosing: Adults

  1. General
    1. Stay near a toilet for 4 hours after dose
    2. Give injection while seated or lying down
    3. Protect medication from light
  2. Opioid Induced Constipation
    1. Subcutaneous (SQ: 12 mg SQ once daily
      1. Renal Dose (GFR <60 ml/min): 6 mg/day SQ
    2. Oral: 450 mg once daily in the morning
      1. Renal Dose (GFR <60 ml/min): 150 mg/day SQ
      2. Take on an empty Stomach (at least 30 minutes before first meal)
  3. Opioid Induced Constipation refractory to Laxatives, in patients with advanced illness
    1. Weight <38 kg: 0.15 mg/kg SQ every other day
    2. Weight 38 to 61 kg: 8 mg SQ every other day
    3. Weight 62 to 114 kg: 12 mg SQ every other day
    4. Weight >115 kg: 0.15 mg SQ every other day
    5. GFR <60 ml/min: Decrease SQ dose 50%

VI. Adverse Effects

VII. Safety

  1. Pregnancy Category B
  2. Contraindicated in Lactation

VIII. Efficacy

  1. In general, results in one more Bowel Movement per week and may spare Laxative use
  2. Best efficacy in those on Opioids for >4 weeks
  3. Consider stopping medication if no effect after 4 doses
  4. Refractory Opioid Induced Constipation in Cancer and Palliative Care
    1. Both oral Naldemedine (Symproic) and SQ Methylnaltrexone (Relistor) are effective with benefits outweighing harms
    2. Brown (2023) Am Fam Physician 107(2):131-2 [PubMed]

IX. Drug Interactions

  1. Avoid with other opioid Antagonists
  2. Stop other Laxatives while taking Methylnaltrexone (may restart as needed in 3 days)

XI. References

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Related Studies

Cost: Medications

relistor (on 1/1/2022 at Medicaid.Gov Survey of pharmacy drug pricing)
RELISTOR 12 MG/0.6 ML SYRINGE $232.20 per ml
RELISTOR 12 MG/0.6 ML VIAL $230.56 per ml
RELISTOR 150 MG TABLET $23.17 each