Parenteral Manual

Methylnaltrexone (NON-FORMULARY)

Disclaimer: Official controlled document is the CHEO online copy. It is the responsibility of user to ensure that any paper copy version is the same as the online version before use.

Alternate Name(s): 
Selective peripheral opioid antagonist
Original Date: 
January 2009
  • Treatment of opioid-induced constipation in patients with advanced illness, receiving palliative care and who have had insufficient response to laxatives
Reconstitution and Stability: 
  • Store unopened vials at room temperature.  Protect from light
  • Available as 12 mg/0.6 mL single-use vial (20 mg/mL)
  • Stable in a syringe for 24 hours at room temperature

- Solutions Compatible:  0.9% NaCl, Sterile Water for Injection


(For approved routes of administration by nursing personnel, refer to Policy for the Administration of Intravenous Medications.)

Rotate injection sites
(upper arm, abdomen or thigh)                           
IV Direct NO
IV Intermittent Infusion NO
IV Continuous Infusion NO



(For neonatal dosages, refer to Neonatal IV Drug Manual.)


  • No dosing information in children or adolescents


  • 38 to less then 62 kg:  8 mg subcutaneously every 2 days (Maximum 1 dose/24 hours)
  • 62 - 114 kg:  12 mg subcutaneously every 2 days (Maximum 1 dose/24 hours) 
  • Less  than 38 kg or greater than 114 kg:  0.15 mg/kg & round volume  to nearest 0.1 mL

Dosage Adjustment in Renal Failure:

  • Creatinine clearance less than 30 mL/minute:
    -38 - less than 62 kg:  4 mg
    -62 - 114 kg:  6 mg
    -Less than 38 kg or greater than 114 kg: 0.075 mg/kg & round volume to nearest 0.1 mL

-No dosing adjustment for hepatic impairment

Potential hazards of parenteral administration: 
  • Immediate (within a few minutes to hours):  abdominal pain (29%), flatulence (13%), nausea (12%), dizziness (7%), diarrhea (6%), pain at injection site (rare)
  • Most patients respond within 4 hours, usually within 30 - 60 minutes (median 24 minutes)
  • Contraindicated in patients with known or suspected mechanical bowel obstruction
  • Does not affect opioid analgesic effects or induce opioid withdrawal symptoms

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