II. Indications
- Opioid Induced Constipation
- Opioid Induced Constipation refractory to Laxatives, in patients with advanced illness
III. Contraindications
- Contraindicated in Intestinal Obstruction
- Exercise caution in intestinal malignancy
IV. Mechanism
V. Dosing: Adults
-
General
- Stay near a toilet for 4 hours after dose
- Give injection while seated or lying down
- Protect medication from light
-
Opioid Induced Constipation
- Subcutaneous (SQ: 12 mg SQ once daily
- Renal Dose (GFR <60 ml/min): 6 mg/day SQ
- Oral: 450 mg once daily in the morning
- Renal Dose (GFR <60 ml/min): 150 mg/day SQ
- Take on an empty Stomach (at least 30 minutes before first meal)
- Subcutaneous (SQ: 12 mg SQ once daily
-
Opioid Induced Constipation refractory to Laxatives, in patients with advanced illness
- Weight <38 kg: 0.15 mg/kg SQ every other day
- Weight 38 to 61 kg: 8 mg SQ every other day
- Weight 62 to 114 kg: 12 mg SQ every other day
- Weight >115 kg: 0.15 mg SQ every other day
- GFR <60 ml/min: Decrease SQ dose 50%
VI. Adverse Effects
- Diarrhea (3 to 8%)
- Abdominal Pain (4 to 13%)
- Hyperhidrosis (2%)
- Headache (1%)
- Vomiting (1%)
-
Opioid Withdrawal (uncommon)
- Chills, anxiety or Yawning
VII. Safety
- Contraindicated in Lactation
- Pregnancy Category B
- No affect on organogenesis in animal studies, but has not been studied in human pregnancy
VIII. Pharmacokinetics
- Rapid onset of action: 2 hours
- Peak serum levels: 0.5 hours SQ or IV, or 3 hours for tablets (1.5 hours if Fasting)
- Elimination Half-Life: 15 hours
- Hepatic metabolism
- Liver conjugation via sulfotransferase and aldo-keto reductase
- Metabolites include Methylnaltrexone sulfate and methyl-6-naltrexol
- Renal excretion
- Most Methylnaltrexone is excreted unchanged in the urine
IX. Efficacy
- In general, results in one more Bowel Movement per week and may spare Laxative use
- Best efficacy in those on Opioids for >4 weeks
- Consider stopping medication if no effect after 4 doses
- Refractory Opioid Induced Constipation in Cancer and Palliative Care
- Both oral Naldemedine (Symproic) and SQ Methylnaltrexone (Relistor) are effective with benefits outweighing harms
- Brown (2023) Am Fam Physician 107(2):131-2 [PubMed]
X. Drug Interactions
- Avoid with other opioid Antagonists
- Stop other Laxatives while taking Methylnaltrexone (may restart as needed in 3 days)
XI. Resources
- Methylnaltrexone (DailyMed)
XII. References
- (2023) Management of Constipation, Presc Lett, #390108
- (2017) Presc Lett 24(12): 70
- Hoopes and LoVecchio (2023) Crit Dec Emerg Med 37(11): 32
- Portenoy (2008) J Pain Symptom Manage 35(5): 458-68 [PubMed]
- Thomas (2008) N Engl J Med 358(22): 2332-43 [PubMed]
Images: Related links to external sites (from Bing)
Related Studies
| 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 | |