Methylnaltrexone

FDA label

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Renal CrCl <60 mL/min (moderate/severe, Cockcroft-Gault): tablets 150 mg QD AM; injection 6 mg SC QD (chronic non-cancer pain). Advanced illness injection QOD — <38 kg 0.075 mg/kg, 38–<62 kg 4 mg, 62–114 kg 6 mg, >114 kg 0.075 mg/kg. Mild impairment (CrCl >60): no adjustment needed.

Hepatic Tablets: Child-Pugh B or C, 150 mg QD AM; Child-Pugh A no adjustment needed. Injection: no adjustment needed for mild or moderate impairment; severe not studied — if adjusting, QOD at <38 kg 0.075 mg/kg, 38–<62 kg 4 mg, 62–114 kg 6 mg, >114 kg 0.075 mg/kg, and monitor.

Advanced illness: no more than one dose per 24-hour period. Every-other-day 12 mg SC dosing is NOT recommended for chronic non-cancer pain (higher rate of nausea, diarrhea, vomiting). Patients on opioids <4 weeks may be less responsive.

Instructions

• Be within close proximity to toilet facilities once administered.
• Chronic non-cancer pain: take tablets with water on an empty stomach at least 30 minutes before the first meal of the day.
• Discontinue all maintenance laxative therapy before starting; laxatives may be resumed as needed if response is suboptimal after 3 days.
• Discontinue if the opioid pain medication is discontinued; re-evaluate continued need whenever the opioid regimen changes.
• Discontinue for severe or persistent diarrhea.
• Injection is SC only — upper arm, abdomen, or thigh; rotate sites. Inspect for particulate/discoloration (normally colorless to pale yellow).
• Single-dose vials: once drawn up, store at ambient room temperature and administer within 24 hours; discard unused portion.

Available strengths

• tab 150 mg
• inj 8 mg/0.4 mL
• inj 12 mg/0.6 mL

Contraindications

• Known or suspected mechanical gastrointestinal obstruction, or increased risk of recurrent obstruction — risk of GI perforation

Cautions

• GI perforation reported where GI wall integrity may be reduced (peptic ulcer, Ogilvie's syndrome, diverticular disease, infiltrative GI malignancy, peritoneal metastases, Crohn's); monitor for severe, persistent, or worsening abdominal pain and discontinue if it develops.
• Severe or persistent diarrhea — discontinue.
• Opioid withdrawal (hyperhidrosis, chills, diarrhea, abdominal pain, anxiety, yawning); patients with a disrupted blood-brain barrier are at higher risk and may lose analgesia — monitor.
• Safety and effectiveness not established in pediatric patients; juvenile rats showed convulsions, tremors, labored breathing.
• Elderly: no dosage adjustment by age, but higher incidence of diarrhea with tablets — monitor.

Adverse reactions

• Tablets, chronic non-cancer pain (≥2%): abdominal pain, diarrhea, headache, abdominal distention, vomiting, hyperhidrosis, anxiety, muscle spasms, rhinorrhea, chills
• Injection, chronic non-cancer pain (≥1%): abdominal pain, nausea, diarrhea, hyperhidrosis, hot flush, tremor, chills
• Injection, advanced illness (≥5%): abdominal pain, flatulence, nausea, dizziness, diarrhea
• Serious: GI perforation; severe/persistent diarrhea; opioid withdrawal
• Postmarketing: cramping, vomiting, diaphoresis, flushing, malaise, pain

Pregnancy Limited human data; may precipitate opioid withdrawal in the fetus (immature fetal blood-brain barrier). No embryofetal effects in rats/rabbits.

Lactation Breastfeeding not recommended during treatment — risk of opioid withdrawal in the breastfed infant; present in rat milk.