Drug type
• A peripheral acting narcotic antagonist, opioid reversing agent
Indications
• Treatment of constipation caused by narcotic (opiate-type) medication for patients with advanced illness who have had poor responses to conventional laxative regimens.
Mechanism of action
• Peripheral mu-opioid receptor antagonist
• Limited ability to cross the blood brain barrier (BBB)
• Methylnaltrexone reduces opioid-induced constipation without abolishing opioid-induced analgesia.
Dosage and administration
• Subcutaneous injectable solution
— 12mg/0.6mL vial
• Opioid-induced constipation (after failure of laxatives)
— Weight-based dosing:
38-62 kg: 8 mg/dose SC every other day
62-114kg: 12 mg/dose SC every other day
<38 kg or >114 kg: 0.15 mg/kg/dose SC every other day
– Not to exceed one dose/24 h
• Renal impairment, severe (creatinine clearance [CrCl] <30 mL/min)
— Give half-dose
— Has not been studied in end stage renal impairment (dialysis dependent)
Pregnancy and lactation
• Pregnancy Category: B
• Lactation: not known if distributed in breast milk
— Use caution
Cautions
• Severe renal impairment
• Discontinue if severe/persistent diarrhea develops
• Rare cases of GI perforation have been reported
— With advanced illness in conditions that may be associated with localized or diffuse reduction of structural integrity in GI tract wall (ie, cancer, peptic ulcer, Ogilvie syndrome)
Adverse effects
• More than 10% of patients
— Abdominal pain (28.5%)
— Flatulence (13.5%)
— Nausea (11.5%)
• 1% to 10% of patients
— Dizziness (7.3%)
— Diarrhea (5.5%)
• Frequency not defined
— Hyperhidrosis
— Gastrointestinal perforation