methylnaltrexone

Action and Spectrum

Actions and Spectrum 

methylnaltrexone selectively binds to peripheral mu-opioid receptors in the gastrointestinal tract, effectively blocking the constipating effects of opioids without affecting central analgesic effects. 

methylnaltrexone is indicated for the treatment of Opioid-induced constipation (OIC) in patients with chronic non-cancer pain or advanced illness who are receiving opioid therapy.

Drug Interaction

Adverse Reaction

Frequency defined  

1-10% 

Diarrhea (5.5%) 

Dizziness (7.3%) 

Hyperhidrosis (6.7%) 

>10% 

Flatulence (13.5%) 

Nausea (11.5%) 

Abdominal pain (28.5%) 

Post marketing Reports 

General disorders and administrative site disorders: Diaphoresis, pain, flushing, malaise 

Gastrointestinal: Cramping, vomiting, perforation 

Black Box Warning

Black Box Warning 

None

Contraindication / Caution

Contraindication/Caution: 

Contraindication: 

• methylnaltrexone is contraindicated in individuals with a known hypersensitivity or allergy to methylnaltrexone or any of its components. 

Caution: 

• methylnaltrexone should be used with caution in patients with known or suspected gastrointestinal (GI) obstruction.  
• Caution should be exercised when using methylnaltrexone in patients with severe renal impairment.

Pregnancy / Lactation

Pregnancy consideration: 

Pregnancy category: N/A 

Lactation: Excretion into human milk is unknown  

Pregnancy Categories:         

Category A: well-controlled and Satisfactory studies show no risk to the fetus in the first or later trimester. 

Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women.  

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women. 

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits. 

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women. 

Category N: There is no data available for the drug under this category. 

Pharmacology

Pharmacology  

Peripheral mu-opioid receptor antagonist; low capacity to cross blood brain barrier, neither abolishes opioid-induced analgesia nor causes withdrawal symptoms but reduces opioid-induced constipation. 

Pharmacodynamics 

methylnaltrexone returns normal gastrointestinal motility by inhibiting the mu-opioid receptors in the GI tract. It stimulates colonic propulsive contractions, hastens the passage of stool through the intestines, and encourages bowel movements. 

Pharmacokinetics 

Absorption   

methylnaltrexone is rapidly absorbed into the systemic circulation. The time to reach peak plasma concentration (Tmax) within 30 minutes. 

Distribution 

methylnaltrexone has a small volume of distribution approximately 1.1 L/kg. 

Metabolism 

methylnaltrexone undergoes minimal hepatic metabolism.  

Elimination and excretion 

methylnaltrexone is eliminated via renal excretion. The elimination half-life of methylnaltrexone is approximately 8 hours.

Adminstartion

Administration 

methylnaltrexone is administered via subcutaneous injection. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: methylnaltrexone 

Why do we use methylnaltrexone? 

methylnaltrexone is indicated for the treatment of OIC in adult patients with chronic non-cancer pain.  methylnaltrexone acts as a peripherally acting mu-opioid receptor antagonist (PAMORA), targeting the opioid receptors in the gastrointestinal tract to restore normal bowel function and alleviate constipation.