methylnaltrexone bromide: clinical use

Prescribing considerations

• Confirm that constipation is opioid-induced and that laxative response has been insufficient.
• Assess for obstruction, acute abdominal pathology, faecal impaction and conditions affecting bowel-wall integrity.
• Review renal and hepatic function and whether the pre-filled syringe is appropriate.
• Consider increased withdrawal or reduced-analgesia risk where the blood–brain barrier is disrupted.

Contraindications and cautions

• Hypersensitivity to methylnaltrexone bromide or an excipient.
• Known or suspected mechanical gastrointestinal obstruction.
• Increased risk of recurrent obstruction.
• Acute surgical abdomen.

Monitoring

• Bowel response and continuing clinical need.
• Severe, persistent or worsening abdominal pain.
• Severe or persistent diarrhoea.
• Opioid-withdrawal symptoms or reduced analgesia.
• Renal and hepatic status where impairment is present.

Clinical pharmacology

A selective peripheral mu-opioid receptor antagonist with restricted blood–brain barrier penetration. It is absorbed rapidly after subcutaneous injection, undergoes modest metabolism and is eliminated mainly unchanged through urine and faeces.

Formulation and product differences

• The selected product is a ready-to-use solution for subcutaneous injection in a pre-filled syringe.
• Vial presentations may be required when an accurately individualised amount cannot be delivered using a pre-filled syringe.
• The solution should be clear, colourless to pale yellow and essentially free from visible particles.

Injection

Route: Parenteral

Strengths: 8 mg, 12 mg, 12 mg/0.6 mL