Skip to Content

Methylnaltrexone Dosage

Applies to the following strength(s): 12 mg/0.6 mL ; 8 mg/0.4 mL

The information at is not a substitute for medical advice. ALWAYS consult your doctor or pharmacist.

Usual Adult Dose for:

Additional dosage information:

Usual Adult Dose for Constipation - Chronic

Opioid-Induced Constipation in Patients with Chronic Non-Cancer Pain:
12 mg subcutaneously once a day

Comments: Prior to initiation, discontinue all maintenance laxative therapy; laxatives can be used as needed for suboptimal response after 3 days.

Opioid-Induced Constipation in Patients with Advanced Illness:
-One-dose subcutaneously every other day as needed, but no more frequently than 1 dose in a 24-hour period; weight-based dosing as follows:
Less than 38 kg: 0.15 mg/kg
38 kg to less than 62 kg: 8 mg (0.4 mL)
62 kg to 114 kg: 12 mg subcutaneously (0.6 mL)
More than 114 kg: 0.15 mg/kg subcutaneously

Comments: To determine injection volume for patients whose weight is less than 38 kg or more than 114 kg: multiply patient weight (kg) by 0.0075 and round up to the nearest 0.1 mL

-For the treatment of opioid-induced constipation in adult patients with chronic non-cancer pain.
-For the treatment of opioid-induced constipation in adult patients with advanced illness who are receiving palliative care, when response to laxative therapy has not been sufficient.

Renal Dose Adjustments

-CrCl 30 to 80 mL/min: No adjustment recommended
-CrCl less than 30 mL/min: Reduce dose by one-half

Liver Dose Adjustments

Mild or moderate hepatic impairment: No adjustment recommended
Severe hepatic impairment: Data not available


Safety and efficacy have not been established in patients younger than 18 years.

Consult WARNINGS section for additional precautions.


Data not available

Other Comments

Administration advice:
-For subcutaneous injection only; do not administer more than 1 dose in a 24-hour period
-Rotation of injection sites is recommended; suggested injection sites are upper legs, abdomen and upper arms
-Once administered, be within close proximity to toilet facilities

Storage requirements:
-Store at room temperature, do not freeze
-If drug has been drawn into a syringe, stable at room temperature for up to 24 hours
-Protect from light

Reconstitution/preparation techniques: See product information.

-If treatment with opioid pain medication is discontinued, this drug should be discontinued; if opioid regimen is change, re-evaluate continued need of this drug.
-In clinical trials in patients with advanced illness, this drug was administered concomitantly with a laxative regimen.
-In patients with chronic non-cancer pain, all maintenance laxative therapy should be discontinued prior to initiating therapy; laxatives can be used as needed after 3 days.
-This drug has been shown to be efficacious in patients who have taken opioids for at least 4 weeks; sustained exposure to opioids prior to starting this drug may increase the patient's sensitivity to this drug.

-Monitor for the development of severe, persistent, or worsening abdominal pain; discontinue therapy if this occurs.

Patient advice:
-Be within close proximity to toilet facilities once the drug is given.
-If unusually severe, persistent, or worsening abdominal pain develops, promptly seek medical attention.
-If severe or persistent diarrhea occurs, patients should be advised to stop therapy and consult their healthcare provider.
-If symptoms of opioid withdrawal such as sweating, chills, anxiety, irritability, and yawning occur, patients should be instructed to let their healthcare provider know.
-Speak to your physician or health care professional if you become pregnant, intend to become pregnant, or are breastfeeding.