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Methylnaltrexone Injection

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Why is this medication prescribed?

Methylnaltrexone injection is a medication used to treat opioid-induced constipation (OIC) in adults who are receiving opioid medications for pain relief, and who have not adequately responded to laxatives. Opioid medications, such as morphine, oxycodone, and others, are commonly used to manage moderate to severe pain. However, a common side effect of opioid use is constipation, which can be severe and long-lasting. Methylnaltrexone helps alleviate this specific side effect without interfering with the pain-relieving effects of opioids.

How should this medicine be used?

Here’s how Methylnaltrexone injection is typically used:

  • Prescription: Methylnaltrexone injection should be prescribed by a healthcare provider who is familiar with its use and the patient’s medical history.
  • Dosage: The dosage is determined by the healthcare provider based on the individual patient’s needs and response to the medication. It is usually administered as a subcutaneous injection, which means it is injected just under the skin.
  • Frequency: The frequency of administration can vary depending on the severity of constipation and the patient’s response to the medication. It can be given every 24 hours if needed.
  • Administration: The injection is typically administered by a healthcare professional, but in some cases, patients or caregivers may be trained to give the injection at home. It is important to follow the healthcare provider’s instructions carefully when administering the injection.
  • Location: The injection site is usually in the upper arm, thigh, or abdomen, and it should be rotated to different sites to prevent injection site reactions.
  • Monitoring: Patients should be monitored for any side effects or changes in their condition while using Methylnaltrexone. If there are any concerning symptoms or side effects, they should contact their healthcare provider.

It’s essential to use Methylnaltrexone exactly as prescribed by your healthcare provider. Do not change the dosage or frequency of administration without consulting your healthcare provider. If you have any questions or concerns about the medication, be sure to discuss them with your healthcare provider or pharmacist. Additionally, Methylnaltrexone is not intended for the treatment of opioid addiction or withdrawal; it is specifically for the management of opioid-induced constipation.

Other uses for this medicine

Methylnaltrexone injection is primarily used for the treatment of opioid-induced constipation in adults who are receiving opioid medications for pain relief and have not responded adequately to laxatives. It is not typically used for other medical conditions. This medication works by blocking the effects of opioids on the gut while not affecting their pain-relieving properties. Therefore, its use is specific to managing constipation caused by opioids.

What special precautions should I follow?

Special Precautions for Methylnaltrexone Injection:

  • Allergies: Inform your healthcare provider of any allergies or sensitivities you may have, especially if you have a known allergy to Methylnaltrexone or any of its components.
  • Medical History: Provide your healthcare provider with a complete medical history, including any underlying medical conditions or gastrointestinal issues you may have, to ensure the medication is safe and appropriate for you.
  • Pregnancy and Breastfeeding: Methylnaltrexone’s safety during pregnancy or breastfeeding has not been extensively studied. Discuss the risks and benefits with your healthcare provider if you are pregnant or nursing.
  • Interactions: Inform your healthcare provider about all medications you are currently taking, including prescription drugs, over-the-counter medications, vitamins, and herbal supplements. Methylnaltrexone may interact with other medications, so your healthcare provider needs to be aware of your complete medication list.
  • Gastrointestinal Issues: If you have a history of severe gastrointestinal conditions, such as perforation or obstruction, it’s important to discuss this with your healthcare provider as Methylnaltrexone may not be suitable for you.
  • Injection Site Reactions: Like with any injectable medication, there is a risk of injection site reactions, including redness, swelling, or discomfort at the injection site. Rotate injection sites as directed by your healthcare provider to minimize these reactions.
  • Overuse of Opioids: Methylnaltrexone does not negate the pain-relieving effects of opioids. Be cautious not to use more opioids than prescribed because Methylnaltrexone is intended to address opioid-induced constipation, not opioid overdose.
  • Side Effects: Be aware of potential side effects of Methylnaltrexone, such as abdominal pain, nausea, diarrhea, sweating, or chills. If any side effects become severe or bothersome, contact your healthcare provider.
  • Follow Instructions: Follow your healthcare provider’s instructions for the administration of Methylnaltrexone closely. If you are administering the injections at home, ensure you are trained on the proper technique.
  • Emergency Situations: In case of an opioid overdose or respiratory distress while taking opioids, Methylnaltrexone may not be effective. It’s important to have access to naloxone (Narcan) in such situations, as naloxone can reverse the effects of opioid overdose.

Always consult with your healthcare provider or pharmacist for specific guidance regarding Methylnaltrexone injection, especially if you have any concerns or questions about its use and potential interactions with other medications or conditions.

What special dietary instructions should I follow?

Special Dietary Instructions for Methylnaltrexone injection:

  • There are no specific dietary restrictions associated with methylnaltrexone injection.
  • However, maintaining a healthy diet with adequate fluid intake is generally recommended to help manage constipation effectively, regardless of whether you are using this medication.
  • Be sure to discuss your dietary habits and any dietary restrictions with your healthcare provider, as they can provide personalized guidance based on your medical condition and treatment plan.

What should I do if I forget a dose?

If you forget a dose, it’s important to contact your healthcare provider or nurse promptly for guidance on what to do next. They can provide specific instructions based on your situation, as the response to a missed dose can depend on the timing and frequency of your injections.

In some cases, if you miss a dose of Methylnaltrexone and it’s close to the time for your next scheduled dose, your healthcare provider may recommend skipping the missed dose and continuing with your regular dosing schedule. Do not double up on doses to make up for a missed one unless explicitly instructed to do so by your healthcare provider.

What side effects can this medication cause?

Methylnaltrexone injection, like any medication, can cause side effects. It’s important to be aware of these potential side effects, but also keep in mind that not everyone will experience them. If you experience any side effects while using Methylnaltrexone, it’s essential to communicate with your healthcare provider. Here are some common and less common side effects associated with Methylnaltrexone:

Common Side Effects:

  • Abdominal Pain: This is one of the most common side effects and may include stomach cramps or discomfort.
  • Nausea: Some people may experience a feeling of nausea after taking Methylnaltrexone.
  • Diarrhea: While Methylnaltrexone is used to alleviate constipation, it can sometimes lead to diarrhea as a side effect.
  • Sweating: Increased sweating, especially during the injection, is a possible side effect.
  • Chills: Some individuals may experience chills or shivering.

Less Common Side Effects:

  • Vomiting: Vomiting is less common but can occur as a side effect.
  • Headache: Some people may experience headaches while taking Methylnaltrexone.
  • Dizziness: Dizziness is less common but has been reported.
  • Fatigue: A feeling of tiredness or weakness can occur as a side effect.
  • Muscle Spasms: In some cases, muscle spasms have been reported.
  • Injection Site Reactions: Redness, swelling, or discomfort at the injection site can occur.
  • Dry Mouth: This is less common but has been reported.
  • Flatulence (Gas): Some individuals may experience increased gas.

Serious allergic reactions to Methylnaltrexone are rare, but they can occur. Seek immediate medical attention if you experience symptoms of a severe allergic reaction, such as difficulty breathing, rash, itching, swelling of the face, lips, or tongue, or severe dizziness.

It’s important to note that Methylnaltrexone is generally well-tolerated and is specifically designed to target opioid-induced constipation without affecting the pain-relieving effects of opioids. If you experience any side effects, consult your healthcare provider. They can help determine whether any adjustments to your medication regimen are necessary or if the side effects are manageable.

Always follow your healthcare provider’s guidance when using Methylnaltrexone, and report any side effects promptly to ensure your safety and well-being while using the medication.

What should I know about storage and disposal of this medication?


  • Storage: Follow the storage instructions provided with the medication, which typically involve keeping Methylnaltrexone injection at room temperature, away from excessive heat or cold. Do not freeze the medication. Keep it out of the reach of children and pets.
  • Protect from Light: Some medications can be sensitive to light. Ensure that the medication is stored in its original packaging or a container that protects it from direct light exposure.
  • Do Not Store for Extended Periods: Use the medication according to your healthcare provider’s instructions. Do not store it for longer than recommended or after the expiration date on the packaging.


  • Dispose of Methylnaltrexone injection properly according to local regulations. Do not dispose of it in household trash or flush it down the toilet unless instructed to do so by your healthcare provider or local guidelines. Ask your pharmacist or healthcare provider for guidance on how to safely dispose of unused or expired medication.

In case of emergency/overdose

In case of emergency or overdose of Methylnaltrexone Injection:

Methylnaltrexone is not used to treat opioid overdose. If you suspect an opioid overdose or encounter someone who may be experiencing one, take the following steps:

  • Call 911: In the United States, calling 911 is the fastest way to access emergency medical assistance. Stay on the line and follow the operator’s instructions.
  • Administer Naloxone (Narcan): If you have access to naloxone (Narcan), administer it according to the instructions provided with the medication. Naloxone is an opioid receptor antagonist that can reverse the effects of opioid overdose, including respiratory depression.
  • Perform CPR: If the person is unresponsive and not breathing or breathing very slowly, initiate cardiopulmonary resuscitation (CPR) until emergency medical personnel arrive.
  • Stay with the Person: Continue to monitor the person’s condition and provide any necessary assistance until professional help arrives.

What other information should I know

  • Follow Your Healthcare Provider’s Instructions: Always adhere to your healthcare provider’s recommendations and instructions regarding the use of Methylnaltrexone injection. Do not adjust the dosage or frequency without consulting them.
  • Inform Healthcare Providers: Let all healthcare providers involved in your care know that you are taking Methylnaltrexone, especially if you are undergoing surgery or any medical procedures.
  • Regular Follow-Ups: Maintain regular follow-up appointments with your healthcare provider to monitor your progress and adjust treatment if necessary.
  • Allergies: If you experience signs of an allergic reaction (e.g., difficulty breathing, rash, swelling of the face or throat), seek immediate medical attention.
  • Keep a Medication Record: It can be helpful to keep a record of your medication use, including the dates and times of Methylnaltrexone injections, to ensure you are following your prescribed treatment plan accurately.
  • Be Informed: Educate yourself about your condition, the medications you are taking, and potential side effects. Knowledge about your treatment can help you manage your health effectively.

Always consult your healthcare provider or pharmacist if you have any questions or concerns about Methylnaltrexone injection, its use, or any aspect of your medical treatment. Your healthcare provider is the best source of guidance tailored to your specific needs and circumstances.

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