What is Methylnaltrexone: Uses, Dosage, Side Effects and More

Methylnaltrexone is a prescription medication that helps relieve constipation caused by opioid pain medications. If you're taking opioids for pain management and struggling with severe constipation, this medication can offer relief without interfering with your pain control. It works by blocking opioid effects specifically in your digestive system while leaving pain relief intact throughout the rest of your body.

What is Methylnaltrexone?

Methylnaltrexone is a specialized medication designed to treat opioid-induced constipation. It belongs to a class of drugs called opioid antagonists, which means it blocks certain opioid effects in specific parts of your body. The medication comes as a subcutaneous injection, meaning it's given as a shot under your skin, similar to how people with diabetes give themselves insulin injections.

This medication is specifically engineered to work only in your digestive system and doesn't cross into your brain. This unique design means it can restore normal bowel function without reducing the pain relief you get from your opioid medications. It's particularly helpful for people who need long-term opioid therapy but are experiencing uncomfortable constipation as a side effect.

What is methylnaltrexone used for?

Methylnaltrexone treats opioid-induced constipation in adults who take opioid pain medications regularly. This type of constipation is different from ordinary constipation because it's caused by opioids slowing down your digestive system. Many people who take opioids for chronic pain, cancer pain, or after surgery experience this challenging side effect.

The medication is typically prescribed when other constipation treatments haven't worked well enough. Your doctor might recommend it if you've tried increased fiber, stool softeners, or laxatives without sufficient relief. It's especially valuable for people who need to continue taking opioids for pain management but want to restore more normal bowel function.

In some cases, doctors also prescribe methylnaltrexone for people with advanced illness who are receiving palliative care. This helps improve quality of life by addressing one of the most uncomfortable side effects of necessary pain medication.

How does methylnaltrexone work?

Methylnaltrexone works by blocking opioid receptors specifically in your digestive system. When you take opioid pain medications, they attach to receptors throughout your body, including in your intestines. While this provides pain relief, it also slows down the movement of food and waste through your digestive tract, leading to constipation.

This medication is designed with a special structure that prevents it from crossing the blood-brain barrier. This means it can't reach the opioid receptors in your brain that control pain relief. Instead, it focuses only on the opioid receptors in your gut, allowing your digestive system to function more normally while keeping your pain medication effective.

The medication is considered moderately strong and typically produces bowel movements within a few hours to a day after injection. Most people find it quite effective for its intended purpose, though individual responses can vary based on factors like your overall health and how long you've been taking opioids.

How should I take methylnaltrexone?

Methylnaltrexone is given as a subcutaneous injection, which means you or a caregiver will inject it under the skin. Your healthcare provider will teach you the proper injection technique and show you the best injection sites, typically your thigh, abdomen, or upper arm. The injection is usually given every other day, but your doctor will determine the right schedule for your specific situation.

You don't need to take this medication with food, and there are no specific dietary restrictions. However, it's important to stay well-hydrated when using any medication that affects bowel function. The injection should be given at room temperature, so you'll need to remove it from the refrigerator about 30 minutes before injecting.

Always rotate your injection sites to prevent skin irritation or tissue damage. Keep track of where you've injected recently and choose a different spot each time. If you're uncomfortable giving yourself injections, a family member or caregiver can learn to help you, or you might be able to receive the injections at your doctor's office.

How long should I take methylnaltrexone for?

The duration of methylnaltrexone treatment depends on how long you need to take opioid pain medications. Since this medication treats a side effect of opioids rather than an underlying condition, you'll typically use it for as long as you're experiencing opioid-induced constipation. This might be weeks, months, or even longer for people with chronic pain conditions.

Your doctor will regularly evaluate whether you still need the medication. If your opioid dose decreases or if you stop taking opioids altogether, you'll likely be able to discontinue methylnaltrexone as well. Some people find that their constipation improves enough that they can manage with other treatments, allowing them to stop the injections.

It's important not to stop methylnaltrexone suddenly without talking to your healthcare provider. While it's not habit-forming, stopping abruptly might cause your constipation to return quickly. Your doctor can help you determine the best approach for your individual situation.

What are the side effects of methylnaltrexone?

Most people tolerate methylnaltrexone well, but like all medications, it can cause side effects. The most common side effects are generally mild and related to changes in your digestive system as it adjusts to more normal function.

Here are the more common side effects you might experience:

• Abdominal pain or cramping, which usually happens as your bowel function returns to normal
• Nausea, particularly in the first few doses as your system adjusts
• Diarrhea, especially if your system overcorrects from constipation
• Injection site reactions like redness, swelling, or mild pain where you received the shot
• Flatulence or gas as your digestive system becomes more active
• Dizziness, which might occur if you become dehydrated from increased bowel activity

These common side effects often improve as your body adjusts to the medication and as your bowel function stabilizes.

There are also some less common but more serious side effects to be aware of:

• Severe abdominal pain that doesn't improve, which could indicate a bowel obstruction
• Persistent vomiting that prevents you from keeping fluids down
• Signs of dehydration like extreme thirst, dry mouth, or reduced urination
• Severe allergic reactions, though these are rare
• Symptoms that might indicate opioid withdrawal, such as sweating, anxiety, or muscle aches

If you experience any severe or concerning symptoms, contact your healthcare provider right away. Most people find that the benefits of improved bowel function outweigh the temporary discomfort of side effects.

Who should not take methylnaltrexone?

Methylnaltrexone isn't safe for everyone, and there are several important situations where it shouldn't be used. Your doctor will carefully review your medical history before prescribing this medication to ensure it's safe for you.

You should not take methylnaltrexone if you have any of these conditions:

• Known bowel obstruction or blockage, as the medication could worsen this dangerous condition
• Active inflammatory bowel disease like Crohn's disease or ulcerative colitis during flare-ups
• Severe kidney disease, since the medication is processed through your kidneys
• Allergy to methylnaltrexone or any ingredients in the injection
• Suspected perforation in your digestive tract

Your doctor will also use extra caution if you have certain other conditions that might increase your risk of complications:

• Mild to moderate kidney problems, which might require dose adjustments
• History of digestive tract surgery, especially recent procedures
• Diverticulitis or other inflammatory conditions of the colon
• Severe liver disease that might affect how your body processes the medication
• Pregnancy or plans to become pregnant, as safety data is limited

Always tell your healthcare provider about all your medical conditions and current medications before starting methylnaltrexone. This helps ensure the medication is both safe and effective for your specific situation.

Methylnaltrexone brand name

Methylnaltrexone is available under the brand name Relistor. This is the most commonly prescribed form of the medication and comes as prefilled syringes for subcutaneous injection. The brand name version and any generic versions contain the same active ingredient and work in the same way.

Some insurance plans may have preferences for brand name versus generic medications, so it's worth checking with your insurance provider about coverage. Your pharmacist can also help you understand your options and any cost differences between available formulations.

Methylnaltrexone alternatives

If methylnaltrexone isn't right for you, there are several other treatment options for opioid-induced constipation. Your doctor might recommend trying these alternatives based on your specific situation and medical history.

Other prescription medications for opioid-induced constipation include:

• Naloxegol (Movantik), which is taken as a daily pill rather than an injection
• Naldemedine (Symproic), another oral medication that works similarly
• Lubiprostone (Amitiza), which works differently by increasing fluid in your intestines

Non-prescription approaches that your doctor might suggest include:

• Osmotic laxatives like polyethylene glycol (Miralax)
• Stimulant laxatives such as senna or bisacodyl
• Stool softeners like docusate
• Increased dietary fiber and fluid intake
• Regular physical activity as tolerated

The best approach often involves combining different strategies. Your healthcare provider can help you develop a comprehensive plan that addresses your constipation while maintaining effective pain control.

Is methylnaltrexone better than naloxegol?

Both methylnaltrexone and naloxegol are effective for treating opioid-induced constipation, but they have different advantages depending on your situation. The choice between them often comes down to your preferences, lifestyle, and how your body responds to each medication.

Methylnaltrexone may be better if you prefer less frequent dosing, since it's typically given every other day rather than daily. Some people also find that the injection works more quickly and reliably than oral medications. It might be a good choice if you have trouble remembering to take daily medications or if you have digestive issues that interfere with pill absorption.

Naloxegol might be preferable if you're uncomfortable with injections or prefer the convenience of taking a pill. It's taken once daily by mouth and doesn't require injection supplies or techniques. Some people find oral medications easier to incorporate into their daily routine.

Both medications work through similar mechanisms and have comparable effectiveness for most people. Your doctor can help you weigh the pros and cons of each option based on your individual needs, preferences, and medical history.