Constipation and Pain Killers

Jul 28, 2015

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

Bubble netting is fascinating and a little scary to watch. I was lucky enough to go on a salmon fishing trip in BC and we saw some humpback whales bubble netting. There were about 6 whales and they blew a circular curtain of bubbles around a school of herring. Then they came up underneath the ball of bait fish they'd enclosed with their mouths open to scoop up their lunch. They bubble netted a little closer to our boat than we thought they were going to. We backed away slowly as humpbacks are enormous animals. As cool as bubble netting is, it wasn't as impressive as Pat's double Tyee morning.

Becoming a whale watcher while fishing was unexpected. An unexpected side effect of some pain killers is that they can cause constipation. These are pain killers with opioids or narcotics in them. Opioids and narcotics are different names for the same thing. These medications originally came from the opium poppy. The most common of these is morphine, but opioids also include codeine, meperidine, oxycodone, hydromorphone, and several others. These medications do a very good job of suppressing pain, but they commonly cause constipation.

For opioids like morphine to kill pain, they attach to an opioid receptor in the brain. For opioids like morphine to cause constipation, they attach to a receptor outside the brain. That is how the diarrhea prevention drug loperamide or immodium works. It binds to the same mu-opioid receptor morphine does, but it isn't able to cross the blood brain barrier. So it just causes constipation, but doesn't cause any pain killing.

Do we have to worry about constipation in everyone on every opioid? Probably not. If someone is on Tylenol #3 (which contains codeine) as needed for a sprained ankle, we probably don't need to worry about constipation. They will probably only need their opioid for 3-4 days. However, if someone is on a regular opioid for a week or longer, we should start talking about constipation prevention.

Prevention of opioid induced constipation should begin by using non-drug measures. These measures include eating more fiber. Choose fruits such as apples and oranges, vegetables such as peas and broccoli, and whole grains such as oats and brown rice to get more fiber. You can also eat foods such as cereal bars with added fiber, or fiber supplements like Metamucil. A person should also drink 6-8 glasses of water per day because the water helps the fiber do its job. Regular exercise like walking will also help with constipation.

Unfortunately, eating more fiber, drinking water and exercise might not help prevent opioid induced constipation. Then we reach for laxatives. The most gentle of these are the osmotic laxatives. Osmotic laxatives like PEG 3350 work by drawing more water into the gut. They are usually well tolerated and not that expensive. They don't cause as much cramping as stimulant laxatives and are considered safe for long term use if a patient needs to be on an opioid pain killer for an extended period of time.

The next step up in strength is the stimulant laxatives like bisacodyl. When I was in pharmacy school ,we were taught they weren't safe for long term use. We were told they would lead to lazy bowels that wouldn't work without laxatives if they were used long term. Lately, it has been found there is limited proof that long term stimulant laxative use will cause lazy bowels and they are considered safe in long term treatment of opioid induced constipation.

Another change has been the use of stool softeners like docusate calcium and docusate sodium. Stool softeners dont seem to be particularly useful for either treating or preventing constipation. So stool softeners aren`t what we should be reaching for opioid induced constipation.

An interesting addition to the opioid induced constipation arsenal is methylnaltrexone or Relistor. Naltrexone has been used for a long time as a reversal agent for opioid overdose. Naltrexone blocks an opioid like morphine from getting to its receptor. Methylnaltrexone also blocks the mu-opioid receptor. However, although it is injected, it doesn't cross the blood brain barrier. That means it stays in the body and not the brain. So it blocks the constipating effects of the opioid, but doesn't get into the brain and block the pain killing effects. Two of the down sides to methylnaltrexone are it is very expensive and right now it is on long term back order, so we can't get it in the pharmacy.

Accidental whale watching was fun, but Pat and I were in a boat together to catch salmon. Pat caught a big Chinook salmon. Chinook or Spring or King Salmon are the biggest species of salmon on the west coast. They have spotted tails and black gums. If you catch a Chinook that is over 30 pounds they call it a Tyee. A Tyee is a trophy sized Chinook and many fishermen never catch even one. Pat caught two in one morning. Despite being a little bit jealous, it was fun to watch Pat's double Tyee day. Lets coin that as a new phrase when something goes really well. Heres hoping you have a Double Tyee day!


As always if you have any questions or concerns about these or other products, ask your pharmacist.

The information in this article is intended as a helpful guide only. It is not intended to be used as a substitute for professional advice. If you have any questions about your medications and what is right for you see your doctor, pharmacist or other health care professional.


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