Constipation and Pain Killers

Jul 25, 2016

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

As Canadian as two Winnipegosis Mounties saving a skunk from a Tim Horton's Cup. A few weeks ago, a video circulated of one RCMP member trapping a skunk with its head in cup under a yellow raincoat. The other one in a blue hazmat looking suit, managed to get the Timmy's cup off the skunk's head. This really goes to show the RCMP are out there to help even the smallest and most vulnerable amongst us. And if you are an RCMP member, I'm sure it highlites that you never know what to expect when you show up at the beginning of your shift.

Some of the medication we dispense throw a skunk-with-his-head-in-a-cup curve ball at patients. An unexpected side effect of some pain killers is constipation. The constipation causing pain killers are the opioids or narcotics. 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 don't 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.

As Canadian as two Winnipegosis Mounties saving a skunk from a Tim Horton's Cup is pretty cool, but you must have better stories than that. What says Canada to you this summer? As Canadian as a prairie thunder storm? As Canadian as a pickerel from Waterhen? As Canadian as rainbow over a yellow field of canola? Whatever you are doing, stockpile your warm Canadian summer memories. It will be January before we know it.

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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