Nov 29, 2010

By Trevor Shewfelt, Pharmacist at the Dauphin Clinic Pharmacy

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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.

Ever heard the expression driving with the brakes on? Thats what I thought of when I first read about a new pain killer called targin. It is made by Purdue, the same company that makes oxycontin. Just like oxycontin, targin has the pain killer oxycodone in it. And like oxycontin, targin is a slow release product so a patient only needs to take the medication every twelve hours. The unusual thing about targin is it has a second ingredient in it. That ingredient is naloxone. Naloxone is an opioid blocker and is usually used as an antidote to stop an opioid like oxycodone from working. I thought adding naloxone to targin was like hitting the brakes on your car when you wanted to accelerate.

How do opioids like oxycodone work? Well, all opioids were originally derived from the opium poppy. People have been using opium as a pain killer and for other medicinal and recreational purposes for 1000s of years. Morphine was the first commercially available opioid pain killer. It was derived from the opium poppy about 200 years ago. It is still a very good pain killer, but over the years chemists have tinkered with it. Within the last century, chemists have come up with several semi-synthetic opioids. One of them was oxycodone. Oxycodone is 2-4 times stronger than morphine so it is a better pain killer. Like all opioids, oxycodone works by attaching to opioid receptors. When it attaches to these receptors it kills the pain and also causes its side effects. Side effects from oxycodone can include: constipation, drowsiness, respiratory depression, nausea and vomiting.

Naloxone is kind of the opposite of oxycodone. Naloxone also attaches to the opioid receptors in the body. But it doesnt cause any pain killing. In fact, we dont think it does much of anything. But it does do a good job of keeping other opioids like oxycodone off of the receptors. That is why naloxone is one of the medications we can use as an antidote for an opioid overdose. If someone shows up at the emergency room with the symptoms of an opioid overdose, one of the medications the doctor may inject into them is naloxone. That can quickly reverse the effects of the opioid and get them conscious and breathing again. So if naloxone is an antidote to an oxycodone overdose, why would you put it in the same pill as oxycodone?

Naloxone works differently if it is taken orally than if it is injected. Naloxone goes into intestine, gets absorbed and goes to the liver. The liver breaks down 97% of the naloxone before it gets to the rest of the body. We call this first pass metabolism. This means that the naloxone never leaves the gut. So, the naloxone blocks the effects of the oxycodone only in the gut but not in the rest of the body. This is actually a very useful effect.

Constipation is a problem whenever we put a patient on an opioid pain killer like oxycodone. Other opioid side effects like being drowsy or being nauseous will get better after a person is on the opioid for a few days. But the problem with constipation never goes away. In fact we often start people on long term opioids on laxatives for the entire length of time they are on the opioid pain killer. So the theory is that if we give the oxycodone and the naloxone together we could get the pain killing of the oxycodone but have the naloxone only block the constipation.

There have been a couple of small studies looking at this. A small study with 265 patients in it by Lowenstein et al in Expert Opinion in Pharmacotherapy in 2009 looked at patients with moderate to severe chronic non-cancer pain for 12 weeks. One half the group had long acting oxycodone (like oxycontin). The other half had long acting oxycodone and long acting naloxone together (like targin). The pain control was similar in both groups, but the group that had the oxycodone and naloxone together had less constipation. Although the trial was small, this is a promising outcome.

Another interesting effect of putting the oxycodone and naloxone together is that makes the drug harder to abuse. Oxycontin has a reputation as a medication that is often abused. Abusers take the medication in ways that were never intended. Targin is intended to be swallowed whole, and not crushed. If targin is taken in ways it was not intended, the naloxone wont just stay in the intestine. The naloxone will go into the rest of the body and the abuser has a good chance of experiencing violent and unpleasant withdrawal symptoms. So targin may be harder to abuse than oxycontin.

The mixture of oxycodone and naloxone in targin is a interesting idea. Although the studies are small, targin may be a decent opioid pain killer that causes less constipation than others in its class. Targin may be harder to abuse than other opioid pain killers. And my initial skepticism about combining an opioid pain killer and an opioid blocker in the same pill seems to be misplaced. Driving with the brakes on may not be such a bad idea after all.

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


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