Although opioids are very effective for treating and managing pain, their use frequently results in opioid-induced constipation (OIC). Treatment options for OIC may be as simple as changing diet or as complicated as requiring several medicines and laxatives.
Changing lifestyle factors is usually the first recommendation that physicians make for the prevention or treatment of constipation. This includes:
Changes in lifestyle, however, may not be possible for many patients. In addition, these changes may be ineffective in treating OIC. If there is a concurrent underlying disease or medicine that is causing constipation, the disease may need to be treated separately or another treatment regimen may have to be considered.
OIC treatment usually requires additional medicines to be prescribed along with the opioid painkillers that are causing the constipation. Withholding the opioid treatment is ill-advised because it results in a decrease in the patient's quality of life. Often, laxatives and/or cathartics are prescribed at the same time as the opioid painkillers so that treatment for the constipation beings immediately. A cathartic accelerates defecation, while a laxative eases defecation, usually by softening the stool; some medicines are considered to be both laxatives and cathartics.
For the treatment of OIC, doctors may prescribe:
Although the treatments listed above are usually successful in treating OIC, sometimes a physician will recommend rectal intervention. As discussed, prophylaxis with laxatives are/or cathartics is considered usual - as some clinicians assume [constipation] to be virtually universal in patients who are prescribed opioid analgesics1.
Rectal interventions are indicated if the appropriate oral measures have been ineffective2. Rectal intervention means the following treatments:
The first choice rectal intervention for uncomplicated constipation is glycerine suppositories2. If these are ineffective, then a stimulant enema might be administered. Oral and rectal stimulant laxatives should be avoided if there is possible or proven bowel obstruction. Gentle rectal measures can sometimes be effective in emptying the rectum and lower colon. Oral softening agents are useful if the obstruction is incomplete. It should be remembered that constipation can cause bowel obstruction.
If none of the rectal laxatives above prove adequate to remove impacted faeces, rectal irrigation with normal saline can be performed3. Manual evacuation should be used as a last resort when all other methods of bowel management have been shown to be ineffective.
Constipation is a known side effect of opioid analgesics and should be addressed before opioid therapy begins. As opioid-induced constipation can be severe and adversely impact quality of life and compliance with therapy, prophylaxis with laxatives is considered to be the best approach. A British Pain Society survey conducted in March 2009 showed that nearly half of GPs (44%) surveyed believe that the negative impact of such side effects is the key factor in patient non-compliance with prescribed opioid treatments.
Concurrent management on initiation of opioids frequently includes recommending certain lifestyle or dietary adjustments (as listed above) and initiating a scheduled regimen of laxatives. Laxative and cathartic therapy may be needed throughout opioid therapy and beyond. Effective management requires a composite of strategies, including behavioral and lifestyle changes (diet, activity, and fluid intake, as appropriate).
However medications used to manage opioid-induced constipation, such as laxatives, do not address the underlying opioid receptor-mediated cause of constipation and are often ineffective4.
Methylnaltrexone (available as Relistor(R)) helps restore bowel function in patients who have advanced illness and receive opioids for pain relief. Methylnaltrexone is delivered via subcutaneous injection and specifically targets opioid-induced constipation. When given alongside opioid therapy, it is designed to displace the opioid from binding to peripheral receptors in the gut, decreasing the opioid's constipating effects and inducing laxation.
Methylnaltrexone is a peripherally acting mu-opioid receptor antagonist that decreases the constipating effects of opioid pain medications in the gastrointestinal tract without diminishing their ability to relieve pain.
Methylnaltrexone blocks peripheral opioid receptors in the gut and unlike other opioid antagonists has restricted ability to cross the blood-brain barrier. As a result, it antagonizes only the peripherally located opioid receptors in the GI tract, so it's action reverses opioid-induced constipation without precipitating withdrawal symptoms or affecting or reversing the central analgesic effects of opioids5.
Another new medication for severe pain (long-term pain that can be experienced as a result of conditions such as back pain, arthritis and osteoarthritis)6, are tablets combining prolonged release oxycodone, an opioid which treats pain, and prolonged release naloxone, a compound which counteracts the potential negative effects of the opioid on the GI function (available as TarginactTM). This novel combination has been proven to provide equivalent pain relief to oxycodone alone, whilst significantly improving bowel function7. Naloxone is an opioid receptor antagonist that, when taken orally, has negligible systemic bioavailability8 providing a full inhibitory effect on local opioid receptors in the gut - counteracting opioid-induced constipation - without impacting on the centrally acting analgesic efficacy of oxycodone.
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