Recent studies have found that opiate antagonists such as naloxone and
naltrexone, if given enterally (e.g. by mouth) in small doses, reverse the gut
actions of the opiate without interfering with the pain-relieving properties.
Methylnaltrexone has been evaluated and found to be helpful if given
intravenously to patients on high opiate doses: it produced laxation and
reversed the opiate slowing of oral-colonic transit times.
These agents may be further evaluated in studies prior to becoming available for treating severe cases of opiate-induced constipation.
DIFFICULTIES ENCOUNTERED WHEN TREATING CONSTIPATION:
- Constipation with colicky abdominal pain: treat with higher doses
of stool softener (docusate) or increased dose of sorbitol. - Stimulant cathartic agents ineffective: try lactulose 30-60cc
twice a day or sorbitol 30ml three times a day - Opioid bowel syndrome: if reducing the opiate dose is not practical,
then an alternative opiate medication may be tried at an equianalgesic
dose. Alternatively, use of other analgesics such as NSAIDs (anti-
inflammatory drugs such as brufen) may be beneficial and allow a
reduced opiate dose - Constipation with partial bowel obstruction: stimulant laxatives
should be avoided as they will cause cramping and bulking agents must
not be given as there would be a risk of bowel perforation. Low dose oral sorbitol is used in palliative care settings, but the problem should be approached under strict medical supervision.
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