Prevention of constipation should start before an opioid analgesic is started.
The goal is to produce stool that has the consistency of toothpaste and that is easy to evacuate without causing incontinence.
General principles:
(1) Keep the patient well-hydrated.
(2) Keep as active as possible.
(3) Avoid other medications that reduce gastrointestinal transit.
(4) Use the lowest dose of analgesic for the shortest period of time.
Many patients will respond to the use of a stool softener plus a laxative.
A high fiber diet may be helpful but should not be a substitute for softener and laxative. If the patient becomes dehydrated then the fiber may contribute to the constipation.
Additional interventions may be necessary if the patient is resistant to simple measures:
(1) stimulant cathartic
(2) osmotic agent (sorbitol, lactulose)
(3) prokinetic agent
(4) Use of a peripherally acting opioid antagonist that does not cross the blood-brain barrier (alvimopan, methylnaltrexone, other).
