A patient being treated with an opioid analgesic may develop itching, which may be severe enough to require discontinuation of the triggering drug.
Morphine sulfate is the opiate most commonly associated with itching.
Possible mechanisms:
(1) direct histamine release
(2) allergic reaction
(3) central effect
(4) stimulation of mu receptors
Factors implicating a particular opioid:
(1) exclusion of other causes
(2) disappearance on discontinuing the implicated agent
(3) disappearance on rotation to a different one (giving hydromorphone in place of morphine)
Factors implicating histamine release or an allergic reaction:
(1) reduction in pruritus following administration of an antihistamine
(2) presence of flushing or skin erythema along with the pruritus
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Specialty: Toxicology, Emergency Medicine, Critical Care
