[The behavior of plasma histamine levels following peridural morphine administration]

One of the frequently reported side effects following epidural morphine administration in clinical trials is a generalized pruritus of several hours duration. Since histamine can elicit pruritus we investigated the plasma histamine levels following epidurally applied morphine (0.05 mg/kg) in 10 urological patients. Plasma histamine levels were determined as an indicator of histamine release. Indeed, in 2 of 10 patients plasma histamine concentrations rose to 2 ng/ml. 5 of 6 criteria for establishing histamine release were fulfilled in both cases. Minor clinical symptoms appeared only in one patient (one single wheal of 1 cm diameter, metallic taste), but no symptoms at all in the other. Considering the low dose of the analgesic and the relatively high incidence of histamine release (2/10) the result of this prospective study seems worth to be emphasisized and followed-up in further studies. Pruritus did not occur in any of the patients, the role of histamine in its pathogenesis is now becoming more doubtful.