[Evolution of plasma histamine after midazolam in patients at risk of histamine liberation]

Changes in plasma histamine levels 2 min (t1) and 10 min (t2) after the intravenous injection of 0.2 mg X kg-1 midazolam were measured in 10 subjects at risk of releasing histamine (group I) and compared with those of 15 other subjects free from any risk of releasing histamine (group II). There was mean increases in plasma histamine levels of 0.78 ng X ml-1 between t0 and t1 (p less than 0.01), and of 0.41 ng X ml-1 between t0 and t2 (p less than 0.01) in group I; they only rose by 0.18 ng X ml-1 between t0 and t2 (p less than 0.01) in group II. The only statistically significant variation between the two groups was that at t1 (p less than 0.03): plasma histamine levels rose higher at the second minute in those cases at risk. This was a rather small increase, within physiological limits, and without any clinical or haemodynamic manifestation.