[Cisatracurium--is the stereoisomer an "ideal" relaxant? Histamine liberation and tryptase determination after bolus administration of cistracurium: a comparison with vecuronium].

Unlabelled: Cisatracurium (51W89, Nimbex, Glaxo-Wellcome), an intermediate-acting non-depolarizing neuromuscular blocking agent, is a stereoisomer of atracurium. Histamine releasing propensities and serum tryptase level have been investigated after administration of cisatracurium (3 x ED95, 5 x ED95) or vecuronium (3 x ED90) in surgical patients.

Methods: After approval by our institutional review board, 62 patients (ASA I-II) were randomly assigned to three groups to receive either 3 x ED95 or 5 x ED95 cisatracurium, or 3 x ED90 vecuronium as a rapid bolus. A prick test was done the day before by scarification of the skin in the forearm. After premedication with 2 mg lormetazepam, anaesthesia was induced with thiopentone (4-12 mg/kg) and maintained with O2/N2O and isoflurane (1.5-2 vol.%). Six minutes after thiopentone, the patients received the relaxant and after further 6 min 0.1-0.2 mg fentanyl was given and the trachea was intubated. Heart rate (HR) and blood pressure (BP) were monitored every minute. Blood samples for histamine were withdrawn 5 min prior 3 and 5 min after each drug administration (thiopentone, relaxants). Plasma histamine was measured by radioimmunoassay (RIA) with a sensitivity of approximately 10 pg/ml. Additionally, serum tryptase was measured by RIA at baseline (-10 and -1 min) and 15 and 60 min after the relaxant administration. Levels for histamine > 1000 pg/ml and for tryptase > 2 micrograms/ml were considered significant. Cutaneous signs of histamine release were documented.

Results: Ten patients showed a positive prick-test reaction. Only after thiopentone some cutaneous signs (4 flush, 1 erythema) of histamine release were observed. There were no cutaneous signs of histamine release correlating with cardiovascular changes. Analysis of the blood samples demonstrated no significant increase in the histamine level in all three groups. Only in 1 patient was a significant higher histamine level (1133 pg/ml) measured 5 min after 5 x ED95 cisatracurium. All measurements of serum tryptase were within the physiological limits.

Discussion: In this study, with the particular time course of drug administration, neither cisatracurium nor vecuronium increased plasma histamine levels. Only after 5 x ED95 cisatracurium was 1 elevated histamine level documented after 5 min. In several studies increased histamine levels have been described, but without clinical manifestations. It is known that cutaneous signs can occur without increased plasma histamine levels due to the structural heterogeneity of mast cells. The cutaneous reactions in this study were caused by thiopentone. The tryptase values were within normal limits even in the patient with histamine release. No relationship between the positive results in the prick test and the incidence of cutaneous reactions and/or histamine release for drugs used in the induction of anaesthesia was observed. Whether cisatracurium has a potential for immunologic release is unknown.