Alcuronium kinetics in patients undergoing cardiopulmonary bypass surgery

1 The disposition of alcuronium was investigated in 10 patients undergoing surgery involving cardiopulmonary bypass (CPB) and compared with results from a group of non-cardiac patients studied previously. 2 After intravenous administration of a combined bolus and infusion dosage regimen, plasma concentrations fell in a bi-exponential fashion to a mean value of 0.55 micrograms/ml immediately before the start of extracorporeal circulation. 3 During CPB an apparent steady-state of alcuronium was reached immediately after commencement of CPB, however plasma concentrations were some 50% higher than those noted prior to commencement of CPB and those predicted using previous pharmacokinetic data from normal surgical patients. 4 Once CPB was completed and the alcuronium infusion terminated, post-infusion alcuronium plasma concentrations again appeared to decline bi-exponentially with time. 5 Of the pharmacokinetic parameters which were calculated model-independently, the apparent volume of distribution (Vss) was unchanged (329 vs 313 ml/kg) and the elimination half-life (t1/2,z) (532 vs 199 min) was prolonged and the plasma clearance (CL) (0.8 vs 1.34 ml min-1kg-1) markedly reduced in these patients compared to non-cardiac surgical patients. 6 As a result of these changes in alcuronium concentration during CPB and the diminished elimination of alcuronium following CPB, a closer monitoring of neuromuscular function may be necessary in cardiac patients undergoing CPB.