Succinylcholine overdose in the African elephant (Loxodonta africana) and impala (Aepyceros melampus) : pharmacokinetics, pharmacodynamics and physiological responses : research article

We investigated the mechanism of the delayed effect of succinylcholine (SuCh) in elephants, by correlating the plasma concentration of SuCh with alterations in respiratory and cardiovascular function and with changes in plasma markers of metabolism. These changes were compared with those in impalas, following a lethal SuCh dose in each species. Total entry of SuCh into the circulation (cumulative dose) and total exposure of neuromuscular receptors to unhydrolysed SuCh (area under curve of plasma [SuCh] versus time), were determined. Absorption of intramuscular SuCh was slower, and the cumulative dose lower in elephant than impala, but exposure to intact SuCh was similar in both. SuCh produced apnoea, a fall in PaCO2 and pH, and rises in the PaCO2 and plasma catecholamine and cortisol concentrations, and variable cardiovascular responses. These changes took longer to develop in elephant than impala, but in both species death was associated with metabolic consequences of severe hypoxia. We conclude that the delayed effect of SuCh in elephant does not arise from differences in SuCh pharmacodynamics between the species but can be attributed to different pharmacokinetics, the lower mass-specific metabolic rate of the elephant, and its greater tolerance of severe metabolic changes before death results.