Serum calcium levels in response to cholecalciferol and calcium carbonate in the Australian brushtail possum
1993
Jolly, S.E. | Eason, C.T. | Frampton, C.
Cholecalciferol (vitamin D3) is essential for calcium homeostasis but is toxic in high doses. It is registered as a rodenticide in some countries and is being evaluated in New Zealand as a toxin for the control of marsupial brushtail possums (Trichosurus vulpecula). In this study we assessed serum calcium as an indicator of the efficacy of cholecalciferol baits for possums and investigated the relationship between serum calcium and toxicosis in cases of accidental cholecalciferol poisoning using possums as models. Groups of possums were dosed with cholecalciferol, CaCO3, or combinations of both compounds. Treatments were designed to achieve a range of hypercalcaemic responses with different levels of mortality. Serum calcium was monitored after treatment and pharmacokinetic parameters were calculated. Maximum serum calcium concentrations did not differ significantly between treatments or between possums that died and possums that survived. The extent of each animal's exposure to elevated serum calcium (the area under the curve) was not related to mortality. Serum calcium concentrations took significantly longer to peak in possums that died, and a slow development of hypercalcaemia after a dose of cholecalciferol may indicate a greater susceptibility to intoxication. The magnitude of the serum calcium increase, however, was a poor indicator of the severity of the toxicosis. Hypercalcaemia is a key diagnostic sign of cholecalciferol poisoning and the timing of serum calcium increases may help to establish a prognosis, but our findings cast doubt on the practice of monitoring serum calcium to assess the progress of treatment.
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