Warfarin and the Grey Squirrel

Abstract

The anticoagulant warfarin [3-(α-acetonylbenzyl)-4-hydroxycoumarin] has been used for controlling the grey squirrel Sciurus carolinensis in Great Britain. Before legislation was passed to allow for its use in Ireland, it was felt that more information on its effectiveness was required. Since the small mammal population of Ireland is low, any toxic effects on the native mammal population could greatly deplete the wildlife in Ireland. No accurate assessment of the toxicity of warfarin for the squirrel appears in the literature.

The squirrel were dosed with warfarin at four different concentrations, 6.0, 1.25, 0.5, 0.01 mg per kg of body weight, by stomach tube, in order to find the least effective dose. The prothrombin times (PT) were monitored as an assessment of the action of the drug. The control prothrombin time and the standard deviation of the mean was 13.83 ± 3.64. Animals that were treated with warfarin showed an elevated PT even at the lowest dose by the 7th day of treatment. The PT was found to be in excess of 30 s and this was statistically significant, p = 0.05.

Within the group receiving 0.5 mg/kg one animal showed a very significant initial rise in PT, but after 22 days of daily dosing, the PT decreased to within the normal range of the controls. Despite continuous dosing for a total of 26 days, it remained within this range.