Statistical evaluation of residue data for the assessment of predicted values (half-life, withdrawal time) as an example of toltrazuril and enrofloxacin in trout

The half-lives and withdrawal times of the veterinary drugs Toltrazuril and Enrofloxacin in trout have been assessed by statistical analysis. Confidence intervals were computed using a normal distribution of residual data and an empirical distribution by the Bootstrap method. Both methods produced similar statistics for the two drugs. Simulation of the residue data according to the regression lines of the decay curves has shown that the Bootstrap method is better for use when the residue patterns are not distributed normally. Using confidence intervals, a statistical mean of withdrawal times can be assessed. Taking into account the decays of the individual antibiotics in all treated trout, tolerance intervals for the regression lines are obtained: the calculated 10-20% longer withdrawal time includes values for which the antibiotic concentration in 95% of the treated trout is decreased below the tolerance level of Toltrazuril or Enrofloxacin.