To decide a Withdrawal Time, an adequate safety margin must be chosen by the treating veterinarian using his or her professional judgement to allow for biological, pharmaceutical and pharmacological variation, thus minimising the possibility that a positive finding will occur on race day. It is incumbent on all veterinary surgeons to exercise full professional judgement, taking into account all relevant circumstances and up-to-date information, before advising when a horse may safely race after drug treatment (Barragry 2006 - Continuing education – Doping and drug detection times in horses: new data for therapeutic agents. Irish vet. J. 59, 394-398).
A Detection Time, as issued by the EHLSC, is not equivalent to a Withdrawal Time. The Withdrawal Time should be longer than a Detection Time to take into account the impact of all sources of animal variability (age, sex, breed, training, racing...) in order to avoid a positive control and those of the medicinal product actually administered (formulation, route of administration, dosage regimen, duration of treatment...). Advice has been publish on the estimation of Withdrawal Tines from Detection Times (P.-L. TOUTAIN (2010) How to extrapolate a withdrawal time from an EHSLC published detection time: A Monte Carlo simulation appraisal Equine Veterinary Journal 42 (3) 248-254