Trace element, toxin and drug elimination in hair with particular reference to the horse

To date, studies in our laboratory have shown that several anti-microbial drugs, including sulphonamides, trimethoprim, metronidazole (Fig. 9 illustrates the extraction of metronidazole from an extract of mane hair), enrofloxacin and procaine benzylpenicillin can be detected in mane and tail hair samples up to 2 years (and in one instance 3 years) after systemic administration. This implies virtually indefinite stability, although a steady decrease over time was reported by Dunnett et al. (2002a), after the therapeutic administration of phenobarbitone to dogs for epilepsy management. Declining drug concentrations may be due to decomposition caused by heat or UV light or hair damage leading to drub leakage (Dunnett et al., 2002b; Dunnett and Lees, 2000). Further studies have also demonstrated the detection of several methylxanthine drugs, including caffeine and theobromine and their metabolites, in mane and tail hair (Dunnett et al., 2002b). Other investigators have detected performance-modifying drugs, including morphine (Beresford et al., 1998), diazepam and clenbuterol (Popot et al., 2000) in equine hair. However, cocaine was not detected in mane hair following systemic administration (Whittem et al., 2000). Studies in progress in our laboratory have extended drug analyses in hair and correlations between administered dose and drug pharmacokinetics to corticosteroids, NSAIDs and sedatives of various classes. It is clear that there are virtually no limitations to qualitative and quantitative analyses of drugs and their metabolites in equine hair.