Long-term monitoring of clodronate in equine hair using liquid chromatography-tandem mass spectrometry

Given the potential for long-term inhibition of bone remodeling/healing and detrimental effects to horses in training, bisphosphonates are tightly regulated in horseracing. Hair has proven to be an effective matrix for detection of drug administration to horses and has been particularly effective in detecting drugs for a long period of time post administration. Thus, hair may prove to be a useful matrix for detection of administration of this class of drugs. The objective of the current study was to develop an assay and assess the usefulness of hair as a matrix for long-term detection of clodronate to horses. Seven horses received a single intramuscular administration of 1.8 mg/kg clodronate. Hair samples were collected prior to and up to 6 months post administration. A liquid chromatography-tandem mass spectrometry method was developed and concentrations of clodronate measured in hair samples. The drug was first detected on day 7 in 4/7 horses, and on days 14, 28 and 35 in the remaining three horses. In 4/7 horses, clodronate was still detectable 6 months post administration. Results of this study demonstrate that, although there was significant inter-individual variability in detection times (63 to 180 days) and several intermediate times where the drug could not be detected but was subsequently detected in later timepoints, clodronate administration was detectable in hair for a prolonged period in most of the horses (4/7) studied.