abs: Epidural and IM Triamcinolone PK/PD in Horses
_{Large Animal Flash Poster Presentations}

Triamcinolone is a frequently used corticosteroid in horses and people, and epidural steroid injection is common in people. The objectives of this study were to investigate pharmacokinetics and pharmacodynamics of epidural and intramuscular triamcinolone. Six horses with chronic, Grade 3/5 (AAEP) lameness received intramuscular and caudal epidural injection of triamcinolone (18 mg) in a crossover study design with a 60 day washout period. Blood samples were collected, and lameness examinations performed (0-60 days pre/post treatment). CSF (C1-C2 centesis) collected 24 hours post treatment and blood samples were analyzed with liquid chromatography-mass spectrometry. Data was analyzed with mixed-effect ANOVAs, with P<0.05 considered significant. Maximum plasma triamcinolone concentration was higher (P=0.001) after epidural (1.17 +/- 0.55 ng/mL; 12 +/- 0 hours) than intramuscular injection (0.27 +/- 0.11 ng/mL; 22 +/-9 hours). Overall drug exposure (AUC) trended higher (P=0.056) and half-life was longer (P=0.003) with intramuscular (70.6 +/- 9.4 hours ng/mL and 192.8 +/- 94.9 hours respectively) compared to epidural (54.4 +/- 13.3 hours ng/mL and 45.7 +/- 31.5 hours respectively) injection. CSF triamcinolone concentration was higher (P=0.002) post epidural (0.18 +/- 0.06 ng/mL) than intramuscular (0.05 +/- 0.02 ng/mL) injection. No difference in lameness improvement between treatments (p=0.84). Triamcinolone appears to readily absorb into the CSF and circulate throughout the spinal canal. Chronic and variable causes of lameness made assessment of effect challenging. Caudal epidural triamcinolone may be a viable treatment option for spinal related issues in horses, including vertebral articular facet pain.