The effects of orally administered trazodone on ambulation and recumbency in healthy horses.
Authors: Hobbs Kallie, Luethy Daniela, Davis Jennifer, Mallicote Martha, Torcivia Catherine, Kulp Jeaneen, Stefanovski Darko, Futterman Catherine, Cooper Freya, van Eps Andrew
Journal: Journal of veterinary internal medicine
Summary
Trazodone, a serotonin antagonist and reuptake inhibitor, has been proposed as an adjunctive therapy for acute laminitis on the hypothesis that reducing weight-bearing ambulation might alleviate pain and facilitate recovery. Researchers administered placebo, 2.5 mg/kg, or 7.5 mg/kg trazodone orally to eight healthy horses every 12 hours for 48 hours in a randomised cross-over design, measuring forelimb step frequency via hoof-mounted accelerometers and monitoring recumbency through continuous video recording. The higher dose produced a clinically significant 44% reduction in step frequency compared to control (area under the curve: 3375 ± 525 versus 6590 ± 1241 steps per hour; P = 0.001), whilst the intermediate 2.5 mg/kg dose showed intermediate results; however, neither dose influenced the frequency or duration of recumbency episodes. Pharmacokinetic analysis revealed adequate steady-state concentrations with predictable accumulation (ratio 1.45), suggesting reasonable dosing reliability. For equine practitioners managing laminitis, these findings suggest trazodone at 7.5 mg/kg twice daily could meaningfully reduce self-imposed weight-bearing activity, though the lack of recumbency induction means this strategy requires complementary pain management and stall confinement rather than functioning as a standalone sedative agent.
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Practical Takeaways
- •Trazodone 7.5 mg/kg q12h significantly reduces movement in horses, which could theoretically benefit acute laminitis management by limiting weight-bearing stress on damaged laminae
- •The drug does not promote lying down, so the movement reduction is from decreased ambulatory activity rather than increased rest — useful distinction when considering acute pain management strategies
- •Pharmacokinetic data suggests steady accumulation occurs, meaning dosing intervals matter; practitioners should be aware of the 1.45 accumulation ratio when calculating multiple-dose protocols
Key Findings
- •Trazodone at 7.5 mg/kg PO q12h reduced forelimb step frequency by 44% compared to control in healthy horses
- •Steps-area under curve was significantly lower at 7.5 mg/kg (3375 ± 525 steps × hour) versus 2.5 mg/kg (5901 ± 2232; P = 0.02) and control (6590 ± 1241; P = 0.001)
- •Trazodone did not affect number of recumbent episodes (P = 0.92) or total duration of recumbency (P = 0.9)
- •Trazodone and metabolite m-CPP achieved steady-state with accumulation ratio of 1.45 ± 0.2 over multiple doses