Pharmacokinetics of intravenous lithium chloride and assessment of agreement between two methods of lithium concentration measurement in the horse.
Authors: Martin L M, Bukoski A D, Whelchel D D, Evans T J, Wiedmeyer C E, Black S J, Johnson P J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Lithium Pharmacokinetics in Horses Lithium chloride has potential therapeutic applications in equine medicine, yet its pharmacokinetic profile and practical monitoring methods remain undetermined in horses. Martin and colleagues administered a single intravenous bolus of lithium chloride (0.15 mmol/kg bodyweight) to eight healthy horses and tracked plasma concentrations over 48 hours using two analytical methods—spectrophotometric enzymatic assay (SEA) and inductively coupled plasma mass spectrometry (ICP-MS)—with pharmacokinetic parameters derived from the reference ICP-MS data. The drug was well tolerated with no adverse effects observed; plasma half-life averaged 25.68 hours, clearance was 0.273 mL/min/kg, and volume of distribution at steady state was 511 mL/kg—values broadly consistent with lithium kinetics in other species. However, whilst the SEA demonstrated acceptable analytical precision (2.5% intraday coefficient of variation, 96.3% recovery), it showed poor agreement with ICP-MS measurements (95% limits of agreement = 0.14 ± 0.13 mmol/L), limiting its utility as a point-of-care monitoring tool. For practitioners considering lithium therapy in horses, these data establish baseline kinetics necessary for dosing calculations, yet the absence of validated bedside testing and lack of clinical efficacy data mean that therapeutic monitoring and treatment protocols remain outstanding challenges requiring further investigation.
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Practical Takeaways
- •Current point-of-care tests for lithium monitoring are unreliable in horses; reference laboratory methods (ICP-MS) should be used if therapeutic lithium monitoring is required
- •Lithium has a long half-life (~26 hours) in horses, suggesting once-daily dosing may be feasible, though clinical efficacy and safety thresholds require further investigation
- •Before implementing lithium therapy clinically, veterinarians need established therapeutic target ranges and toxicity thresholds specific to horses, which are not yet defined in this study
Key Findings
- •Lithium chloride administered at 0.15 mmol/kg IV bolus in horses showed terminal elimination half-life of 25.68 hours with clearance of 0.273 mL/min/kg
- •Spectrophotometric enzymatic assay demonstrated good precision (2.5% intraday coefficient of variation, 96.3% recovery) but poor agreement with ICP-MS reference method
- •Nonlinear mixed-effects modelling results showed good agreement with traditional two-stage pharmacokinetic analysis
- •No adverse side effects were observed during the 48-hour sampling period following lithium chloride administration