Intramuscular tranexamic acid results in lower peak plasma concentrations but comparable systemic absorption to intravenous administration in healthy dogs.

OBJECTIVE: To determine the pharmacokinetics of IM and IV tranexamic acid (TXA) in healthy dogs. METHODS: There were 6 healthy client-owned dogs that received TXA (20 mg/kg) in a randomized crossover study design with a 6-week washout period between IM and IV administration. Venous blood samples were collected from baseline to 8 hours after injection. Plasma TXA concentrations were measured using LC-MS-MS. RESULTS: For IM administration, mean ± SD maximum plasma concentration (Cmax) was 46.8 ± 26.6 μg/mL, total area under the curve was 173.8 ± 25.0 μg/mL·h, time to Cmax was 1.6 ± 1.4 hours, half-life (t1/2) was 2.8 ± 2.1 hours, and bioavailability was 120.9 ± 10.0%. For IV administration, Cmax was 119.8 ± 17.6 μg/mL, total area under the curve was 143.3 ± 10.5 μg/mL·h, and t1/2 was 2.1 ± 1.8 hours. CONCLUSIONS: IM Cmax reached approximately 39% of IV Cmax and exhibited a 33% longer t1/2, consistent with slower absorption. Despite the lower Cmax, bioavailability was 120.9%, suggesting that IM TXA maintained a higher plasma concentration for a longer duration. CLINICAL RELEVANCE: Although the prolonged time to Cmax associated with IM administration may limit its use in patients requiring rapid intervention, it offers practical advantages when IV access is delayed, allowing prehospital treatment prior to definitive veterinary care. Further investigation into IM dosing protocols is needed before it can be recommended in clinical patients.