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. 2025 Mar;48(2):103-109.
doi: 10.1111/jvp.13481. Epub 2024 Sep 15.

Pharmacokinetics and Plasma Protein Binding of Flunixin in Rainbow Trout (Oncorhynchus mykiss)

Kamil Uney  1 , Orhan Corum  2 , Duygu Durna Corum  2 , Devran Coskun  3 , Fatih Sakin  2 , Muammer Elmas  1
Affiliations

Pharmacokinetics and Plasma Protein Binding of Flunixin in Rainbow Trout (Oncorhynchus mykiss)

Kamil Uney et al. J Vet Pharmacol Ther. 2025 Mar.

Abstract

Flunixin's pharmacokinetics, bioavailability, and plasma protein binding were examined in rainbow trout. The experiment involved 252 rainbow trout (Oncorhynchus mykiss) maintained at 12 ± 0.6°C. Flunixin was administered to rainbow trout via intravascular (IV), intramuscular (IM), and oral routes at a dosage of 2.2 mg/kg. Plasma samples were collected at times 0 (control), 0.25, 0.5, 1, 2, 4, 6, 8, 10, 12, 24, 48, 72, and 96 h. High-pressure liquid chromatography-ultraviolet was employed to quantify flunixin concentrations. The elimination half-life (t1/2ʎz) for flunixin was 8.37 h for IV, 8.68 h for IM, and 8.76 h for oral. The t1/2ʎz was similar between administration groups. The volume of distribution at a steady state and total body clearance were 55.81 mL/kg and 6.83 mL/h/kg, respectively, after IV administration. The mean peak plasma concentration was 6.24 ± 0.41 μg/mL at 4 h for oral administration and 13.98 ± 0.86 μg/mL at 2 h for IM administration. The in vitro protein binding ratio of flunixin in rainbow trout plasma was 96.34 ± 2.29%. The bioavailability of flunixin after oral (25.74%) administration was lower than that after IM (66.70%) administration. Thus, developing an oral pharmaceutical formulation that can be administered with feed and has high bioavailability could enhance the therapeutic effect.

Keywords: bioavailability; flunixin; pharmacokinetics; plasma protein binding; rainbow trout.

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