Pharmacokinetics and Antibacterial Activity of Cefquinome in Green Turtles (Chelonia mydas)

Background/Objectives: Species-specific pharmacokinetic data are needed to guide the rational use of cefquinome (CFQ), a fourth-generation cephalosporin, in managing complicated bacterial infections in green turtles (Chelonia mydas). This study characterized CFQ pharmacokinetics after a single intramuscular administration and evaluated its in vitro activity against bacterial isolates recovered from rescued green turtles, providing preliminary evidence to inform culture-guided antimicrobial therapy. Methods: Five clinically healthy rehabilitated green turtles received CFQ at 2 mg/kg intramuscularly. Serial blood samples were collected through 120 h, and serum CFQ concentrations were quantified using liquid chromatography–tandem mass spectrometry. Pharmacokinetic parameters were calculated by non-compartmental analysis. Minimum inhibitory concentrations (MICs) were determined for 36 bacterial isolates, including 10 Enterococcus faecalis isolates, 15 Vibrio spp. isolates, and 11 isolates belonging to other bacterial taxa. Total serum CFQ concentrations were compared descriptively with the MIC values of the tested isolates. Results: The mean maximum serum concentration was 8.35 ± 5.25 µg/mL, and the median time to maximum concentration was 3.0 h. Mean AUC0–120 and MRT0–120 were 146.88 ± 14.65 h·µg/mL and 22.57 ± 3.77 h, respectively. Using 72–120 h as a candidate apparent terminal phase, the mean apparent terminal half-life was 32.70 ± 4.03 h, AUC0–∞ was 151.46 ± 15.75 h·µg/mL, CL/F was 13.33 ± 1.48 mL/h/kg, and Vz/F was 0.630 ± 0.116 L/kg; extrapolated AUC accounted for 1.67–3.94% of AUC0–∞. CFQ remained quantifiable through 120 h in all turtles, and no adverse clinical reactions were observed. For Vibrio spp. and E. faecalis, MIC50/MIC90 values were 1/8 and 8/32 µg/mL, respectively. Among the 11 additional isolates, ten had MICs of 0.031–0.25 µg/mL, whereas one Proteus sp. isolate had an MIC of 32 µg/mL. Conclusions: A single intramuscular dose of CFQ produced prolonged systemic exposure and was well tolerated in green turtles. These findings provide preliminary data to inform culture- and susceptibility-guided consideration of CFQ in green turtles, although clinical efficacy remains to be evaluated.