Comparison of Oxytetracycline Pharmacokinetics After Multiple Subcutaneous Injections in Three Sea Turtle Species

Abstract

Oxytetracycline (42 mg/kg SC q6d) was injected into the dorsal shoulder region of 29 sea turtles during clinical management after stranding, including 10 Kemp's ridley (Lepidochelys kempii), 10 loggerhead (Caretta caretta), and nine green sea turtles (Chelonia mydas). Before injection, the drug was diluted into a suitable fluid for injection (5–20 ml/kg) as chosen by the attending veterinarian. Turtles were treated for as long as clinically indicated prior to discontinuing the drug (range 2–10 doses, median four). After the final injection, blood was collected at 1, 2, 4, 8, 72, 144, and 288 h and plasma harvested for measurement of the oxytetracycline plasma concentration. To limit the volume of blood collected, a sparse sampling strategy was used with samples collected at only three or four time points per turtle. The plasma oxytetracycline concentration was measured with high pressure liquid chromatography. Population pharmacokinetics using nonlinear mixed effects modeling produced the following results: half-life, 36 h; volume of distribution, 0.78 L/kg; and area-under-the-curve, 2,799 µg*h/ml. Using this dose and method of administration, the plasma oxytetracycline concentrations were maintained above a minimum inhibitory concentration value of approximately 4 µg/ml for approximately 6 days.