Pharmacokinetics of ceftiofur crystalline-free acid in plasma and seminal plasma in beef bulls

The objective of this study was to compare the plasma (PL) and seminal plasma (SP) pharmacokinetic profile of ceftiofur (CEFT) and desuroylceftiofur acetamide (DFCA) after administration of CEFT crystalline-free acid (CCFA) by SC route in two sites of the ear in beef bulls. Four clinically healthy Hereford bulls received a comprehensive physical exam and subsequently a breeding-soundness examination, CBC, and chemistry profile panel. All bulls were diagnosed healthy and satisfactory potential breeders. In one group (n = 2), a single dose of CCFA was administered SC route at the base of the ear (BOE) at a dose of 6.6 mg/kg of body weight. The second group (n = 2) was also administered by SC route in the middle third of the posterior aspect of the ear (MTE). The concentrations of CEFT and DFCA in PL and SP were determined by a high-performance liquid chromatography mass spectrometry (HPLC-MS). Blood and semen samples were collected before the administration of CCFA and at 12, 24, 36, 48, 72, 96, 120, 144, and 168 h after injection. No levels of CEFT were detected in PL and only in 20 of the 40 SP samples (P = 0.0001). The mean level of CEFT in SP was 0.11 % in comparison with the DFCA level. DFCA was found in all PL and SP samples. Therefore, DFCA was chosen to be utilized in the study of the pharmacokinetics parameters both in PL and SP. There were no differences in the mean PL levels of DFCA for the two sites of SC administration between the BOE (102.9 +/- 78.9 ng/mL; X +/- SD) and to MTE (116.1 +/- 70.2 ng/ mL; P = 0.58). The mean SP levels of DFCA after administration in the BOE was 857 +/- 747 ng/mL, and for the MTE was 549 +/- 488 ng/mL without differences between both sites (P = 0.15). The mean level of DFCA in PL was 109.5 +/- 74.0 ng/mL, which was lower than the mean SP levels of 695 +/- 103 ng/mL (P = 0.001). Moreover, the PL peak DFCA concentration (C max ) was 229 +/- 46 ng/mL at 36.0 +/- 29.4 h (T max ) post-administration. The SP C max was 1851 +/- 533 ng/mL at 30.0 +/- 28.6 h (T max ) post-administration. The C max between PL and SP were distinctive (P = 0.004) without any differences in T max between PL and SP (P = 0.60). The terminal half-life for PL DFCA (47.4 +/- 29.3 h) was not different than in SP (53.1 +/- 23.6 h; P = 0.77). The PL area under the curve concentration time from the first to the last sample (AUC 0 -last ) was 18,984 +/- 4841 ng/mL/h, which was significatively smaller compared with 125,677 +/- 59,445 ng/mL/h for SP AUC 0 -last (P = 0.04). The PL mean residence time from the first to the last sample (MRT 0 -last ) was 69.7 +/- 15.1 h, and it was similar than for SP of 66.5 +/- 7.7 h (P = 0.69). From the present investigation, based in its pharmacokinetic features, it was concluded that CCFA should be an appropriate antibiotic that could be used for the treatment of bull genital infections when its indication is properly outlined. To study the pharmacokinetics of CCFA in SP, DFCA metabolite was appropriated.