A novel tulathromycin oil suspension injection: preparation, characterization, and pharmacokinetics in goats

Tulathromycin (TUL), a semisynthetic macrolide antibiotic, is effective against respiratory tract infections across diverse animal species and is widely used for their prevention and treatment in veterinary medicine. However, the clinical application of TUL is currently limited by the sole availability of an injectable formulation, which may restrict its broader clinical adoption. In the present study, an injection of a TUL oil suspension with 10% drug loading was prepared using the colloid mill dispersion method, and corresponding pharmacokinetic studies were conducted in goats. The resulting preparation was obtained as a milky white suspension whose sedimentation volume ratio, redispersibility, syringeability and injectability, and pH value conformed to the technical standards of the Ministry of Agriculture of the People’s Republic of China. In vitro release studies revealed that the TUL oil suspension exhibited a slower release rate compared with the commercially available injection. Furthermore, in vivo pharmacokinetic studies in goats demonstrated that it significantly delayed absorption (Tmax: 2.33 ± 0.52 h vs. 0.58 ± 0.13 h, P < 0.01) and increased AUC0−∞ by 50.44% (14382.53 ± 1654.23 h·ng/mL vs. 9567.98 ± 1166.02 h·ng/mL, P < 0.01), corresponding to a relative bioavailability of 150.44%. CL was reduced by 37.93% (P < 0.01), and T1/2 was prolonged by 12.64 h (83.32 h vs. 70.68 h). These results highlight the therapeutic potential of this novel formulation, which, with its demonstrated sustained-release profile and enhanced bioavailability, presents a commercially viable and therapeutically promising option against respiratory infections in goats.