Increased bioavailability of tylosin phosphate as in-feed medication formulated for long-action pellets in broiler chickens

Circadian variation of serum concentrations of tylosin in broiler chickens after in-feed medication prompted a comparison study of the serum profiles of this drug after in-feed medication with standard tylosin phosphate (Tprf reference formulation group), and after in-feed medication with a sustained-release pellet formulation (Tpsr group), based on Patent No.MX/a/2012/013222 and PCT/MX2013/000137, in broiler chickens. Six hundred 4-week-old Ross broiler chickens were in-feed medicated with tylosin phosphate at an approximate dose of 25.2 mg/kg/d, based on daily feed consumption values and a final concentration of tylosin in feed of 200 mg/kg of feed. Approximately 2 to 3 mL of blood were obtained per 5 chickens every 2 h, avoiding the sampling of a bird more than once and during 72 h after making medicated feed available for the first time. Serum concentrations of tylosin were determined by HPLC. Gaussian multi-peak regressions were then fitted to serum concentration vs. time profiles. Day by d areas under the serum concentration vs. time profiles (AUC(0-24)), as well as over all AUC(0-72), were statistically higher for the Tpsr group (P < 0.001). Also, maximum serum concentrations obtained and relative bioavailability for the Tpsr formulation were statistically higher (382.8%) as compared to the Tprf group (P < 0.01). Considering the referred improved values of AUC observed in the Tpsr formulation, as well as the fact that tylosin is a time-dependent antibacterial drug, better clinical responses are postulated with this pharmaceutical preparation intended for chickens. Tissue deposition studies for this new formulation of tylosin are required.