Few publications are describing the pharmacokinetics of tylvalosin (TVN) antibiotic, so the aims of this work were to study its pharmacokinetics with evaluation the effect of vitamin (vit) E on its kinetics after single and repeated oral administration in broiler chickens. The mean serum concentrations of the drug were markedly lower in tylvalosin alone when compared with tylvalosin pre-treated with vit E after single and repeated oral administration at the corresponding time intervals. The peak of serum concentration (C max ), absorption half-life (t 0.5ab ) and elimination half-life (t 0.5 el ) were 2.11±0.3, 3.27±0.2 ug mLG 1 , 0.94±0.04, 0.88±0.02 h and 1.61±0.05, 2.42±0.1, after single tylvalosin and tylvalosin-vit E, respectively. While after repeated dosing, the maximum serum levels were 5.01±0.13 and 5.9±0.1 ug mLG 1 with pharmacokinetic parameters (C max ), (t 0.5ab ) and (t 0.5 el ) 4.1±0.14, 5.67±0.4 ug mLG 1 , 1.39±0.4, 0.86±0.07 h and 2.78±0.16, 3.05±0.3 h after repeated tylvalosin and tylvalosin-vit E, respectively. The combination of tylvalosin with vit E allows a prolongation of the dosage intervals in broiler for more 12 and 24 h after single and repeated dosing, respectively, indicated by longer elimination half-life and Mean Residence Time (MRT) of tylvalosin-vit E than tylvalosin alone after single and repeated administration which is very important for the dosage intervaland increasing the drug serum efficacy.

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The pharmacokinetic profile and some pharmacodynamic aspects of cefquinome were studied after intramuscular (IM) and subcutaneous (SC) administration of a single dose of 2 mg kg -1 b.wt. in chickens. Tissue distribution and residues of cefquinome after repeated IM injection for 5 consecutive days were also estimated. Cefquinome was rapidly absorbed after IM and SC injection as indicated by short half-lives of absorption (t 0.5(ab) ) of 0.170 and 0.262 h., respectively, while the elimination half-lives (t 0.5(el) ) were 3.428 and 25.023 h., respectively. Repeated IM doses of cefquinome (2 mg kg -1 b.wt., once daily) for 5 consecutive days caused no change in serum enzyme activities of ALT and AST, but induced significant increase in serum uric acid concentration after 72 to 120 hours of administration. The withdrawal time of cefquinome from tissue of chickens is 5 days following the last dose. Cefquinome has a wide spectrum of activity against Esherchia coli, Proteus mirabilis and Pseudomonas aeroginosa.

The pharmacokinetic profile of ceftiofur sodium, a third generation cephalosporin, was studied in both Friesian and buffalo calves following a single intravenous and intramuscular administration of 2.2 mg kg -1 b.wt. in a cross over study with 15-day wash out period. After i.v administration the serum concentration-time curve of ceftiofur sodium was best fitted using two-compartments open model, with distribution half-lives (t ½(α) ) of 0.384 and 0.176 h., elimination half-lives (t ½(β) ) of 5.047 and 1.607 h., mean residence time (MRT) of 6.926 and 2.072 h., volumes of distribution at steady-state (Vd ss ) of 0.206 and 0.134 L kg -1 and total body clearance (Cl B ) of 0.029 and 0.065 L kg -1 h -1 in Friesian and buffalo calves, respectively. Following intramuscular administration, the drug absorbed with half-lives of absorption (t ½(ab) ) of 1.010 and 0.217 h., maximum serum concentrations (C max ) of 5.539 and 9.663 µg ml -1 which attained after (t max ) of 3.147 and 0.825 h. and the drug was eliminated with half-lives (t ½(el) ) of 5.239 and 1.750 h. in Friesian and buffalo calves, respectively. The systemic intramuscular bioavailabilities were 89.82 and 99.7 %, while the in-vitro serum proteinbinding tendencies were 39.68 and 14.44 % in Friesian and buffalo calves, respectively.

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