Pharmacokinetics of Colistin in Chickens at Different Ages

Colistin is a decapeptide antibiotic with a narrow spectrum of antibacterial activity mainly against Gram-negative microorganisms (Ziv,1981). It is also able to inactivate bacterial toxins in vitro (Ziv et al., 1978). That is why it is commonly used for treatment of diseases caused by sensitive Gram-negative bacteria (Roy et al., 1997; van Hattum et al., 2000).Despite the fact that this antibiotic is used for many years, the investigations on its pharmacokinetics in poultry are limited. The data about its oral absorption are contradictory. The lack or the very low values of absorption are well known (Roudaut, 1989). However, there are also data showing significant blood levels after oral (p.o.) administration in broiler chickens (Lashev and Haritova, 2003), and its absorption is probably influenced by the age. The data from the literature show that the age of chickens can influence the behaviour in the organism of several antibacterial drugs, although the reported results are contradictory (Pashov, 1983; Pashov and Kanelov, 1994; Santos et al., 1996; Lashev, 2000). The aim of the present study was to investigate the pharmacokinetics of colistin in chickens at different ages. Colistin sulfate (21200 UI = 1 mg), batch No 9498, was provided by Zavet Ltd, Zavet, Bulgaria.The antibiotic was used as a water solution for i.v. administration. A drug formulation Colistinpulvis (containing 120 000 000 UI colistin sulfate and excipientes ad 100.0), provided by Zavet Ltd, was used for oral administration. Experiments were carried out on 178 chikens (Gallus domesticus, breed Decalb) at the age of 1 week, 1 month and 2 monthd from both genders, weighing 50.88 ± 0.68 g, 204.0 ± 1.2 g and 1068.0 ± 4.0 g, respectively. Six one−year old hens (Gallus domesticus, breed Decalb) weighing 1840 ± 5.0 g were also included in the experiments. The chickens and hens were kept in cages (six birds in a cage) and given free access to food (commercial antibiotic free diet) and water. Two experiments were carried out: