Anticoccidial activity in a series of alkyl 6,7-dialkoxy-4-hydroxy-3-quinolinecarboxylates

Synthesis and Anticoccidial Activities of Eight Novel Ethyl 7-Alkyl-6-(2-Aryloxyethoxy)-4-Hydroxyquinoline-3-Carboxylates

Eight novel ethyl 7-alkyl-6-(2-aryloxyethoxy)-4-hydroxyquinoline-3-carboxylates were synthesised and their structures were identified by 1H NMR, MS, and IR spectra. The anticoccidial activities of these compounds were evaluated according to the ACI (the anticoccidial index) method. The results showed that two of these compounds exhibited anticoccidial activities against Eimeria tenella in the chicken’ diet with a dose of 27 mg kg−1.

Synthesis and Anticoccidial Activity of ethyl 6-substitutedbenzyloxy-7-alkoxy-4-hydroxyquinoline-3-carboxylates

A series of novel ethyl 6-substitutedbenzyloxy-7-alkoxy-4-hydroxyquinoline-3-carboxylates have been designed and synthesised from 4-nitro-2-alkoxyphenol. Their structures have been characterised by 1H NMR, HRMS and IR spectra. Anticoccidial activities of these compounds were evaluated according to the ACI (the anticoccidial index) method. The results indicated that three of the tested compounds exhibited anticoccidial activities against Eimeria tenella in chicken feed with a dose of 27 mg/kg.

The mode of action of anticoccidial quinolones (6-decyloxy-4-hydroxyquinoline-3-carboxylates) in chickens

The anticoccidial mode of action of quinolones (6-decyloxy-4-hydroxyquinoline-3-carboxylates) against Eimeria tenella and E. acervulina in chickens has been investigated, using decoquinate and M&B 15,584 as examples. The well known static effect on sporozoites of relatively high continuous drug concentrations in the food masked other components of the mode of action, newly described here. Lower concentrations of quinolones allowed sporozoites to continue their development. First-stage schizonts were susceptible to a secondary cidal effect, although later schizonts seemed to be rather refractory. Furthermore, the sporulation of oocysts produced by E. tenella that completed its life cycle in the presence of suboptimal concentrations of quinolones was inhibited: this probably reflects a drug effect on gametocytes. Quinolones were absorbed rapidly from the chicken intestine, probably in less than 1 h. Drug withdrawal experiments showed that quinolones persisted in chicken tissues at active concentrations for up to 48 h. Despite their static effect on sporozoites, they may nevertheless be expected to exert a therapeutic effect against drug-sensitive coccidia in interrupted regimes that allow the later cidal effect to come into play. This allows immunity to coccidiosis to develop in the presence of drug. These new results, with the previously available data have been combined in an updated account of the anticoccidial mode of action of quinolones in the chicken.

Chick embryo infections for the evaluation of anticoccidial drugs

Chick embryos have been infected with sporozoites of Eimeria tenella, but not with E. brunetti, and died from coccidiosis 5 days after infection.

Chick embryos can be protected from death due to coccidiosis by some but not all drugs which give a therapeutic response in chickens. The system is therefore not satisfactory as a screening tool, but may have applications in studies on the nature of drug activity.