Laboratory Animals (1990) 24, 341-344 In vivo activity of orally administered antibiotics and chemotherapeutics against acute septicaemic pasteurellosis in rabbits 341 L. OKERMANI L. A. DEVRIESE, D. GEVAERT, E. UYTTEBROEK & F. HAESEBROUCK Faculty of Veterinary Medicine, Casinoplein 24, B-9000 Gent, Belgium Summary Different antibiotics and chemotherapeutics were tested for therapeutic efficacy in rabbits, in an experimental model using a Pasteurella multocida strain which causes hyperacute septicaemia in this animal species. Only enro- f1oxacin, administered in the drinking water at a concentration of 50-100 mg/I cured the rabbits, provided that a daily intake of 5 mg/kg body weight was achieved. The other drugs tested (tetracycline, spiramycin, erythromycin and a combination of sulfamerazine with trimethoprim), at doses recommended for rabbits, showed little or no activity at all, with the exception of chlor- amphenicol, which was only partially effective. Keywords: Rabbit; Pasteurellosis; Antibiotic Various bacterial diseases may follow a septi- caemic course in rabbits, e.g. salmonellosis, pasteurellosis, staphylococcosis and listeriosis (Flatt, 1974). Although septicaemia is not common, morbidity and mortality in infected flocks may be very high, especiallywith Salmonella and Pasteurella multocida infections. Although anti-infectious therapy is often prescribed for rabbits, reports on the efficacy of antibiotic treatment are scarce. Individual rabbits suffering from chronic forms of pasteurellosis, e.g. snuffles, otitis media and enzootic pneu- monia, do not respond well to treatment with antibiotics (akerman, 1988). Antibiotic treat- ment is often guided by treatment experiences 'Present address: Klinisch Labo Dendermonde. Hoogveld 10, B-9330 Dendermonde, Belgium. Received 9 October 1989; accepted 6 February 1990 with similar diseases in other animal species, but evidence for therapeutic activity is lacking. Therefore, we studied the effect of different anti- biotics and chemotherapeutics, in an experimental model using a P. multocida strain which causes hyperacute septicaemia and rapid death in rabbits. Few data on plasma antibiotic con- centrations are available in rabbits (Guillot et al. , 1988; Percy & Black, 1988) and it is not known whether or not these predict accurately thera- peutic outcome in this animal species. The choice of antibiotics in rabbits is restricted, because many disturb the intestinal flora, resulting in clostridial enterotoxaemia (Morisse, 1976; Borriello & Carman, 1983). In the experiments described below, only antibiotics and chemo- therapeutics which are frequently prescribed for rabbits, were tested at their usual oral doses. Oral administration of drugs is the most practical way of treatment in large groups of animals. Materials and methods Rabbits All rabbits belonged to the Belgian Silver breed (a local breed related to Argente de Champagne), and were purchased from a closed colony, which had been free from P. multocida as well as from enteropathogenic E. coli for at least 12years. This colony had shown a very low mortality rate (under 30/0) over the years. During this period no P. multocida nor enteropathogenic E. coli bio- types were recovered from nasal resp. rectal swabs which were taken at different occasions from breeders and/or young animals; neither were the pathogens isolated at routine necropsies of animals which died in this farm. The colony was, however, infected with Bordetella bronchiseptica