Antibiotic concentration in the serum of dogs and cats following a single oral dose of cephalexin.

Six dogs and six cats were given a single oral tableted dose containing approximately 15 mg/kg bodyweight of the semisynthetic cephalosporin antibiotic, cephalexin. Three dogs and four cats were similarly dosed using a liquid preparation of the same antibiotic. At intervals after dosing, blood samples were taken and the level of antibiotic in the serum was determined by bioassay. After fitting the results to a mathematical model the calculated peak serum level of antibiotic was found to be about 15 micrograms/ml and to occur between one and two hours after dosing. Results agree with the performance of the antibiotic in human medicine.

Cephalexin: interpretation of sensitivity disc testing in veterinary practice.

A regression study using 30 micrograms cephalexin sensitivity discs with bacterial strains isolated from veterinary sources is described. Techniques suitable for use in veterinary investigation laboratories were used and critical zone sizes calculated from a linear regression analysis. Zone sizes of less than or equal to 18 mm, 19 to 20 mm and greater than or equal to 21 mm were found to be suitable to categorise strains as resistant, intermediate or sensitive, respectively. Experience in the use of these recommended critical zone sizes in clinical practice will be necessary before firm recommendations can be made.