The effect of bacterial infection on antibiotic activity and penetration of parenterally administered ceftiofur into implanted tissue chambers was studied in cattle. Tissue chambers were implanted subcutaneously in the paralumbar fossae of eight calves (256-290 kg body weight). Approximately 80 days after implantation, the two chambers on one side of each animal were inoculated with Pasteurella haemolytica (10(6) CFU/chamber). Eighteen hours after inoculation, ceftiofur sodium was administered intravenously (5 mg/kg) to each of the calves. Non-infected chamber fluid, infected chamber fluid and heparinized blood samples were collected immediately before and at 1, 3, 6, 12 and 24 h after drug administration. Concentrations of ceftiofur and desfuroylceftiofur metabolites and ceftiofur-equivalent microbiological activity were measured by high-pressure liquid chromatography and microbiological assay respectively. Concentrations of ceftiofur and desfuroylceftiofur metabolites and anti-microbial activity in P. haemolytica-infected tissue chambers were significantly higher than those in non-infected tissue chambers at all sampling times, indicating that ceftiofur, regardless of the method used for analysis, localizes at higher concentrations at tissue sites infected with P. haemolytica. Antibiotic activity-concentration ratios were lower in plasma and infected chamber fluid compared with non-infected chamber fluid, suggesting that antibiotic was bound to proteins. However, higher antimicrobial activity in the infected chamber fluid compared with the non-infected chamber fluid, suggests that active drug is reversibly bound to proteins. Protein-bound desfuroylceftiofur may represent a reservoir for release of active drug at the site of infection in the animal.

The objectives of this study were t o investigate the determinants of the anion gap (AG) in cattle and t o evaluate the utility of AG in detecting hyperlactatemia in sick neonatal calves and adult cattle. The AG was calculated as AG = ("a'] + [K'I) -"CI-1 + [HCOSI), with all values in mEq/L.The AG of healthy neonatal calves (n = 16) was 29.6 i 6.2 mEq/L (mean i SD), and the blood L-lactate concentration ranged from 0.5 t o 1.2 mM/L. The AG was significantly ( P < .05) correlated with serum phosphate (r = .66) and creatinine (r = .51) concentrations. The AG of neonatal calves with experimentally induced diarrhea (n = 16) was 28.6 i 5.6 mEq/L, and the blood L-lactate concentration ranged from 1.1 t o 2.9 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .67), serum phosphate concentration (r = .63), creatinine concentration (r = .76), and blood pH (r = -.61). The AG of adult cattle with abomasal volvulus (n = 41) was 20.5 ? 7.8 mEq/L, and the blood L-lactate concentration ranged from 0.6 t o 15.6 mM/L. The he anion gap (AG) is considered helpful in the evalua-T tion of acid-base disorders in human,'.' small animal,& and equine5~' medicine, whereas its usefulness in evaluating acid-base disorders in cattle currently is unknown. The AG concept arose from the concept of electroneutrality,'2 where AG represents the difference between the concentration of unmeasured anions [UA] and unmeasured cations [UC] in serum. This can be expressed by the general equation:which can be rearranged to provide:indicating that a change in [UA] or [UC) will cause a change in the AG. Normally, approximately two thirds of the AG originates from the net negative charge of serum proteins, whereas the remainder reflects the serum concentration of phosphate and strong anions, such as lactate, sulfate, /3-OH butyrate, acetoacetate, and anions associated with uremia."The normal range for AG depends partly on the formula used for calculation.' Some investigators prefer not to include [K'] when calculating the AG, on the basis that [K'] varies to a much smaller degree than does [Na'], [Cl-1, and [HC0J3 and therefore exerts minimal influence on the AG. Other investigators substitute total CO, concentration for [HCOJ, permitting calculation of the AG from serum biochemical analysis without the need for blood gas determination.' Calculating the AG using equation (B), the normal AG for humans is considered to be 12 to 19 mEq/L.' An AG greater than 30 mEq/L is commonly accepted to indicate the presence of organic acidosis in humans,','" whereas values between 20 and 30 niEq/L are more difficult to interpret.'.9The normal range for AG also depends on the age and species. The normal range for AG of 2-to 3-week-old foals (9 to 22 mEq/L) is significantly greater than that of 2-yearold horses (8 to 13 mEq/L) probably because of a greater serum phosphate concentration and lower serum calcium concentration in foals.' It is currently unknown whether the normal range for AG varies with age in cattle. The range of AG (mean 2...

Following RIVP, high florfenicol concentrations were achieved in DV blood and SYNF, whereas the CV blood concentration remained low. In cattle, RIVP of florfenicol may be useful in the treatment of infectious processes involving the distal portion of limbs.

No abstract