Seven clinically healthy dairy cows were each given 2.5 g phenylbutazone (approximately 5 mg/kg body weight) by oral administration twice daily for 8 days. The concentrations of phenylbutazone in plasma and milk and several blood parameters were studied. The minimum plasma concentration during steady state was 100.4 +/- 7.3 micrograms/ml. During the same period the milk concentration never exceeded 1% of the plasma concentration. The elimination half-life in plasma was 38.6 +/- 3.7 h. Five days after administration had been discontinued, the milk concentration was 0.05 +/- 0.01 microgram/ml. All seven cows were clinically healthy throughout the experiment. The most pronounced side-effect of the blood parameters studied was a decreased concentration of leucocytes to about two-thirds of the control value. This might have a pronounced influence on the effectiveness of the immune system. There was also a significant decrease in total bilirubin indicating a decrease in the breakdown of erythrocytes.
The pharmacokinetics of chloramphenicol (CAP) were studied in four colostrum-deprived and 4 colostrum-fed newborn piglets after an intravenous bolus dose of CAP, 77 mumol kg-1 (25 mg kg-1). The elimination half-lives in the colostrum deprived piglets had a tendency to be longer (17.2 +/- 3.9 hrs) than in the colostrum-fed piglets (12.7 +/- 1.1 hrs) and in both groups they were considerably longer than reported in older pigs. The long half-lives of CAP in the newborn pigs were a reflexion of very low clearance (Cl) values, 0.0391 +/- 0.007 and 0.0512 +/- 0.007 1 kg-1 hr-1, in the two groups, while the volume of distribution was of the same size in the two groups, 0.9549 +/- 0.247 and 0.9411 +/- 0.211 1 kg-1. The protein binding of CAP in pooled piglet plasma was concentration dependent, 53-45%, (P less than 0.001) in the concentration range 31-232 microM (10-75 micrograms ml-1) and the binding degree was significantly higher in plasma from colostrum deprived piglets, 53.0 +/- 0.8% compared to plasma from colostrum fed, 47.5 +/- 1.3% (P less than 0.01).
The distribution of 14C‐chloramphenicol has been studied in new‐born pigs with the aid of whole‐body autoradiography. In the lung, liver, adrenal cortex, kidney, myocardium, pancreas, thyroid, spleen and skeletal muscle the amounts of radioactivity were higher than that of the blood short time after injection and remained higher than the blood up to 8 hrs. After 4 and 8 hrs the brain concentration of 14C was also higher than that of the blood. In the bone marrow, however, the concentration did not reach that of the blood during the whole experiment. In the organs more than 90% of the radioactivity was represented by chloramphenicol; the excretory organs, thyroids, and adrenals being exceptions.
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