The authors have compared the serum concentrations and the factors affecting blood bioavailability of chloramphenicol after intramuscular administration of canadian commercial preparations containing 500 mg/mL of antibiotic.

The animals (dairy cows and heifers) received each drug (20 mg/kg) in one or two injection sites. The serum samples, analysed by colorimetric or microbiological methods, showed that considerable differences in concentration exist between the two methods.

The evolution of biodisponibility factors proved identical in both cases. It appears that therapeutic levels of chloramphenicol are reached only by drug A for four to five hours.

The usual dosage (2-10 mg/kg), by intramuscular route, is not sufficient to attain these active concentrations using the other drugs. However, the important variability obtained during the experiment and reflected in the standard deviation values, has not proved that drug A has a better bioavailability based on the criteria of the only microbiological analysis.