Chloramphenicol Procaine penicillin

Apart from the pathophysiological condition of the animal, the mode of drug application may also significantly influence the pharmacokinetic profile of a drug (48, 49). For example, drug residues may persist at the injection site for prolonged periods of time (2). In a study in which various sulfonamides and trimethoprim were injected intramuscularly into swine, detectable residues were found at most sites 6 days after the injection, and with the sulfonamides at 30 days in almost half of the animals (50). Other drugs such as dihydrostreptomycin persist for up to 60 days, while positive residues of chloramphenicol are found at 7 days postinjection. Sodium and procaine penicillin, neomycin, tylosin, and oxytetracycline residues have also been determined at 24 h or more postinjection (51). 

On the other hand, formation of a prodrug such as a phosphate ester may increase hydrophilicity, thus enhancing solubility. For example, the solubility and dissolution rate of the 77-hydroxymethyl derivative of lomefloxacin is higher than those of the parent compound, and it can be converted readily back to the original molecule. Commonly used prodrugs are procaine penicillin metronidazole phosphate and chloramphenicol sodium succinate. 

Gjessii HC, Od ard K. Oral chloramphenicol alone and with intramuscular procaine penicillin in the treatment ofgononboea. BrJ VenerDis 961) 43, 133-6. 

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