Procaine penicillin, pharmacokinetics

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). 

Parenteral preparations with antimicrobial activity, which depends on the causative pathogenic microorganism, and pharmacokinetic properties that meet most of these criteria include procaine penicillin G (aqueous suspension), amoxicillin trihydrate-clavulanate potassium combination (aqueous suspension), and enro-floxacin (solution). Enrofloxacin is not approved for use... 

Firth, E.C., Nouws, J.F.M., Driessens, F., Schmaetz, P., Peperkamp, K. Klein, W.R. (1986) Effect of the injection site on the pharmacokinetics of procaine penicillin G in horses. American Journal of Veterinary Research, 47, 2380-2384. 

B. Pharmacokinetics Penicillins vary in their resistance to gastric acid and therefote vary in their oral bioavailability. They are polar compounds and are not metabolized extensively. They are usually excreted unchanged in the urine via gloinemlar filtration and tubular secretion, the latter process being inhibited by probenecid. Ampicillin and nafcillin are excreted partly in the bile. The plasma half-lives of most penicillins vary from one-half to 1 hour. Procaine and benzathine forms of penicillin G are administered intramuscularly and have long plasma half-lives because the active drug is released very slowly into the bloodstream. Most penicillins cross the blood-brain barrier only when the meninges are inflamed. 

---