Effect of experimental synovitis on disposition of penicillin and oxytetracycline in neonatal calves

The effect of experimental synovitis on the distribution of antibacterial drugs into the joint space was studied in 7-day-old calves. Intrasynovial sodium urate was used to induce inflammation in the tibio-tarsal joint of calves and oxytetracycline (OTC) (11 mg/kg) or sodium penicillin G (PEN) (13.2 mg/kg) was administered intravenously 3 hours after synovitis was induced. Oxytetracycline and PEN concentrations were measured in serum and synovial fluid and pharmacokinetic parameters were calculated. The data indicate that synovitis neither enhanced nor impaired the levels of antibiotics achieved in the joint fluid. Mean peak concentrations (micrograms/ml) of the drugs in control and inflamed joints were, respectively, 8.04 and 8.79 for OTC and 9.35 and 8.92 for PEN. Rates of elimination of OTC and PEN were similar in joint fluid and serum; t1/2 beta ranged from 11.83-19.81 h for OTC and 0.980-1.125 h for PEN. The distribution and elimination of OTC and PEN from serum was described by a two-compartment model whereas elimination from joint fluid was described using a single-exponential model.