Description of Plasma Penicillin G Concentrations after Intramuscular Injection in Double-Muscled Cows to Optimize the Timing of Antibiotherapy for Caesarean Section

Abstract: In order to improve the efficacy of penicillin injection during caesarean section, we aimed
to identify the optimal timing of its preoperative administration. A study was conducted in 12
adult, non-pregnant Belgian Blue cows. To evaluate the plasma penicillin concentrations, blood
samples were taken from the jugular vein at 􀀀5, 15, 30, 45, 60, 120, 240, 480 min relative to the
intramuscular (IM) injection of 21,000 IU/kg of body weight of penicillin G. Results showed that
plasma concentrations at 15 min after IM injection (668.3 73.7 ng/mL) largely exceeded the minimal
inhibitory concentration (MIC) of penicillin-sensitive bacteria (MIC < 125 ng/mL).With increasing
time, plasma concentrations continued to rise, attaining an increasing proportion of moderately
sensitive bacteria (250 ng/mL > MIC < 2000 ng/mL). The maximal concentration was reached
between 1 and 4 h (average: 1.495.1 181.7 ng/mL) after IM injection in the majority of cows,
and decreased non-significantly to 1002.1 93.2 ng/mL at 8 h. In conclusion, plasma penicillin
concentrations at 15 min after an IM injection inhibit penicillin-sensitive bacteria. However, in order
to obtain the maximal protective effect of the antibiotherapy, surgery should be started at 1 to 2 h
after IM penicillin injection.