The choice of Piperacillin/Tazobactam covers almost all pathogens encountered in severe intra-abdominal infections, including gram positive organisms, gram negative organisms and anaerobes. The addition of Vacomycin only adds coverage for MRSA, which is infrequently the pathogen in an intra-abdominal infection. Also consider that the combination of Vancomycin and Piperacillin/Tazobactam has been associated with acute renal failure.
Indications to add MRSA coverage:
*For any toxic patient, consider a Vancomycin loading dose of 25 mg/kg followed by 15 mg/kg every 12 hours. Every Vancomycin order requires pharmacokinetic consult.