It is normally used together with a beta-lactamase inhibitor such as tazobactam.
The combination drug of piperacillin and tazobactam is commercially available as TAZOMED(NEOMED) Tazocin, or Zosyn and BRODACTAM.
The combination has activity against many Gram-positive and Gram-negative pathogens and anaerobes, including Pseudomonas aeruginosa.
However, you should always check this with your pharmacist.