A method of preparing a solution for use during a dialysis, hemodialysis, or Continuous Renal Replacement Therapy (CRRT) treatment of a patient is provided. An antibiotic or other drug is added (48, 50, 52) to a solution and the concentration or dosing of the antibiotic or other drug within the solution is adjusted (72) as required based on a determination (64) of serum level of the antibiotic in a blood sample of a patient.