A nurse is caring for a client who received penicillin for pneumonia. Which laboratory value will the nurse assess to evaluate the therapeutic effect of this medication?

A. Trough level: Penicillin dosing is not routinely guided by serum trough levels in clinical practice. Therapeutic drug monitoring is reserved for medications with narrow therapeutic ranges, such as vancomycin or aminoglycosides. Penicillin effectiveness is assessed through clinical and laboratory response rather than drug levels. B. White blood cell (WBC) count: An elevated WBC count is a common marker of bacterial infection and systemic inflammation. Effective antibiotic therapy leads to a reduction in infection burden and normalization of leukocyte levels. Trending the WBC count helps evaluate response to treatment for pneumonia. C. Blood urea nitrogen (BUN): BUN reflects renal function and hydration status rather than infection resolution. While renal monitoring may be necessary with certain antibiotics, it does not indicate therapeutic effectiveness. Changes in BUN do not correlate with pneumonia improvement. D. Liver enzymes: Liver function tests are monitored for hepatotoxicity with specific medications. Penicillin is not primarily assessed through hepatic enzyme trends. Liver enzymes do not measure the antimicrobial effectiveness of treatment.