To ensure vancomycin is effective, peak and trough levels are measured to keep drug concentration above what?

• A. Renal function threshold
• B. Serum glucose
• C. Blood pressure
• D. Minimum inhibitory concentration

Answer: (D)

The main idea is that vancomycin works best when the drug concentration stays above the organism’s minimum inhibitory concentration. The minimum inhibitory concentration, or MIC, is the smallest amount of antibiotic that will inhibit visible bacterial growth in the lab. Because vancomycin’s effect depends on keeping levels above that threshold for as long as possible (time above MIC), monitoring troughs helps ensure there’s ongoing exposure to the drug and that the bacteria can’t start growing again between doses. If levels drop below the MIC, the bacteria can resume growth and the treatment may fail. The other items listed—renal function threshold, serum glucose, and blood pressure—don’t measure the drug’s antimicrobial activity; they relate to kidney function, metabolic state, and hemodynamics, not the concentration needed to inhibit bacteria.