What is the MIC and how is it used clinically?

• A. The maximum tolerated dose during therapy.
• B. The minimum inhibitory concentration; the lowest antibiotic concentration preventing visible growth and guiding drug choice and dosing.
• C. A measure of time-to-kill for a drug.
• D. The amount of antibiotic needed to kill 99% of bacteria.

Answer: (B)

MIC, or minimum inhibitory concentration, is the lowest antibiotic concentration that prevents visible growth of a microorganism in standardized lab testing. Clinically, this value helps choose an effective drug and guides dosing by aiming to keep drug levels in the patient above the MIC for a sufficient portion of the dosing interval. Lab reports provide an MIC for each drug‑organism pair, and clinicians interpret these against established breakpoints to decide if the organism is susceptible, intermediate, or resistant. Dosing is then tailored using pharmacokinetics and pharmacodynamics to ensure that the drug concentration surpasses the MIC for the needed duration or exposure. This concept is different from the maximum tolerated dose (toxicity), time-to-kill measurements (how quickly a drug kills), or the bactericidal concentration that kills a large percentage of organisms, which are related but distinct concepts.