Calculate the therapeutic index (TI) of a hypothetical antimicrobial when the median toxic dose in humans (TD50) is 200 mg and the median effective dose (ED50) is 10 mg. Based on TI, assess the drug's selective toxicity.

• A. Therapeutic index = 190 indicating extremely high safety and no need for monitoring
• B. Therapeutic index = 0.05; indicates the drug is highly toxic to humans and unsafe for use
• C. Therapeutic index cannot be calculated from TD50 and ED50 values
• D. Therapeutic index = 20; indicates a reasonable margin of safety and selective toxicity in typical clinical contexts

Answer: (D)