What does it mean if a drug has selective toxicity?

When a drug exhibits selective toxicity, it means that the drug is specifically designed to target the microbe while sparing the host's cells. This is a crucial characteristic for antimicrobial agents, as it allows them to effectively eradicate or inhibit the growth of pathogens without causing harm to the human body or other higher organisms.

This selectivity is achieved through the differences in cellular structures and metabolic pathways between the microbial agents and the host. For example, many antibiotics target bacterial cell wall synthesis, which is a feature that human cells do not possess. By exploiting the differences in biology, such drugs can eliminate pathogens while preserving host tissues, minimizing side effects and toxicity to the patient.

Other options incorrectly imply either harm to the host or a lack of specificity: attacking the host or affecting both equally would undermine the purpose of a therapeutic agent and result in adverse reactions. This distinction highlights the importance of selective toxicity in the development of effective and safe antimicrobial treatments.