How is INH activated in the body?

Isoniazid (INH) is specifically activated in the body through the action of the bacterial enzyme catalase-peroxidase, designated as KatG. This enzyme plays a crucial role in the activation process by converting INH into its active form, which is responsible for exerting its anti-tuberculosis effects. The activation of INH is essential because it transforms the drug into a reactive compound that can inhibit the synthesis of mycolic acids, vital components of the bacterial cell wall.

The mechanism of activation highlights the targeting aspect of INH, as it relies on the presence of this specific bacterial enzyme found in Mycobacterium tuberculosis. This is significant in understanding the pharmacodynamics of INH and its selective action against tuberculosis.

Intestinal absorption and liver enzymes are involved in the pharmacokinetics of many drugs but do not specifically activate INH as it is done by KatG. Similarly, systemic circulation is the pathway through which drugs travel throughout the body but does not contribute to the activation of INH into its therapeutic form. Thus, the known mechanism of activation underscores the importance of the relationship between the drug and the specific bacterial enzyme in achieving its clinical effectiveness.