How does INH impact the metabolism of other drugs in the liver?

The correct choice highlights that isoniazid (INH) can inhibit cytochrome P450 enzymes, which are crucial for drug metabolism in the liver. These enzymes are responsible for the biotransformation of various medications, and when INH inhibits them, it can lead to altered levels of other drugs metabolized through the same pathways.

This inhibition can result in increased plasma concentrations of other drugs, potentially leading to heightened therapeutic effects or adverse reactions due to decreased clearance from the system. Understanding this interaction is essential for managing patient treatment plans, particularly for those on multiple medications, as it can inform necessary adjustments in dosages to avoid toxicity.

The other options present inaccurate portrayals of INH's metabolic effects: it does not speed up the metabolism of all medications, nor is it true that INH has no effect on drug metabolism. While there may be some medications, such as corticosteroids, that are influenced by INH, the claim that it only affects corticosteroids is overly restrictive and doesn’t encompass the broader impact of INH on various drugs processed by the liver.