Drug metabolism is a core process that transforms pharmaceutical substances to facilitate their elimination and affect their therapeutic efficacy. The complexity of drug metabolism influences dosing, therapeutic effects, and the risk of toxicity. Clarifying commonly misunderstood concepts is essential for safe and effective drug administration.

Therapeutic Window

The therapeutic window is defined as the range of plasma drug concentrations within which a drug exerts its therapeutic effects without causing significant adverse or toxic effects. Maintaining drug levels within this window ensures maximum benefit with minimal risk. It reflects the balance between efficacy and safety.

Statement 1 is true: The therapeutic window represents this range of plasma concentrations for safe and effective treatment.

Specificity of Drug-Metabolizing Enzymes

Drug metabolism involves various enzymes, especially those in the cytochrome P450 family, which can metabolize multiple drugs. No enzyme is usually exclusive to a single drug; instead, many enzymes process a range of substrates.

Therefore,

Statement 2 is false: Drug-metabolizing enzymes are not dedicated to a single drug but often metabolize multiple compounds.

Metabolizer Types and Their Risks

• Ultrafast metabolizer: An individual with significantly increased metabolic activity for a drug. This causes the drug to be broken down rapidly, often resulting in subtherapeutic drug levels and risk of underdose or therapeutic failure, not overdose.

• Poor metabolizer: An individual with reduced metabolic capability, leading to slower drug clearance and increased plasma levels, which raises the risk of drug toxicity or overdose since the drug accumulates.

Thus,

• Statement 3 is false: Ultrafast metabolizers tend to risk underdosage, not overdose.

• Statement 4 is false: Poor metabolizers face overdose risk, not underdose.

Conclusion

The only true statement regarding drug metabolism among the options is:

(1) The therapeutic window is simply the range of plasma drug concentrations in which the drug has therapeutic benefits without causing extra safety risks due to drug toxicity.