Smoking is an environmental factor that influences pharmacokinetics by increasing which process?

Smoking is an environmental factor that influences pharmacokinetics by increasing which process?

• A. Metabolism
• B. Excretion
• C. Absorption
• D. Distribution

Answer: (A)

Smoking changes pharmacokinetics mainly by boosting metabolism. It does this through inducing hepatic enzymes, especially CYP1A2, so drugs that rely on this pathway are cleared faster. As a result, plasma levels of these drugs drop and their effects can be reduced unless the dose is increased to compensate. Classic examples include theophylline and certain antipsychotics like clozapine or olanzapine, where smoking can necessitate higher doses to achieve the same effect. If a patient quits smoking, the opposite happens: enzyme induction wanes, drug levels can rise, raising the risk of toxicity unless the dose is adjusted. This is why smoking is considered an important factor in pharmacokinetics due to metabolism, not primarily because of absorption, distribution, or excretion changes.

Smoking changes pharmacokinetics mainly by boosting metabolism. It does this through inducing hepatic enzymes, especially CYP1A2, so drugs that rely on this pathway are cleared faster. As a result, plasma levels of these drugs drop and their effects can be reduced unless the dose is increased to compensate. Classic examples include theophylline and certain antipsychotics like clozapine or olanzapine, where smoking can necessitate higher doses to achieve the same effect. If a patient quits smoking, the opposite happens: enzyme induction wanes, drug levels can rise, raising the risk of toxicity unless the dose is adjusted. This is why smoking is considered an important factor in pharmacokinetics due to metabolism, not primarily because of absorption, distribution, or excretion changes.