Factors Affecting Drug Response: Overview

Infants and young children have underdeveloped organ functions, making them less efficient at metabolizing and eliminating drugs. Additionally, their blood-brain barrier is more permeable, allowing high drug concentrations to penetrate the central nervous system and potentially cause neurological damage. Smaller doses protect developing systems from harm.

Aging significantly influences drug disposition, requiring elderly patients to receive smaller doses. When elderly patients with multiple chronic diseases take numerous medications simultaneously, the risk of adverse reactions increases substantially. Dose adjustments account for reduced metabolic capacity and increased drug sensitivity.

Drugs can cross the placenta and reach the developing fetus, potentially causing teratogenic effects that result in fetal developmental abnormalities. This placental transfer poses significant risks to fetal health and development. Pregnant women require careful medication selection and dosing to minimize fetal exposure.

A damaged liver cannot efficiently metabolize or detoxify drugs, so patients with liver disease require lower doses administered over longer intervals. This modification prevents drug accumulation and reduces the risk of toxicity. Hepatic impairment significantly slows drug elimination from the body.

Intravenous administration allows drugs to enter the bloodstream directly, bypassing the gastrointestinal tract and hepatic metabolism, resulting in a quick drug response. Oral drugs must pass through the GI tract and undergo hepatic metabolism before entering systemic circulation, producing a slower response. Routes of drug administration overview explains these differences in detail.

Orally administered drugs pass through the gastrointestinal tract where they are absorbed, then undergo hepatic metabolism in the liver before entering the systemic circulation. This first-pass metabolism can reduce drug bioavailability and delay therapeutic effects. Understanding routes of drug administration enteral helps clarify this process.

Intravenous drugs bypass hepatic metabolism entirely by entering the bloodstream directly, avoiding first-pass metabolism. Oral drugs undergo hepatic metabolism before systemic circulation, which can significantly alter drug concentration and effectiveness. This metabolic difference explains why intravenous administration produces faster therapeutic responses than oral routes.