After I.V. drug administration, elimination of a drug depends on
**Core Concept**
The elimination of intravenously administered drugs depends on the drug's pharmacokinetic properties, particularly its distribution, metabolism, and excretion (DME). The liver plays a crucial role in metabolizing many drugs, while the kidneys are responsible for excreting them.
**Why the Correct Answer is Right**
After IV administration, the initial distribution of the drug to the bloodstream and tissues occurs rapidly. Subsequently, the drug is subjected to metabolism and excretion. The rate and extent of these processes determine the drug's elimination half-life, which is the time required for the plasma concentration of the drug to reduce by half. The liver enzyme system, particularly cytochrome P450, is involved in the metabolism of many drugs. The kidneys excrete the drug and its metabolites through the urine.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because distribution alone does not determine the elimination of a drug. While distribution affects the drug's initial plasma concentration, it does not influence its eventual removal from the body.
**Option B:** This option is incorrect because it is too narrow in scope. While the kidneys play a crucial role in drug elimination, particularly for water-soluble drugs, they are not the sole determinants of elimination. The liver's metabolic capacity also significantly impacts drug elimination.
**Option C:** This option is incorrect because distribution is not the primary factor influencing drug elimination. While distribution affects the drug's initial plasma concentration, it does not determine its eventual removal from the body.
**Clinical Pearl / High-Yield Fact**
The liver's metabolic capacity can be overwhelmed by high doses of certain drugs, leading to a decrease in their elimination half-life and increased risk of toxicity. This phenomenon is known as "zero-order kinetics."
**Correct Answer: C. DME (Distribution, Metabolism, and Excretion)**