What is the process by which a drug is transported by circulating body fluids to receptor sites?

Choice A: Excretion

Excretion is the process by which drugs and their metabolites are eliminated from the body, primarily through the kidneys (urine), but also via bile, sweat, saliva, and other routes. While excretion is a crucial phase of pharmacokinetics, it is not directly impacted by the first pass effect. The first pass effect primarily involves the metabolism of a drug before it reaches systemic circulation, which occurs prior to the excretion phase.

Choice B: Metabolism

The first pass effect, also known as first-pass metabolism or presystemic metabolism, significantly impacts the metabolism phase of pharmacokinetics. This phenomenon occurs when a drug is metabolized at a specific location in the body, such as the liver or gut wall, before it reaches systemic circulation. As a result, the concentration of the active drug is reduced, affecting its bioavailability. The liver is the primary site for this metabolic process, where enzymes break down the drug, potentially leading to a significant reduction in its therapeutic effect.

Choice C: Distribution

Distribution refers to the process by which a drug is transported from the bloodstream to various tissues and organs in the body. This phase is influenced by factors such as blood flow, tissue permeability, and binding to plasma proteins. However, the first pass effect does not directly alter the distribution phase. Instead, it affects the amount of drug that enters systemic circulation, which in turn can influence the extent of distribution.

Choice D: Absorption

Absorption is the process by which a drug enters the bloodstream from its site of administration. This phase is crucial for determining the onset of a drug’s action. While the first pass effect occurs after absorption, it does not directly change the absorption phase itself. Instead, it affects the drug’s concentration after it has been absorbed and before it reaches systemic circulation.

Choice A Reason:

Respiratory alkalosis occurs when a person breathes rapidly (hyperventilates), causing a decrease in carbon dioxide (CO2) levels in the blood. This reduction in CO2 leads to an increase in blood pH, resulting in alkalosis. Hyperventilation can be triggered by anxiety, fever, or other conditions that increase respiratory rate.

Choice B Reason:

Metabolic alkalosis is caused by an increase in bicarbonate (HCO3-) or a loss of hydrogen ions (H+), often due to vomiting, diuretic use, or excessive bicarbonate intake. It is not directly related to hyperventilation, which primarily affects CO2 levels rather than bicarbonate levels.

Choice C Reason:

Metabolic acidosis occurs when there is an excess of acid in the body or a loss of bicarbonate, often due to conditions like diabetic ketoacidosis, renal failure, or severe diarrhea. Hyperventilation does not cause metabolic acidosis; instead, it can be a compensatory response to metabolic acidosis to help lower CO2 levels and increase pH.

Choice D Reason:

Respiratory acidosis is caused by hypoventilation, where there is inadequate removal of CO2 from the body, leading to an increase in CO2 levels and a decrease in blood pH. This condition is the opposite of what occurs during hyperventilation, making this choice incorrect.