Which statement is correct regarding beta receptors?

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:

Beta2 agonists, such as terbutaline, are commonly used to manage premature labor. These drugs work by stimulating beta2 adrenergic receptors in the smooth muscles of the uterus, leading to relaxation and suppression of contractions. Therefore, questioning the use of a beta2 agonist in this scenario would not be appropriate.

Choice B Reason:

Anticholinergic drugs are not typically used to manage premature labor. They work by blocking the action of acetylcholine in the nervous system, which can lead to various effects such as reduced secretions and relaxation of smooth muscles. However, they are not specifically indicated for stopping uterine contractions, so questioning their use in this context is less relevant.

Choice C Reason:

This is the correct answer. Beta2 antagonists, also known as beta-blockers, work by blocking beta2 adrenergic receptors, which can lead to increased uterine contractions. Using a beta2 antagonist in a patient experiencing premature labor would be counterproductive and could exacerbate the condition. Therefore, it is appropriate to question the use of beta2 antagonists in this scenario.

Choice D Reason:

Alpha1 agonists are not typically used in the management of premature labor. These drugs stimulate alpha1 adrenergic receptors, leading to vasoconstriction and increased blood pressure. They do not have a direct effect on uterine contractions, so questioning their use in this context is less relevant.