What does the term “bioavailability” mean?

Correct Answer: C

Rationale: The correct answer is C: Fraction of an uncharged drug reaching the systemic circulation following any route administration. Bioavailability refers to the percentage of an administered drug that reaches the systemic circulation in an unchanged form. This definition excludes options A, B, and D as they do not directly relate to the concept of bioavailability. Plasma protein binding (A) refers to the extent to which a drug binds to proteins in the blood, brain-blood barrier permeability (B) is related to drug penetration into the brain, and the amount of a substance in urine relative to the initial dose (D) is more related to drug excretion rather than bioavailability. Thus, option C is correct as it specifically describes the concept of bioavailability.

Correct Answer: D

Rationale: The correct answer is D because the choice of a local anesthetic for specific procedures should consider multiple factors, including the duration of action (A), water solubility (B), and the capability of rapid penetration through the skin or mucosa with limited diffusion away from the site of application (C). Duration of action is important for ensuring adequate pain relief during the procedure, water solubility affects the onset of action and tissue penetration, and limited diffusion helps in maintaining the anesthetic effect at the target site. Therefore, considering all these factors collectively ensures the most appropriate choice of local anesthetic for a specific procedure. Choices A, B, and C on their own do not encompass all the essential considerations for selecting a local anesthetic, making them incorrect.

Correct Answer: B

Rationale: Rationale: 1. Atropine is a muscarinic receptor antagonist. 2. It competes with pilocarpine and choline esters for the muscarinic receptors. 3. By binding to the receptors, atropine blocks the excessive stimulation. Summary: - A: Edrophonium is an acetylcholinesterase inhibitor, not a muscarinic receptor antagonist. - C: Pralidoxime is used to treat organophosphate poisoning, not muscarinic receptor overstimulation. - D: Echothiophate is a long-acting acetylcholinesterase inhibitor, not a muscarinic receptor antagonist.

Correct Answer: D

Rationale: Succinylcholine is the correct answer because it is a depolarizing agent with an extremely brief duration of action. It rapidly metabolizes by plasma cholinesterase, leading to a short duration of effect. Mivacurium, Rocuronium, and Rapacuronium are non-depolarizing agents with longer durations of action due to their mechanisms of action and metabolism, making them incorrect choices.

Correct Answer: B

Rationale: The correct answer is B because methoxamine is a direct-acting alpha1-receptor agonist that increases blood pressure by causing vasoconstriction and increasing total peripheral resistance. It does not increase heart rate, contractility, or cardiac output; instead, it can cause reflex bradycardia due to its hypertensive effect. Therefore, the statement that it increases heart rate, contractility, and cardiac output is incorrect. The other choices (A, C, and D) are all characteristics of methoxamine, making them incorrect options for this question.