Elimination is expressed as follows:

Correct Answer: B

Rationale: The correct answer is B because elimination is defined as the clearance speed of a substance from the blood, indicating how efficiently the kidneys remove a substance from the bloodstream over a given period. This process is quantified by measuring the volume of blood cleared of the substance per unit time. Choices A, C, and D do not directly refer to the process of elimination as described, making them incorrect. Choice A refers to reabsorption, not elimination. Choice C describes half-life, not elimination rate. Choice D refers to clearance of a xenobiotic from an organism, which is related but not the precise definition of elimination in the context of pharmacokinetics.

Correct Answer: A

Rationale: Step 1: Acetylcholine is a direct-acting cholinomimetic that quickly hydrolyzes by acetylcholinesterase, leading to a short duration of action. Step 2: Methacholine, Carbachol, and Bethanechol are also direct-acting cholinomimetics but are more resistant to enzymatic degradation, resulting in longer durations of action. Summary: Acetylcholine has the shortest duration of action due to rapid enzymatic degradation compared to the other choices. Methacholine, Carbachol, and Bethanechol have longer durations of action as they are more resistant to enzymatic degradation.

Correct Answer: D

Rationale: Step-by-step rationale: 1. Atropine is an antimuscarinic drug that blocks muscarinic acetylcholine receptors. 2. In mushroom poisoning, toxins can lead to excessive stimulation of muscarinic receptors. 3. Atropine counteracts this effect by blocking the receptors, reducing symptoms like excessive salivation, sweating, and bradycardia. 4. Pralidoxime is used for organophosphate poisoning, not mushroom poisoning. 5. Pilocarpine and homatropine are muscarinic agonists, which would worsen symptoms of mushroom poisoning by further stimulating muscarinic receptors.

Correct Answer: C

Rationale: The correct answer is C: Methoxamine. Beta receptor agonists stimulate beta receptors, leading to various effects like increased heart rate and bronchodilation. Methoxamine is an alpha-1 adrenergic agonist, not a beta receptor agonist. Epinephrine, Isoproterenol, and Dobutamine are all beta receptor agonists, so they are incorrect choices. Epinephrine acts on both alpha and beta receptors, Isoproterenol is a non-selective beta agonist, and Dobutamine primarily targets beta-1 receptors.

Correct Answer: B

Rationale: The correct answer is B, Reserpine, as it inhibits the storage of norepinephrine and other neurotransmitters in vesicles, indirectly blocking adrenoreceptor activation. Tolazoline (A) is a vasodilator, Carvedilol (C) is a non-selective beta-blocker with alpha-blocking activity, and Prazosin (D) is a selective alpha-1 adrenergic receptor antagonist. Reserpine is the only indirect-acting adrenoreceptor blocking drug among the choices provided.