Idiosyncratic reaction of a drug is:

Correct Answer: C

Rationale: Step-by-step rationale: 1. Idiosyncratic reaction refers to unusual, unpredictable responses to a drug. 2. Choice C correctly defines idiosyncratic reaction as inherent, abnormal, and unpredictable. 3. Choices A and B are incorrect as they do not accurately describe idiosyncratic reactions. 4. Choice A refers to hypersensitivity reactions, not idiosyncratic reactions. 5. Choice B refers to drug antagonism, which is different from idiosyncratic reactions. 6. Choice D is incorrect as it describes a quantitatively exaggerated response, not an idiosyncratic reaction. Summary: Choice C is correct as it accurately defines idiosyncratic reactions. Choices A, B, and D are incorrect as they describe different concepts that do not align with the definition of idiosyncratic reactions.

Correct Answer: A

Rationale: Atropine causes spasmolitic activity by blocking acetylcholine receptors, leading to relaxation of smooth muscles. This is beneficial in conditions like irritable bowel syndrome. Intestinal hypermotility, stimulation of gut contraction, and secretory activity are all effects opposite to what atropine causes due to its anticholinergic properties. Atropine's mechanism of action supports choice A as the correct answer.

Correct Answer: C

Rationale: The correct answer is C: Tachycardia. Direct beta1-adrenoreceptor stimulation leads to an increase in heart rate by enhancing the conduction of electrical impulses in the heart. Beta1 receptors are primarily located in the heart, particularly in the sinoatrial node, atria, and ventricles. This stimulation results in an increased rate of depolarization, leading to tachycardia. Choices A and B are incorrect because beta2 receptors are responsible for bronchodilation and vasodilation, respectively. Choice D is incorrect because bradycardia is not associated with direct beta1-adrenoreceptor stimulation.

Correct Answer: B

Rationale: The correct answer is B: Phentolamine. This drug is a nonselective alpha receptor antagonist, blocking both alpha-1 and alpha-2 receptors. It is used to treat hypertensive emergencies. Prazosin (A) is a selective alpha-1 receptor antagonist, used for hypertension and BPH. Metoprolol (C) is a beta blocker, mainly blocking beta-1 receptors for heart conditions. Reserpine (D) inhibits the uptake of norepinephrine into vesicles, reducing sympathetic activity.

Correct Answer: D

Rationale: The correct answer is D because all three options (A, B, and C) are used in the treatment of insomnia. Benzodiazepines, such as diazepam, help induce sleep. Imidazopyridines, like zolpidem, also aid in sleep. Barbiturates, such as phenobarbital, have sedative effects. Therefore, all of the above options are valid treatments for insomnia.