Which effect may lead to toxic reactions when a drug is taken continuously or repeatedly?

Correct Answer: B

Rationale: The correct answer is B: Cumulative effect. Continuous or repeated intake of a drug can lead to the accumulation of the drug in the body, causing a higher concentration than intended, leading to toxic reactions. Refractoriness (A) refers to decreased response to a drug over time. Tolerance (C) is the need for higher doses to achieve the same effect, not necessarily leading to toxicity. Tachyphylaxis (D) is a rapid decrease in response to a drug with repeated administration, not directly related to toxicity.

Correct Answer: D

Rationale: The correct answer is D because ganglion-blockers (A) and neuromuscular junction blockers (C) both belong to the group of nicotinic receptor-blocking drugs. Ganglion-blockers act on nicotinic receptors in autonomic ganglia, while neuromuscular junction blockers act on nicotinic receptors at the neuromuscular junction. Atropine-similar drugs (B) do not directly block nicotinic receptors, so they are not part of this particular group of drugs. Therefore, choices A and C cover all the drugs that block nicotinic receptors, making D the correct answer.

Correct Answer: D

Rationale: The correct answer is D: Diaphragm. The diaphragm is more resistant to block and recovers rapidly due to its involuntary nature and vital role in breathing. The diaphragm contracts and relaxes continuously, making it more resilient compared to voluntary muscles like the hand, leg, and neck. The other choices are incorrect because voluntary muscles are more susceptible to fatigue and blockage due to their reliance on conscious control and are not essential for immediate survival like the diaphragm.

Correct Answer: C

Rationale: Rationale: Isoproterenol is a non-selective beta-adrenergic agonist that primarily acts on beta-1 and beta-2 receptors. It increases heart rate and contractility, leading to an increase in cardiac output (A) and tachycardia (D). Isoproterenol causes vasodilation, resulting in a fall in diastolic and mean arterial pressure (B). However, it does not cause bronchoconstriction (C) as it stimulates beta-2 receptors leading to bronchodilation. Therefore, the correct answer is C.

Correct Answer: C

Rationale: Rationale: Propranolol is a non-selective beta-blocker that can block beta-2 receptors leading to bronchoconstriction (A). Rapid withdrawal can cause beta-adrenergic receptor supersensitivity (B). Propranolol can cause sedation, sleep disturbances, depression, and sexual dysfunction (D). However, propranolol is associated with hypoglycemia, not hyperglycemia. Therefore, the correct answer is C.