Which one of the following statements about the metabolism of local anesthetics is incorrect?

Correct Answer: A

Rationale: Rationale: A: Incorrect. Local anesthetics are not metabolized at the site of administration but rather at systemic sites like plasma or liver. B: Correct. Local anesthetics are metabolized in the plasma or liver, not at the administration site. C: Incorrect. Ester anesthetics like procaine are metabolized by pseudocholinesterase in the plasma, not systemically. D: Incorrect. Amides like lidocaine are metabolized in the liver by microsomal mixed function oxidases, not at the administration site. Summary: Choice A is incorrect as local anesthetics are not metabolized at the site of administration but rather at systemic sites like plasma or liver. Choices B, C, and D provide accurate information about the metabolism of local anesthetics.

Correct Answer: D

Rationale: The correct answer is D because hexamethonium is a ganglionic blocker that inhibits the sympathetic nervous system, leading to reduced peripheral vascular resistance and venous return (Choice A), partial mydriasis and loss of accommodation (Choice B), and constipation and urinary retention (Choice C). Stimulation of thermoregulatory sweating is not a systemic effect of hexamethonium, making Choice D incorrect. Hexamethonium does not affect the thermoregulatory sweating mechanism in the body.

Correct Answer: D

Rationale: Step-by-step rationale: 1. Norepinephrine is a direct-acting sympathomimetic that stimulates alpha1, alpha2, and beta1 receptors. 2. Activation of alpha1 receptors causes vasoconstriction. 3. Activation of alpha2 receptors inhibits norepinephrine release. 4. Activation of beta1 receptors increases heart rate and contractility. Summary: A. Isoproterenol is a non-selective beta agonist. B. Ephedrine acts mainly by releasing norepinephrine. C. Dobutamine is a beta1-selective agonist. D. Norepinephrine is the correct choice as it stimulates alpha1, alpha2, and beta1 receptors.

Correct Answer: D

Rationale: The correct answer is D: Αlfa-receptor antagonists. Alpha-receptor antagonists, such as phenoxybenzamine and phentolamine, are used in the management of pheochromocytoma to block the effects of excess catecholamines released by the tumor. These agents help control hypertension and other symptoms associated with pheochromocytoma. A: Selective beta2-receptor antagonists are not typically used in the management of pheochromocytoma because they do not target the alpha-receptors responsible for the symptoms. B: Nonselective beta-receptor antagonists may be used as adjunct therapy in pheochromocytoma to control tachycardia, but they do not directly address the alpha-receptor effects. C: Indirect-acting adrenoreceptor antagonist drugs do not specifically target the alpha-receptors involved in pheochromocytoma symptoms. In summary,

Correct Answer: D

Rationale: The correct answer is D because barbiturates act by increasing the duration, frequency, and direct activation of GABA-gated Cl- channels. This leads to hyperpolarization of neurons, resulting in sedative and hypnotic effects. Choice A is correct as barbiturates prolong the opening of Cl- channels. Choice B is incorrect as barbiturates enhance, not directly activate, the Cl- channels. Choice C is incorrect as barbiturates increase the duration, not frequency, of Cl- channel opening events. Therefore, the correct answer is D as it encompasses all the mechanisms of barbiturate action.