Which of the following topical decongestant agents is an alfa2-selective agonist?

Correct Answer: B

Rationale: Rationale: 1. Xylometazoline is an alpha2-selective agonist, which means it selectively activates alpha2 adrenergic receptors. 2. This action leads to vasoconstriction and reduces nasal congestion without affecting blood pressure. 3. Phenylephrine (choice A) is an alpha1-selective agonist, causing increased blood pressure. 4. Ephedrine (choice C) is a mixed agonist affecting both alpha and beta receptors. 5. Epinephrine (choice D) is a non-selective agonist acting on both alpha and beta receptors.

Correct Answer: C

Rationale: The correct answer is C: Phenobarbital. Phenobarbital enhances GABA-mediated inhibition by increasing the duration of GABA-A receptor channel opening, leading to increased chloride ion influx. This enhances inhibitory neurotransmission, reducing neuronal excitability and seizure activity. Ethosuximide (A) works by blocking T-type calcium channels, Carbamazepine (B) by blocking voltage-gated sodium channels, and Lamotrigine (D) by inhibiting sodium channels and reducing glutamate release, none of which directly enhance GABA-mediated inhibition.

Correct Answer: A

Rationale: The correct answer is A: TRUE. In Parkinson's disease, there is a reduction in dopamine levels in the basal ganglia, leading to the characteristic motor symptoms. This is due to the degeneration of dopamine-producing neurons in the substantia nigra. Choice B is incorrect because the statement is true. Choice C (None) and D (All) are incorrect as they do not provide any meaningful explanation.

Correct Answer: D

Rationale: The correct answer is D because fentanyl can produce significant respiratory depression by inhibiting brain stem respiratory mechanisms (choice A) and by causing truncal rigidity (choice C). Inhibiting brain stem respiratory mechanisms affects the control of breathing, leading to decreased respiratory rate and depth. Truncal rigidity can impair chest wall movement, further reducing respiratory function. Choice B, suppression of the cough reflex leading to airway obstruction, is incorrect as it does not directly relate to respiratory depression caused by fentanyl.

Correct Answer: C

Rationale: Step-by-step rationale for choice C (Analgin) being the correct answer for possible adverse effect of Methemoglobinemia: 1. Analgin contains metamizole, which can lead to methemoglobinemia by causing the oxidation of hemoglobin. 2. Methemoglobinemia is a condition where hemoglobin is unable to transport oxygen efficiently. 3. Aspirin (choice A), Paracetamol (choice B), and Ketorolac (choice D) do not typically cause methemoglobinemia. Summary: - Choice A (Aspirin) is incorrect because it does not cause methemoglobinemia. - Choice B (Paracetamol) is incorrect because it does not cause methemoglobinemia. - Choice D (Ketorolac) is incorrect because it does not cause methemoglobinemia. - Choice C (Analgin) is correct due to its potential to cause methemoglobinemia through the presence of metamizole.