Which of the following drugs is associated with extreme photosensitivity as a reaction?

Correct Answer: C

Rationale: The correct answer is C: Tetracycline. Tetracycline is associated with extreme photosensitivity due to its mechanism of action causing phototoxic reactions when exposed to sunlight. Digitalis (A) is a cardiac medication, niacin (B) is a B vitamin, and fluoroquinolones (D) are antibiotics, none of which are known to cause extreme photosensitivity reactions.

Correct Answer: B

Rationale: The correct answer is B: Tachycardia. Atenolol is a beta-blocker that works by slowing down the heart rate, so tachycardia is not related to its toxicity. A: CHF can be exacerbated by Atenolol due to its negative inotropic effects. C: AV block can occur as Atenolol can further slow down the heart's conduction system. D: Sedative appearance can be a side effect of Atenolol due to its action on the central nervous system. In summary, tachycardia is not related to Atenolol toxicity because it decreases heart rate.

Correct Answer: D

Rationale: The correct answer is D: Procainamide. Procainamide is a class IA antiarrhythmic drug that blocks sodium channels, prolonging the action potential duration. This helps to stabilize the heart's rhythm. Mexiletine (A) is a class IB antiarrhythmic drug that blocks sodium channels with fast recovery kinetics. Amiodarone (B) is a class III antiarrhythmic drug that prolongs repolarization by blocking potassium channels. Quinidine (C) is a class IA antiarrhythmic drug that also blocks sodium channels, but it is not a class IB sodium channel blocker like Procainamide.

Correct Answer: A

Rationale: The correct answer is A: Quinidine. Quinidine is a class IA antiarrhythmic drug that blocks sodium channels in a use-dependent manner, which means it preferentially blocks channels that are open or have a rapid firing rate during depolarization. This action results in a decrease in conduction velocity and refractory period. Disopyramide is a class IA antiarrhythmic but does not specifically block sodium channels. Amiodarone is a class III antiarrhythmic that primarily affects potassium channels. Propafenone is a class IC antiarrhythmic that has minimal effects on sodium channel blockade. Therefore, Quinidine is the correct choice as a class IA sodium channel blocker.

Correct Answer: D

Rationale: The correct answer is D: Distal convoluted tubule. Potassium-sparing diuretics, such as spironolactone, act on the distal convoluted tubule by blocking the aldosterone receptor, which leads to decreased sodium reabsorption and potassium retention. This mechanism helps to promote diuresis while preventing potassium loss. Choices A, B, and C are incorrect because potassium-sparing diuretics do not primarily affect the proximal convoluted tubule, loop of Henle, or collecting duct in the kidney.