Chloramphenicol has the following unwanted effects:

Correct Answer: B

Rationale: The correct answer is B: Pancytopenia. Chloramphenicol is known to cause bone marrow suppression, leading to a decrease in red blood cells, white blood cells, and platelets. This results in pancytopenia, which can manifest as anemia, increased risk of infections, and easy bruising or bleeding. Nephrotoxicity (A), hepatotoxicity (C), and ototoxicity (D) are not common side effects of chloramphenicol. Pancytopenia is a well-documented adverse effect of this antibiotic due to its impact on bone marrow function.

Correct Answer: A

Rationale: Acyclovir is an antiviral drug used to treat herpes infections, not influenza. Amantadine and Rimantadine are anti-influenza agents that target the influenza A virus. Interferons are proteins that help the immune system fight viruses, including influenza. Therefore, the correct answer is A (Acyclovir) because it is not used specifically to treat influenza infections.

Correct Answer: C

Rationale: Rationale: 1. Digoxin inhibits Na+/K+ ATPase, leading to intracellular Na+ accumulation. 2. Increased intracellular Na+ reduces the activity of Na+/Ca2+ exchanger, causing Ca2+ to remain in the cell. 3. Elevated intracellular Ca2+ levels enhance cardiac contractility, resulting in positive inotropic effects. Summary: A: Closing of calcium channels would decrease Ca2+ influx, contrary to the inotropic effect. B: Increased release of Ca2+ from the sarcoplasmic reticulum is not the primary mechanism of digoxin's action. D: Activation of the Ca2+/Na+ exchanger would lead to Ca2+ extrusion, opposing the inotropic effect.

Correct Answer: G

Rationale: Ibutilide is the correct choice as it is a class III antiarrhythmic drug used for converting atrial fibrillation/flutter. It has a rapid onset of action and is effective in patients with normal renal function. Amiodarone (B) is a class III antiarrhythmic but is not first-line due to its potential side effects. Procainamide (C) is a class Ia antiarrhythmic and may not be suitable for this patient. Sotalol (D) is a class III antiarrhythmic but has a higher risk of proarrhythmia compared to ibutilide.

Correct Answer: A

Rationale: In this question, the correct answer is A) Digoxin. Digoxin is a cardiac glycoside that acts by inhibiting the sodium-potassium pump, leading to an increase in intracellular calcium levels. This increase in calcium enhances cardiac contractility, making the heart muscle more efficient at pumping blood. Digoxin also predictably prolongs the PR interval by slowing down the conduction of electrical impulses through the atrioventricular (AV) node. This effect is important to note as it can be seen on an electrocardiogram (ECG) when monitoring patients on digoxin therapy. Now, let's discuss why the other options are incorrect: - B) Lidocaine is a local anesthetic and antiarrhythmic drug that primarily works by blocking sodium channels in the heart to prevent abnormal electrical activity. It does not affect the PR interval or increase cardiac contractility. - C) Propranolol is a beta-blocker that decreases heart rate and blood pressure by blocking beta-adrenergic receptors. It does not predictably prolong the PR interval or increase cardiac contractility. - D) Quinidine is an antiarrhythmic medication that works by blocking sodium and potassium channels in the heart. While it can prolong the QT interval on an ECG, it does not specifically prolong the PR interval or increase cardiac contractility like digoxin. In an educational context, understanding the effects of different cardiovascular drugs on the heart's electrical conduction system and contractility is crucial for healthcare professionals, especially those working in cardiology or critical care settings. Recognizing the unique actions of each medication helps in making informed decisions regarding treatment options and monitoring for potential side effects or complications.