Ciprofloxacin:

Correct Answer: B

Rationale: Ciprofloxacin is effective in Pseudomonas infections (B), particularly Pseudomonas aeruginosa, due to its potent Gram-negative coverage, making it a key drug for urinary tract infections, pneumonia, and chronic wounds in adults. It's not a first choice for Streptococcus pneumoniae (A), where beta-lactams or macrolides excel, as its Gram-positive activity is weaker. It should be avoided in children (C) due to cartilage damage risks, though used in specific cases like cystic fibrosis. It's cautioned in epileptics (D) for rare seizure risk, but not contraindicated. It's effective orally (original E is incorrect). As a fluoroquinolone, it inhibits DNA gyrase, offering broad-spectrum bactericidal action, though tendon rupture and resistance concerns limit its use to severe infections.

Correct Answer: D

Rationale: Oseltamivir (D) is used in the prophylaxis and treatment of influenza, a neuraminidase inhibitor reducing viral spread by preventing release from infected cells, effective against influenza A and B. Amantadine (A) was used for influenza A prophylaxis/treatment, but resistance limits its role today. Palivizumab (B) prevents RSV, not influenza. Entecavir (C) treats hepatitis B, unrelated to influenza. Zanamivir (original E) also treats influenza, but D is selected. Oseltamivir's oral administration and efficacy within 48 hours of symptoms make it a primary choice in seasonal flu and pandemics, shortening illness duration and reducing complications.

Correct Answer: C

Rationale: Psychosis paired with mefloquine (C) is correct, a known neuropsychiatric side effect (e.g., hallucinations, anxiety), limiting its use in those with psychiatric history. Acneiform eruption with chloroquine (A) is rare; retinopathy is more typical. Stevens-Johnson syndrome with quinine (B) is incorrect; it's linked to hypersensitivity but not a hallmark. QTc prolongation with proguanil (D) is wrong; quinine causes this. Hemolytic anemia with primaquine (original E) is accurate in G6PD deficiency. Mefloquine's schizonticidal action is effective for prophylaxis and treatment, but its CNS toxicity, including rare seizures, necessitates careful patient selection and counseling.

Correct Answer: C

Rationale: Daunorubicin paired with cardiomyopathy (C) is correct, an anthracycline causing dose-dependent cardiotoxicity via oxidative stress and topoisomerase inhibition, common in leukemia treatment, mitigated by dexrazoxane. Etoposide (A) causes myelosuppression, not neuropathy (vincristine does). Paclitaxel (B) causes alopecia, a hallmark taxane effect. Irinotecan (D) causes diarrhea, due to cholinergic and mucosal damage. 6-Mercaptopurine with pulmonary fibrosis (original E) is incorrect; myelosuppression is typical. Daunorubicin's efficacy in acute leukemias is balanced by lifetime dose limits to protect cardiac function, monitored via echocardiography.

Correct Answer: B

Rationale: The correct answer is that the half-life is the same regardless of the plasma concentration (B). First-order kinetics implies that the rate of drug elimination is proportional to its plasma concentration, meaning a constant fraction of the drug is removed per unit time. This results in a consistent half-life, independent of the initial concentration, as seen with most drugs like aspirin. Option A is incorrect because multiple metabolic pathways can exist in first-order kinetics. Option C describes first-pass metabolism but isn't inherent to first-order kinetics. Option D is false as elimination rate depends on concentration, not administration rate. Option E (original) about vascular confinement is unrelated. This principle is foundational in pharmacokinetics, allowing predictable dosing regimens, unlike zero-order kinetics where half-life varies with concentration, as with ethanol.