Interactions with other drugs of phosphorus is:

Correct Answer: D

Rationale: Step 1: Phosphorus is primarily excreted renally. Step 2: Calcitonin is a hormone that regulates calcium and phosphorus metabolism. Step 3: Calcitonin inhibits renal reabsorption of phosphorus. Step 4: Therefore, Calcitonin increases renal excretion of phosphorus. Step 5: This mechanism makes option D correct. Summary: A: Amiloride doesn't directly affect phosphorus excretion. B: Glucocorticoids affect calcium absorption, not phosphorus. C: Loop diuretics increase sodium and water excretion, not phosphorus.

Correct Answer: A

Rationale: The correct answer is A: Oxacillin. Oxacillin is penicillinase-resistant due to its side chain that protects it from penicillinase enzymes. This side chain confers resistance against beta-lactamase enzymes produced by certain bacteria. On the other hand, choices B, C, and D are not penicillinase-resistant. Amoxicillin and Penicillin G are susceptible to penicillinase enzymes, while Bicillin-5 is a combination of penicillin G and penicillinase-sensitive benzathine penicillin. Thus, Oxacillin is the only penicillinase-resistant drug among the options provided.

Correct Answer: A

Rationale: The correct answer is A: Pyrazinamide. Pyrazinamide is not a bactericidal drug but rather a bacteriostatic drug. It inhibits the growth of mycobacteria rather than directly killing them. Streptomycin, Rifampin, and Isoniazid are all bactericidal drugs that directly kill mycobacteria. Streptomycin disrupts protein synthesis, Rifampin inhibits RNA synthesis, and Isoniazid inhibits mycolic acid synthesis in mycobacteria, leading to their death. Therefore, Pyrazinamide is the only drug among the options that does not have a bactericidal effect.

Correct Answer: A

Rationale: The correct answer is A: Foscarnet. Foscarnet is a derivative of pyrophosphate as it contains a phosphonoformic acid group that mimics pyrophosphate. This structural similarity allows foscarnet to inhibit viral DNA polymerase by binding to the pyrophosphate-binding site. Zidovudine (B), Vidarabine (C), and Acyclovir (D) are not derivatives of pyrophosphate and act through different mechanisms to inhibit viral replication. Zidovudine is a nucleoside reverse transcriptase inhibitor, Vidarabine is a nucleoside analog, and Acyclovir is a guanosine analog.

Correct Answer: B

Rationale: The correct answer is B: Triamterene. Triamterene is a potassium-sparing diuretic that helps prevent new stone production by inhibiting sodium reabsorption in the kidneys, reducing the risk of stone formation. Mannitol (A) is an osmotic diuretic used for specific medical conditions, not for preventing stone formation. Conivaptan (C) is a vasopressin receptor antagonist primarily used for hyponatremia, not for preventing stone formation. Acetazolamide (D) is a carbonic anhydrase inhibitor that can help with certain types of kidney stones but is not typically used for preventing new stone production.