BCSE Pharmacology and Toxicology 5

Question 1

A patient taking isoniazid for tuberculosis develops peripheral neuropathy. What is the mechanism of this adverse effect?

Accepted Answer

Isoniazid competes with pyridoxine (vitamin B6) for binding to apoenymes

Answer

Isoniazid forms hydrazones with pyridoxal phosphate (active B6), depleting the coenzyme needed for GABA synthesis and amino acid metabolism in peripheral neurons, causing neuropathy preventable with B6 supplementation.

Question 2

Which class of drugs causes hyperkalemia by blocking aldosterone's action in the collecting duct?

Accepted Answer

Potassium-sparing diuretics (spironolactone)

Answer

Spironolactone competitively antagonizes aldosterone receptors in the collecting duct, preventing sodium reabsorption and potassium secretion, leading to potassium retention and hyperkalemia.

Question 3

Which toxic effect is associated with methanol poisoning but not ethanol poisoning?

Accepted Answer

Severe metabolic acidosis with visual disturbances and blindness

Answer

Methanol is metabolized to formaldehyde and formic acid by alcohol dehydrogenase; formate accumulates in the retina and optic nerve, causing irreversible blindness and severe anion-gap metabolic acidosis.

Question 4

Beta-blockers are contraindicated in patients with reactive airway disease primarily because they:

Accepted Answer

Block beta-2 receptors in bronchial smooth muscle, causing bronchoconstriction

Answer

Non-selective beta-blockers block beta-2 adrenergic receptors in bronchial smooth muscle, preventing epinephrine-mediated bronchodilation and triggering potentially life-threatening bronchoconstriction in asthmatic patients.

Question 5

Cyclosporine prevents organ rejection by blocking which step in T-cell activation?

Accepted Answer

Inhibiting calcineurin, preventing NFAT-mediated IL-2 transcription

Answer

Cyclosporine binds cyclophilin, and this complex inhibits calcineurin phosphatase, preventing dephosphorylation and nuclear translocation of NFAT, thereby blocking IL-2 gene transcription essential for T-cell clonal expansion.

BCSE - Basic and Clinical Sciences Examination Practice Test

BCSE - Basic and Clinical Sciences Examination Practice Test

BCSE Pharmacology and Toxicology 5