USMLE step 1 qbook Pharmacology

328 questions with answers and explanations
Q NO 1: After a positive PPD test, a 64-year-old male begins isoniazid therapy. One month later he presents complaining of fever, anorexia and nausea. What is the most likely cause of his current symptoms?
A. Peripheral nerve damage
B. Hepatocyte damage
C. Gastric mucosal damage
D. Serum sickness
E. Factitious disorderExplanation:
Isoniazid (INH) is directly hepatotoxic in 10-20% of patients causing acute mild hepatic dysfunction with transient increases in serum AST (SGPT) ALT (SGPT) and bilirubin and symptoms like fever, anorexia, and nausea. This adverse effect usually occurs during the first 4-6 months of treatment and in most cases liver function tests return to baseline with continued INH therapy. In rare instances however severe hepatitis and progressive liver dysfunction bilirubinuria, and jaundice occur.
(Choice A) Peripheral neuropathy is also a potential side effect of INH therapy if simultaneous pyridoxine is not administered. However peripheral neuropathy would not cause the above symptoms.
(Choice D) Serum sickness drug hypersensitivity generally causes fever urticaria, arthralgias, proteinuria and lymphadenopathy 5-10 days after exposure to the drug (antigen). This patient does not have arthralgias or skin findings.Educational Objective:
Isoniazid (INH) can be directly hepatotoxic causing acute mild hepatic dysfunction in 10-20% of patients. In a smaller percentage of cases frank hepatitis may develop causing fever anorexia and nausea.