Thursday, January 25, 2018

Pharmacology MCQs 113







A 26 year old man complains of cough, night fever, loss of weight, anorexia and night sweats for six weeks presents to his physician. Physical examination reveals vital signs within normal limits except for slight fever. Chest x-ray shows a small cavity in the right middle lobe and enlarged bronchopulmonary lymph nodes. Blood analysis reveals lymphocytosis and his sputum is positive for acid-fast bacilli.

A treatment plan is discussed with the patient and he starts taking his medications.

Which of these drugs acts by inhibition of formation of mycolic acid?

A-Ethambutol

B-Isoniazid

C-Pyrazinamide

D-Rifampin

E-Streptomycin

Answer






This a case of primary tuberculosis (TB) confirmed by positive sputum analysis. Tuberculosis can be primary or secondary. Primary TB represents by Ghon’s complex which consists of a sub-pleural lesion between the upper and lower lobes and enlarged pulmonary lymph nodes while secondary TB is located in the apex of one or both lungs. Primary TB is characterized by cough, night fever, evening sweats, and anorexia and weight loss as seen in this patient. Anti-tuberculous drugs contain all the drugs listed in the question. Isoniazid is the only drug on the list that acts by inhibition of mycolic acid in the outer layer of mycobacteria. It is a synthetic analogue of Vitamin B6 (pyridoxine). Ethambutol and pyrazinamide have unknown mechanism. Rifampin inhibits bacterial DNA-dependent RNA polymerase leading to inhibition of RNA synthesis. Streptomycin is aminoglycoside inhibits protein synthesis by binding to 30S ribosomal unit.

The correct answer is B





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