Professional and Linguistic Assessments Board (PLAB) Practice Exam

Which tuberculosis drug is known to cause red-green color blindness?

1. Rifampin

2. Isoniazid

3. Ethambutol

4. Pyrazinamide

The correct answer is: Ethambutol

Ethambutol is known to cause red-green color blindness, a condition that arises due to the drug's potential to affect the optic nerve. Ethambutol works as an antibacterial agent by inhibiting the synthesis of the mycobacterial cell wall, which is critical for the survival of the bacteria that cause tuberculosis. However, one of the significant side effects associated with this medication is ocular toxicity, which can lead to visual disturbances, including a loss of color discrimination, particularly affecting the red and green visual spectrum. While rifampin, isoniazid, and pyrazinamide are also important drugs in the treatment of tuberculosis, they are not associated with causing red-green color blindness. Rifampin mainly causes orange discoloration of body fluids and other mild side effects, isoniazid can lead to peripheral neuropathy and hepatitis, and pyrazinamide may cause hepatotoxicity or gout, but none have a direct link to color vision impairment as seen with ethambutol. Understanding the unique side effects of these medications is essential for monitoring and patient education during tuberculosis treatment.