Which of the following drugs is NOT used to treat tuberculosis?

The choice of Penicillin as the drug not used to treat tuberculosis is based on the specific nature of the bacteria that cause the disease, which is primarily Mycobacterium tuberculosis. This bacterium exhibits unique characteristics that make it resistant to the effects of Penicillin.

Penicillin is a beta-lactam antibiotic that works by inhibiting bacterial cell wall synthesis. However, Mycobacterium tuberculosis has a cell wall that is not significantly affected by this mechanism, rendering Penicillin ineffective against it. The other drugs listed—Isoniazid, Rifampin, and Ethambutol—are specifically designed to target the metabolic processes and cell walls of mycobacteria, making them effective treatments for tuberculosis. These medications are often used in combination to ensure effective treatment and prevent the development of drug resistance.

Thus, Penicillin's lack of effectiveness against tuberculosis underscores why it is not included in the treatment regimen for this disease.