Why are several drugs used together to treat active tuberculosis?

Several drugs are used simultaneously to treat active tuberculosis primarily to prevent the tubercle bacillus from developing antibiotic resistance.12

When a patient is treated with only one drug or fails to complete the full course of medication, the surviving bacilli can mutate and become resistant to that specific agent. If treatment remains incomplete, these bacteria may eventually become resistant to multiple drugs, leading to multidrug-resistant tuberculosis (MDR TB) or even more severe forms like extensively drug-resistant tuberculosis (XDR TB).12

By using a combination of agents—such as isoniazid, rifampicin, ethambutol, and pyrazinamide—clinicians can effectively target the bacteria through different mechanisms, significantly delaying or preventing the emergence of resistant strains. This multi-drug approach is essential for ensuring that the infection is fully eradicated and that the patient does not relapse with a harder-to-treat form of the disease.123