- Multidrug-resistant Mycobacterium tuberculosis (MDR-TB) refers to strains of the bacterium that cause tuberculosis (TB) but are resistant to at least isoniazid and rifampicin, the two most powerful first-line anti-TB drugs.
- TB itself is a chronic infectious disease that primarily affects the lungs, although it can spread to other organs, and is caused by M. tuberculosis, a slow-growing, acid-fast bacterium. The emergence of MDR-TB represents one of the most severe challenges in global public health because it complicates treatment, prolongs illness, increases healthcare costs, and contributes to higher rates of disability and death.
- MDR-TB develops through a combination of spontaneous genetic mutations and selection pressure from improper antibiotic use. Mutations in specific genes confer resistance to drugs: for instance, mutations in the katG or inhA genes result in resistance to isoniazid, while mutations in the rpoB gene confer resistance to rifampicin. These mutations alter drug targets or metabolic pathways, allowing the bacterium to survive even in the presence of antibiotics. Resistance is further amplified when patients do not complete their treatment regimens, take inadequate doses, or receive substandard drugs, which allows partially resistant strains to flourish and spread.
- Clinically, MDR-TB behaves similarly to drug-sensitive TB but is much more difficult to treat. Symptoms include persistent cough, fever, night sweats, weight loss, and fatigue. However, unlike drug-sensitive TB, which can usually be cured with a standard six-month regimen of first-line drugs, MDR-TB requires longer and more complex treatment, often lasting 18–24 months or more. Treatment involves the use of second-line drugs such as fluoroquinolones (e.g., levofloxacin, moxifloxacin) and injectable agents like amikacin, kanamycin, or capreomycin, which are less effective, more toxic, and more expensive. Newer drugs such as bedaquiline and delamanid have brought hope, but access remains limited in many regions.
- A more severe form, known as extensively drug-resistant TB (XDR-TB), has emerged in some cases. XDR-TB strains are resistant not only to isoniazid and rifampicin but also to fluoroquinolones and at least one injectable second-line drug. This makes them extremely difficult, sometimes nearly impossible, to treat, leaving patients with very few therapeutic options. Both MDR-TB and XDR-TB are associated with poorer outcomes, higher treatment failure rates, and significant mortality.
- From a public health perspective, MDR-TB is a major global burden. According to the World Health Organization (WHO), hundreds of thousands of new MDR-TB cases are reported annually, with the highest incidence in regions such as Eastern Europe, South and Southeast Asia, and parts of Africa. MDR-TB is not only a threat to individual patients but also to communities, as resistant strains can be transmitted directly from person to person in the same way as drug-sensitive TB. Crowded living conditions, weak healthcare systems, poverty, and HIV co-infection exacerbate the spread and severity of the disease.
- Efforts to combat MDR-TB focus on prevention, early detection, and effective treatment. Rapid molecular diagnostic tools, such as the GeneXpert MTB/RIF assay, allow for quicker identification of resistant strains, enabling appropriate therapy to be started sooner. Strengthening TB control programs, ensuring reliable drug supplies, monitoring patient adherence, and minimizing treatment interruptions are critical to preventing resistance from developing or spreading. On a larger scale, global initiatives such as the WHO’s End TB Strategy aim to reduce MDR-TB incidence through integrated health interventions, research into new drugs and vaccines, and international collaboration.
