🦠 The Persistent Global Threat of Tuberculosis

Tuberculosis, commonly known as TB, remains one of the world's most formidable infectious diseases. Caused by the bacterium Mycobacterium tuberculosis, it primarily affects the lungs but can spread to other parts of the body, such as the brain, kidneys, and spine. Transmission occurs through the air when an infected person coughs, sneezes, or speaks, releasing tiny droplets containing the bacteria. While many people carry the bacteria in a latent form without symptoms, about 5 to 10 percent develop active disease, particularly those with weakened immune systems, like individuals living with HIV/AIDS or malnutrition.

According to recent estimates from the World Health Organization, approximately 10.8 million people fell ill with TB in 2024, resulting in around 1.25 million deaths. This makes TB the second-leading cause of death from a single infectious agent, surpassed only by COVID-19 in recent years. The disease disproportionately burdens low- and middle-income countries, with India, Indonesia, China, the Philippines, and Pakistan accounting for over half of global cases. Despite available vaccines like the Bacille Calmette-Guérin (BCG) vaccine, which offers partial protection mainly against severe forms in children, and effective standard treatments for drug-susceptible TB—a six-month regimen of four antibiotics—no cure-all exists yet.

The standard treatment for drug-susceptible pulmonary TB involves a combination of isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA), and ethambutol (EMB) for two months, followed by INH and RIF for four more months. Success rates hover around 85 to 90 percent when adhered to properly, but challenges like poor access to healthcare, stigma, and side effects complicate outcomes. Latent TB infection, affecting about one-quarter of the world's population or roughly 2 billion people, requires preventive therapy to avert progression to active disease.

• TB primarily targets the lungs (pulmonary TB), causing symptoms like persistent cough, chest pain, weight loss, night sweats, and hemoptysis (coughing up blood).
• Extrapulmonary TB affects lymph nodes, pleura, bones, or meninges, often mimicking other conditions.
• Diagnosis relies on sputum smear microscopy, culture, GeneXpert MTB/RIF test for rapid detection and rifampicin resistance, and chest X-rays.

Efforts to control TB have been hampered by the COVID-19 pandemic, which disrupted diagnostics and treatments, leading to backsliding in progress toward the End TB Strategy goals of 90 percent reduction in deaths and 80 percent in incidence by 2030.

The Growing Crisis of Drug-Resistant Tuberculosis

Drug-resistant tuberculosis poses an escalating threat, undermining decades of progress. Multidrug-resistant TB (MDR-TB) resists at least isoniazid and rifampicin, the two most effective first-line drugs. Extensively drug-resistant TB (XDR-TB) is MDR-TB plus resistance to any fluoroquinolone and at least one injectable second-line drug like bedaquiline or linezolid. Rifampicin-resistant TB (RR-TB) includes both MDR and some mono-resistant cases.

In 2024, an estimated 390,000 people developed RR/MDR-TB, but only about 164,000—or 42 percent—received treatment. Treatment success for MDR/RR-TB stands at around 60 percent globally, far below the 85 percent target. Traditional regimens for MDR/XDR-TB last 18 to 24 months, involving daily injections of toxic drugs like kanamycin or capreomycin, which cause hearing loss, kidney damage, and psychosis. Oral options like bedaquiline, approved in 2012 as the first new TB drug in 40 years, marked progress but were limited to limited-duration use due to cardiac risks.

MDR/XDR-TB emerges from improper treatment, poor adherence, counterfeit drugs, and transmission person-to-person. High-burden regions include Eastern Europe, southern Africa, and central Asia. Economic costs exceed $13 billion annually in treatment alone, not counting lost productivity.

• Key risk factors: Previous TB treatment, HIV co-infection, contact with resistant cases.
• Diagnosis: Drug susceptibility testing (DST) via phenotypic culture or molecular tests like MTBDRsl.
• Challenges: High pill burden (up to 14,000 pills), toxicity leading to 20-30 percent discontinuation.

This crisis demanded innovation, leading to the development of shorter, safer all-oral regimens.

🎯 FDA's Historic Approval of Pretomanid

On August 14, 2019, the U.S. Food and Drug Administration (FDA) approved pretomanid tablets, marking the first new chemical entity for TB in nearly 50 years. Developed by the nonprofit TB Alliance over 15 years with $750 million in funding from donors like the Bill & Melinda Gates Foundation, pretomanid addresses pulmonary XDR-TB and treatment-intolerant or non-responsive MDR-TB in adults.

Pretomanid is used strictly as part of the BPaL regimen: bedaquiline, pretomanid, and linezolid for six months. This approval stemmed from the phase 3 Nix-TB trial, granting priority review under the Limited Population Pathway for Antibacterial and Antifungal Drugs (LPAD). TB Alliance ensured affordable access, licensing generic manufacturers for low- and middle-income countries.

The approval highlighted collaborative R&D, bypassing traditional profit-driven pharma models. Mel Spigelman, TB Alliance CEO, emphasized the nonprofit advantage in prioritizing patient access over shareholder returns.

The BPaL Regimen: A Paradigm Shift

The BPaL regimen—bedaquiline (400 mg daily for 2 weeks, then 200 mg 3x/week), pretomanid (200 mg daily), linezolid (1,200 mg daily, adjustable)—offers a fully oral, six-month treatment. Bedaquiline inhibits ATP synthase, starving the bacteria of energy. Linezolid blocks protein synthesis at the ribosome. Pretomanid complements by targeting both replicating and dormant bacilli.

Compared to legacy regimens, BPaL slashes duration by 70 percent, eliminates injectables, and boasts triple the success rate. WHO has endorsed shorter regimens like BPaLM (adds 2 months moxifloxacin) and BPaL for eligible patients, with 2025 updates from CDC/ATS/ERS/IDSA recommending it for those 14 and older.

Implementation varies: Over 50 countries adopted by 2025, saving lives and costs—projected 191,000 lives and $1.29 billion by 2034.

Photo by Thought Catalog on Unsplash

Robust Evidence from the Nix-TB Trial

The landmark Nix-TB trial, published in the New England Journal of Medicine, enrolled 109 South African patients (65 percent XDR-TB, 35 percent MDR-intolerant; 51 percent HIV-positive). All received BPaL for 26 weeks, extendable to 39 if needed.

Primary outcome: Favorable status six months post-treatment (culture-negative, clinically resolved, no relapse). Results: 90 percent overall (95% CI 83-95), 89 percent XDR, 92 percent MDR. Culture conversion occurred rapidly, in 100 percent by end.

Adverse events affected all: Peripheral neuropathy (81 percent, mostly grade 1-2, managed by reducing linezolid to 600 mg), anemia/myelosuppression (48 percent), liver enzyme elevations (17 percent), QT prolongation (minor). No permanent discontinuations; 93 percent completed full course with adjustments.

This data revolutionized perceptions, proving high efficacy despite toxicities.

Mechanism, Safety, and Considerations

Pretomanid, a nitroimidazooxazine prodrug, enters bacterial cells and is activated by deazaflavin-dependent nitroreductase (Ddn), generating reactive nitrogen species that damage DNA, proteins, and lipids. It disrupts mycolic acid synthesis, weakening the waxy cell wall crucial for survival. Effective against hypoxic, non-replicating persisters.

Safety profile includes black-box warnings for hepatotoxicity, myelosuppression, and QT prolongation. Monitoring: Monthly labs, audiology, nerve checks. Contraindicated in drug-sensitive TB, extrapulmonary, or children under 14 (pediatric trials ongoing). Drug interactions with strong CYP3A4 inducers/inhibitors noted.

Post-approval, real-world data confirms trial outcomes, with neuropathy reversible in most.

Global Rollout and Public Health Impact

BPaL's adoption accelerates: BRICS nations expanded access in 2025. WHO's 2025 guidelines prioritize shorter regimens, projecting 78 percent DR-TB uptake by 2026. Challenges persist: Supply chains, training, funding gaps ($22 billion needed annually).

Impact: Reduced mortality (XDR ~30 percent untreated), transmission, healthcare burden. For vulnerable populations, it means hope—HIV patients, miners in South Africa, migrants.

Learn more via the TB Alliance.

Looking Ahead: Innovations in TB Drug Pipeline

Pretomanid paves the way for pan-TB regimens. TB Alliance's pipeline includes TBAJ-876 (sorfequiline), a safer bedaquiline analog showing promise in NC-009 trial (phase 2, 2025 data: potential 8-week intensive +4-week continuation). Sutezolid and Q203 target 4-month DS-TB treatments.

Phase 3 trials for SPaL (sorfequiline-pretomanid-linezolid) aim to shorten further, addressing neuropathy with lower linezolid doses.

Academic researchers drive this: Opportunities abound in clinical trials, epidemiology, and drug discovery.

Photo by Marek Studzinski on Unsplash

Opportunities for Researchers and Educators

The TB field offers exciting prospects for academics. Infectious disease specialists, microbiologists, and public health experts contribute via trials, modeling resistance spread, and vaccine development. Explore research jobs, clinical research jobs, or higher ed jobs in pharmacology.

Professors shaping future experts? Check professor jobs or academic CV tips. Share insights on platforms like Rate My Professor.

In summary, pretomanid's approval heralds a new era. Stay informed, pursue higher ed jobs, rate courses at Rate My Professor, and advance TB research through university jobs.