Pulmonary · Topic 24 of 28

Tuberculosis

Infectious disease · mycobacteria

Tuberculosis

Isolate first, then three sputa: active TB gets four drugs for 2 months and two drugs for 4 more; latent TB gets a short rifamycin course.

Key numbers

Three sputum samples for AFB3 sputa, 8–24 h apart

RIPE 2 months, then INH + rifampin2 + 4 months

TST cutoffs: 5, 10, 15 mmTST ≥ 5 / 10 / 15 mm

Cavity plus positive 2-month culture: treat 9 months9 mo: cavity + culture+

Hold hepatotoxic TB drugs for ALT riseALT > 3× ULN sx / 5× ULN

01 · DoAirborne isolation, N95 respirator

Place suspected pulmonary TB in airborne isolation — a negative-pressure room with 6–12 air changes per hour — and wear a fit-tested N95 (or higher) respirator, not a surgical mask, to enter.

02 · DoThree sputum samples for AFB

Collect ≥ 3 sputum specimens 8–24 hours apart (≥ 1 early-morning) for AFB smear and mycobacterial culture, with NAAT on at least one; a positive NAAT generally confirms TB, and culture gives susceptibilities.

03 · GiveRIPE 2 months, then INH + rifampin

Drug-susceptible TB: isoniazid, rifampin, pyrazinamide and ethambutol for a 2-month intensive phase, then isoniazid plus rifampin for a 4-month continuation phase (6 months total). Stop ethambutol once the isolate is pan-susceptible.

Diagnosis & monitoring

Work-up

TST cutoffs: 5, 10, 15 mmRead induration at 48–72 hours. ≥ 5 mm: HIV, recent contact, fibrotic CXR, transplant or immunosuppression; ≥ 10 mm: endemic-country birth, high-risk settings, diabetes, severe kidney disease, drug misuse; ≥ 15 mm: no risk factors.

Ethambutol: check visual acuity and color visionEthambutol causes dose-related optic neuritis — first loss of blue-green color discrimination, then acuity; get baseline visual acuity and color vision and ask about vision monthly.

Hold hepatotoxic TB drugs for ALT riseIsoniazid, pyrazinamide and rifampin are hepatotoxic: interrupt them if ALT exceeds 3× ULN with hepatitis symptoms or jaundice, or 5× ULN without symptoms, then rechallenge one drug at a time.

Do right now

In this order

First moves

Airborne isolation, N95 respirator

→

Three sputum samples for AFB3 sputa, 8–24 h apart

→

Start empiric RIPE when suspicion is high

→

Test every TB patient for HIV

Why each step

Airborne isolation, N95 respiratorPlace suspected pulmonary TB in airborne isolation — a negative-pressure room with 6–12 air changes per hour — and wear a fit-tested N95 (or higher) respirator, not a surgical mask, to enter.

Three sputum samples for AFBCollect ≥ 3 sputum specimens 8–24 hours apart (≥ 1 early-morning) for AFB smear and mycobacterial culture, with NAAT on at least one; a positive NAAT generally confirms TB, and culture gives susceptibilities.

Start empiric RIPE when suspicion is highWith high clinical suspicion — compatible symptoms, exposure and imaging, especially if life-threatening — start the 4-drug regimen promptly without waiting for smear, NAAT or culture results.

Test every TB patient for HIVOnce TB is diagnosed, test for HIV, screen for hepatitis B and C when risk factors exist, and obtain baseline CBC, renal and liver tests.

Management

Orders

Latent TB: 3HP, 4R or 3HR must knowPreferred latent TB regimens are short rifamycin courses: isoniazid plus rifapentine weekly for 3 months (12 doses), rifampin daily for 4 months, or isoniazid plus rifampin daily for 3 months. Exclude active TB first.

4-month rifapentine–moxifloxacin regimen optionFor drug-susceptible pulmonary TB at age 12 or older, a 4-month isoniazid–rifapentine–moxifloxacin–pyrazinamide regimen is a conditional alternative; its trial excluded weight < 40 kg, CNS, bone or miliary TB, and known resistance.

Give pyridoxine with isoniazid to at-risk patientsIsoniazid can cause peripheral neuropathy through pyridoxine depletion; give pyridoxine 25–50 mg daily in pregnancy, breastfeeding, diabetes, HIV, alcohol use disorder, malnutrition, uremia or older age.

Report to public health; consider DOTNotify the health department for contact investigation and treatment support; directly observed (or video-observed) therapy is used especially for HIV, substance use, psychiatric illness, prior failure or drug resistance.

Red flags & don'ts

Avoid harm

Rifampin induces CYP3A4: check every drug interactionRifampin is a potent CYP3A4 inducer that lowers levels of warfarin, oral contraceptives, glucocorticoids, oral hypoglycemics, methadone and many antiretrovirals; rifabutin is substituted when interactions are unacceptable.

The rules

Know these

Cavity plus positive 2-month culture: treat 9 monthsExtend the continuation phase to 7 months (9 months total) when the initial chest radiograph shows cavitation and the sputum culture is still positive after the 2-month intensive phase.

End isolation after 3 negative smearsRelease a hospitalized patient from airborne isolation after 3 negative sputum smears on effective therapy with clinical improvement; at home, transmission precautions usually continue for at least 5 days of effective treatment.

Latent TB infection or active TB?

Commonly confused

Symptoms	None
TST or IGRA	Positive
Chest imaging and sputum	No active disease; sputum not needed
Contagious	No
Treatment	3HP, 4R or 3HR

More detail

Reference

Show 7 reference facts

Reactivation TB classically shows apical or posterior upper-lobe infiltrates, often cavitary; primary TB shows middle or lower infiltrates, hilar adenopathy or effusion. HIV may blunt cavitation and give a normal film.

About 5–15% of immunocompetent people with latent TB develop active disease over a lifetime; untreated HIV raises the risk to roughly 3–16% per year.

MDR-TB is resistance to at least isoniazid and rifampin; rifampin-resistant, fluoroquinolone-susceptible TB is now treated with the 6-month all-oral BPaLM regimen (bedaquiline, pretomanid, linezolid, moxifloxacin) by specialists.

Add glucocorticoids (e.g., dexamethasone) for TB meningitis and TB pericarditis, for acute respiratory failure from TB, and for severe immune reconstitution inflammatory syndrome.

Adult daily doses: isoniazid 5 mg/kg (max 300 mg), rifampin 10 mg/kg (max 600 mg), pyrazinamide 30–40 mg/kg (max 2 g), ethambutol 15–25 mg/kg (max 2.5 g).

Count doses, not calendar time: missed doses extend therapy until the total number of doses for each phase is completed.

Isoniazid raises aminotransferases transiently in up to 20% and causes clinical hepatitis in about 1 in 1000, more often over age 35, with alcohol use, chronic liver disease or postpartum.

Pearl

Latent TB is infection without disease — not contagious; active pulmonary TB spreads by air until effective therapy takes hold.

Sources · Merck Manual Professional — Tuberculosis (TB) · Saukkonen JJ et al. Updates on the Treatment of Drug-Susceptible and Drug-Resistant Tuberculosis: An Official ATS/CDC/ERS/IDSA Clinical Practice Guideline. Am J Respir Crit Care Med 2025 · CDC — Treatment for Latent Tuberculosis Infection (clinical guidance) · CDC — Tuberculin Skin Test (clinical testing guidance) · Saukkonen JJ et al. An Official ATS Statement: Hepatotoxicity of Antituberculosis Therapy. Am J Respir Crit Care Med 2006;174:935–952 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).