Infectious Diseases

Tuberculosis

Clinical overview and exam mastery guide for latent versus active TB, RIPE regimen logic, toxicity monitoring, and resistant TB strategy.

Latent TB
No active disease symptoms
Active TB Core
RIPE initial phase
Major Safety
Hepatotoxicity monitoring
High-Yield Add-on
Pyridoxine with INH

Latent vs Active TB Decision Frame

Latent TB Infection (LTBI) Positive test, no symptoms No active disease signs Active TB Cough > 3 weeks, weight loss Night sweats, hemoptysis Treat latent TB to prevent progression; treat active TB to cure disease and stop transmission Accurate classification determines duration and drug count

1. Types of TB

Latent TB Infection (LTBI)

  • Positive test for TB infection
  • No symptoms
  • No active disease findings

Active TB

  • Cough lasting more than 3 weeks
  • Weight loss and night sweats
  • May include hemoptysis

2. Latent TB Treatment

Goal: prevent progression from latent infection to active disease.

Regimen Dose / Duration Key Safety Points
Isoniazid (INH) 300 mg orally daily for 6 to 9 months
Alternative: 900 mg weekly with rifapentine (DOT)		 Hepatotoxicity, peripheral neuropathy; add pyridoxine 25 to 50 mg daily
Rifampin 600 mg orally daily for 4 months Useful when INH not tolerated; drug interactions via CYP induction
Baseline LFTs are especially important in higher-risk patients.

3. Active TB Treatment (RIPE)

Initial phase: 2 months Continuation: 4 months Standard total: 6 months
Drug Dose MOA High-Yield Toxicities / Notes
Isoniazid (INH) 5 mg/kg daily (max 300 mg daily) Inhibits mycolic acid synthesis Hepatitis, peripheral neuropathy; always add pyridoxine
Rifampin 10 mg/kg daily (max 600 mg daily) Inhibits RNA polymerase Hepatotoxicity, orange body fluids, strong CYP450 inducer, lowers OCP effectiveness
Pyrazinamide 20 to 25 mg/kg daily Disrupts mycobacterial membrane metabolism Hepatotoxicity, hyperuricemia, gout risk
Ethambutol 15 to 20 mg/kg daily Inhibits cell wall synthesis Optic neuritis, red-green color vision changes; baseline vision testing needed

4. Monitoring During Active TB

Laboratory and Clinical Monitoring

  • Monthly LFTs if high risk
  • Uric acid monitoring with pyrazinamide when indicated
  • Evaluate adherence and adverse effects at each follow-up

Targeted Safety Checks

  • Baseline and follow-up vision for ethambutol
  • Stop or adjust therapy if severe hepatitis is suspected

5. Drug-Resistant TB (Brief Overview)

  • MDR-TB: resistance to at least INH and rifampin
  • Common second-line components: fluoroquinolones, linezolid, bedaquiline
  • Treatment duration often extends to 18 to 24 months

6. Important Counseling Points

  • Strict adherence is critical; do not skip doses
  • Orange urine/tears with rifampin is expected
  • Use backup contraception due to rifampin interaction with OCPs
  • Report visual changes, severe fatigue, jaundice, or persistent nausea promptly

TB Treatment Phase Flow

Latent TB pathway INH 6-9 months or rifampin 4 months Active TB initial phase RIPE for 2 months Continuation phase INH + rifampin for 4 months Always combine INH with pyridoxine and monitor for toxicity Adjust regimen based on susceptibility and tolerability

Management Recap Drill

Latent TB: INH 6 to 9 months OR rifampin 4 months.
↓
Active TB: RIPE for 2 months, then INH + rifampin for 4 months.
↓
Always: add vitamin B6 with INH and monitor safety.

Guideline References (Management)

CDC Tuberculosis Guidance

https://www.cdc.gov/tb

WHO Tuberculosis Guidance

WHO TB Programme
Local policy and susceptibility data should guide final regimen choices.

7. Common Exam Traps

Rifampin induces CYP450 and can reduce oral contraceptive effectiveness.
Ethambutol can cause optic neuritis and red-green vision changes.
Pyrazinamide can raise uric acid and trigger gout.
INH should be paired with pyridoxine to reduce neuropathy risk.
Standard drug-susceptible active TB is RIPE-based with a 6-month total course.

8. Quick Revision Summary

Must Remember

  • Latent TB is not the same as active disease
  • RIPE is the standard initial active TB regimen
  • Hepatotoxicity risk exists with INH, rifampin, and pyrazinamide
  • Vitamin B6 supplementation is routine with INH

High-Yield Subtopics

  • LTBI regimen selection
  • RIPE phase timing and doses
  • Drug-specific toxicities and interactions
  • MDR-TB overview and duration

Practice Questions

1) What are two key differences between latent and active TB?

Answer: Latent TB has no active disease symptoms and no contagious pulmonary disease, while active TB has clinical disease (for example cough and constitutional symptoms) and requires multi-drug treatment.

2) Why is pyridoxine co-prescribed with INH?

Answer: To reduce INH-associated peripheral neuropathy risk.

3) Which RIPE drug is most associated with optic neuritis?

Answer: Ethambutol.

4) What major interaction should be remembered with rifampin?

Answer: Strong CYP450 induction, including reduced hormonal contraceptive effectiveness.

5) What defines MDR-TB in this overview?

Answer: Resistance to at least isoniazid and rifampin.