7.5 Introduction to Tuberculosis and Antitubercular Drugs

Tuberculosis, a bacterial infection primarily affecting the lungs, poses a significant global health challenge. Understanding its pathophysiology and diagnostic methods is crucial for effective management. This section explores how TB spreads, its symptoms, and various tests used for diagnosis.

Antitubercular drugs play a vital role in treating TB, with first-line and second-line options available. We'll examine these medications, their mechanisms of action, and potential side effects. Nursing considerations and patient education are key to ensuring successful treatment outcomes.

Tuberculosis Pathophysiology and Diagnosis

Pathophysiology of tuberculosis

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• Tuberculosis (TB) caused by Mycobacterium tuberculosis bacteria
  • Spreads through inhalation of airborne droplets from infected person (coughing, sneezing)
• M. tuberculosis primarily infects lungs (pulmonary TB)
  • Can spread to other organs (extrapulmonary TB) (lymph nodes, bones, meninges)
• Bacteria engulfed by immune cells (macrophages) but survive within them
  • Leads to formation of granulomas containing bacteria
  • Granulomas can rupture releasing bacteria causing tissue damage and spread of infection
• Active TB manifests with chronic cough >2-3 weeks
  • Hemoptysis (coughing up blood)
  • Fever night sweats weight loss
  • Chest pain shortness of breath (dyspnea)
• Latent tuberculosis infection (LTBI) occurs when individuals are infected but asymptomatic and not contagious

Diagnostic methods for tuberculosis

• Tuberculin skin test (TST) or purified protein derivative (PPD) test
  • Intradermal injection of TB antigens
  • Positive result indicates TB exposure but not necessarily active disease
• Interferon-gamma release assays (IGRAs)
  • Blood tests measuring immune response to TB antigens
  • More specific than TST less affected by prior BCG vaccination
• Chest X-ray shows characteristic findings of TB
  • Cavities or infiltrates in upper lung lobes
• Sputum smear microscopy and culture
  • Acid-fast bacilli (AFB) staining of sputum samples
  • Culture is gold standard for diagnosing active TB
• Nucleic acid amplification tests (NAATs)
  • Rapid molecular tests detecting M. tuberculosis DNA
  • Used for early detection and identifying drug resistance

Antitubercular Drugs and Treatment

Classes of antitubercular drugs

• First-line drugs:
  • Isoniazid (INH) inhibits mycolic acid synthesis disrupting bacterial cell wall
  • Rifampin (RIF) inhibits bacterial RNA polymerase blocking transcription
  • Pyrazinamide (PZA) disrupts bacterial membrane potential and transport
  • Ethambutol (EMB) inhibits arabinosyl transferase disrupting cell wall synthesis
• Second-line drugs:
  • Fluoroquinolones (levofloxacin, moxifloxacin) inhibit bacterial DNA gyrase and topoisomerase IV
  • Aminoglycosides (amikacin, kanamycin) inhibit bacterial protein synthesis
  • Capreomycin inhibits bacterial protein synthesis
  • Ethionamide inhibits mycolic acid synthesis similar to INH
  • Cycloserine inhibits bacterial cell wall synthesis

Side effects of antitubercular medications

• Isoniazid (INH)
  • Hepatotoxicity peripheral neuropathy drug-induced lupus
  • Interacts with phenytoin carbamazepine warfarin
• Rifampin (RIF)
  • Hepatotoxicity orange discoloration of bodily fluids flu-like symptoms
  • Potent inducer of cytochrome P450 enzymes leading to numerous drug interactions
• Pyrazinamide (PZA)
  • Hepatotoxicity hyperuricemia arthralgia
• Ethambutol (EMB)
  • Optic neuritis color vision changes
• Second-line drugs
  • Fluoroquinolones cause QT prolongation tendinopathy CNS effects
  • Aminoglycosides cause ototoxicity nephrotoxicity
  • Ethionamide causes GI disturbances hypothyroidism

Nursing considerations for antitubercular drugs

• Assess for contraindications and precautions before starting therapy
• Monitor for signs of hepatotoxicity (jaundice, abdominal pain, fatigue)
  • Get baseline and periodic liver function tests
• Educate patients on importance of adherence to full treatment course
• Watch for adverse reactions and promptly report them
• Give medications with food to minimize GI upset except rifampin
• Encourage patients to avoid alcohol during treatment
• Monitor for drug interactions and adjust medications as needed
• Ensure proper infection control measures to prevent transmission
• Implement directly observed therapy (DOT) to improve adherence and treatment outcomes

Patient education for tuberculosis treatment

• Stress importance of completing full treatment course even if symptoms improve
• Educate on common side effects of antitubercular drugs and when to seek medical attention
• Instruct to avoid alcohol during treatment
• Advise to inform all healthcare providers about TB treatment to avoid drug interactions
• Teach proper cough hygiene and infection control measures to prevent TB spread
• Encourage healthy lifestyle with balanced diet and adequate rest to support recovery
• Emphasize importance of regular follow-up visits and adherence to prescribed regimen

First-line vs second-line antitubercular drugs

• First-line drugs
  • Used for initial treatment of drug-susceptible TB
  • Combination of isoniazid rifampin pyrazinamide ethambutol for 2 months then isoniazid rifampin for 4 months
  • Generally well-tolerated but can cause significant side effects
  • Limitations: development of drug resistance potential for drug interactions
• Second-line drugs
  • Used for drug-resistant TB or when first-line drugs cannot be used due to side effects or contraindications
  • Regimens are longer (18-24 months) and more complex often involving multiple drugs
  • Generally less effective and more toxic than first-line drugs
  • Limitations: higher rates of adverse reactions increased cost longer treatment duration

Global TB Control and Prevention

• World Health Organization (WHO) leads global efforts to eliminate TB
• Multidrug-resistant tuberculosis (MDR-TB) poses significant challenge to TB control
• Bacille Calmette-Guérin (BCG) vaccine used in many countries to prevent severe forms of TB in children
• Emphasis on early detection, proper treatment, and infection control measures to reduce TB transmission