Chapter 22: Drug Therapy for Tuberculosis and Mycobacterium avium Complex Disease

Definition and Affected Organs

Tuberculosis (TB) is an infectious disease primarily affecting the lungs, but it can also involve other organs such as lymph nodes, pleurae, bones, joints, kidneys, and the gastrointestinal tract. The causative agents are pathogenic bacilli, notably Mycobacterium tuberculosis, which multiply slowly and may remain dormant for years. These bacteria resist phagocytosis and can develop drug resistance.

• Primary site: Lungs

• Other sites: Lymph nodes, pleurae, bones, joints, kidneys, GI tract

• Pathogenic features: Slow multiplication, dormancy, resistance to phagocytosis, drug resistance

• Example: TB infection in the bones is known as skeletal tuberculosis.

Global Epidemiology

TB remains a major global health concern, with an estimated one-third of the world's population affected and approximately 1.5 million deaths in 2020. Most new cases occur in foreign-born immigrants, and large numbers of people have inactive or latent infections.

• High prevalence: Many parts of the world

• Latent infection: Large numbers with inactive TB

• Contributing factors: Immigration from endemic countries, increasing immunosuppression

Phases of Tuberculosis Initiation and Progression

Four Phases

The initiation and progression of TB can be divided into four distinct phases:

• Transmission: Spread of TB bacilli from person to person

• Primary infection: Initial infection following exposure

• Latent tuberculosis infection (LTBI): Bacilli remain dormant, no symptoms

• Active tuberculosis: Bacilli multiply, symptoms appear

Drug-Resistant Tuberculosis

Types and Causes

Drug-resistant TB is a major public health concern. Resistance develops due to poor patient compliance, mutations, and biologic adaptation. It is especially problematic in immunocompromised patients and those with HIV.

• Multidrug-resistant tuberculosis (MDR-TB): Resistant to most effective medications

• Extensively drug-resistant tuberculosis (XDR-TB): Resistant to second-line medications; no effective drugs for treatment

• Contributing factors: Delayed diagnosis, delayed determination of medication efficacy, lack of adequate diagnostic laboratories

Tuberculosis Control and Prevention

Public Health Strategies

Organizations such as the CDC, ATS, and IDSA emphasize expanded efforts to identify and treat LTBI and control TB among specific populations (children, adolescents, foreign-born persons, HIV-positive individuals, homeless persons, and residents of facilities).

• Identification and treatment: Focus on LTBI and high-risk populations

• Techniques: TB testing, contact tracing, risk assessment, education

Nurses' Role

Nurses play a critical role in TB control, including administering medications, performing and reading TB tests, managing clinics, tracking contacts, and educating patients.

• Directly Observed Therapy (DOT): Healthcare provider observes ingestion of anti-TB medications; mandatory for intermittent dosing and MDR-TB

• Failure to diagnose/treat MDR-TB: Leads to XDR-TB development

Antitubercular Medications

Classification and Use

Antitubercular drugs are classified as primary (first-line) and second-line agents. First-line drugs treat latent, active, and drug-resistant TB when possible. Second-line drugs are used for patients unable to tolerate first-line drugs or infected with resistant bacilli.

• First-line agents: Isoniazid, rifampin, ethambutol, pyrazinamide

• Second-line agents: Used for resistance or intolerance

Treatment of Active Tuberculosis

Adequate drug therapy leads to improvement within 2–3 weeks, with decreased fever and cough, weight gain, and improved well-being. Treatment continues for at least 6 months or 3 months after cultures become negative.

• Sputum cultures: Usually negative within 3–6 months

• Persistent symptoms or positive cultures: May indicate nonadherence or drug resistance; alternate therapy required

Mycobacterium avium Complex (MAC)

Characteristics and Transmission

MAC consists of two similar pathogenic mycobacteria found in water and soil throughout the United States. Transmission occurs by inhalation of infected water droplets. MAC rarely causes disease in immunocompetent individuals.

• Transmission: Inhalation of water droplets

• Human-to-human/animal spread: No evidence

• Risk: Immunocompromised individuals

Goals of Therapy

The primary goals of TB therapy are to cure latent or active infection, avoid development of drug-resistant TB, and minimize transmission. For active infection, therapy aims to decrease symptoms, make the patient noninfectious, and ensure adherence.

• Cure infection

• Prevent drug resistance

• Minimize transmission

• Ensure adherence

General Guidelines for TB Drug Therapy

Principles

Effective TB treatment requires multiple drugs to inhibit emergence of drug-resistant bacilli. The duration of therapy depends on the purpose, extent of disease, adherence, and clinical response. MDR-TB may occur anywhere, especially in AIDS patients, closed environments, and urban areas.

• Multiple drugs: Required for effective treatment

• Duration: Specific to clinical factors

• MDR-TB treatment: More medications, longer therapy, daily administration, DOT

• XDR-TB: Limited treatment options

Strategies to Increase Adherence

Adherence to TB therapy is crucial to prevent resistance and ensure cure. Strategies include short-course regimens, DOT, education, support services, individualized treatment, and continuity of care.

• Short-course regimens

• Directly Observed Therapy (DOT)

• Patient and family education

• Support services

• Individualized regimens

Monitoring Anti-TB Therapy

Clinical Monitoring

All patients require clinical monitoring, including education about adverse effects and regular assessment by healthcare providers. Signs of liver disease should be monitored.

• Adverse effects: Educate patients

• Regular assessment: By healthcare provider

• Liver disease: Monitor for signs

Laboratory Monitoring

Baseline laboratory tests are indicated for patients with possible liver disease, HIV, pregnancy/early postpartum, or alcohol use.

• Baseline labs: Liver function, HIV status, pregnancy, alcohol use

Use in Special Populations

TB drug therapy must be adapted for special populations, including HIV-positive patients, children, older adults, those with abnormal kidney function, hepatic impairment, and those receiving home care.

• HIV-positive patients: Increased risk, drug interactions

• Children: Dosage adjustments

• Older adults: Monitor for adverse effects

• Renal/hepatic impairment: Adjust therapy

• Home care: Support adherence

Signs and Symptoms of Active Tuberculosis

Exposure to TB does not cause symptoms; symptoms appear only in active disease.

• Persistent cough

• Chest pain

• Chills, fever

• Hemoptysis (coughing blood)

• Night sweats

• Weight loss, weakness, anorexia

• Abnormal chest x-ray

• Positive smear/culture

Summary Table: Types of Drug-Resistant Tuberculosis

Summary Table: Phases of Tuberculosis

Summary Table: First-Line and Second-Line Antitubercular Drugs

Key Equations and Concepts

Drug Resistance Mechanism

Drug resistance in TB is often due to genetic mutations in the bacterial genome. The probability of resistance increases with monotherapy and poor adherence.

• Mutation rate: where is the mutation rate per cell division, and is the number of cell divisions.

• Combination therapy: Reduces probability of resistance by targeting multiple pathways.

Duration of Therapy

• Standard duration:

Additional info: The notes have been expanded to include definitions, examples, and tables for clarity and completeness. Drug names and mechanisms are inferred based on standard TB treatment protocols.