Tuberculosis
Introduction
Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis and is transmitted primarily by inhalation.
- After primary infection, 90% of individuals with intact immunity control further replication control of the bacilli, which may then be cleared or enter a "latent" phase. The person remains asymptomatic, but latent disease has the potential to become active at any time.
- The remaining 10% of individuals develop progressive to primary tuberculosis. It most commonly affects the lungs, although it can affect other parts of the body.
NOTE: In general, individuals with pulmonary and laryngeal TB are infectious (higher risk if sputum smear is positive), whereas those with extrapulmonary TB are regarded as non-infectious.
Clinical Presentation
Pulmonary TB is characterized by its slow onset and initial mild symptoms. The cough is chronic in nature and sputum production can vary from mild to severe with associated haemoptysis. Other symptoms of the condition are malaise, fever, night sweats and weight loss. However, not all patients will experience all symptoms.
On the other hand, symptoms and signs due to extrapulmonary TB vary according to the organs involved and may be non-specific.
Diagnostic Tools
- Chest X-ray
- Sputum acid-fast bacilli (AFB) smear
- Nuclear acid amplification testing (NAA)
- Tuberculin skin test (Mantoux test or TST)
- Interferon-γ release assay (IGRA)
First Line Treatment
Presently, six-month regimen consisting of 2 months of daily EHRZ (intensive phase), followed by 4 months of daily HR (maintenance phase) is recommended for newly diagnosed pulmonary TB.
- Rifampicin and isoniazid should be taken with an empty stomach to have better absorption.
WHO recommends the use of fixed-dose combination (e.g. Akurit-4 and Akurit-2) over separate drug formulations in the treatment of patients with drug-susceptible tuberculosis.
NOTE: Multiples of 18
NOTE: The currently available adult anti-TB fixed dose combination tablet is not suitable for use in children <25 kg.
NOTE: Based on WHO operational handbook on tuberculosis, 2022, the upper limit of ethambutol in adult is 25 mg/kg, but daily maximum dose remains 1600 mg.
NOTE: Medication dose requires recalculation every 2 to 4 weeks as children gain weight rapidly, particularly in neonates and young children.
On the other hand, all extrapulmonary TB should be treated with anti-TB for a minimum of 6 months except for bone (including spine) and joint tuberculosis for 6-9 months and tuberculosis for 9-12 months.
Renal Impairment
The clearance of ethambutol and pyrazinamide metabolites are impaired in patients with chronic renal failure when their creatinine clearance falls below 30 ml/min. Hence, thrice weekly dosing is recommended in international guidelines.
Conversely, rifampicin and isoniazid do not require dose adjustment in renal failure as they are metabolized by the liver.
Drug Counselling
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