Chapter 46: Antitubercular Drugs – TB Treatment & Prevention

tuberculosis (MTB). MTB is characterized as an aerobic, rod-shaped bacillus that typically leads to the formation of granulomas, most frequently affecting the lungs due to the organism’s high oxygen requirement. Treating TB is complicated because the slow metabolic rate of the tubercle bacilli makes them less susceptible to cell-killing medications, necessitating prolonged, highly adherent, and often multi-drug therapy regimens. The diagnostic sequence for TB begins with screening, typically using the tuberculin skin test or the more specific interferon gamma release assays (IGRAs), followed by a chest X-ray, and confirmation via culture of sputum specimens. Global TB control efforts face significant challenges due to the increasing prevalence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB). The treatment protocol is divided into an initial intensive phase and a continuation phase, requiring a minimum of two effective drugs throughout to prevent resistance. Standard initial treatment for active TB in Canada uses a four-drug combination of first-line agents: isoniazid (INH), rifampin (RMP), pyrazinamide (PZA), and ethambutol (EMB). These medications target the mycobacteria through diverse mechanisms, including inhibiting protein synthesis or disrupting cell wall integrity. Nursing care emphasizes strict patient adherence, often monitored via directly observed treatment (DOT), and careful assessment for adverse effects. Isoniazid, a primary drug, is associated with hepatotoxicity and peripheral neuropathy, which is mitigated by concurrent use of pyridoxine (Vitamin B6) supplementation. Rifampin, the most potent drug in its class, is notable for causing a harmless but prominent red–orange–brown discoloration of all bodily fluids and acting as a potent enzyme inducer, rendering oral contraceptives ineffective. Other important toxicities include optic neuritis and potential blindness with ethambutol, and ototoxicity and nephrotoxicity with second-line injectable agents like streptomycin. Successful therapy is measured by the patient's clinical improvement, such as reduced cough and fever, alongside positive changes in laboratory and radiological findings.