The ability of the tubercle bacillus to remain dormant but viable and capable of causing disease is a major therapeutic challenge. The mycobacteria are slow-growing intracellular organisms that require the administration of a combination of drugs for extended periods to achieve effective therapy and to prevent the emergence of resistance. The risk of adverse reactions therefore must be a major consideration in drug selection.
The three basic concepts in tuberculosis treatment are as follows: (1) Regimens must contain multiple drugs to which the organism is susceptible. (2) Drugs must be taken regularly. (3) Drug therapy must con tinue for a sufficient time. Traditionally, antituberculosis drugs that are classified as first-line drugs are superior in efficacy and possess an acceptable degree of toxicity. These agents include isoniazid, rifampin, pyrazinamide, ethambutol, and streptomycin. Most patients with tuberculosis can be treated successfully with these drugs.
Second-line drugs are more toxic and less effective, and they are indicated only when the M. tuberculosis organisms are resistant to the first-line agents. Therapy with second-line agents may have to be prolonged beyond the standard period of treatment, depending on the clinical, radiographic, and microbiological response to therapy. The second-line agents include cycloserine, ethionamide, aminosalicylic acid, rifabutin, quinolones, capreomycin, viomycin, and thiacetazone.
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