Tuberculosis is an infectious disease that most commonly affects the pulmonary system. It is highly contagious and spread by individuals with active tuberculosis disease. Symptoms of active tuberculosis include chronic cough, chest pain and sometimes the coughing up of blood. Most people who are infected with tuberculosis mycobacteria do not develop active disease but do have a latent tuberculosis infection.
Description of Latent Tuberculosis
Persons with latent tuberculosis do not display symptoms of active tuberculosis disease but have either had past episodes of tuberculosis or have been recently exposed and infected with tuberculosis mycobacteria. The initiation of treatment for individuals with latent tuberculosis is primarily dependent on whether they are immune compromised or at high risk for developing the disease. The Centers for Disease Control and Prevention report that people who are at high risk for developing active tuberculosis include those who have had active tuberculosis in the past, are HIV positive, are on immunosuppressive drugs, are diabetic, or have cancer or chronic renal failure. Additionally, recent immigrants from countries with a high prevalence of tuberculosis, health care workers, and intravenous drug users are at high risk for developing tuberculosis after exposure.
Tuberculin Testing
Latent tuberculosis is diagnosed by the tuberculin skin test. In this test proteins collected from tuberculosis mycobacteria cultures are injected subcutaneously. The injection site is evaluated for its immune response after 48 to 72 hours. The size of induration, or hardening of the skin, at the test site determines whether the person has been exposed and infected with tuberculosis mycobacteria. If the test is positive or the person is at high risk for developing tuberculosis the CDC recommends one of four different treatment regimens. However, the diagnosis of active tuberculosis should be ruled out before initiating treatment. This can be done by physical examination, an evaluation of a chest x-ray and bacteriologic studies, when possible.
Nine Month Isoniazid Regimen
The CDC-preferred treatment for latent tuberculosis is daily administration of isoniazid for nine months. An acceptable alternative isoniazid regimen is twice weekly dosing for nine months. This treatment regimen is also recommended for adolescents and children. Isoniazid is an antibacterial drug that prevents the growth of tuberculosis mycobacteria. The Food and Drug Administration official label for isoniazid warns that it may cause liver damage that could be fatal. The occurrence of liver damage is age-related. The FDA recommends people who have liver damage attributed to isoniazid treatment be treated with alternative drugs to treat tuberculosis. Other side effects of isoniazid treatment include nerve damage, nausea, diarrhea, blood disorders, skin hypersensitivity, hyperglycemia, metabolic acidosis and immune system dysfunction.
Six Month Isoniazid Regimen
The CDC reports that six month treatment with isoniazid was effective in clinical trials, but it was not as effective as a 12 month treatment regimen. The six month isoniazid treatment regimen is an acceptable alternative for the treatment of latent tuberculosis infection. The daily treatment for six months may also be reduced to twice weekly administration and still be considered acceptable.
Two Month Rifampin/Pyrazinamide Regimen
Another acceptable alternative treatment regimen for latent tuberculosis infection is the daily administration of rifampin and pyrazinamide. In this case the frequency of treatment may again be reduced to twice weekly, but only when other treatment regimens cannot be offered or tolerated. Rifampin and pyrazinamide are also anti-bacterial drugs that kill and prevent the growth of tuberculosis mycobacteria. The National Library of Medicine reports that rifampin may also cause liver toxicity. Other side effects of rifampin include gastrointestinal disorders, headache, fever fatigue, numbness and more rarely blood disorders, renal toxicity, skin hypersensitivity and muscular weakness. The FDA official label for pyrazinamide warns that this drug may additionally cause adverse liver effects and recommends that people with liver dysfunction be closely monitored. Other side effects of pyrazinamide include gout, gastrointestinal disturbances, muscle and joint pain and, more rarely, blood disorders and skin hypersensitivity.
Four Month Rifampin Regimen
The last CDC-recommended acceptable alternative regimen for the treatment of latent tuberculosis is daily administration of rifampin for four months.
