Tuberculosis (TB) is an infectious disease caused by a
bacterium, most commonly
Mycobacterium tuberculosis. It affects
tissues in the human body, mainly the lungs
(pulmonary tuberculosis). It causes small
tumors that destroy the tissue.
Symptoms include cough, fatigue, weight loss, difficulty breathing, and fever.
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Tuberculosis is treated using a strict regimen of antibiotics. It requires
long treatment periods (more than 6 months) to completely eliminate the
bacteria. TB is often treated with a combination of several antibiotics taken at
the same time, which reduces the risk of the bacteria developing a
resistance to
antibiotics.
Treatment is initially made using the so-called “first line”
drugs. The most common first line drugs are isoniazid and rifampicin, and others
are ethambutol, pyrazinamide and streptomycin. If the disease becomes resistant
to those first line drugs, namely if it is resistant to both rifampicin and
isoniazid, it is referred to as
“multidrug-resistant tuberculosis” (MDR-TB),
and requires the use of second-line drugs.
"Second line" because they are less effective or have more
toxic side-effects. There are six classes of second-line drugs, each composed of
a number of different antibiotics. If resistance develops toward one of the drug
in a particular class, it usually means that the other drugs in that class will
also become ineffective. When tuberculosis develops resistance to any of the
drugs in the fluoroquinolones class, and to any one of the second-line anti-TB
injectable drugs (Amikacin, Kanamycin or Capreomycin), then it is refered to as
“extensively drug-resistant tuberculosis”
(XDR-TB).