December 5, 2012
Tuberculosis (TB) can be effectively treated with combinations of oral antibiotics. The drugs for first-line treatment of TB include the following:
Additional first-line agents include the following:
Resistance to therapy is an important issue in TB treatment for the following reasons:
Shortly after the introduction of antibiotics in the 1950s, TB-causing bacteria began to develop resistance to one or more agents. Infection with drug-resistant TB bacteria can have serious consequences for affected people. Not only do regimens become more complex and expensive, but also the risk of death increases. For instance, researchers from Quebec have found that resistance to the antibiotic pyrazinamide is associated with an increased risk of death. Researchers with the U.S. Centers for Disease Control and Prevention (CDC) have found that people who have TB that is resistant to rifampin or rifabutin are also at increased risk of death.
Today, in such cases of drug-resistant TB, agents for second-line therapy are available. However, drugs used in second-line therapy are generally more toxic, may need to be injected and are less effective than first-line agents. Examples of drugs used for second-line therapy include the following:
Strains of TB-causing bacteria that are resistant to two or more antibiotics are called multiple drug resistant (MDR-TB). In such cases, third-line agents are used, which include antibiotics such as linezolid (Zyvox, Zyvoxam), clofazimine and clarithromycin. They have not generally been tested in large clinical trials for the treatment of TB. Several drugs are being developed for the treatment of TB.
Strains of TB-causing bacteria that are resistant to at least isoniazid and rifampin, and at least moxifloxacin or levofloxacin and at least one second-line injectable antibiotic are called extremely drug-resistant (XDR-TB). Such strains of TB are very hard to treat and require prolonged courses of antibiotics.
Researchers at the CDC have reviewed data whereby fluid samples from TB patients were grown (or cultured) in labs to assess their potential for resisting antibiotics. The CDC review encompassed tests that were done across the U.S. between 1993 and 2008, using samples from 222,897 people with TB and focusing on test results from 14,770 people who had resistance testing before and at the end of therapy.
Key results were as follows:
Statistical analysis found that participants who became resistant to second-line injectable antibiotics while on treatment were likely to have the following profile:
There were 32 people who became resistant to ofloxacin, nine of whom were HIV positive. The only risk factor found for developing this problem was having MDR-TB when initial resistance testing was done.
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