In the continuing evolution of bacteria in response to our antibiotics, investigators have identified a strain of Mycobacterium tuberculosis, the cause of TB, that is resistant to all known anti-TB drugs, in India. It is known as TDR for Totally Drug Resistant tuberculosis. This is not a new development, since TDR TB organisms have been found in Italy in 2007 and in Iran in 2009, but it does make one pay attention to this ominous situation.
TDR tuberculosis is the natural progression from Multi-Drug Resistant (MDR) and Extensively Drug Resistant (XDR) tuberculosis. The World Health Organization says that XDR-TB is present in at least in 58 countries, with an estimated 25,000 cases occurring each year. It is critical to identify people who are infected with these drug resistant bacteria, since they are contagious and can spread the infection to many other people if diagnosis is delayed. In addition, having these infected people take the usual anti-TB drugs is useless, as they will not work in this clinical situation. Specific combinations of second and third line drugs, often with significant toxicities (which is one reason they are not used as first line therapy) must be used, requiring participation of specialists familiar with the treatment of these hard to treat infections.
Possibly because tuberculosis has been a problem primarily in the developing world, where expensive drugs are not affordable, there has been relatively little research being done to identify new anti-TB drugs. There have been no new first line drugs introduced for the treatment of TB for over 50 years. However, one of the later generation fluoroquinolones, moxifloxacin, has been identified as a potent and very useful agent for the use in people infected with tuberculosis susceptible to the drug. This is both good news and bad news. The bad news is the use of moxifloxacin (and other fluoroquinolones) in many patients with pneumonia of unknown cause. If the person actually has tuberculosis and not the garden variety of community acquired pneumonia, then they are effectively being treated with only one drug for tuberculosis. Single drug therapy for tuberculosis is guaranteed to result in the development of resistance. Moreover, for a short period of time, the person with tuberculosis and not just simple bacterial pneumonia may clinically improve, since the fluoroquinolones (including levofloxacin) are so active against the organisms. However, once resistance develops the pneumonia and symptoms return and the disease marches on until a correct diagnosis is made. When cough and other symptoms worsen, the ill person’s contacts are exposed to the new mutant bacteria, now resistant to the antibiotic and the disease now spreads well beyond the initial index case.
In this era of easy global travel, what happens on the other side of the world today, can easily happen in our area tomorrow. This is no time to be complacent.
Posted by DrSugar on 01/17/2012 at 3:38 PM