Drug Resistant TB

Drug Resistant TB can be MDR or XDR or TDR. TB which is resistant at least to isoniazid and rifampicin the two most powerful first-line anti-TB drugs is called the Multi-drug-resistant tuberculosis (MDR-TB). It develops because the when the course of antibiotics is interrupted and the levels of drug in the body are insufficient to kill 100% of bacteria. This means that even if the patient forgets to take medicine, there are chances of developing MDR-TB.

MDR-TB is treated with secondline of antituberculosis drugs such as a combination of several medicines called SHREZ (Streptomycin+isonicotinyl Hydrazine+ Rifampicin+ Ethambutol+ pyraZinamide)+ MXF+ cycloserine.

When the rate of multidrug resistance in a particular area becomes very high, the control of tuberculosis becomes very difficult. This gives rise to a more serious problem of extensively drug-resistant tuberculosis (XDR-TB). XDR-TB is caused by strains of the disease resistant to both first- and second-line antibiotics. This confirms the urgent need to strengthen TB control. Thus, Extensively-drug resistant TB (XDR-TB) is a sub-set of MDR-TB which is further resistant to at least two more drugs which are second line drugs and is thus virtually incurable. XDR TB was first described in March 2006 following a joint survey of laboratories by the WHO, IUATLD, and CDC, Atlanta.

The new fangled TDR refers to Totally drug-resistant tuberculosis (TDR-TB).

ü It is a form of tuberculosis which is resistant to all currently-used drugs. TDR-TB was first discovered in 2007 in Italy and later in 2009 among a small percentage of patients in a multi-drug-resistant tuberculosis outbreak in Iran but not widely reported until 2012. In January 2012, TDR TB has been reported in India. Thus, India is the second country to have identified this deadly form of the disease after Iran.

TDR-TB is caused as a result of the latest mutation of the bacilli bacteria after Multi-Drug-Resistant TB and Extensively Drug-Resistant TB diagnosed earlier. As is known, none of the known TB combination drugs work on patients infected by the deadly bacteria. The drug resistance develops mainly because patients fail to complete the 6 to 9 months first treatment phase. As the patients feel better within a couple of months of taking the drugs, they stop taking them and as the TB causing bacteria in the body are not completely killed, they tend to multiply.

However, Union health ministry later clarified that it’s not totally drug resistant tuberculosis but XXDR TB that has hit Mumbai. The Ministry officials said that it had been “premature” in labelling 12 patients as TDR-TB patients. XXDR TB stands for extensively drug-resistant TB as against XDR (extremely) and MDR (multi) versions.