Multidrug-resistant TB (MDR-TB) begins when an antibiotic fails to eradicate all the bacteria that it targets, with the surviving bacteria producing resistance to that antibiotic and usually others at the same time. Primary Multidrug resistant, MDR-TB occurs in patients who was not earlier been infected with TB but who became infected with a strain which is resistant to the treatment. Acquired multidrug resistance for TB occurs in patients during treatment with a drug regimen that is not competent of killing the particular strain of TB with which they have been infected. MDR-TB requires treatment with second-line drugs, often four or more anti-TB drugs for a minimum of 6 months and a maximum for 18–24 months, if rifampin resistance has been identified in the specific strain of TB with which the patient has been infected. Under ideal program conditions, MDR-TB cure rates can approach 70%. In general, second-line drugs are less effective, more toxic and much more expensive than first-line drugs.