<prompt> Multi drug resistant T.B is defined as resistance toINH and pyrizinamideINH and RifampicinRifampicin and PyrizinamideResistance to all first line of drugs  <response>: multidrug-resistant TB MDR-TB--a form of the disease caused by bacilli resistant at least to isoniazid and rifampin--occurred in 2013. Ref Harrison 19th edition pg 1103 