Rifazid 300 +Z is a combination of three medicines: Isoniazid, Pyrazinamide and Rifampicin which treat tuberculosis. Isoniazid prevents the TB bacteria from forming their own protective covering while Rifampicin works by inactivating a bacterial enzyme (RNA-polymerase) which is required by these bacteria to make essential proteins and to reproduce. Together, they kill the bacteria and eradicate the infection. Pyrazinamide, on the other hand works by slowing the growth of these bacteria.