Reappraisal of the activity of morphazinamide against M. tuberculosis

Morphazinamide was shown to have an in vitro activity similar to an equimolar concentration of pyrazinamide. This activity was not due, as had been previously assumed, to pyrazinamide formed by hydrolysis from morphazinamide, since it was demonstrated in slide cultures containing tubercle bacilli which were incubated with freshly prepared dilutions of morphazinamide in acid medium for several successive periods of only 1 hour, during which time little hydrolysis occurred. A new method was used for measuring morphazinamide and pyrazinamide separately in plasma. In man, the estimated in vitro antibacterial activity was similar after approximately equimolar oral doses of morphazinamide or pyrazinamide. However, it is uncertain whether the in vivo activity of morphazinamide is the same as its in vitro activity.