Effect of Ro 23-6240 on sensitive and resistant intracellular mycobacteria

The activity of Ro 23-6240 and rifampicin against intracellular Mycobacterium fortuitum and Mycobacterium chelonei was assessed in vitro over a 48-hour period. Both agents, at an extracellular concentration of 2.0 mg/l (Ro 23-6240) and 1.0 mg/l (rifampicin), produced a significant intracellular killing of the sensitive Mycobacterium fortuitum at both 20 and 48 hours. However, neither agent was effective against the resistant Mycobacterium chelonei. It was concluded that Ro 23-6240 has a direct antimicrobial effect against sensitive intracellular mycobacteria.