Edito ria l C OMBINED THERAPY IN PRINCIPLE AND PRACTICE FOR THE C ONTROL OF DAPSONE RESIST ANCE The widespread emergence of dapsone-resistant strains of Mycobacterium leprae in patients with lepromatous leprosy who had been treated with dapsone

The widespread emergence of dapsone-resistant strains of Mycobacterium leprae in patients with lepromatous leprosy who had been treated with dapsone as monotherapy, is now fully accepted (WHO, 1 977). This growing problem of acquired (secondary) dapsone resistance among the large pool of dapsone­ treated lepromatous patients at risk, could be still more foreboding with the recent reports of new and previously untreated lepromatous patients presenting de novo with dapsone resistance (primary resistance) in known are as with secondary dapsone resistance (Pearson et aI., 1 9 7 7 ; J acobson, 1 977). While it was anticipated that cases of primary dapsone resistance would be likely to occur eventually, once secondary resistance was proven, these reports substantiate our worst fears and establish that dapsone-resistant strains of M. leprae are infectious for man. Although the cases reported had lepromatous type leprosy all types will present with primary dapsone-resistant infections. In fact a proven case of primary, dapsone resistance presenting as tuberculoid leprosy is reported by Waters and colleagues on page 1 27. Therefore alternative drugs are already required for treatment of the very substantial numbers of relapsed lepromatous patients with acquired dapsone resistance ; if primary dapsone resistance should reach serious proportions, alternative drugs will also be required for tuberculoid as well as lepromatous patients and then the future use of dapsone would be uncertain. Any significant spread of primary dapsone resistance would be catastrophic for the control of leprosy, because there is no sure way Df distinguishing in the field a dapsone-sensitive infection from a dapsone-resistant one, and therefore all new cases would require additional alternative drugs even if dapsone was given in combination. (While only the mouse footpad technique can identify a dapsone-resistant strain of M. leprae, the test takes at least 6 months, and can only be applied to bacilliferous patients. Hence the technique would not be universally applicable for identifying primary dapsone, since no tuberculoid patients could be tested and treatment of the lepromatous patients would have had to be initiated long before results were available from the mouse test.) N ow the existence of sec ' ondary dapsone resistance is proven and its seriousness appreciated, it is, clear from the discussions above that unless therapeutic regimens are rapidly introduced to diminish the emergence of secondary resistance and the chances of the spread of prirnary resistance, the whole future" of the control and treatment of leprosy by chemotherapy, including dapsone, will be in jeopardy. Therefore it is essential to introduce urgently other available anti-leprosy