Macrolides and host defences to respiratory tract pathogens.

An ever-expanding list of macrolides is being developed for therapeutic use. In addition to their direct antimicrobial action, it is being increasingly recognized that these drugs exhibit some degree of immunomodulatory capacity. Some are able to affect polymorphonuclear (PMN) leukocytes, chemotaxis (josamycin, roxithromycin) or respiratory burst (roxithromycin), accumulate within the phagocytic cell (all drugs to a greater or lesser extent) and exhibit intracellular bioactivity (erythromycin, josamycin, roxithromycin). Some of the newer macrolides (rokitamycin and clarithromycin) have not yet been tested in this respect. Nor have the in-vitro effects of the drugs been demonstrated in vivo although indirectly it is well recognized that many of the macrolides are clinically efficacious in the treatment of respiratory tract infections.