Immunostimulation by clarithromycin in healthy volunteers and chronic bronchitis patients

The immune response to infecting pathogens may be either enhanced or depressed by therapeutic antimicrobial agents. Some macrolides have been shown to enhance aspects of the immune response. This study evaluates the effects of clarithromycin, a new broad-spectrum macrolide antibiotic, on leukocyte function in both healthy volunteers (single 500 mg dose) and chronic bronchitis patients (500 mg b.i.d.) by testing blood samples collected at baseline and at 2, 4, 8 and 12 hours after clarithromycin administration. Clarithromycin did not affect leukocyte chemotaxis but did significantly increase (P < 0.01) phagocytosis (both frequency and index), intracellular killing and natural killer activity, in healthy volunteers. In patients, clarithromycin enhanced phagocytosis frequency, index and intracellular killing. Clarithromycin appears to enhance the human immune response; the mechanism, pharmacodynamics, and clinical significance of this enhancement remain unknown.