Evaluation of the immunomodulatory effects of the macrolide antibiotic, clarithromycin, in female B6C3F1 mice: A 28-day oral gavage study

The macrolide antibiotic, clarithromycin, is used extensively to treat bact erial infections associated with pneumonia, duodenal ulcers, and the advanc ed stages of human immunodeficiency viral (HIV) infection. In addition to i ts antimicrobial properties, several studies have indicated that clarithrom ycin also has anti-inflammatory and immunomodulatory properties. In this st udy, clarithromycin's immunomodulatory properties were evaluated using fema le B6C3F1 mice and a panel of immune assays that were designed to evaluate potential changes in innate, and acquired cellular and humoral immune respo nses. Female B6C3F1 mice were treated daily by gavage with clarithromycin ( 0, 125. 250, and 500 mg/kg) for 28 days then evaluated for immunomodulation . Minimal immunological changes were observed after 28 days of treatment. A slight increase in the number of spleen antibody-forming cells was observe d at the 250 mg/kg treatment level, but not at other doses. Serum IgM level s were unaffected by the clarithromycin treatment. A significant increase i n the number of splenic macrophages was also observed in mice treated with 125 mg/kg of clarithromycin, but this increase was not observed at the othe r treatment levels. Innate and cell-mediated immunity, as measured by natur al killer cell activity, and mixed leukocyte and cytotoxic T cell response, respectively, were unchanged following treatment with clarithromycin. Thes e results suggest that the immune system is not a target for clarithromycin at doses of 500 mg/kg or below.