Influence of metabolized clarithromycin, M-1 (A), M-4 (B) and M-5 (C) on NO production from NPFs in response to LPS stimulation. NPFs at a concentration of 5 × 105 cell/ml were stimulated with 1.0 μg/ml LPS in the presence of various concentrations of the agents. After 24 hours, culture supernatants were obtained and NO (NO2-/NO3-) levels were assayed by the Griess method. Data are the mean ± SE of five different subjects. NO, nitric oxide; NPFs, nasal polyp fibroblasts; LPS, lipopolysaccharide; NS, not significant (P > 0.05).