UPTAKE OF AZITHROMYCIN BY VARIOUS CELLS AND ITS INTRACELLULAR ACTIVITY UNDER IN-VIVO CONDITIONS

The concentrations of azithromycin in polymorphonuclear leukocytes (PM NLs), monocytes, erythrocytes, and plasma were measured in six healthy volunteers after the last treatment of a 3-day regimen of 500 mg once daily, Marked enrichment of azithromycin was found in PMNLs and monoc ytes. The drug concentrations after the last dose amounted to 114 +/- 43 (mean +/- standard deviation) mg/liter at 12 h in PMNLs and 34 +/- 17 mg/liter at 6 h in monocytes, Fourteen days thereafter, azithromyci n was still detectable in the PMNLs at 53 +/- 34 mg/liter and in the m onocytes at 1 +/- 2 mg/liter, although the drug was no longer detectab le in plasma (<0.02 mg/liter), Maximum drug concentrations for azithro mycin in plasma (0.40 +/- 0.30 mg/liter) and erythrocytes (0.15 +/- 0. 05 mg/liter) at 3 h after the last administration were much lower and occurred earlier than those observed in the phagocytic cells, The mean enrichment factors (cellular/extracellular ratios) of azithromycin in phagocytes relative to plasma came to 231 +/- 150 and 3,924 +/- 584 a t 3 and 120 h, respectively, for PMNLs and 83 +/- 55 and 523 +/- 255 a t 3 and 120 h for monocytes, respectively, after the last dose, The ph agocytosis tests with PMNLs separated from the blood of volunteers at various times after the last treatment confirmed the enhanced intracel lular activity of these cells against staphylococci.