Objectives: Fluoroquinolones and tetracyclines inhibit subgingival bacterial pathogens and are useful adjuncts in periodontal therapy. Through mechanisms that remain unclear, both types of antimicrobial agents attain higher levels in gingival fluid than in serum. We hypothesized that gingival fibroblasts possess active transporters that accumulate ciprofloxacin and minocycline in the gingiva. This hypothesis was tested with cultured fibroblasts obtained from human gingival explants.

Methods: Since both agents are fluorescent, transport was assayed by measuring cell-associated fluorescence. Intracellular volume was determined from the radioactivity associated with cells incubated with [3H]-water. Lineweaver-Burk analysis was used to determine the Km and Vmax of transport.

Results: The transport of both agents was saturable and their kinetics obeyed the Michaelis-Menten equation. Fibroblasts transported ciprofloxacin and minocycline with Km values of 133 and 112 µg/ml, respectively, at maximum velocities of 3.68 and 13.0 ng/min/µg cell protein, respectively. For both agents, transport activity was highest at pH 7.2 and was significantly lower at pH 6.2. Ciprofloxacin transport also decreased significantly when the pH was increased to 8.2. Fibroblasts transported both agents in a sodium-independent manner. When fibroblasts were incubated for 15 minutes at 37° C in balanced salts solution containing 1 µg/ml of ciprofloxacin or minocycline, the intracellular concentration of these agents exceeded 5.0 µg/ml.

Conclusions: Gingival fibroblasts possess transporters that accumulate fluoroquinolones and tetracyclines, which could enhance the redistribution of these agents from the bloodstream to the gingiva. This may account for the relatively high levels these antimicrobial agents attain in gingival fluid.

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