Quantitative comparison of cytocidal effects of tetracyclines and fluoroquinolones on human periodontal ligament fibroblasts

The cytocidal effects of tetracyclines and fluoroquinolones on human periodontal ligament fibroblasts (Pel cells) were studied. Pel cells were treated for 24 h with tetracycline (TC), demeclocycline (DMC), minocycline (MINO), chlortetracycline (CTC), tosufloxacin (TFLX), enoxacin (ENX), sparfloxacin (SPFX), lomefloxacin (LFLX) or ofloxacin (OFLX), and allowed to form colonies. The cytocidal effects of the antibacterial agents, as determined by a decrease in colony-forming efficiency, increased as the dose increased. However, CTC was an exception. As a quantitative measure of the cytocidal effect, LD50, the concentration which results in a 50% decrease in colony-forming efficiency relative to control cells, was extrapolated from the dose-response curves. The rank-order of cytocidal effects (LD50) was DMC [symbol: see text] MINO [symbol: see text] TC > CTC. DMC, MINO and TC were at least 5.6-6.6 times more cytocidal than CTC. The cytocidal effects of the fluoroquinolones were in the following order: TFLX > ENX > SPFX > LFLX > OFLX. TFLX, ENX, SPFX and LFLX were 36.3, 11.4, 7.7 and 3.1 times more cytocidal than OFLX, respectively. Little cytocidal effect was observed when the cells were treated with either < or = 0.03 mM tetracyclines or < or = 0.01 mM fluoroquinolones. The results provide useful estimates concerning the relative toxicities against human periodontal ligament of antibacterial agents used to treat periodontitis.