Poly(L-lactic acid)microspheres containing tetracycline (TC-PLA-MS) were experimentally produced for periodontal therapy, and the sustained release of tetracycline(TC) in this preparation was examined. TC-PLA-MS were prepared by the oil-in-oil emulsion method(average diameter of MS : 10∼20 μ ; TC : 5, 10, 20% loading ; MW : 3700, 5400, 8700). The in vitro test of TC release was conducted using the UV method, while sustained release in vivo was determined by bioassay using S. aureus as verification bacteria. For the latter test, TC-PLA-MS(TC 10% loading ; MW : 5400)were prepared with hydrophilicpetrolatum (VH) or 3% atelocollagen solution(AC)as the base to yield gel, and injected into periodontal pockets. The test was performed 1, 2, 3, 4, 7, 10 and 14 days after administration. Sites treated by irrigation with TC solution (50 mg/ml, 200 mg/ml) were used as positive controls. In the in vitro test of TC release, about 50% of TC was released by day 1 after administration, and the release tended to be suppressed thereafter. In testing of sustained release in vivo percentage occurrence of the inhibition zone was decreased to about 50% by 2 or 3 days after administration, and was maintained at the same level until day 14. TC concentration remained almost stable (30∼60 μg/ml) after day 2. There was no noticeable difference in the pattern of sustained TC release by different bases(VH and AC). In the irrigation-tereated group, the inhibition zone appeared until day 4, and TC concentration decreased daily.
