Methods: Experimental gingivitis was induced over 21 days in one maxillary posterior sextant in four periodontally healthy subjects. Subjects were then given 500 mg of azithromycin followed by 250 mg 24 hours later. After the final dose, plaque was removed from the gingivitis site. GCF samples were collected from the mesial surfaces of four teeth in the gingivitis sextant and the contralateral healthy control sextant exactly 24, 48 and 168 hrs after the final dose. GCF samples were eluted with water and extracted with diethyl ether. Azithromycin content was determined with an agar diffusion bioassay.
Results: During the first 24 hours after plaque removal from gingivitis sites, mean GCF volume per 30 seconds was approximately 2.5-fold higher at gingivitis sites than at control sites (P <0.03). Thereafter, GCF volume was not significantly different at gingivitis and control sites. At the 24 hour time point, but not at later points, mean azithromycin content per 30 sec GCF sample was significantly higher at gingivitis sites than control sites (9.8 ± 2.2 ng vs 3.3 ± 1.0 ng, P < 0.04). When expressed as concentration (ng/µl), however, there were no significant differences in azithromycin levels between gingivitis and control sites at any point.
Conclusions: The azithromycin content of a 30 second GCF sample increased in the presence of gingivitis, but converged toward the content found at healthy sites as gingivitis resolved. However, the absolute concentration of azithromycin was not significantly different between gingivitis and control sites, possibly because of dilution by the increased GCF volume associated with gingivitis.