A rapid spectrophotometric assay for tetracycline in gingival crevicular fluid

Aim: The aim of this study was to investigate a rapid spectrophotometric as say for its potential to measure tetracycline levels in gingival crevicular fluid (GCF). Materials and methods: The technique involves complexation of tetracycline with molybdenum in order to shift the absorbance spectrum away from that re gion where interference with plasma proteins is a problem. The sensitivity of the assay and reproducibility of elution were examined together with an assessment of the effect of plasma proteins. The assay was also tested in a small pilot clinical project, measuring tetracycline levels in GCF followi ng placement of a test gel formulation in 25 periodontal pockets in 5 patie nts. Results: The in vitro results showed good sensitivity of the assay over the concentration range tested (0.5-200 mug tetracycline) and with little effe ct of plasma proteins. Elution from the paper strips was reproducible with a good linear correlation between direct and filter absorbed assays (r=0.99 89, p<0.01). The pilot clinical study indicated a mean half-time of tetracy cline in GCF of 28 min with confidence intervals of 21 to 34 min, although wide variation between the drug levels of individual periodontal pockets wa s seen. Conclusions: The results indicate good sensitivity for this assay to measur e tetracycline hydrochloride in vivo. The potential for rapidly processing large numbers of samples contrasts with the assay time and limited sample t hroughput of other methods such as high pressure liquid chromatography (HPL C) and suggests that the technique may be a useful addition to current tech niques for measuring tetracycline hydrochloride in vivo.