title: A rapid spectrophotometric assay for tetracycline in gingival crevicular fluid.
abstract: OBJECTIVE
  The aim of this study was to investigate a rapid spectrophotometric assay for its potential to measure tetracycline levels in gingival crevicular fluid (GCF).
  
  
  METHODS
  The technique involves complexation of tetracycline with molybdenum in order to shift the absorbance spectrum away from that region 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 following placement of a test gel formulation in 25 periodontal pockets in 5 patients.
  
  
  RESULTS
  The in vitro results showed good sensitivity of the assay over the concentration range tested (0.5-200 microg tetracycline) and with little effect of plasma proteins. Elution from the paper strips was reproducible with a good linear correlation between direct and filter absorbed assays (r=0.9989, p<0.01). The pilot clinical study indicated a mean half-time of tetracycline in GCF of 28 min with confidence intervals of 21 to 34 min, although wide variation between the drug levels of individual periodontal pockets was seen.
  
  
  CONCLUSIONS
  The results indicate good sensitivity for this assay to measure tetracycline hydrochloride in vivo. The potential for rapidly processing large numbers of samples contrasts with the assay time and limited sample throughput of other methods such as high pressure liquid chromatography (HPLC) and suggests that the technique may be a useful addition to current techniques for measuring tetracycline hydrochloride in vivo.
authors.affiliation: Department of Periodontology, Eastman Dental Institute, University College London, UK. i.needleman@eastman.ucl.ac.uk
authors.forename: I G
authors.initials: IG
authors.lastname: Needleman
authors.forename: M F
authors.initials: MF
authors.lastname: Grahn
authors.forename: N V
authors.initials: NV
authors.lastname: Pandya
mesh_terms: D000900:Anti-Bacterial Agents / Q000032:analysis*; D001798:Blood Proteins / Q000737:chemistry; D002138:Calibration; D005883:Gingival Crevicular Fluid / Q000737:chemistry*; D006801:Humans; D016014:Linear Models; D008982:Molybdenum / Q000737:chemistry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013053:Spectrophotometry / Q000379:methods*; D013752:Tetracycline / Q000032:analysis*
chemical_list: D000900:Anti-Bacterial Agents; D001798:Blood Proteins; D008982:Molybdenum; D013752:Tetracycline