Rapid determination of doxycycline based on luciferase assay of bacterial adenosine triphosphate

The effect of the bacteristatic antimicrobial doxycycline on intracellular adenosine triphosphate (ATP) levels in bacterial cultures was used to develop a rapid method to assay the drug in clinical serum specimens. ATP was quantified with the firefly luciferin/luciferase system. When compared with an agar disc diffusion technique results were well correlated within the range of 1 to 16 μg/ml. The accuracy of the luciferase assay expressed as recovery of doxycycline over the therapeutic range varied between 95 and 111% and a coefficient of variation of 4 to 15%. Seventy-six serum specimens from 46 patients were assayed and results with the two methods compared (r=0.89). Volumes required were 0.1 ml serum and results were available within 3 h.