A mobile microvolume UV/visible light spectrophotometer for the measurement of levofloxacin in saliva

Abstract

Introduction: Therapeutic drug monitoring (TDM) for personalized dosing of fluoroquinolones has been recommended to optimize efficacy and reduce acquired drug resistance in the treatment of MDR TB. Therefore, the aim of this study was to develop a simple, low-cost, robust assay for TDM using mobile UV/visible light (UV/VIS) spectrophotometry to quantify levofloxacin in human saliva at the point of care for TB endemic settings.

Methods: All experiments were performed on a mobile UV/VIS spectrophotometer. The levofloxacin concentration was quantified by using the amplitude of the second-order spectrum between 300 and 400 nm of seven calibrators. The concentration of spiked samples was calculated from the spectrum amplitude using linear regression. The method was validated for selectivity, specificity, linearity, accuracy and precision. Drugs frequently co-administered were tested for interference.

Results: The calibration curve was linear over a range of 2.5-50.0 mg/L for levofloxacin, with a correlation coefficient of 0.997. Calculated accuracy ranged from -5.2% to 2.4%. Overall precision ranged from 2.1% to 16.1%. Application of the Savitsky-Golay method reduced the effect of interferents on the quantitation of levofloxacin. Although rifampicin and pyrazinamide showed analytical interference at the lower limit of quantitation of levofloxacin concentrations, this interference had no implication on decisions regarding the levofloxacin dose.

Conclusions: A simple UV/VIS spectrophotometric method to quantify levofloxacin in saliva using a mobile nanophotometer has been validated. This method can be evaluated in programmatic settings to identify patients with low levofloxacin drug exposure to trigger personalized dose adjustment.

Figure 1.

Spectra of levofloxacin in saliva. (a) Full zero-order spectra of levofloxacin in saliva at 2.5, 5, 10, 20 and 40 mg/L, (b) detail of the zero-order spectra and (c) detail of second-order spectra [S-G(8,61)].

Figure 2.

Calibration curve in drug-free saliva (n = 3) with 95% CI.

Figure 3.

Differences in second-order derivative spectra of different co-administered drugs. (a) Clofazimine at a concentration of 0.4 mg/L gives a lower response than the response of the levofloxacin LLOQ and (b) pyrazinamide at a concentration of 42 mg/L gives a higher response than the response of the levofloxacin LLOQ.