Membrane Filtration Is Suitable for Reliable Elimination of Mycobacterium tuberculosis from Saliva for Therapeutic Drug Monitoring

Salivary Therapeutic Drug Monitoring of Antimicrobial Therapy: Feasible or Futile?

Personalised drug dosing through therapeutic drug monitoring (TDM) is important to maximise efficacy and to minimise toxicity. Hurdles preventing broad implementation of TDM in routine care include the need of sophisticated equipment and highly trained staff, high costs and lack of timely results. Salivary TDM is a non-invasive, patient-friendly alternative to blood sampling, which has the potential to overcome barriers with traditional TDM. A mobile UV spectrophotometer may provide a simple solution for analysing drug concentrations in saliva samples. Salivary TDM utilising point-of-care tests can support personalised dosing in various settings including low-resource as well as remote settings. In this opinion paper, we describe how hurdles of implementing traditional TDM may be mitigated by salivary TDM with new strategies for patient-friendly point-of-care testing.

Supercritical fluid extraction-supercritical fluid chromatography of saliva: Single-quadrupole mass spectrometry monitoring of caffeine for gastric emptying studies†

Saliva is an attractive sampling matrix for measuring various endogenous and exogeneous substances but requires sample treatment prior to chromatographic analysis. Exploiting supercritical CO₂ for both extraction and chromatography simplifies sample preparation, reduces organic solvent consumption, and minimizes exposure to potentially infectious samples, but has not yet been applied to oral fluid. Here, we demonstrate the feasibility and benefits of online supercritical fluid extraction coupled to supercritical fluid chromatography and single-quadrupole mass spectrometry for monitoring the model salivary tracer caffeine. A comparison of ¹³ C- and ³² S-labeled internal standards with external standard calibration confirmed the superiority of stable isotope-labeled caffeine over nonanalogous internal standards. As proof of concept, the validated method was applied to saliva from a magnetic resonance imaging study of gastric emptying. After administration of 35 mg caffeine via ice capsule, salivary levels correlated with magnetic resonance imaging data, corroborating caffeine's usefulness as tracer of gastric emptying (R²  = 0.945). In contrast to off-line methods, online quantification required only minute amounts of organic solvents and a single manual operation prior to online bioanalysis of saliva, thus demonstrating the usefulness of CO₂ -based extraction and separation techniques for potentially infective biomatrices.

Saliva-based linezolid monitoring on a mobile UV spectrophotometer

BACKGROUND

In TB, therapeutic drug monitoring (TDM) is recommended for linezolid; however, implementation is challenging in endemic settings. Non-invasive saliva sampling using a mobile assay would increase the feasibility of TDM.

OBJECTIVES

To validate a linezolid saliva assay using a mobile UV spectrophotometer.

METHODS

The saliva assay was developed using NanoPhotometer NP80® and linezolid concentrations were quantified using second-order derivative spectroscopy. Sample preparation involved liquid-liquid extraction of saliva, using saturated sodium chloride and ethyl acetate at 1:1:3 (v/v/v). The assay was validated for accuracy, precision, selectivity, specificity, carry-over, matrix effect, stability and filters. Acceptance criteria were bias and coefficient of variation (CV) <15% for quality control (QC) samples and <20% for the lower limit of quantification (LLOQ).

RESULTS

Linezolid concentrations correlated with the amplitude between 250 and 270 nm on the second-order derivative spectra. The linezolid calibration curve was linear over the range of 3.0 to 25 mg/L (R2 = 0.99) and the LLOQ was 3.0 mg/L. Accuracy and precision were demonstrated with bias of -7.5% to 2.7% and CV ≤5.6%. The assay met the criteria for selectivity, matrix effect, carry-over, stability (tested up to 3 days) and use of filters (0.22 μM Millex®-GV and Millex®-GP). Specificity was tested with potential co-medications. Interferences from pyrazinamide, levofloxacin, moxifloxacin, rifampicin, abacavir, acetaminophen and trimethoprim were noted; however, with minimal clinical implications on linezolid dosing.

CONCLUSIONS

We validated a UV spectrophotometric assay using non-invasive saliva sampling for linezolid. The next step is to demonstrate clinical feasibility and value to facilitate programmatic implementation of TDM.

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

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.

Levofloxacin pharmacokinetics in saliva as measured by a mobile microvolume UV spectrophotometer among people treated for rifampicin-resistant TB in Tanzania

BACKGROUND

Early detection and correction of low fluoroquinolone exposure may improve treatment of MDR-TB.

OBJECTIVES

To explore a recently developed portable, battery-powered, UV spectrophotometer for measuring levofloxacin in saliva of people treated for MDR-TB.

METHODS

Patients treated with levofloxacin as part of a regimen for MDR-TB in Northern Tanzania had serum and saliva collected concurrently at 1 and 4 h after 2 weeks of observed levofloxacin administration. Saliva levofloxacin concentrations were quantified in the field via spectrophotometry, while serum was analysed at a regional laboratory using HPLC. A Bayesian population pharmacokinetics model was used to estimate the area under the concentration-time curve (AUC0-24). Subtarget exposures of levofloxacin were defined by serum AUC0-24 <80 mg·h/L. The study was registered at Clinicaltrials.gov with clinical trial identifier NCT04124055.

RESULTS

Among 45 patients, 11 (25.6%) were women and 16 (37.2%) were living with HIV. Median AUC0-24 in serum was 140 (IQR = 102.4-179.09) mg·h/L and median AUC0-24 in saliva was 97.10 (IQR = 74.80-121.10) mg·h/L. A positive linear correlation was observed with serum and saliva AUC0-24, and a receiver operating characteristic curve constructed to detect serum AUC0-24 below 80 mg·h/L demonstrated excellent prediction [AUC 0.80 (95% CI = 0.62-0.94)]. Utilizing a saliva AUC0-24 cut-off of 91.6 mg·h/L, the assay was 88.9% sensitive and 69.4% specific in detecting subtarget serum AUC0-24 values, including identifying eight of nine patients below target.

CONCLUSIONS

Portable UV spectrophotometry as a point-of-care screen for subtarget levofloxacin exposure was feasible. Use for triage to other investigation or personalized dosing strategy should be tested in a randomized study.

Evaluation of Saliva as a Potential Alternative Sampling Matrix for Therapeutic Drug Monitoring of Levofloxacin in Patients with Multidrug-Resistant Tuberculosis

Saliva may be a useful alternative matrix for monitoring levofloxacin concentrations in multidrug-resistant tuberculosis (MDR-TB) patients. The objectives of this study were (i) to evaluate the correlation between plasma and salivary levofloxacin (Lfx) concentrations in MDR-TB patients and (ii) to gauge the possibility of using saliva as an alternative sampling matrix for therapeutic drug monitoring of Lfx in areas where TB is endemic. This was a prospective pharmacokinetic study that enrolled MDR-TB patients receiving levofloxacin (750- to 1,000-mg once-daily dosing) under standardized treatment regimen in Nepal. Paired blood and saliva samples were collected at steady state. Lfx concentrations were quantified using liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated using noncompartmental kinetics. Lfx drug exposures were evaluated in 23 MDR-TB patients. During the first month, the median (interquartile range [IQR]) areas under the concentration-time curve from 0 to 24 h (AUC_0-24) were 67.09 (53.93 to 98.37) mg ⋅ h/liter in saliva and 99.91 (76.80 to 129.70) mg ⋅ h/liter in plasma, and the saliva plasma (S/P) ratio was 0.69 (0.53 to 0.99). Similarly, during the second month, the median (IQR) AUC_0-24 were 75.63 (61.45 to 125.5) mg ⋅ h/liter in saliva and 102.7 (84.46 to 131.9) mg ⋅ h/liter in plasma, with an S/P ratio of 0.73 (0.66 to 1.18). Furthermore, large inter- and intraindividual variabilities in Lfx concentrations were observed. This study could not demonstrate a strong correlation between plasma and saliva Lfx levels. Despite a good Lfx penetration in saliva, the variability in individual saliva-to-plasma ratios limits the use of saliva as a valid substitute for plasma. Nevertheless, saliva could be useful in semiquantitatively predicting Lfx plasma levels. (This study has been registered at ClinicalTrials.gov under identifier NCT03000517.).

Systematic Review of Salivary Versus Blood Concentrations of Antituberculosis Drugs and Their Potential for Salivary Therapeutic Drug Monitoring

BACKGROUND

Therapeutic drug monitoring is useful in the treatment of tuberculosis to assure adequate exposure, minimize antibiotic resistance, and reduce toxicity. Salivary therapeutic drug monitoring could reduce the risks, burden, and costs of blood-based therapeutic drug monitoring. This systematic review compared human pharmacokinetics of antituberculosis drugs in saliva and blood to determine if salivary therapeutic drug monitoring could be a promising alternative.

METHODS

On December 2, 2016, PubMed and the Institute for Scientific Information Web of Knowledge were searched for pharmacokinetic studies reporting human salivary and blood concentrations of antituberculosis drugs. Data on study population, study design, analytical method, salivary Cmax, salivary area under the time-concentration curve, plasma/serum Cmax, plasma/serum area under the time-concentration curve, and saliva-plasma or saliva-serum ratio were extracted. All included articles were assessed for risk of bias.

RESULTS

In total, 42 studies were included in this systematic review. For the majority of antituberculosis drugs, including the first-line drugs ethambutol and pyrazinamide, no pharmacokinetic studies in saliva were found. For amikacin, pharmacokinetic studies without saliva-plasma or saliva-serum ratios were found.

CONCLUSIONS

For gatifloxacin and linezolid, salivary therapeutic drug monitoring is likely possible due to a narrow range of saliva-plasma and saliva-serum ratios. For isoniazid, rifampicin, moxifloxacin, ofloxacin, and clarithromycin, salivary therapeutic drug monitoring might be possible; however, a large variability in saliva-plasma and saliva-serum ratios was observed. Unfortunately, salivary therapeutic drug monitoring is probably not possible for doripenem and amoxicillin/clavulanate, as a result of very low salivary drug concentrations.