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.

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A high performance liquid chromatographic method for estimation of Transitmycin (Tr) in human plasma was developed. The analyte was extracted using solid phase cartridges and the analysis of the eluent was carried out using Atlantis T3 column (150 cm × 4.6 mm ID) and photo diode array detector set at wavelength of 214 nm. The assay was specific for Tr and linear from 0.5 µg/mL to 20.0 µg/mL. The relative standard deviations for intra-day and inter-day assays were less than 10%. The method yielded a recovery for Tr that ranged from 94% to 107% and could be used in toxicology and pharmacokinetic studies.

OBJECTIVE: A high-performance liquid chromatography method for the estimation of Linezolid in human plasma was developed and validated. METHODS: Samples (100µµL) were deproteinized with acetonitrile and analyzed using LiChrospher 100, RP18e column with PDA detection at 254 nm. The flow rate of the isocratic mobile phase comprising of 0.1% formic acid in 1000 ml of water and acetonitrile in the ratio of 60:40 (v/v) was set at 1.0 ml/min. RESULTS: The calibration curve ranged from 0.50 to 20.0 µg/ml and was linear. The recovery ranged from 96% to 101%. The accuracy ranged from 98 to 101% and intra- and inter-day relative standard deviation was <4.58%. The method reliably eliminated interfering materials from plasma and R2 was 0.9973. The method described was applied to the determination of plasma LZD concentration in multi-drug-resistant tuberculosis patients who are treated with a dose of 600 mg LZD once daily. CONCLUSIONS: The developed method is suitable for determination of plasma LZD in routine care and considered feasible in less-resourced settings

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