Isolation and characterization of process-related impurities in linezolid

Characterization of Five Oxidative Degradation Impurities and One Process Impurity of Suvorexant Drug Substance by LC-MS/MS, HR-MS and 1D, 2D NMR: Validation of Suvorexant Drug Substance and Process Impurities by HPLC and UPLC

During the oxidative (10% H2O2) degradation of suvorexant drug substance, around 1.0% of one impurity and less than 1.0% four impurities were found by a new high-performance liquid chromatography (HPLC) assay and related substance method. The mass numbers of 1.0% impurity was 469 [M + H]+, remaining four impurities were 172 [M + H]+, 467 [M + H]+, 483 [M + H]+ and 485 [M + H]+. The 469 [M + H]+, 485[M + H] and 172 [M + H]+ impurities were characterized by using the LC-MS/MS, HR-MS and 1D, 2D NMR spectroscopic data. The 172 [M + H]+ impurity was prepared synthetically and co-injected in HPLC. The retention time of synthesized 172 [M + H]+ impurity was matching with the unknown degradation impurity in HPLC. The developed mass compatible HPLC and ultra performance liquid chromatography methods were validated for drug substance and process impurities by following ICH Q2 (R1) guidelines.

A critical review of HPLC-based analytical methods for quantification of Linezolid

Linezolid is a synthetic antimicrobial agent belonging to the oxazolidinone class. Since its approval in the year 2000 until now, linezolid remains the main representative drug for the oxazolidinone class of drugs, which is used in therapy due to its unique mode of action, which involves inhibition of protein synthesis. As linezolid holds great importance in antimicrobial therapy, it is necessary to compile the various analytical methods that have been reported in the literature for its analysis. Analytical techniques used for pharmaceutical analyses and therapeutic drug monitoring play an important role in comprehending the aspects regarding bioavailability, bioequivalence, and therapeutic monitoring during patient follow-ups. Even though linezolid has had the approval for clinical use for more than 18 years now, most of the analytical methods for its determination reported in the scientific literature are the ones which utilize HPLC. Therefore, the present review provides a summary of the HPLC-based methods used in the determination and quantification of linezolid in different matrices since the time of its discovery.

Two and three way spectrophotometric-assisted multivariate determination of linezolid in the presence of its alkaline and oxidative degradation products and application to pharmaceutical formulation

Linezolid (LIN) is determined in the presence of its alkaline (ALK) and oxidative (OXD) degradation products without preliminary separation based on ultraviolet spectrophotometry using two-way chemometric methods; principal component regression (PCR) and partial least-squares (PLS), and three-way chemometric methods; parallel factor analysis (PARAFAC) and multi-way partial least squares (N-PLS). A training set of mixtures containing LIN, ALK and OXD; was prepared in the concentration ranges of 12-18, 2.4-3.6 and 1.2-1.8 μg mL(-1), respectively according to a multilevel multifactor experimental design. The multivariate calibrations were obtained by measuring the zero-order absorbance from 220 to 320 nm using the training set. The validation of the multivariate methods was realized by analyzing their synthetic mixtures. The capabilities of the chemometric analysis methods for the analysis of real samples were evaluated by determination of LIN in its pharmaceutical preparation with satisfactory results. The accuracy of the methods, evaluated through the root mean square error of prediction (RMSEP), was 0.058, 0.026, 0.101 and 0.026 for LIN using PCR, PLS, PARAFAC and N-PLS, respectively. Protolytic equilibria of LIN and its degradation products were evaluated using the corresponding absorption spectra-pH data obtained with PARAFAC. The obtained pKa values of LIN, ALK and OXD are 5.70, 8.90 and 6.15, respectively. The results obtained were statistically compared to that of a reported HPLC method, and there was no significant difference between the proposed methods and the reported method regarding both accuracy and precision.

An efficient and practical synthesis of antibacterial linezolid

A convergent and efficient synthesis of linezolid was developed using the cycloaddition of commercially available ( R)-epichlorohydrin with morpholine substituted phenylisocyanate catalysed by MgI2 or MgBr2 etherate as the key step in the 50% overall yield.

Characterization of a novel impurity in bulk drug of lisinopril by multidimensional NMR technique

During the routine impurity profile of lisinopril bulk drug by HPLC (high-performance liquid chromatography), a potential impurity was detected. Using multidimensional NMR (nuclear magnetic resonance) technique, the trace-level impurity was unambiguously identified to be 2-(-2-oxo-azocan-3-ylamino)-4-phenyl-butyric acid after isolation from lisinopril bulk drug by semi-preparative HPLC. Formation of the impurity was also discussed. To our knowledge, this is a novel impurity and not reported elsewhere.

Further method development for measurement of linezolid in human serum by MEKC

A method for determining linezolid concentration in human serum using micellar electrokinetic capillary chromatography by direct injection of serum is described. A borate buffer (pH 8.0) containing sodium dodecyl sulfate was used as a run buffer and detection of linezolid was performed at 250 nm (its absorption maximum). The migration time of linezolid was 5.5 min and the detection limit was 0.5 mg/l (S/N = 3). The precision and accuracy of this method was good with no interference with the detection from bilirubin, hemoglobin and chyle of high concentrations. This provides a simple and easy method where samples of micro-quantity are used.

Stability Indicating HPTLC Determination of Linezolid as Bulk Drug and in Pharmaceutical Dosage Form

A simple, selective, precise, and stability-indicating high-performance thin layer chromatographic method of analysis of Linezolid both as a bulk drug and in formulations was developed and validated in pharmaceutical dosage form. The method employed TLC aluminium plates precoated with silica gel 60F-254 as the stationary phase. The solvent system consisted of toluene-acetone (5:5, v/v). This system was found to give compact spots for Linezolid (Rf value of 0.29 +/- 0.01). Linezolid was subjected to acidic, alkali hydrolysis, oxidation, and photodegradation. The degraded products also were well separated from the pure drug. Densitometric analysis of Linezolid was conducted in the absorbance mode at 254 nm. The linear regression data for the calibration plots showed good linear relationship with r2 = 0.997 +/- 0.001 in the concentration range of 300-800 ng/spot. The mean value of correlation coefficient, slope, and intercept were 0.998 +/- 0.003, 0.15 +/- 0.009, and 19.52 +/- 1.66 respectively. The method was validated for precision, accuracy, ruggedness, and recovery. The limits of detection and quantification were 20 ng/spot and 50 ng/spot, respectively. The drug undergoes degradation under acidic and basic conditions, oxidation and photo degradation. All the peaks of degraded product were resolved from the standard drug with significantly different Rf values. This indicates that the drug is susceptible to acid-base hydrolysis, oxidation, and photo degradation. Statistical analysis proves that the method is reproducible and selective for the estimation of the said drug. Because the method could effectively separate the drug from its degradation products, it can be used as a stability indicating one.