Simultaneous Determination of Ezetimibe and Simvastatin in Pharmaceutical Formulations by Dual-Mode Gradient LC

Dual-Mode Gradient HPLC and TLC Densitometry Methods for the Simultaneous Determination of Paracetamol and Methionine in the Presence of Paracetamol Impurities

Background

Paracetamol is one of the most widely analgesic and antipyretic drugs recently integrated into the supportive therapy of COVID-19. The pharmaceuticals containing methionine with paracetamol may contribute to avoid hepatotoxicity and eventual paracetamol overdose-dependent death.

Objective

The current work purposes to develop and validate two chromatographic methods for the simultaneous determination of methionine and paracetamol in presence of two paracetamol impurities (4-nitrophenol and 4-aminophenol).

Methods

Two chromatographic methods were established and validated according to the International Conference on Harmonization guidelines. The first one was a RP-HPLC/UV method based on applying a “dual-mode” gradient elution. The separation was realized via varying both the composition of the ternary mobile phase (acetonitrile–methanol–water) and its flow rate. This strategy enabled a relatively rapid analysis with a satisfactory resolution, although the investigated compounds exhibit a significant difference in lipophilicity. The second one relied on TLC- densitometry, where the optimum separation was realized using a quaternary mobile phase system composed of butanol–dioxane–toluene–methanol (8: 2.5: 3.5: 0.3, by volume). Both methods were monitored at 220 nm.

Results

The developed methods were proven to be robust, accurate, specific, and appropriate for the routine analysis of paracetamol in its pure form or in pharmaceutical formulations with methionine in quality control laboratories.

Conclusions

The corresponding methods are suitable to determine methionine and paracetamol in the presence of paracetamol impurities.

Highlights

The study achieves the analysis of methionine and paracetamol in the presence of paracetamol impurities via the application of HPLC and TLC- densitometry methods.

Novel absorptivity centering method utilizing normalized and factorized spectra for analysis of mixtures with overlapping spectra in different matrices using built-in spectrophotometer software

A novel, simple, rapid, accurate, and economical spectrophotometric method, namely absorptivity centering (a-Centering) has been developed and validated for the simultaneous determination of mixtures with partially and completely overlapping spectra in different matrices using either normalized or factorized spectrum using built-in spectrophotometer software without a need of special purchased program. Mixture I (Mix I) composed of Simvastatin (SM) and Ezetimibe (EZ) is the one with partial overlapping spectra formulated as tablets, while mixture II (Mix II) formed by Chloramphenicol (CPL) and Prednisolone acetate (PA) is that with complete overlapping spectra formulated as eye drops. These procedures do not require any separation steps. Resolution of spectrally overlapping binary mixtures has been achieved getting recovered zero-order (D⁰) spectrum of each drug, then absorbance was recorded at their maxima 238, 233.5, 273 and 242.5 nm for SM, EZ, CPL and PA, respectively. Calibration graphs were established with good correlation coefficients. The method shows significant advantages as simplicity, minimal data manipulation besides maximum reproducibility and robustness. Moreover, it was validated according to ICH guidelines. Selectivity was tested using laboratory-prepared mixtures. Accuracy, precision and repeatability were found to be within the acceptable limits. The proposed method is good enough to be applied to an assay of drugs in their combined formulations without any interference from excipients. The obtained results were statistically compared with those of the reported and official methods by applying t-test and F-test at 95% confidence level concluding that there is no significant difference with regard to accuracy and precision. Generally, this method could be used successfully for the routine quality control testing.

Simultaneous determination of some cholesterol-lowering drugs in their binary mixture by novel spectrophotometric methods

Four simple, specific, accurate and precise spectrophotometric methods manipulating ratio spectra were developed and validated for simultaneous determination of simvastatin (SM) and ezetimibe (EZ) namely; extended ratio subtraction (EXRSM), simultaneous ratio subtraction (SRSM), ratio difference (RDSM) and absorption factor (AFM). The proposed spectrophotometric procedures do not require any preliminary separation step. The accuracy, precision and linearity ranges of the proposed methods were determined, and the methods were validated and the specificity was assessed by analyzing synthetic mixtures containing the cited drugs. The four methods were applied for the determination of the cited drugs in tablets and the obtained results were statistically compared with each other and with those of a reported HPLC method. The comparison showed that there is no significant difference between the proposed methods and the reported method regarding both accuracy and precision.

Ezetimibe

Ezetimibe is a drug substance which can be used for lowering low-density lipoprotein cholesterol. Its crystal form and polymorphism have been determined using X-ray diffraction and thermal methods. Quantitative and qualitative analysis of Ezetimibe as well as study of its impurities and degradations were summarized in this chapter.