Validation of a stability-indicating assay method for epalrestat using UV detection high-performance liquid chromatography

Introduction
Phosphomannomutase 2 deficiency is the most common congenital glycosylation disorder. This genetic disease causes significant cerebellar developmental disorders, with a highly variable phenotype depending on the patient. There is currently no curative treatment, but several clinical studies show that epalrestat, an antidiabetic drug not marketed in Europe, may be effective in treating the cerebellar symptoms of this condition. A clinical study on the repositioning of this drug for this indication is currently underway.

Objective
The objective of this work is to develop and validate a stability-indicating assay method using High-Performance Liquid Chromatography (HPLC) according to ICH criteria to validate the pharmaceutical formulation and stability of a hospital-grade preparation of epalrestat capsules.

Matérials & Methods
A stability-indicating analytical method using reverse-phase HPLC coupled with a diode array UV detector was developed and validated according to ICH Q2 R1 guidelines. The chromatographic system includes a Polaris® C18 column and a mobile phase composed of a mixture of acetonitrile and 25 mM phosphate buffer, pH 6.5 (32-68% v/v). Detection and quantification were performed at a wavelength of 396 nm. Forced degradation tests were performed under the following stress conditions: acidic (0.01 M HCl), basic (0.005 M NaOH), and oxidizing (1.5% H2O2) media at room temperature for 1 hour. Degradation under natural light was also performed in solution and on pure powder for 1 hour.

Results
The stability indicator method is linear (R² = 0.984), reliable (repeatability <0.3%; intermediate precision CV <1%), and accurate (relative error <2% across the different control levels). The degradation study revealed degradation products, without coelution with the peak of our molecule. Furthermore, no distortion of the peak or UV spectrum was observed; our method is specific. Exposure of the powder to natural light did not reveal photosensitivity, but exposure of epalrestat in solution revealed a 27% degradation in 10 min.

Conclusion-Discussion
The method is validated according to the criteria of the international ICH Q2 (R1) guideline and allows for the establishment of an epalrestat assay. Since photosensitivity in solution requires a strict handling protocol, optimization of the latter is required to improve accuracy.

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