Analytical Method Validation as the First Step in Drug Quality Control

The authors have developed and validated some chromatographic methods with the aim of quantifying drugs as drug substance and drug product, suitable for stability and quality control studies, as at original products as at its remainder doses. The stability of a pharmaceutical is defined by its resistance to different chemical, physical, and microbiological reactions that may change their original properties. The stability of a pharmaceutical product is closely related to its potency; therefore, whether the compounds are degraded, a decrease of the therapeutic effect or changes in their toxicological properties can be produced, affecting their efficacy and safety, which becomes important to maintain a stable pharmaceutical product and to have the analytical tools to demonstrate stability. Therefore, stability-indicating methods are required to the quality control of pharmaceuticals. Analytical methods presented here are useful stability-indicating methods to analyze drugs and have adequate linearity, precision, accuracy, selectivity, and LOD/LOQ values. The examples presented here are stability-indicating methods since they allow the determination of drugs in the presence of their degradation products, according to the International Conference on Harmonization (ICH) guidelines

STRUCTURAL EFFECTS OF VERAPAMIL ON CELL MEMBRANES AND MOLECULAR MODELS

ABSTRACT Verapamil is one of the frequently prescribed calcium channel blockers used in the treatment of hypertension and angina pectoris . Results of evaluations of the therapy have led to reports of toxic effects. This study presents several evidences that verapamil affects human cells. Scanning electron microscopy observations of intact human erythrocytes indicated that they underwent morphological alterations as increasing verapamil concentrations starting from 5 μM changed their discoid normal shape, and finally to hemolysis. Fluorescence spectroscopy on isolated unsealed human erythrocyte membranes confirmed these outcomes. In fact, the assays showed that verapamil induced a significant increase of the anisotropy parameters and a moderate one of the generalized polarization, indicative of enhanced order at the acyl chain and polar head regions of the erythrocyte membrane lipid bilayer. X-ray diffraction experiments on dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine bilayers, classes of the major phospholipids present in both outer and inner sides of the erythrocyte membrane, respectively showed that verapamil perturbed the polar head and acyl chain regions of both lipid bilayers. These interactions were found to be stronger with DMPC bilayers. On the other hand, human SH-SY5Y neuroblastoma cells incubated with verapamil suffered a sharp decrease of cell viability

Chemical stability of enalapril maleate drug substance and tablets by a stability-indicating liquid chromatographic method

The chemical stability of enalapril drug substance and tablets was studied by a stability-indicating liquid chromatographic method. Stress testing was performed on drug substance under various conditions. Accelerated stability testing was carried out for different formulations of enalapril tablets. Chromatographic separation was achieved on a RP-18 column, using a mobile phase of methanol phosphate buffer at 1.0 mL min"1 and UV detection. Degradation of the drug substance was greater under hydrolytic conditions. After 180 days of accelerated stability testing most enalapril tablets showed more than 10% of degradation. Enalapril drug substance and tablets showed instability under stress and accelerated testing respectively, with possible implications on the therapeutic activity

High performance thin layer chromatographic determination of nifedipine in human serum after liquid-liquid extraction

A method using HPTLC for quantitation of nifedipine in serum was developed and validated. It includes a liquid-liquid extraction, and carbamazepine as internal standard. Chloroform: ethyl acetate: cyclohexane (19:2:2, v/v/v) was the mobile phase. The method showed good relationship (r = 0.996) (2.00 to 25.00 ng/band, corresponding to 0.02 and 0.25 ng/µL in serum). The % RSD of intra-assay and inter-assay, were between 0.57 and 3.56 and 1.16 to 3.60, respectively. LOD and LOQ were 0.72 and 0.86 ng/band, respectively. The recovery values were between 93 and 102%. Rf for nifedipine and carbamazepine were 0.31 and 0.10, respectively