Current Pharmaceutical Analysis - Volume 9, Issue 3, 2013

Ibandronate is a potent nitrogen-containing bisphosphonate with a tertiary amine group, which does not easily form chromophore derivatives that can be detected by UV light of fluorescence emission. Here, a simple and straightforward automated multicommutated flow system, making use of water-soluble mercaptopropionic acid-capped CdTe quantum dots, was implemented for the fluorescence quantitation of ibandronate in pharmaceutical formulations. The developed approach was based on the analyte ability to establish surface interactions that resulted in quenched nanocrystals fluorescence intensity, being this effect proportional to the target compound's concentration. Size and concentration of quantum dots and pH of the media were some of the most relevant and influencing parameters studied. The proposed methodology allowed the determination of ibandronate in the range of 20-200 µg mL-1, with good repeatability (RSD<3%) and a sampling frequency of about 70 samples per hour. The results obtained in the analysis of pharmaceuticals showed excellent agreement with those provided by the manufacturer.

The present study proposes an agar diffusion microbiological assay for quantitation of the antibiotic doripenem in powder for injection. The method was developed according to official guidelines and its stability-indicating performance was studied by stress testing in pre-defined conditions of heat and UV-C radiation. Based on the response obtained from growth inhibition of a strain of Staphylococcus epidermidis ATCC 12228, the quantitation was carried out in the range of 1.0 - 4.0 µg ml-1. The percentage of drug estimated was 99.42% (RSD=3.12%), with satisfactory intra-day and inter-day precision. In the recovery test, the method was found to be reliable and accurate in quantitation of doripenem (mean recovery = 100.30%). Through alkaline hydrolysis experiments and by comparison to HPLC, bioassay was found to be specific. In kinetics degradation experiments, where the influence of temperature (45 ºC) and UV-C radiation were evaluated, higher rate of degradation was observed for the first, with a drug remaining content of 55.74% after 12h of storage. The reactions could be described by zero-order kinetics. The proposed bioassay was statistically compared to HPLC and CE methods concerning quantitative purposes and the results indicated they are equivalent, which demonstrates that the bioassay can be routinely used for determination of antibiotic potency, besides of being a complementary tool in stability studies of drugs.

The aim of this study was to investigate the effects of ionizing radiation on the physicochemical properties of four excipients used in pharmaceutical technology (microcrystalline cellulose, methylcellulose, hydroxyethylcellulose and hydroxypropyl methylcellulose) with the view of using ionizing radiation for their sterilization. A number of analytical methods (FT-IR, XRD, TG,CPMAS NMR and measurements of pH and viscosity) were used to determine the radiostability of cellulose derivatives to ionizing radiation. The odour, form, microscopic presentation and water content determined by the Karl Fischer method of cellulose derivatives did not change after irradiation up to 200 kGy. There was a small difference (+/- 0.1 to 2 °C) between irradiated and non-irradiated samples for the decomposition temperature determined via DTG/TG method and for relaxation times determined by the CPMAS NMR. Significant changes were observed however in the colour and the pH of aqueous solutions (or suspensions). The viscosity was reduced as a result of irradiation and thixotropic properties disappeared. In the FT-IR spectra, a new peak was observed at ca 1730 cm-1 indicating the presence of either carbonyl or carboxylic groups. It was concluded that radiosterilization method as a way of decontamination of cellulose derivatives should not be used in doses exceeding 25 kGy because ionizing radiation may lead to changes in physicochemical properties and to the formation of radiolysis products.

The state-of-the-art and possibilities offered by derivative spectrophotometry in the field of pharmaceutical analysis during the period 2008 - 2012 are reviewed. This paper draws attention to the fact that derivative treatment continues to be a promising tool for analysis of spectra composed of unresolved bands as it provides selective, validated, simple and cost effective analytical methods.

Quinapril undergoes a significant degradation in the solid state, specially in the presence of humidity, temperature and pharmaceutical excipients. Since dissolution increases the degradation, hydrolytic reactions are among the most common processes involved in drug degradation. Improving the knowledge regarding drug stability, particularly concerning the critical factors that can influence the stability of the active substance in solutions, such as the temperature, the pH and the concentration of catalytic species usually acids or bases are essential for pharmaceutical use. The aim of this study was therefore to develop a new chromatographic method for rapidly and accurately assessing the chemical stability of quinapril and to study the mechanism of quinapril degradation in acidic, neutral and alkaline media at 80°C according to the ICH guidelines. Ultra High Performance Liquid Chromatography (UPLC) coupled with electrospray ionization tandem mass spectrometry and/or diode array detector was used for the rapid and simultaneous analysis of quinapril and its by-products. Separation was achieved using a BEH C18 column and a mixture of acetonitrile-ammonium hydrogencarbonate buffer (pH 8.2; 10 mM) (65:35, v/v) at a flow rate of 0.4 mL/min as a mobile phase. This method allowed drug byproducts profiling, identification, structure elucidation and quantitative determination under stress conditions. The developed method also provides the determination of the kinetic rate constants for the degradation of quinapril and the formation of its major by-products. A complete model including degradation pathway observed under all tested conditions was proposed according to the kinetic study and the structure elucidation of by-products.

The electrochemical behavior of sotalol was investigated on a graphene oxide nanosheets-modified glassy carbon electrode in a phosphate buffer solution, pH 7.4. Cyclic voltammetry and chronoamperometry were employed to obtain information about the electrooxidation process. During the electrooxidation of sotalol, one irreversible anodic peak appeared in the voltammograms. Some kinetic parameters, such as the diffusion and charge transfer coefficients were obtained. An amperometric procedure was developed for the determination of sotalol, a detection limit of 7.57 μM, a linear dynamic range of 0.1 to 2.24 mM, and a calibration sensitivity of 0.945 mA M-1 were obtained. The method was applied to the analysis of sotalol tablets, and applicability of the method to direct assays of spiked human serum and urine fluids was investigated.

Levodropropizine is a cough suppressant and easily oxidizable at the carbon-base electrodes. The electrooxidative behavior and determination of levodropropizine on glassy carbon and boron-doped diamond electrodes were investigated using cyclic, linear sweep, differential pulse, and square wave voltammetric methods. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were examined. In this study, also simple and fully validated reverse phase-liquid chromatography (RP-LC) method for the assay of levodropropizine in syrup dosage form has been developed using X-Select RP-18 column (250x4.60 mm ID x 5μ) at 25 ºC with the mobile phase (containing 15 mM o-phosphoric acid) of acetonitrile:water (30:70, v/v) adjusted to pH 8.0. The proposed methods allow a number of cost and time saving benefits. Levodropropizine was also exposed to thermal, photolytic, oxidative stress, acid and base hydrolysis conditions, and the stressed samples were detected by the proposed LC method. The proposed methods were successfully applied for the determination of levodropropizine from pharmaceutical dosage forms.

Azithromycin dihydrate is a semi-synthetic macrolide antibiotic drug, effective against a wide variety of bacteria. It is primarily used to treat the bacterial infections associated with weaker immune system. A simple, accurate, rapid and cost effective spectrometric method for the estimation of azithromycin has been developed and validated by the acidic hydrolysis of the drug with sulphuric acid and monitoring the absorbance at 482nm. The validated method was successfully applied for dissolution studies of azithromycin dihydrate tablets. The developed method was validated as per ICH Q2 (R1) guidelines, which include linearity, precision, accuracy, specificity, robustness, detection and quantitation limits. The method has shown good linearity over the range of 10.0 to 50.0 µg/mL with a correlation coefficient of 0.9995. The percentage recovery of 99.98 % showed that the method was highly accurate. The precision demonstrated relative standard deviation of less than 2.5 %. The specificity of the method was proven as the excipients present in the tablets did not interfere with the assay. The developed and validated method was successfully applied for dissolution studies with a cumulative release of 99.3 % in 45 minutes. The proposed method might be applied in routine quality control in the pharmaceutical industries as it has shown very good precision, accuracy and simplicity.

This paper describes the development and validation of a most economical and sensitive isocratic stability indicating HPLC method for the assay of recombinant human insulin (RHI) from yeast origin (Hansenula polymorpha). The method employs a Thermo Biobasic, C-18 (250 x 4.6 mm, 300 A°, 5 µm) column with a mobile phase of acetonitrile - potassium dihydrogen phosphate ( pH 2.5; 50 mM) (35:65, v/v) and UV detection at 242 nm. Factorial design was used to facilitate method development. Buffer pH and concentration of acetonitrile were considered as the independent variable to study capacity factor of RHI. Sixteen experiments were undertaken, and a quadratic model was derived for the capacity factor of RHI. The method produced well defined, sharp peaks having lower tailing factor (1.114). A linear response with a correlation coefficient (r2) of 0.999 was observed over the range of 0.025 - 2.0 IU mL-1. Developed method was employed to analyze RHI samples from forced degradation and stability study. Degradation of RHI under different ICH prescribed stress conditions was carried out. Four batches of RHI formulation were exposed to different conditions of temperature and humidity for forty-five days. Degradation of RHI during stability study followed first-order kinetics. Data obtained from degradation kinetics were employed to find out the rate constant; time left for 50% potency, and time left for 90% potency. Rate constants obtained from different conditions were employed to plot the Arrhenius plot.