Determining the Distribution of Active Pharmaceutical Ingredients in Combination Tablets Using Near IR and Low-Frequency Raman Spectroscopy Imaging.

Combination tablets containing multiple active pharmaceutical ingredients (APIs) are expected to improve patient convenience by decreasing the number of tablets to be taken; thus, numerous formulations containing multiple APIs have recently been developed. To allow for dose adjustments based on patient conditions, many tablets have a bisection line to allow equal division of tablets. However, there have been no investigations regarding content uniformity among divided combination tablets. Therefore, in this study, the content uniformity of combination tablets after division was investigated using near IR and low-frequency (LF) Raman spectroscopy imaging as well as the Japanese Pharmacopoeia (JP) content uniformity tests. As model drugs, five tablets of three combination drugs containing 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA) and benserazide hydrochloride (BNS) as APIs for treating Parkinson's disease were bisected; the resultant 10 samples were subjected to the JP content uniformity tests. We found that acceptance values of L-DOPA and BNS were 11.0-21.9% and 13.3-17.5%, respectively, with some non-conformity to the maximum allowed acceptance value (15.0%) as per the current JP. Image analyses by near IR showed that L-DOPA, BNS, lactose, and corn starch were uniformly distributed in each tablet; moreover, LF Raman spectroscopy imaging also supported the result that L-DOPA, BNS, and lactose were evenly distributed. Therefore, drug content in the tablets was uniform; thus, careful manipulation was recommended in the tablet bisection. However, the results of bisection line specifications and hardness tests revealed that the ease of division differed depending on the tablets, which warrants attention.

Development and Validation of a Robust and Efficient HPLC Method for the Simultaneous Quantification of Levodopa, Carbidopa, Benserazide and Entacapone in Complex Matrices.

PURPOSE: A variety of fixed-dose combination products is used in the therapy of Parkinson Disease. However, to date a proper analytical method applicable for comparative screening of different antiparkinson products was not available. The objective of the present work was thus to develop and validate an analytical method for the simultaneous quantification of levodopa, carbidopa, benserazide and entacapone. The method should be applicable for quantifying samples from drug release experiments with marketed products and prototype formulations performed under compendial and biorelevant test conditions. METHODS: A fast and robust method applicable for separation and quantification of the four compounds was developed and validated according to International Conference on Harmonization guidelines. Method validation covered applicability to a wide concentration range of all compounds and peak separation in complex sample matrices such as biorelevant dissolution media. RESULTS: The compounds were successfully separated by using a gradient elution method on an endcapped LiChrospher 100 RP-18 (250 x 4.6 mm, 5 µm) column coupled with a LiChrospher 100 RP-18 precolumn (4 x 4 mm, 5 µm) at a column temperature of 35.0 °C and a flow rate of 1.50 mL/min. The injection volume was 30 µL and the detection wavelengths were 280 and 210 nm, respectively. For all drug/media combinations the method was linear (r2 > 0.999) for a concentration range corresponding to 1.25 - 125 % label claim (i.e. 200 mg levodopa/entacapone and 50 mg carbidopa/benserazide) released. All other validation parameters were in the specified limits over the same concentration range. CONCLUSION: The new method allows for robust and fast separation of levodopa, carbidopa, benserazide and entacapone without any interference caused by excipients or ingredients of compendial and biorelevant dissolution media and thus presents a valuable tool in both formulation development and in vitro drug release screening of numerous fixed-dose combinations of antiparkinson drugs. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Application of ionic liquid-TiO2 nanoparticle modified carbon paste electrode for the voltammetric determination of benserazide in biological samples.

An ionic liquid-TiO2 nanoparticle modified carbon paste electrode (IL-TiO2/CPE) was used as a fast and sensitive tool for the investigation of the electrochemical oxidation of benserazide using voltammetry. This modified electrode has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. The modified electrode offers a considerable improvement in voltammetric sensitivity toward benserazide, compared to the bare electrode. Using differential pulse voltammetry (DPV), the electrocatalytic oxidation peak current of benserazide shows a linear calibration curve in the range of 1.0-600 µmol L(-1) benserazide. The limit of detection was equal to 0.4 µmol L(-1). The relative standard deviation (RSD%) for eight successive assays of 10 µmol L(-1) benserazide was 1.1%. Finally, the proposed method was successfully applied to the determination of benserazide in real samples such as blood serum and urine.

Simultaneous voltammetric determination of levodopa, carbidopa and benserazide in pharmaceuticals using multivariate calibration.

An analytical methodology based on differential pulse voltammetry (DPV) on a glassy carbon electrode and the partial least-squares (PLS-1) algorithm for the simultaneous determination of levodopa, carbidopa and benserazide in pharmaceutical formulations was developed and validated. Some sources of bi-linearity deviation for electrochemical data are discussed and analyzed. The multivariate model was developed as a ternary calibration model and it was built and validated with an independent set of drug mixtures in presence of excipients, according with manufacturer specifications. The proposed method was applied to both the assay and the uniformity content of two commercial formulations containing mixtures of levodopa-carbidopa (10:1) and levodopa-benserazide (4:1). The results were satisfactory and statistically comparable to those obtained by applying the reference Pharmacopoeia method based on high performance liquid chromatography. In conclusion, the methodology proposed based on DPV data processed with the PLS-1 algorithm was able to quantify simultaneously levodopa, carbidopa and benserazide in its pharmaceuticals formulations using a ternary calibration model for these drugs in presence of excipients. Furthermore, the model appears to be successful even in the presence of slight potential shifts in the processed data, which have been taken into account by the flexible chemometric PLS-1 approach.

Simultaneous chemiluminometric determination of levodopa and benserazide in a multi-pumping flow system with multivariate calibration.

An automated multi-pumping flow system is proposed for the simultaneous chemiluminometric determination of benserazide and levodopa using multivariate calibration methods. The developed methodology is based on chemiluminescence (CL) emission generated by the reaction of benserazide with luminol, and on a concurrent inhibiting effect of levodopa on this reaction. A multi-pumping flow system comprising multiple solenoid micro-pumps as the only active components was developed to implement a stopped-flow approach for signal acquisition and processing. Artificial neural networks were used to establish a relationship between the CL emission profile and the concentration of both drugs. The concentration values used to establish the experimental calibration samples were varied between 5 and 30 mg l(-1) for levodopa and between 2.5 and 20 mg l(-1) for benserazide. The proposed method was successfully applied to the simultaneous determination of levodopa and benserazide in pharmaceutical formulations combining both drugs.

Simultaneous determination of benserazide and levodopa by capillary electrophoresis-chemiluminescence using an improved interface.

A capillary electrophoresis coupling with indirect chemiluminescence detection method for the simultaneous determination of benserazide and levodopa has been developed. The detection interface was improved to simplify the capillary electrophoresis-chemiluminescence (CE-CL) system and the features of this improved interface were illustrated in this paper. The CE-CL conditions for the simultaneous determination of benserazide and levodopa were optimized. Under the optimal conditions, the CL intensity was linear with concentrations of levodopa in the range of 1.0 to 100.0 microg ml(-1), and benserazide in the range of 10.0 to 1,000 microg ml(-1), respectively. The detection limits (S/N=3) in turn were 1.85 microg ml(-1) for BS and 0.12 microg ml(-1) for L-dopa with relative standard deviations of less than 3%. The proposed method has been successfully applied to the determination of benserazide and levodopa in medopar tablets and spiked urine samples, demonstrating the feasibility and reliability of the proposed method.

A spectroscopic study on applicability of spectral analysis for simultaneous quantification of l-dopa, benserazide and ascorbic acid in batch and flow systems.

The usefulness of derivative spectrophotometry for simultaneous assay of l-dopa, benserazide and ascorbic acid in pharmaceuticals was studied. The parameters of derivatisation depends on composition of solution in which particular compound was determined. For quantification of l-dopa in mixtures with benserazide or ascorbic acid the first derivative was used. Its determination in ternary mixture (l-dopa+benserazide+ascorbic acid) is possible by third derivative spectra. Benserazide was assayed in presence of l-dopa using first derivative while in ternary mixture by third derivative. Direct determination of ascorbic acid is possible applying first derivative only in presence of l-dopa. The elaborated derivative spectrophotometric methods were used for assaying of l-dopa and benserazide in their commercial form "Madopar". The proposed spectrophotometric derivative method of simultaneous determination of l-dopa and benserazide was combined with FIA technique.

Simultaneous determination of levodopa and benserazide by stopped-flow injection analysis and three-way multivariate calibration of kinetic-spectrophotometric data.

The simultaneous determination of levodopa and benserazide in pharmaceutical formulations is described, based on the application of multidimensional partial least-squares regression to the kinetic-spectrophotometric data provided by diode-array detection within a stopped-flow injection method where analytes react with periodate. Flow injection parameters were adequately optimized. Accurate analysis is performed with no sample pre-treatment steps, and with minimum experimental effort. Satisfactory recovery results were obtained on a number of synthetic and commercial samples, in the latter case including the comparison with liquid chromatography measurements.

Chiral and non chiral determination of Dopa by capillary electrophoresis.

The suitability of capillary electrophoresis for determining the enantiomeric purity of levodopa in a pharmaceutical formulation also containing benserazide was assessed. To this end, the pharmaceutical components were separated in a non-chiral medium that allowed the total amount of Dopa and that of benserazide to be quantified. The addition of a chiral crown ether to the background electrolyte allows to separate the enantiomers of this compounds. Optimizing the variables influencing the enantioresolution of Dopa affords a resolution high enough resolution to determine the amount of dextrodopa (the distomer) contained in levodopa (the eutomer) in a pharmaceutical. A relative limit of detection (RLD) is proposed as a measure of the lowest detectable enantiomeric impurity. The RLD for the determination of dextrodopa contained in levodopa was 0.1% and found to depend on the enantiomer migration order. The enantiomeric purity of levodopa in the pharmaceutical preparation and dextrodopa from Sigma was 99.5 and 99.95%, respectively.