Effect of catechin and commercial preparation of green tea essence on the pharmacokinetics of l-dopa in rabbits.

The aim of this study was to investigate drug interactions of L-dopa/carbidopa with catechin and green tea essence in rabbits following the simultaneous administration via an intramuscular injection of catechin or via an intragastric route for green tea essence with L-dopa/carbidopa. The results indicated that catechin at doses of 10, 20 and 50 mg/kg increased the area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration (AUC0-t ) of L-dopa by about 69, 78 and 42%, respectively. The metabolic ratios of the AUC0-t for 3-O-methyldopa (3-OMD)/L-dopa significantly decreased by about 56, 68 and 76% (P < 0.05), respectively. In addition, a single dose of 5/1.25 mg/kg L-dopa/carbidopa was co-administrated with 150 mg/kg green tea essence via an intragastric route with an oral-gastric tube. Comparing the related pharmacokinetic parameters of L-dopa, the clearance and metabolic ratio of L-dopa decreased by 20 and 19% (P < 0.05), respectively. In conclusion, catechin and green tea essence can significantly affect the metabolism of L-dopa by the catechol-O-methyltransferase (COMT) metabolic pathway. Catechin can enhance L-dopa bioavailability, and both catechin and green tea essence decreased 3-OMD formation. Therefore, catechin and green tea essence may increase L-dopa efficacy for Parkinson's disease treatment.

The Accordion Pill®: unique oral delivery to enhance pharmacokinetics and therapeutic benefit of challenging drugs.

Accordion Pill® (AP) is a novel gastric-retention oral delivery platform based on folded multilayer films (Intec Pharma, Jerusalem, Israel). Phase II clinical trials have evaluated gastric retention and pharmacokinetics (PK) of AP in healthy volunteers and efficacy and safety of AP containing carbidopa and levodopa (AP-CD/LD) in patients with Parkinson's disease (PD). AP was retained in the stomach for approximately 8 h, without special meal requirements. AP-CD/LD demonstrated improved absorption, more stable levodopa exposure and improved ON time compared with immediate-release CD/LD in advanced PD patients. AP provides a novel treatment platform for improving PK and efficacy for drugs with narrow absorption windows or poor solubility. Furthermore, AP allows multiple drug release profiles in a single capsule and can provide fixed-dose combinations.

Levodopa-carbidopa intestinal gel high concentration formulation is clinically bioequivalent to commercial formulation.

A new levodopa-carbidopa intestinal gel (LCIG) system featuring a higher levodopa/carbidopa (LD/CD) concentration and viscosity, LCIG-HV, is being developed to reduce the intrajejunal volume of LD/CD that is administered as compared to the current commercial formulation, LCIG-LV. This study characterizes the LCIG-HV formulation and compares it to the LCIG-LV formulation via dissolution testing and a clinical pharmacokinetic bioequivalence study. In vitro release profiles of LD/CD were determined using a USP Dissolution Apparatus 2 with 500 mL of phosphate buffer (pH 4.5) operating at 25 RPM. A single dose, open-label study was conducted according to a two-period, randomized, crossover design in 28 healthy subjects. The point estimate (PE) of the levodopa Cmax geometric mean for the LCIG-HV formulation was 4% higher than that of the LCIG-LV formulation. PEs of levodopa AUCt and AUCinf geometric means were comparable for both formulations. PEs of carbidopa Cmax , AUCt and AUCinf geometric means for the LCIG-HV formulation were 3%-5% higher than those of the LCIG-LV formulation. For both formulations, the median Tmax for levodopa was 1.0 and 3.0 hours for carbidopa. The levodopa half-life harmonic mean was 1.6 hour for both formulations. The carbidopa half-life harmonic mean was 1.9 and 2.0 hour, respectively, for the LCIG-HV and LCIG-LV formulations. Cmax , AUCt and AUCinf of LD/CD carbidopa were comparable for both formulations. The current study demonstrates that the LCIG-LV and LCIG-HV formulations are clinically bioequivalent for LD/CD according to FDA guidance. However, the dissolution method was over discriminatory of formulation differences.

Micellar HPLC-UV method for the simultaneous determination of levodopa, carbidopa and entacapone in pharmaceuticals and human plasma.

A method based on micellar liquid chromatography to quantify levodopa, carbidopa and entacapone in plasma is reported. The sample pretreatment was a simple dilution in a pure micellar solution then filtration and direct injection, without requiring extraction or purification steps. The three drugs were resolved from the matrix in 7 min, using an aqueous solution of 0.1 M sodium dodecyl sulphate-10% n-propanol-0.3 tiethylamine, adjusted at pH 2.8 with 0.02 M orthophosphoric acid as mobile phase, running under isocratic mode at 1.0 mL/ min through VP-ODS column. The detection was done by UV (ultraviolet) absorbance at 225 nm. The method was successfully validated by the International Conference Harmonization guidelines in terms of: selectivity, linearity (r2 > 0.998) over the concentration ranges of 0.025-1.2, 0.05-1.0 and 0.3-2.0 µg mL-1 with limits of detection of 0.01, 6.16 × 10-3 and 0.02 µg mL-1 and limits of quantification of 0.03, 0.02 and 0.07 µg mL-1 for levodopa, carbidopa and entacapone, respectively. The proposed method was applied successfully for quantification of the studied drugs in their different dosage forms. Moreover, the method was further extensive to the quantification of the studied drugs in spiked human plasma and was successfully validated by the guidelines of the European Medicines Agency. The proposed procedures were successfully evaluated to determine the studied drugs in real human plasma. The procedure was found reliable, practical, cost-effective, available, short period, easy-to-handle, low-cost, environmental-friendly, secure, useful for the analysis of numerous samples per day. Lastly, the method was performed to the analysis of incurred, using quality control samples in the same analytical run, with adequate results. Therefore, it can be implementable for custom analysis in clinical laboratories.

Report: Preparation of levodopa/carbidopa compound drug resins.

The main objective of this study was to prepare the levodopa/carbidopa compound drug resins and investigate affecting factors such as drug concentration, temperature, particle size. The drug resins were made by bath method and the effects of above factors during the process of preparation was studied. Studies on the stabilities of drugs and drug resins were carried out by HPLC. The Results showed that the preparation of drug resins was influenced by drug concentration, resin particle size, reaction temperature and solvent concentration. In certain conditions the degradation peaks were found in the chromatograms of levodopa and carbidopa while the drug-resins remained undegraded. The study indicates that the drug resin technology is an effective way of improving stability of the drug and possesses certain sustained-release effects.

Fluorous l-Carbidopa Precursors: Highly Enantioselective Synthesis and Computational Prediction of Bioactivity.

New fluorous enantiopure (S)-α-aminated ß-keto esters were prepared through a highly enantioselective electrophilic α-amination step in the presence of europium triflate and (R,R)-phenyl-pybox. These compounds are precursors of fluorinated analogues of l-carbidopa, which is known to inhibit DOPA decarboxylase (DDC), a key protein in Parkinson's disease. Fluorination provides better stability for biological applications, which could possibly lead to DDC inhibitors better than l-carbidopa itself. Induced fit docking computational simulations performed on the new structures interacting with DDC highlight that for an efficient binding at the DDC site, at least one hydroxyl substituent must be present at the aromatic ring of the l-carbidopa analogues and show that the presence of fluorine can further fix the position of the ligand in the active site.

The Design and Evaluation of an l-Dopa-Lazabemide Prodrug for the Treatment of Parkinson's Disease.

l-Dopa, the metabolic precursor of dopamine, is the treatment of choice for the symptomatic relief of the advanced stages of Parkinson's disease. The oral bioavailability of l-dopa, however, is only about 10% to 30%, and less than 1% of the oral dose is estimated to reach the brain unchanged. l-Dopa's physicochemical properties are responsible for its poor bioavailability, short half-life and the wide range of inter- and intrapatient variations of plasma levels. An l-dopa-lazabemide prodrug is proposed to overcome the problems associated with l-dopa absorption. Lazabemide is a monoamine oxidase (MAO)-B inhibitor, a class of compounds that slows the depletion of dopamine stores in Parkinson's disease and elevates dopamine levels produced by exogenously administered l-dopa. l-Dopa was linked at the carboxylate with the primary aminyl functional group of lazabemide via an amide, a strategy which is anticipated to protect l-dopa against peripheral decarboxylation and possibly also enhance the membrane permeability of the prodrug. Selected physicochemical and biochemical properties of the prodrug were determined and included lipophilicity (logD), solubility, passive diffusion permeability, pKa, chemical and metabolic stability as well as cytotoxicity. Although oral and i.p. treatment of mice with the prodrug did not result in enhanced striatal dopamine levels, 3,4-dihydroxyphenylacetic acid (DOPAC) levels were significantly depressed compared to saline, l-dopa and carbidopa/l-dopa treatment. Based on the results, further preclinical evaluation of the l-dopa-lazabemide prodrug should be undertaken with the aim of discovering prodrugs that may be advanced to the clinical stages of development.

Carbidopa: a selective Ah receptor modulator (SAhRM).

The aryl hydrocarbon receptor (AhR) was discovered as the intracellular receptor that bound with high affinity to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and the AhR is required for mediating the toxicity induced by TCDD. Subsequent studies show that the AhR binds structurally diverse chemicals including plant-derived compounds that promote health and several AhR-active pharmaceuticals that exhibit anticancer activity. In this issue, there is a report that carbidopa, a drug used for treating Parkinson's disease, is also an AhR ligand, and this compound inhibits pancreatic cancer cell and tumor growth. These results are consistent with activities of other AhR-active compounds that inhibit carcinogenesis. Like carbidopa, these chemicals are selective AhR modulators with potential clinical applications that are AhR-dependent.

Continuous Transdermal Delivery of L-DOPA Based on a Self-Assembling Nanomicellar System.

PURPOSE: When levodopa (L-DOPA) is administered orally, it is eliminated from the body very quickly resulting in a series of sharp fluctuations in its blood concentrations. These frequent changes in blood levels are considered to be responsible for the development of late motor complications and dyskinesias, which are troubling clinical and treatment issues in Parkinson's disease. Transdermal drug delivery is a patient-compliant method for delivering therapeutics into the systemic circulation in a continuous and controlled manner. Transdermal delivery of L-DOPA can achieve continuous dopaminergic stimulation (CDS), thus reducing motor fluctuations. METHODS: However, there are two technical difficulties in the development of a transdermal patch for L-DOPA: (a) L-DOPA is poorly soluble in most pharmaceutically-acceptable solvents, and (b) L-DOPA has a limited permeability through the skin even from saturated solutions. We have, therefore, investigated the transdermal delivery of L-DOPA using an innovative self-assembling nano-micellar system (SANS), loaded with 2% L-DOPA and 1% carbidopa. RESULTS: In vitro testing as well as in vivo pharmacokinetic studies (multiple-dose regimen) in rabbits have demonstrated for the first time a significantly increased percutaneous permeation and systemic absorption of L-DOPA. CONCLUSIONS: It has therefore been proposed that either a once-daily or a twice-daily regimen could be therapeutically effective depending on the severity of the disease.

Investigation of different spectrophotometric and chemometric methods for determination of entacapone, levodopa and carbidopa in ternary mixture.

New, simple, accurate and sensitive UV spectrophotometric and chemometric methods have been developed and validated for determination of Entacapone (ENT), Levodopa (LD) and Carbidopa (CD) in ternary mixture. Method A is a derivative ratio spectra zero-crossing spectrophotometric method which allows the determination of ENT in the presence of both LD and CD by measuring the peak amplitude at 249.9nm in the range of 1-20µgmL-1. Method B is a double divisor-first derivative of ratio spectra method, used for determination of ENT, LD and CD at 245, 239 and 293nm, respectively. Method C is a mean centering of ratio spectra which allows their determination at 241, 241.6 and 257.1nm, respectively. Methods B and C could successfully determine the studied drugs in concentration ranges of 1-20µgmL-1 for ENT and 10-90µgmL-1 for both LD and CD. Methods D and E are principal component regression and partial least-squares, respectively, used for the simultaneous determination of the studied drugs by using seventeen mixtures as calibration set and eight mixtures as validation set. The developed methods have the advantage of simultaneous determination of the cited components without any pre-treatment. All the results were statistically compared with the reported methods, where no significant difference was observed. The developed methods were satisfactorily applied to the analysis of the investigated drugs in their pure form and in pharmaceutical dosage forms.

Multi-Drug-Loaded Microcapsules with Controlled Release for Management of Parkinson's Disease.

Parkinson's disease (PD) is a progressive disease of the nervous system, and is currently managed through commercial tablets that do not sufficiently enable controlled, sustained release capabilities. It is hypothesized that a drug delivery system that provides controlled and sustained release of PD drugs would afford better management of PD. Hollow microcapsules composed of poly-l-lactide (PLLA) and poly (caprolactone) (PCL) are prepared through a modified double-emulsion technique. They are loaded with three PD drugs, i.e., levodopa (LD), carbidopa (CD), and entacapone (ENT), at a ratio of 4:1:8, similar to commercial PD tablets. LD and CD are localized in both the hollow cavity and PLLA/PCL shell, while ENT is localized in the PLLA/PCL shell. Release kinetics of hydrophobic ENT is observed to be relatively slow as compared to the other hydrophilic drugs. It is further hypothesized that encapsulating ENT into PCL as a surface coating onto these microcapsules can aid in accelerating its release. Now, these spray-coated hollow microcapsules exhibit similar release kinetics, according to Higuchi's rate, for all three drugs. The results suggest that multiple drug encapsulation of LD, CD, and ENT in gastric floating microcapsules could be further developed for in vivo evaluation for the management of PD.

Gas-phase acidity and dynamics of the protonation processes of carbidopa and levodopa. A QM/QD study.

The present work details, our efforts to investigate and compare the acid-base properties of levodopa (LD) and carbidopa (CD), a drug combination being used in the treatment of Parkinson's disease. Protonation and deprotonation were examined for all possible sites in the two drugs. Proton affinity and proton detachment enthalpies were computed at the B3LYP/6-311++G** level of theory. Results of the present work reveal that CD is more basic and can abstract protons in solution much more efficiently than LD. Furthermore, at all deportation sites considered, CD is more acidic than LD. DFT-based ADMP, dynamic simulations have been performed to explore the dynamics of the protonation processes in LD and CD. Thus, while the dynamics of the protonation process of LD is very straightforward leading to the formation of the corresponding cation, the protonation process in CD is very complex involving a major geometry change and rearrangement. Results of the present work reveal that the active species in acid medium is not CD in its normal geometry but a carbonyl hydrazine form instead. The presence of the carbonyl group ß to the hydrazine group may very well underlie its enhanced activity which allows it to bind to the active site of the DDC enzyme. The relative stabilities of various water-water-CD complexes have been computed and compared.

[Levodopa: the story continues].

The history of development of the drug levodopa is described. It is emphasized that the conception of continuous dopaminergic stimulation in treatment of Parkinson's disease is of great importance. Special attention is drawn to the studies on efficacy and safety of levodopa-carbidopa intestinal gel, quality of life of patients treated with this drug as well as to the experience of long-term treatment.

Multivariate analysis for resolving interactions of carbidopa with dsDNA at a fullerene-C60/GCE.

For the first time, interactions of carbidopa (CD) with double-stranded calf thymus DNA (dsDNA) in a phosphate buffered solution (PBS, 0.05M, pH=4.0) at a fullerene-C60/glassy carbon electrode (FLR/GCE) has been studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and square wave voltammetry (SWV). The interaction of CD with dsDNA was also monitored using fluorescence (F) and UV-vis spectroscopic techniques. New information was obtained when a row- and column-wise augmented matrix consisting of SWV, LSV, F and UV-vis data was resolved using multivariate curve resolution-alternating least squares (MCR-ALS) as a powerful chemometric tool. Pure electrochemical and spectroscopic signals of CD, dsDNA and dsDNA-CD2 complex, and their concentration profiles were then successfully resolved. Molecular docking studies confirmed that the binding of CD with dsDNA shows minor groove binding mode which was in accordance with experimental results. Under optimized conditions, the SWV responses were linearly related to dsDNA concentration between 0.1 and 25.0nM and a limit of detection (LOD) of 0.03nM was calculated (3Sb/b=3). Moreover, the modified electrode exhibited long term stability, good repeatability, and reproducibility, and high sensitivity and selectivity toward dsDNA determination in human serum samples, demonstrating its feasibility toward dsDNA sensing.

Asymmetric synthesis of L-carbidopa based on a highly enantioselective α-amination.

A stereoselective synthesis of L-carbidopa in seven steps and 50% overall yield from commercial compounds is described. The key step involves a highly enantioselective α-amination reaction of an acyclic ß-ketoester with di-tert-butyl azodicarboxylate induced by europium and (R,R)-diphenyl-pybox.

Chaotropic agents in liquid chromatographic method development for the simultaneous analysis of levodopa, carbidopa, entacapone and their impurities.

The simultaneous pharmaceutical analysis of multi-component drugs represents a challenge due to a large total number of analytes present in the sample. These analytes are not only the active pharmaceutical ingredients, but also the impurities that might follow the active substances. The aim of this study was to develop an efficient reversed-phase LC method for the simultaneous analysis of antiparkinsonian drugs levodopa, carbidopa and entacapone along with their six related impurities. For the achievement of desirable separation, different acids with anions possessing different properties according to Hofmeister classification (ortho-phosphoric, trifluoroacetic and perchloric acid) were tested. Finally, in order to draw the unbiased conclusions when optimizing the analytical method, for the final tuning of the gradient program, Box-Behnken experimental design and Derringer's desirability function were used. The experiments were performed on Zorbax Extend C18, 150 mm × 4.6 mm, 5 µm particle size column with the UV detection at 280 nm and mobile phase flow rate of 1 mL/min. The optimal mobile phase consisted of methanol and 20mM trifluoroacetic acid (pH 2.0 adjusted with NaOH), while their ratio is changed according to previously defined gradient program. The method was tested for selectivity, sensitivity, linearity, accuracy and precision, and proved to be suitable for routine qualitative and quantitative analysis of levodopa, carbidopa, entacapone and their impurities in their mixture.

Voltammetric detection of L-dopa and carbidopa on graphene modified glassy carbon interfaces.

The present work reports on the use of graphene nanosheets, deposited on glassy carbon, as electrode materials, and their electrochemical characterization. The graphene nanosheets were obtained by chemical reduction of graphene oxide using hydrazine. The possibility of analyzing L-dopa and carbidopa, two important catecholamines found in pharmaceutical products, separately and simultaneously by differential pulse voltammetry utilizing graphene modified GC interfaces is investigated. Voltammetric peak currents showed a linear response for both catecholamines in the range of 1-16 µM. The detection limit was about two times lower for L-dopa than carbidopa being 0.8 µM and 1.8 µM, respectively with a current sensitivity of (2.15 ± 0.5) and (0.48 ± 0.3) µA µM(-1). Simultaneous detection of both catecholamines can be achieved on these electrodes. Equivalent amounts of L-dopa and carbidopa have no effect on the detection limit of L-dopa. In addition, the presence of L-dopa with concentrations 4 times higher than carbidopa has no influence on the voltammetric profile.

Pharmacokinetics of levodopa, carbidopa, and 3-O-methyldopa following 16-hour jejunal infusion of levodopa-carbidopa intestinal gel in advanced Parkinson's disease patients.

Motor complications of Parkinson's disease (PD) are a consequence of pulsatile dopaminergic stimulation from standard oral levodopa therapy. Levodopa-carbidopa intestinal gel (LCIG) is infused continuously via an intrajejunal percutaneous gastrostomy tube. This was the first study designed to characterize the full pharmacokinetic profiles of levodopa, carbidopa, and levodopa metabolite, 3-O-methyldopa (3-OMD) with 16-h LCIG infusion. Nineteen advanced PD patients (mean age, 65 years) who were on LCIG therapy for ≥30 days were enrolled. Patients received their individualized LCIG infusion doses, and serial pharmacokinetic samples were collected. Eighteen patients completed the study; 19 were assessed for safety. Mean (SD) total levodopa and carbidopa doses were 1,580 (403) and 395 (101) mg, respectively. Mean (SD) C(avg) (µg/mL) were 2.9 (0.84) for levodopa, 17.1 (4.99) for 3-OMD, and 0.22 (0.08) for carbidopa. The degree of fluctuation [defined as (C(max)-C(min))/C(avg)] in levodopa, 3-OMD, and carbidopa plasma concentrations was very low (0.52, 0.21, and 0.96, respectively) during hours 2-16 of infusion. Accordingly, the within-subject coefficients of variation in levodopa, 3-OMD, and carbidopa concentrations were low (13%, 6%, and 19%, respectively). Three patients (16%) reported ≥1 treatment-emergent adverse event; none were considered severe. Continuous intrajejunal LCIG infusion maintained stable plasma levodopa levels over 16 h. Consistent exposure has been shown to reduce motor and nonmotor complications associated with oral medications. LCIG was well tolerated, consistent with previous reports.

Evaluation and optimization of preparative variables for controlled-release floating microspheres of levodopa/carbidopa.

Levodopa, a prodrug of dopamine, is the first line drug in the treatment of Parkinson's disease. All current levodopa products are formulated in combination with aromatic amino acid decarboxylase inhibitors such as carbidopa or benserazide to prevent the peripheral metabolism of levodopa. The objective of the present investigation was to produce floating microspheres of carbidopa (CD)/levodopa (LD) to enhance their efficacy by increasing their gastric residence time, which is major technique to improve efficacy of narrow absorption window drugs. The microspheres were prepared by the o/w emulsion-solvent diffusion method using polymers hydroxypropylmethyl cellulose K15 M (HPMC K15 M) and ethyl cellulose (EC). The effects of various formulation and process variables on the particle size, in vitro floating behavior, percent drug entrapment, and in vitro drug release were studied. The size and surface morphology of prepared microspheres were characterized by optical and scanning electron microscopy, respectively. In vitro drug release studies were performed and drug release kinetics was evaluated using the linear regression analysis. The prepared microspheres exhibited prolonged drug release (approximately 10h) and remained buoyant for >12 h. Spherical and smooth-surfaced microspheres with encapsulation efficiency ranging from 43% to 80% were obtained. In vitro studies demonstrated diffusion-controlled drug release from the microspheres.