Fasting state is one of the factors associated with plasma levodopa fluctuations during levodopa‒carbidopa intestinal gel treatment

INTRODUCTION

Some patients with Parkinson's disease (PD) undergoing levodopa‒carbidopa intestinal gel (LCIG) treatment experience motor fluctuations in the afternoon. The migrating motor complex, a specific periodic migrating contraction pattern occurring in the stomach and small intestine during the fasting state, can affect drug absorption. We aimed to compare the pharmacokinetic parameters between two conditions (with and without lunch) and assessed the influence of the fasting state on the levodopa pharmacokinetics in LCIG treatment.

METHODS

We evaluated the levodopa pharmacokinetics from 12:00 p.m. to 6:00 p.m. in 10 LCIG-treated PD patients in the presence and absence of lunch.

RESULTS

The maintenance dose of LCIG correlated strongly with the mean plasma concentration of levodopa in the absence (r = 0.94, coefficient of determination (R²) = 0.89, p < 0.001) or presence of lunch (r = 0.96, R² = 0.93, p < 0.001). Comparison of the pharmacokinetic parameters revealed that the coefficient of variation was significantly greater in the condition without lunch than in the condition with lunch (p = 0.004): 16.73% (4.88%) without lunch and 9.22% (3.80%) with lunch. There were no significant differences in the mean plasma concentration of levodopa (p = 0.49) and area under the plasma concentration‒time curve (p = 0.27) between the two conditions.

CONCLUSIONS

Plasma concentrations of levodopa fluctuated more in patients undergoing LCIG treatment without than with lunch. Our results indicate that a small amount of food intake may be a better corrective approach for worsening of symptoms in the fasting state rather than additional levodopa.

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.

Using Spontaneous Eye-blink Rates to Predict the Motor Status of Patients with Parkinson's Disease

Objective Assessing daily motor fluctuations is an important part of the disease management for patients with Parkinson's disease (PD). However, the frequent recording of subjective and/or objective assessments is not always feasible, and easier monitoring methods have been sought. Previous studies have reported that the spontaneous eye-blink rate (EBR) is correlated with the dopamine levels in the brain. Thus, the continuous monitoring of the EBR may be useful for predicting the motor status in patients with PD. Methods Electrooculograms (EOGs) were recorded for up to 7.5 hours from three PD patients using a wearable device that resembled ordinary glasses. An receiver operating characteristic (ROC) analysis was performed to compare the ability of the EBR estimates at each time-point (Blink Index) and the plasma levodopa levels to predict the motor status. Results The Blink Index was correlated with the plasma levodopa levels. When an indicator for the first hour of the observation period was included in the model, the Blink Index discerned wearing-off and dyskinesia as accurately as the plasma levodopa level. Conclusion Our study provides preliminary evidence regarding the utility of continuous EBR monitoring for the non-invasive evaluation of the motor status in patients with PD.

Effects of Levodopa on Vowel Articulation in Patients with Parkinson's Disease

OBJECTIVES

The effects of levodopa on articulatory dysfunction in patients with Parkinson's disease remain inconclusive. This study aimed to investigate the effects of levodopa on isolated vowel articulation and motor performance in patients with moderate to severe Parkinson's disease, excluding speech fluctuations caused by dyskinesia.

METHODS

21 patients (14 males and 7 females) and 21 age- and sex- matched healthy subjects were enrolled. Together with motor assessment, the patients phonated five Japanese isolated vowels (/a/, /i/, /u/, /e/, and /o/) 20 times before and 1 h after levodopa treatment. We made the frequency analysis of each vowel and measured the first and second formants. From these formants we constructed the pentagonal vowel space area which should be the good indicator for articulatory dysfunction of vowels. In control subjects, only speech samples were analyzed. To investigate the sequential relationship between plasma levodopa concentrations, motor performances, and acoustic measurements after treatment, entire drug cycle tests were performed in 4 patients.

RESULTS

The pentagonal vowel space area was significantly expanded together with motor amelioration after levodopa treatment, although the enlargement is not enough for the space area of control subjects. Drug cycle tests revealed that sequential increases or decreases in plasma levodopa levels after treatment correlated well with expansion or decrease of the vowel space areas and improvement or deterioration of motor manifestations.

CONCLUSIONS

Levodopa expanded the vowel space area and ameliorated motor performance, suggesting that dysfunctions in vowel articulation and motor performance in patients with Parkinson's disease are based on dopaminergic pathology.

[The therapeutic plasma concentrations of antiparkinson dopamine agonists and their in vitro pharmacology at dopamine receptors]

This review discusses the relationship between therapeutic plasma concentrations of antiparkinson dopamine agonists (rotigotine, pergolide, cabergoline, apomorphine, bromocriptine, ropinirole, pramipexole, and talipexole) and their in vitro pharmacology at dopamine D1, D2 and D3 receptors. A significant correlation was found between therapeutic plasma concentrations of these dopamine agonists and their agonist potencies (EC50) at D2 receptors, although no such correlation existed at D1 or D3 receptors, suggesting that D2 receptors could be the primary and common target for the antiparkinson action of all dopamine agonists. However, D1 receptor stimulation is also important for maintaining swallowing reflex, bladder function and cognition. In particular, continuous D1 and D2 receptor stimulation may be reduced to low levels among Parkinson's disease patients. Our findings revealed therapeutic plasma concentrations of rotigotine were similar to its agonist potencies at both D1 and D2 receptors. Thus, rotigotine may be beneficial for the treatment of Parkinson's disease patients in that this dopamine agonist has the potential of continuous stimulation of both D1 and D2 receptors in the clinical setting.

Zonisamide suppresses endoplasmic reticulum stress-induced neuronal cell damage in vitro and in vivo

Zonisamide has been reported to have protective effects on epilepsy and Parkinson׳s disease and to work via various mechanisms of action, such as inhibition of monoamine oxidase-B and enhancement of tyrosine hydroxylase. Recently, it has been suggested that zonisamide itself shows neuroprotective actions. Therefore, in the present study we investigated the neuroprotective effects of zonisamide against endoplasmic reticulum (ER) stress. We used human neuroblastoma (SH-SY5Y) cells and investigated the protective effects of zonisamide against tunicamycin- and thapsigargin-induced neuronal cell death. In addition, we investigated the effect of zonisamide against 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell death and the mechanism of protection against ER stress. In vivo, we investigated the effect of zonisamide (20 mg/kg, p.o.) in the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced mouse model of Parkinson׳s disease. Zonisamide not only suppressed MPP⁺-induced cell death, but also inhibited ER stress-induced cell death and suppressed the expression of ER stress-related factors such as C/EBO homologous protein (CHOP) in vivo. Furthermore, zonisamide inhibited the activation of caspase-3 in vitro. These results suggest that zonisamide affected ER stress via caspase-3. We think that ER stress, particularly the mechanism via caspase-3, is involved in part of the neuroprotective effect of zonisamide against the experimental models of Parkinson׳s disease.

A new HILIC-MS/MS method for the simultaneous analysis of carbidopa, levodopa, and its metabolites in human plasma

Monitoring of the plasmatic levels of levodopa (LEV) and carbidopa (CAR) is necessary to adjust the dose of these drugs according to the individual needs of Parkinson's disease patients. To support drug therapeutic monitoring, a method using HILIC mode and LC-MS/MS was developed for the simultaneous determination of carbidopa, levodopa, and its metabolites (3-o-methyldopa (3-OMD) and dopamine (DOPA)) in human plasma. A triple quadrupole mass spectrometry was operated under the multiple reaction-monitoring mode (MRM) using the electrospray ionization technique. After straightforward sample preparation via protein precipitation, an Atlantis HILIC (150 × 2.1 mm, 3 μm, Waters, USA) column were used for separation under the isocratic condition of acetonitrile/water (79:21, v/v) containing 0.05% formic acid and 3 mmol/L ammonium formate and the total run time was 7 min. Deuterated LEV was used as internal standard for quantification. The developed method was validated in human plasma with a lower limit of quantitation of 75 ng/mL for LEV, 65 ng/mL for CAR and 3-OMD, and 20 ng/mL for DOPA. The calibration curve was linear within the concentration range of 75-800 ng/mL for LEV, 65-800 ng/mL for CAR and 3-OMD, and 20-400 ng/mL for DOPA (r>0.99). The assay was accurate and precise, with inter-assay and intra-assay accuracies within ±13.44% of nominal and inter-assay and intra-assay precision≤13.99%. All results were within the acceptance criteria of the US FDA and ANVISA guidelines for method validation. LEV, CAR, 3-OMD and DOPA were stable in the battery of stability studies, long-term, bench-top, autosampler, and freeze/thaw cycles. Samples from patients undergoing treatment were analyzed, and the results indicated that this new method is suitable for therapeutic drug monitoring in Parkinson's disease patients.

The effect of different dosing regimens of levodopa/carbidopa/entacapone on plasma levodopa concentrations

BACKGROUND

Repeated dosing of levodopa/carbidopa/entacapone (LCE) has shown a favourable pharmacokinetic (PK) profile compared with levodopa/carbidopa (LC), but increases maximum plasma levodopa concentrations (C(max)) during the day. High levodopa concentrations are associated with peak-dose dyskinesias.

PURPOSE

To determine whether administering LCE 75/18.5/200 and 125/31.5/200 mg (LCE 75 and LCE 125) following a morning dose of LCE 100/25/200 and 150/37.5/200 mg (LCE 100 and LCE 150), respectively, would avoid the increase in levodopa C(max) values observed during multiple dosing of LCE 100 and LCE 150.

METHODS

This was an open, randomized, three-period, crossover PK trial in healthy volunteers (n = 19). Subjects were randomized to Group 1 or 2. Group 1 received in random sequence: LCE 150 followed by LCE 125 three times daily (tid); LCE 150 four times daily (qid); LC 150 qid. Group 2 received in random sequence: LCE 100 followed by LCE 75 tid; LCE 100 qid; LC 100 qid. Levodopa C(max), minimum plasma concentration (C(min)), area under the curve (AUC(0-14)) and peak-trough fluctuation (PTF) were calculated up to 14 h after the first dose.

RESULTS

Levodopa C(max) was not increased when the LCE dose was decreased by 25 mg after the morning dose. In comparison to LC, levodopa C(min) levels and AUC(0-14) values for LCE were significantly higher, while the levodopa PTF was significantly smaller.

CONCLUSIONS

Reducing the dose of LCE by 25 mg following the first morning dose results in a more consistent levodopa C(max) profile, avoiding levodopa accumulation while maintaining significantly higher C(min) levels and AUC(0-14) values compared with LC.

[Pharmacokinetics of hemantane in rats]

The pharmacokinetics ofhemantane after administration in different ways has been studied in rats. It is established that hemantane introduced both orally (p.o.) and intravenously (i.v.) is very intensively metabolized, with the main metabolites characterized by m/z = 250 and 266 and detected for 6 hours after the administration in both ways. Hemantane shows high rate of permeability into its target organ--brain--whereas the permeation of its metabolites is extremely low. The absolute bioavailability ofhemantane upon p.o. administration was 14.1%. The substance is subject to the "first-pass effect". The unchanged substance was determined in daily urine and feces in very small fractions of the administered dose: 0.23% in urine and 0.08% in feces after i.v. administration and 0.02% in feces after p.o. administration. Thus, it may be concluded that the substance is completely absorbed in rats from the gastro-intestinal tract into systemic blood circulation.

[Severe kyphosis and esophagus hiatal hernia affected in the levodopa absorption of a patient with Parkinson's disease]

An 82 year-old woman with Parkinson's disease complained of a tendency to fall. She has had an extensive kyphosis since she was 66 years old. Over the last 6 months, she has repeatedly fallen. Even though she took anti-parkisonian drugs, she had also developed camptocormia. Her plasma levodopa concentration was analyzed for 4 hrs after administrating an oral dose of levodopa (200 mg) plus carbidopa (20 mg) at the time of fasting. The change in the plasma levodopa concentration showed bimodal peaks. The physical symptoms depended on the plasma concentration and improved twice. Esophageal tortuosity and esophageal hiatal hernia were detected by esophagography and upper gastric endoscopy. Such physical symptoms were speculated to have been caused by the transit disturbance of the drug in the gastrointestinal duct. During a second analysis of the plasma levodopa concentration, the patient was instructed to keep extending her back after consuming the same dose of drugs but with a greater amount of water than in the first analysis. A single and a higher peak were observed for the plasma levodopa concentration, and the physical symptoms, including camptocormia and parkinsonism, were improved. Hunched posture could influence the absorption of antiparkinsonian drugs.

Determination of memantine in human plasma by liquid chromatography–electrospray tandem mass spectrometry: Application to a bioequivalence study

A simple, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of memantine (I) in human plasma is presented. Sample preparation consisted of the addition of amantadine (II) as internal standard (IS), liquid-liquid extraction in basic conditions using a mixture of diethyl ether-chloroform (7:3, v/v) as extracting solvent, followed by centrifugation, solvent evaporation and sample reconstitution in methanol. Both I and II (internal standard) were analyzed using a C18 column and a mobile phase composed of methanol-water-formic acid (80:20:0.1, v/v/v). Eluted compounds were monitored using positive mode electrospray (ES) tandem mass spectrometry. The analyses were carried out by selected reaction monitoring (SRM) using the parent to daughter combinations of m/z 180>163 (memantine) and m/z 152>135 (amantadine). The peak areas from the analyte and IS were used for quantification of I. The achieved limit of quantification (LOQ) was 0.1 ng/mL; the assay exhibited a linear dynamic range of 0.1-50.0 ng/mL with a determination coefficient (r2) of at least 0.98. Validation results on linearity, specificity, accuracy, precision and stability, as well as on application to the analysis of samples taken up to 320 h after oral administration of 20mg (two 10mg capsules) of I in healthy volunteers demonstrated the applicability to bioequivalence studies.

Quantitative determination of amantadine in human plasma by liquid chromatography–mass spectrometry and the application in a bioequivalence study

A sensitive liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method is developed and validated for rapid determination of amantadine in human plasma. Desloratadine was used as the internal standard (I.S.). Human plasma (0.2 mL) was first alkalified with 100 microL of sodium hydroxide (3M) and then extracted with 1 mL of n-hexane containing 1% isopropanol (v/v) and 10% dichloromethane (v/v) by vortex-mixer for 3 min. The mixture was centrifuged at 14,000 rpm for 5 min. The supernatant was evaporated to dryness and the residue was dissolved in mobile phase. Samples were separated using a Thermo Hypersil-HyPURITYC18 reversed-phase column (150 mm x 2.1 mm i.d., 5 microm). Mobile phase consisted of methanol-acetonitrile-20 mM ammonium acetate (45:10:45, v/v/v) containing 1% acetic acid with pH 4.0. Amantadine and I.S. were measured by electrospray ion source in positive selective ion monitoring mode. The good linearity ranged from 3.9 to 1000 ng/mL and the lowest limit of quantification was 3.9 ng/mL. The extraction efficiencies were approximately 70% and recoveries of method ranged from 98.53 to 103.24%. The intra-day relative standard deviations (R.S.D.) were less than 8.43% and inter-day R.S.D. below 10.59%. The quality control samples were stable when kept at room temperature for 12h, at -20 degrees C for 30 days and after four freeze/thaw cycles. The method has been successfully used to evaluation of the pharmacokinetics and bioequivalence of amantadine in 20 healthy volunteers after an oral dose of 100 mg amantadine.

Acute effects of immediate and controlled-release levodopa on mood in Parkinson's disease: A double-blind study

Mood fluctuations related to levodopa (LD) dosing are well-known psychiatric complications of Parkinson's disease (PD). No formal studies explored how affective response to LD relates to the type of motor response to oral LD (stable or wearing-off) and to different pharmacokinetic profiles of oral LD. We used an intrasubject randomized double-blind crossover design to study 14 patients (7 stable, 7 wearing-off) who were monitored for motor status, mood, anxiety, and plasma LD levels 1 hour before and 6 hours after an oral dose of immediate-release (IR) and controlled-release LD formulations. Analysis of the dose-response curves showed a significant interaction between the type of motor response and the type of LD. Only the wearing-off patients had a significant mood elevation, and this effect was only significant following challenge with IR LD. Motor status strongly correlated with LD plasma levels and anxiety but not with mood ratings. Mood changes in PD patients are related to the patient's type of motor response to oral LD and also to the kinetic profile of the LD formulation used for dopaminergic replacement.

The effect of Madopar on the pharmacokinetics of ropinirole in healthy Chinese volunteers

Ropinirole is a nonergoline dopamine D(2)-receptor agonist and has been proven to be effective in both monotherapy and combination therapy for idiopathic Parkinson's disease. The purpose of the present study was to examine the effect of Madopar on the pharmacokinetics of ropinirole in healthy Chinese volunteers by using liquid chromatography tandem mass spectrometry (HPLC/MS/MS). A single dose of 1mg ropinirole was given orally after administration of the placebo or Madopar (containing 200 mg levodopa and 50 mg benserazide) to six healthy males and six healthy females in a cross-over randomized study with a minimum washout period of 8 days. Pharmacokinetic parameters were calculated for both treatments. Coadministration of ropinirole and Madopar did not result in a notable change in rate or extent of availability of ropinirole, as shown by the ratios (90% confidence intervals) of 1.045 (0.900, 1.222) for C(max) (maximum plasma concentration) and 1.167 (1.086, 1.262) for AUC(0-inf) (the area under the concentration-time curve). Likewise, no significant difference in any of the other pharmacokinetic parameters [T(max) (the time needed to reach the C(max)), MRT (mean residence time), volume of distribution (V/F), and clearance (CL/F)] was observed between the treatment groups. No clinically relevant adverse effects were detected under either conditions and there are no pharmacokinetic grounds for adjusting the dose of ropinirole when given in combination with Madopar in Chinese patients.

DHEA improves symptomatic treatment of moderately and severely impaired MPTP monkeys

The steroid dehydroepiandrosterone (DHEA) is abundant in men and women and decreases rapidly during aging. Parkinson's disease (PD) is the second most common neurodegenerative disorder just behind Alzheimer. l-3,4-Dihydroxyphenylalanine (l-Dopa) therapy remains the most effective treatment but many patients develop motor complications. This study investigated the acute effect of DHEA alone and with l-Dopa in 12 females monkeys lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to model PD. DHEA administration alone improved the mean parkinsonian score at 1, 5 and 15mg/kg in moderately and severely impaired MPTP monkeys and increased blood DHEA concentrations. DHEA with a low dose of l-Dopa increased the l-Dopa effect in moderately and severely impaired MPTP monkeys. DHEA lengthened duration of the effect of the low dose of l-Dopa by 15-45min. DHEA at 1, 5 and 15mg/kg combined with a high dose of l-Dopa did not increase dyskinesias. DHEA could act by reducing inhibitory GABAergic activity in the striatal output pathways. DHEA could also be metabolized into estradiol in the brain and increase acutely dopamine activity.

Quantitative study of salivary secretion in Parkinson's disease

We examined basal and reflex salivary flow rate and composition in 46 patients with Parkinson's disease (PD), both in off and on conditions, compared to 13 age-matched controls without underlying disease or treatment affecting autonomic function. Whole saliva was collected 12 hours after withdrawal of dopaminergic drugs and at the peak of levodopa-induced motor improvement. Twenty-three of the 46 PD patients had received domperidone a week before the study. Basal salivary flow rate was significantly lower in PD patients in the off state compared to controls (P<0.005). Levodopa increased salivary flow rate (P<0.05) both in the domperidone-pretreated and untreated groups. Citric acid stimulated salivary flow rate in both the off and on states in PD patients. This effect was higher in the domperidone-pretreated patients. Salivary concentration of sodium, chloride, and amylase was higher in PD patients than in controls and was not affected by levodopa or domperidone treatment. Levodopa stimulates both basal and reflex salivary flow rate in PD. The mechanism appears to be central, as the effect is not blocked by domperidone. Domperidone may have a peripheral effect that potentiates reflex salivary secretion. Salivary composition is abnormal in PD and is not affected by levodopa treatment.

Effects of caffeine on levodopa pharmacokinetics and pharmacodynamics in Parkinson disease

The authors studied the acute effect of caffeine on the levodopa pharmacokinetics and pharmacodynamics in 12 patients with idiopathic Parkinson disease. This double-blind, randomized, crossover study revealed that caffeine shortened the maximal plasma concentration of levodopa, decreased the latency to levodopa walking and tapping motor response, and increased the magnitude of walking response. Caffeine administered before levodopa may improve its pharmacokinetics in some parkinsonian patients.

Intravenous levodopa administration in humans based on a two-compartment kinetic model

Levodopa, when combined with a decarboxylase inhibitor, essentially delivers dopamine directly to the brain, with no net effect on brain blood vessels. For future neuroimaging studies of Parkinson disease and Tourette syndrome, we sought to rapidly produce a biologically relevant levodopa concentration in plasma and then maintain that concentration long enough to assess motor, cognitive, emotional, and neuroimaging responses, while minimizing side effects in levodopa-naive individuals. Based on available pharmacokinetic data and a two-compartment model, we designed a decreasing-exponential-rate infusion to meet these goals. This report gives results of double-blind levodopa and placebo infusions in six healthy subjects. Mean plasma levodopa concentrations were within 3% of their 1200 ng/mL target at 20 and 40 min into the infusion, and within 20% between approximately 12 and 90 min. Levodopa significantly reduced serum prolactin and raised serum growth hormone concentrations. Volunteers had no significant side effects.

Evidence for L-dopa incorporation into cell proteins in patients treated with levodopa

Levodopa (L-dopa) is the most widely used agent for the symptomatic relief of Parkinson's disease. There is concern that chronic L-dopa treatment may be detrimental, with some studies suggesting that L-dopa may be neurotoxic. A potentially important mechanism whereby L-dopa may exert neurotoxic effects has been overlooked: that of the incorporation of L-dopa into proteins by protein synthesis. L-Dopa competes with tyrosine as a substrate in protein synthesis in vitro. We provide evidence that L-dopa can also be incorporated into proteins in vivo. Blood from L-dopa-treated and -non-treated patients was separated into protein, erythrocyte and lymphocyte fractions and levels of protein-incorporated dopa quantified by HPLC. Levels of protein-incorporated dopa were significantly increased in lymphocyte cell proteins from L-dopa-treated patients. This has not arisen from oxidative pathways as there was no evidence of oxidative damage to proteins. In addition, there was no increase in protein-incorporated dopa in erythrocytes, which are not actively synthesizing proteins. We suggest that protein-incorporated dopa could also be generated in the CNS. The accumulation of protein-incorporated dopa in cells is associated with oxidative stress and impaired function and could contribute to some of the problems associated with long-term L-dopa treatment.

Levodopa availability improves with progression of Parkinson’s disease

BACKGROUND

Previous pharmacokinetic trials with standard levodopa formulations showed a different behaviour of levodopa degradation in plasma of patients with Parkinson's disease (PD) in various stages.

OBJECTIVES

To investigate associations between levodopa plasma levels in relation to the scored intensity of PD.

SUBJECTS AND METHODS

We administered water soluble 100 mg levodopa and 25 mg benserazide to 50 PD patients, taken off medication for at least 12 hours, and assessed the levodopa plasma concentrations during an 180 minutes period under standardised conditions.

RESULTS

The computed area under the curve (AUC) values of levodopa plasma levels were significant higher in advanced PD patients. PD rating scores significantly correlated to the AUC outcomes and the maximum levodopa plasma concentration.

CONCLUSIONS

Levodopa availability improves with progression of PD. This may result from deteriorated peripheral activity of levodopa metabolising enzymes or an increasing enteric dysfunction with subsequent better duodenal levodopa absorption or both.

Optimal design for multivariate response pharmacokinetic models

We address the problem of designing pharmacokinetic experiments in multivariate response situations. Criteria, based on the Fisher information matrix, whose inverse according to the Rao-Cramer inequality is the lower bound of the variance-covariance matrix of any unbiased estimator of the parameters, have previously been developed for univariate response for an individual and a population. We extend these criteria to design individual and population studies where more than one response is measured, for example, when both parent drug and metabolites are measured in plasma, multi-compartment models, where measurements are taken at more than one site, or when drug concentration and pharmacodynamic data are collected simultaneously. We assume that measurements made at distinct times are independent, but measurements made of each concentration are correlated with a response variance-covariance matrix. We investigated a number of optimisation algorithms, namely simplex, exchange, adaptive random search, simulated annealing and a hybrid, to maximise the determinant of the Fisher information matrix as required by the D-optimality criterion. The multiresponse optimal design methodology developed was applied in two case studies, where the aim was to suggest optimal sampling times. The first was a restrospective iv infusion experiment aimed to characterise the disposition kinetics of tolcapone and its two metabolites in healthy volunteers. The second was a prospective iv bolus experiment designed to estimate the tissue disposition kinetics of eight beta-blockers in rat.

A cluster-based quantitative procedure in an fMRI study of Parkinson's disease

Parkinson's disease is a neurological disorder associated with disfunction of dopaminergic pathways of the basal ganglia. In this study, we report the effects of decreasing plasma concentrations of the dopamine-agonist apomorphine on the size and extents of activity clusters observed with functional magnetic resonance imaging during a simple motor task. Eight patients at advanced disease stage and six healthy volunteers were studied during four consecutive sessions. We observed consistent activations in the primary sensorimotor area of the contralateral side and in the supplementary motor area of both patients and controls during the first session. During subsequent sessions, while the drug concentration gradually decreased in patients, they showed a fragmentation of the activity areas, with an overall decrease of involved volume and a decline of activity in the supplementary motor area. The appearing of activity in the ipsilateral motor area matched a partial recovery of supplementary motor area activation. During the last session, when patients showed severe dyskinesia, a widespread region of positive and negative correlations between signal and task was observed. We conclude that the lack of subcortical circuitry is partially reversible by apomorphine and that when the drug effects are reduced, there is a possible mechanism recruitment of alternate subcortical pathways.

Age-related differences in levodopa dynamics in Parkinson's: implications for motor complications

Treatment-related motor complications in Parkinson's disease have been previously linked to disease-induced pre-synaptic alterations: dopaminergic denervation and changes in dopamine (DA) release patterns. The occurrence of such complications is also known to be partly dependent on the age of disease onset, occurring more frequently in patients with disease onset at a younger age. Using positron emission tomography (PET) and 4-h-long 18F-fluorodopa (FD) scans we have investigated in vivo an age dependence of disease-induced changes in DA turnover as a possible contributing factor to the age-related differences in treatment-related motor complications. We evaluated the relative changes in DA turnover (measured by its direct inverse, effective DA distribution volume--EDV) and DA synthesis and vesicular storage capacity (quantified by the plasma input uptake rate constant Ki) in Parkinson's disease patients as a function of age (n = 27, age range 38-79 years). After correcting for disease severity, a significant negative correlation was found between age and magnitude of disease-induced decrease in EDV and in Ki in the putamen (P < 0.001, P = 0.02, respectively). However, the difference between the disease-induced decrease in EDV and that in Ki also exhibited an age dependence (P < 0.001), indicating a relatively higher disease-induced increase in DA turnover (inverse of EDV) compared with the decrease in DA synthesis and storage rate in patients of younger age compared with older patients. This finding implies that DA turnover in younger-onset patients undergoes a relatively greater alteration and thus likely contributes to a greater imbalance between DA synthesis, storage and release, which could lead to larger swings in synaptic DA levels. It has indeed been suggested on theoretical grounds that such imbalance may contribute to the greater propensity for motor fluctuations. These results provide one possible explanation for the age-dependent occurrence of complications and support the existence of a pre-synaptic contribution to the occurrence of motor complications.

Evaluation of Solid-Phase Sorbents for the Analysis of Ropinirole in Whole Blood

In this paper, the extraction and analysis of ropinirole from whole blood using solid-phase cartridges is presented. Previously published methods for the analysis of this drug have employed plasma samples using C(18) cartridges. Liquid-liquid extraction has been employed for analysis of postmortem samples. In the method, drug free blood was spiked with ropinirole (0 to 10 ng) and an internal standard (quinidine). The samples were buffered with distilled water and centrifuged. The supernatant liquid was applied to previously conditioned endcapped C(6), C(18), and C(8)/SCX solid-phase extraction columns. The columns were washed, dried, and eluted with various solvents systems. The eluants were collected and evaporated. The residue was dissolved in 100 microL of aqueous 0.1% trifluoroacetic acid and analyzed by liquid chromatography using a C(18) (4.6 x 150 mm, 5-microm particle size) column and monitored at 250 nm, using diode-array detection. A mobile phase consisting of methanol/0.1% TFA in distilled water (22:78 v/v) was employed. The data was collected and appraised. It was found that 3-mL 200-mg CEC06 C6 (Hexyl endcapped) solid-phase columns that had been washed with 3 x 3 mL water and 3 x 3 mL acetonitrile and eluted with a solvent system consisting of 95:5 v/v acetonitrile/ammonia performed best. The linear range for this analysis was found to be from 0 to 10 ng/mL. The limit of detection was determined to be 1 ng/mL with a limit of quantification of 2.5 ng/mL.

Efficacy and safety of high-dose cabergoline in Parkinson's disease

OBJECTIVES

To assess the efficacy and safety of high-dose (up to 20 mg/day) cabergoline in Parkinson's disease (PD) patients with motor fluctuations and/or dyskinesias.

MATERIALS AND METHODS

Thirty-four PD patients had cabergoline up-titrated and their levodopa (L-dopa) reduced over a maximum of 20 weeks, followed by at least 6 weeks steady cabergoline dosing. Primary endpoint was change in mean hyperkinesia intensity at the final visit (week 26).

RESULTS

Mean (+/- SD) cabergoline was increased from 6.43 +/- 2.66 to 12.78 +/- 5.67 mg/day and mean L-dopa reduced from 606.6 +/- 263.9 to 370.6 +/- 192.5 mg/day. A significant reduction (P < 0.001) in mean hyperkinesia intensity occurred from baseline (day 0) to week 26. Improvements in 'on with dyskinesias', mean dystonia intensity (P < 0.05), time spent in 'severe off' condition, severity of 'off' periods as well as clinical/patient global impression, and health-related quality of life were observed. Twenty-four drug-related adverse events were recorded of which four were regarded as serious.

CONCLUSION

High-dose cabergoline was well tolerated and provided significant improvements in the Parkinson symptomatology and a reduced requirement for L-dopa.

Increased gastric motility during 5-HT4 agonist therapy reduces response fluctuations in Parkinson's disease

We investigated the clinical efficacy and tolerability of 45 mg/day mosapride, a selective 5-hydroxytryptamine type 4 (5-HT4) agonist, in an open-label study involving five patients with Parkinson's disease (PD) who had response fluctuations (RFs). 'On' time and motor function scores were determined, and gastric motility was measured by a radionuclide gastric emptying (GE) test, the most reliable quantitative method available. We found that mosapride therapy significantly shortened GE half-time, reduced RFs, and improved motor functions in all patients. There were no adverse reactions. We conclude that selective 5-HT4 agonist therapy is beneficial for patients with PD who have RFs.

High-performance liquid chromatography method for the quantification of entacapone in human plasma

A simple, sensitive and selective HPLC method with UV detection (315 nm) was developed and validated for quantitation of entacapone in human plasma, the newest addition to the group of antiparkinsonian agents. Following a single-step liquid-liquid extraction (LLE) with ethyl acetate/n-hexane (30/70, v/v), the analyte and internal standard (rofecoxib) were separated using an isocratic mobile phase of 30 mM phosphate buffer (pH 2.75)/acetonitrile (62/38, v/v) on a reverse phase C18 column. The lower limit of quantitation was 25 ng/mL, with a relative standard deviation of less than 8%. A linear range of 25-2500 ng/mL was established. This HPLC method was validated with between-batch and within-batch precision of 2.2-4.2% and 1.7-7.8%, respectively. The between-batch and within-batch accuracy was 98.7-107.5% and 97.5-106.0%, respectively. Frequently coadministered drugs did not interfere with the described methodology. Stability of entacapone in plasma was excellent, with no evidence of degradation during sample processing (autosampler) and 30 days storage in a freezer. This validated method is sensitive, simple and repeatable enough to be used in pharmacokinetic studies.

The effect of ascorbic acid on the pharmacokinetics of levodopa in elderly patients with Parkinson disease

Levodopa (LD) is one of the most effective drugs for clinical symptoms in patients with Parkinson disease (PD). Most PD patients are advanced in age and may have trouble with LD absorption because aging influences drug absorption processes. Previous reports have indicated that ascorbic acid (AsA) can reduce LD dosage without losing its effectiveness. The current study sought to determine whether AsA affects LD absorption in elderly PD patients. Sixty-seven elderly PD patients took a tablet orally containing 100 mg LD and 10 mg carbidopa following an overnight fast. Plasma LD concentrations were determined at 6 points up to 3 hours, using high-performance liquid chromatography with electrochemical detection. The area under the curve (AUC), peak drug concentration (Cmax), and time to peak drug concentration (Tmax) were calculated. The pharmacokinetic evaluation was repeatedly performed 1 week later in the same way except for adding 200 mg AsA to the tablet. The changes in AUC, Cmax, and Tmax between the tests were evaluated. Significant changes in these parameters were not observed when analyzed using data from all patients. However, significant increases in AUC and Cmax, and a significant reduction in Tmax by adding AsA were observed in 25 patients with baseline AUC < or =2500 ng.hour/mL. In conclusion, AsA can improve LD absorption in elderly PD patients with poor LD bioavailability. LD therapy in combination with AsA may be one of the strategies for PD treatment.

Transdermal apomorphine permeation from microemulsions: a new treatment in Parkinson's disease

We studied absorption, efficacy, and tolerability in Parkinson's disease (PD) of a new preparation of apomorphine included in a microemulsion and administered by transdermal route (Apo-MTD). Twenty-one PD patients were treated with levodopa plus oral dopamine-agonists (T0), with levodopa alone (T1), finally with levodopa plus Apo-MTD (T2). Apo-MTD provided therapeutic plasma levels for many hours, improved Unified Parkinson's Disease Rating Scale III scores, and reduced total duration of off periods compared to T0 and T1. We concluded that Apo-MTD is absorbed and demonstrates clinical efficacy and long action. Therefore, it seems a promising add-on treatment for uncontrolled prolonged off phases in PD patients, but chronic tolerability needs further study.

[Influence of levodopa on cognition of idiopathic Parkinson's disease]

INTRODUCTION

Idiopathic Parkinson's disease induces alterations both motor and cognitive. Levodopa, the treatment of choice, offers initial improvement, but causes long term important complications. It is ignored if it provokes or not a similar situation in cognitive function.

METHOD

Two groups of idiopathic parkinsonian patients were studied. One of them was using levodopa as a regular treatment, the other had de novo patients. A group of healthy controls was also studied. The levodopa group was evaluated when levodopa plasma concentration was maximum and when it was minimum. A cognitive battery was used in order to assess the cognitive status of all subjects.

RESULTS

Significant differences between the two groups of patients and the healthy controls were found when the treated group had a maximum plasmatic concentration of levodopa. There were also significant differences when they had a minimum concentration in comparison with the healthy controls. The performances of the patients taking levodopa varied between both conditions.

CONCLUSIONS

Parkinson's disease provokes a wide variety of cognitive alterations, therefore basal ganglia can be related to a more general function as learning and storing cognitive and motor programs. Levodopa influences in a different way different cognitive functions differently and its influence varies between highest and lowest plasmatic concentrations periods. These results allow us to draw important conclusions about the cognitive alterations caused by the natural course of Parkinson's disease, the introduction of treatment with levodopa and the relationship between basal ganglia and human cognition.

A fatal overdose of the ergot derivative cabergoline

A 79-year-old woman, with Parkinson's disease treated with cabergoline, was admitted to a hospital due to jaundice and weakness. She was found confused, absent minded, and died after 2 weeks. Autopsy showed an extrahepatic bile duct adenocarcinoma with spread to the gall bladder, the liver, and regional lymphnodes. While cleaning the hospital bed after her death, the nurses found several tablets hidden in the bed. Biological samples obtained at the autopsy were screened for common drugs and narcotics. Several drugs such as buprenorphine, codeine, paracetamol, and propranolol were detected in the blood at therapeutic levels. A method to determine cabergoline in whole blood and other forensic matrices was developed, and further investigations determined cabergoline concentrations in whole blood and liver tissue of 94 and 3100 microg/kg, respectively. The blood concentration was 100 times above the therapeutic level reported on cabergoline in plasma and in combination with her symptoms, suggest she took a fatal overdose of cabergoline.

Treatment of idiopathic restless legs syndrome (RLS) with slow-release valproic acid compared with slow-release levodopa/benserazid

We aimed to compare the efficacy of valproic acid (VPA) on paresthesias and sleep in RLS to that of levodopa (LD). Twenty patients with idiopathic restless legs syndrome (RLS) were treated with 600 mg slow-release VPA and 200 mg slow-release LD+50mg benserazid in a randomized, placebo-controlled, cross-over, double-blind setting with polysomography (PSG) at the end of each 3-week treatment periods. There was no major difference between the efficacy of valproic acid or LD. Periodic leg movements in sleep (PLMS) and PLM arousal index (PLMAI) significantly decreased with LD (p < or= 0.005). However, LD, but not VPA, significantly increased arousals not associated with PLMS (p = 0.002). Decrease of intensity and duration of RLS symptoms were more pronounced with VPA (p < or= 0.022) than with LD (NS). We conclude that slow-release VPA provides a treatment alternative for RLS.

Chronic levodopa intake increases levodopa plasma bioavailability in patients with Parkinson's disease

Previous pharmacokinetic trials with standard levodopa formulations showed a different behavior of levodopa degradation in plasma of patients with Parkinson's disease (PD) in various advanced stages. The objective of this trial was to compare levodopa plasma metabolism in PD patients with and without previous long-term levodopa intake after oral intake of a dispensable levodopa/benserazide formulation (DLB). The over a 150 min interval computed area under the curve values of levodopa plasma levels after DLB administration were significantly (ANCOVA: F(1,19) = 7.88, P = 0.01) higher in PD patients with chronic levodopa treatment compared to patients without prior levodopa treatment. The maximum plasma levodopa concentration did not differ (ANCOVA: F(1.19) = 1.17, P = 0.29). Long-term levodopa administration results in an increased levodopa plasma bioavailability in PD patients.

The safety and tolerability of a mixed lineage kinase inhibitor (CEP-1347) in PD

CEP-1347 is an inhibitor of members of the mixed lineage kinase family, key signals triggering apoptotic neuronal death. The authors performed a randomized, blinded, placebo-controlled study assessing the safety, tolerability, pharmacokinetics, and acute symptomatic effects of CEP-1347 in 30 patients with Parkinson's disease (PD). In this short-term study, CEP-1347 was safe and well tolerated. It had no acute effect on parkinsonian symptoms or levodopa pharmacokinetics, making it well suited for larger and longer studies of its potential to modify the course of PD.

Levodopa pharmacokinetics and dyskinesias: are there sex-related differences?

We examined the potential sex-related differences in levodopa pharmacokinetics and their relation with the presence of dyskinesias in a group of 115 patients (67 men, 49 women) with Parkinson's disease. The patients were given a standard oral dose of levodopa plus benserazide (100/25 mg). The area under the levodopa plasma concentration time curve, corrected for the levodopa test dose (in mg/kg body weight), (AUC(w)) was significantly higher in women than in men, with a reduced oral clearance. No difference in the proportion of men and women experiencing dyskinesias was observed.

Motor-learning impairment by amantadine in healthy volunteers

NMDA receptor antagonists impair learning and memory in animal models, presumably by inhibiting long-term potentiation in the motor cortex. Human studies are limited and restricted by the paucity of safe NMDA antagonists. Here, we investigated the contribution of glutamatergic neurotransmission to the capacity of acquiring motor-adaptation learning in humans. In a double-blind design, 200 mg of amantadine (a low-affinity NMDA receptor channel blocker) or a matching placebo were given orally to groups of 14 and 13 human healthy young volunteers, respectively. Blood samples were collected 3 h after treatment to assay plasma concentrations, and the subjects were then tested using a motor-adaptation paradigm consisting of an eight-target-pointing task. To rule out drug-related generalized impairments such sedation, tests measuring motor dexterity and attention were also administered pre- and post-treatment. Comparison of the mean performance levels on the motor-adaptation task revealed that subjects in the amantadine group performed at a lower level than those in the placebo group, but this difference did not reach significance. Interestingly, however, despite plasma amantadine concentrations being relatively low, ranging from 2.09 to 4.74 microM (mean=3.3 microM), they nevertheless correlated negatively with motor learning. Furthermore, when the amantadine group was divided into low-performance and high-performance subgroups, subjects in the former subgroup displayed mean amantadine concentrations 36% higher than the latter subgroup, and performed significantly worser than the placebo group. No change in performance was found on the motor-dexterity and attention tests. Altogether, our results lend support to the hypothesis that normal NMDA receptor function is necessary for the acquisition of motor adaptation.

Clinical pharmacokinetics of cabergoline

Cabergoline is a synthetic ergoline dopamine agonist with a high affinity for D(2) receptors indicated for use in both early and advanced Parkinson's disease and in hyperprolactinaemic disorders. Following oral administration, peak plasma concentrations of cabergoline are reached within 2-3 hours. Over the 0.5-7mg dose range, cabergoline shows linear pharmacokinetics in healthy adult volunteers and parkinsonian patients. Cabergoline is moderately bound (around 40%) to human plasma proteins in a concentration-independent manner; concomitant administration of highly protein-bound drugs is unlikely to affect its disposition. The absolute bioavailability of cabergoline is unknown. Cabergoline is extensively metabolised by the liver, predominantly via hydrolysis of the acylurea bond of the urea moiety. Cytochrome P450-mediated metabolism appears to be minimal. The major metabolites identified thus far do not contribute to the therapeutic effect of cabergoline. A significant fraction of the administered dose undergoes a first-pass effect. Less than 4% is excreted unchanged in the urine. The elimination half-life of cabergoline estimated from urinary data of healthy subjects ranges between 63 and 109 hours. Mild to moderate renal and hepatic impairment, administration of food and the use of concomitant antiparkinsonian medications, such as levodopa and selegiline, have no effect on the pharmacokinetics of cabergoline.The pharmacokinetic properties of cabergoline allow once daily administration in patients with Parkinson's disease and twice weekly administration in patients with hyperprolactinaemia, making this drug advantageous over other dopaminergic agents in term of both therapeutic compliance and better symptom control.

Assessing dopaminergic function in Parkinson?s disease: levodopa kinetic-dynamic modeling and SPECT

Levodopa pharmacokinetic-phamacodynamic (PK-PD) modeling may be able to test the functional integrity of the nigrostriatal dopaminergic system in Parkinson's disease (PD). [(123)I]-FP-CIT SPECT imaging of striatal dopamine transporters has also been introduced for the evaluation of presynaptic dopaminergic homeostasis. We aimed to assess the intrapatient relation between levodopa PK-PD and SPECT measures of dopaminergic function in PD. Thirty-five PD patients, 1 to 4 on the Hoehn and Yahr (H&Y) scale, enrolled in the study. Each patient was examined by levodopa PK-PD modeling and SPECT imaging. Primary measure outcomes were the levodopa half-life in the effect compartment (t1/2(eq)) for PKPD modeling and the ratio of specific to non specific (SP/NSP) tracer striatal uptake for SPECT. Levodopa t1/2(eq) was highly significantly correlated with H&Y scale (r = -0.815, p < 0.0001), Unified Parkinson's disease Rating Scale (UPDRS) (r = -0.691, p < 0.0001) and PD symptom duration (r = -0.647, p < 0.0001). SPECT contralateral putamen SP/NSP ratio showed the most significant correlations with clinical indicators of disease severity: H&Y, r = -0.526, p < 0.002; UPDRS, r = -0.523, p < 0.002; symptom duration, r = -0.513, p < 0.002. Significant correlations were observed between levodopa t1/2(eq) and putamen SP/NSP ratios, yielding the closest correlation for the contralateral region (r = 0.522, p < 0.002). An indirect PK-PD dopaminergic functional variable and direct SPECT measures of presynaptic dopaminergic system homeostasis were in close agreement with clinical data and correlated to each other. Levodopa PK-PD modeling can be a practical clinical tool indirectly assessing the functional integrity of the nigrostriatal dopaminergic system in PD patients.

Catechol-O-methyltransferase inhibition in erythrocytes and liver by BIA 3-202 (1-[3,4-dibydroxy-5-nitrophenyl]-2-phenyl-ethanone)

The present study evaluated the relationship between the degree of catechol-O-methyltransferase (COMT) inhibition in erythrocytes and liver by BIA 3-202 (1-[3,4-dihydroxy-5-nitrophenyl]-2-phenyl-ethanone) and determined its effects upon the O-methylation of L-DOPA in rats orally treated with L-DOPA plus benserazide. The soluble form of COMT (S-COMT) in erythrocytes was endowed with the same affinity as liver S-COMT for the substrate adrenaline. BIA 3-202 inhibited erythrocytes and liver S-COMT with ED50's of 1.9 (0.7, 3.1) and 1.9 (0.5, 3.2) (95% confidence limits) mg kg(-1), respectively. BIA 3-202 reduced the L-DOPA-induced rise of 3-O-methyl-L-DOPA in the peripheral circulation, striatal dialysate levels and striatum, and increased dopamine striatal levels. In BIA 3-202-treated rats the increase in L-DOPA in peripheral blood and striatal dialysates was significantly greater than in vehicle-treated rats. It is concluded that S-COMT activity in erythrocytes may provide important information on the pharmacodynamic profile of COMT inhibitors. The novel COMT inhibitor BIA 3-202 is a potent COMT inhibitor that enhances the availability of L-DOPA to the brain by reducing its O-methylation, which may prove beneficial in patients with Parkinson's disease treated with L-DOPA.

Optimizing levodopa pharmacokinetics: intestinal infusion versus oral sustained-release tablets

Continuous duodenal infusion of carbidopa/levodopa has been shown to control motor fluctuations in advanced Parkinson's disease (PD). The authors compared the pharmacokinetics of levodopa and 3-O-methyldopa in patients with advanced PD after administration of an oral sustained-release levodopa preparation and after continuous intestinal levodopa infusion with a new formulation as a gel suspension. A randomized crossover trial was carried out in 12 patients. Carbidopa/levodopa was administered as an oral sustained-release tablet and by nasoduodenal continuous infusion for 3-week periods for each treatment. Plasma levodopa concentrations and motor performance were evaluated every 30 minutes during 3 test days of each treatment period. The average intraindividual coefficient of variation for the plasma levodopa concentrations after oral therapy was 34% and was significantly lower (14%, p < 0.01) during continuous infusion. Hourly video evaluations showed a significant increase in ON time during infusion and a significant decrease in OFF time and dyskinesia. Continuous intraduodenal delivery of a new carbidopa/levodopa formulation offers a means for markedly improved control of motor fluctuations in late stages of PD.

Electroanalytical characteristics of piribedil and its differential pulse and square wave voltammetric determination in pharmaceuticals and human serum

The electrochemical oxidative behavior of piribedil (PR) was described. It was investigated by cyclic, linear sweep, differential pulse (DPV) and square wave (SWV) voltammetric techniques. The redox behavior of PR was found irreversible. Different parameters were tested to optimize the conditions for the determination of PR. The dependence of intensities of currents and potential on pH, concentration, scan rate, nature of the buffer was investigated. Two sensitive methods for the measurement of PR were described. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in 0.1 M H(2)SO(4) and pH 5.7 acetate buffer. The determination peaks are obtained at 1.27 and 0.95 V for differential pulse and 1.29 and 0.97 V for SWV in 0.1 M H(2)SO(4) and pH 5.7 acetate buffer, respectively. The linear response was obtained in the ranges of 2 x 10(-6)-1 x 10(-3) M in 0.1 M H(2)SO(4) and 2 x 10(-6)-8 x 10(-4) M in pH 5.7 acetate buffer for both techniques. The proposed techniques were successfully applied to the determination of PR in tablet dosage forms and human serum. Excipients did not interfere in the determination. The necessary statistical validation reveals that the proposed methods are free from significant systematic errors.

Pharmacologically modulated fMRI--cortical responsiveness to levodopa in drug-naive hemiparkinsonian patients

According to the basal ganglia-thalamocortical circuit model, dopamine depletion in the nigrostriatal system leads to hypoactivation in the supplementary motor area (SMA) and the primary motor cortex (M1) in Parkinson's disease. This functional cortical deafferentation and its reversibility by levodopa (L-dopa) treatment has been established in previous studies for SMA but remains controversial for M1. We used functional MRI (fMRI) and a simple finger opposition task to correlate blood oxygenation level-dependent (BOLD) signal changes with motor performance, assessed separately for each hand between fMRI scanning sessions. Eight drug-naive patients with an akinetic idiopathic hemiparkinsonian syndrome (Hoehn and Yahr stage 1-1.5) and 10 healthy controls were studied. Patients performed a simple, auditory-paced random finger- opposition task every 3 s before and repeatedly every 20 min after intake of 300 mg of fast-release L-dopa. M1 contralateral to the affected hand and SMA, predominantly of the contralateral side, showed a BOLD signal increase after L-dopa intake. Furthermore, comparing BOLD responses of M1 and SMA between the patients and controls revealed that these areas were hypoactive before L-dopa treatment. Signal changes in M1 and SMA were highly correlated with motor performance, which increased after L-dopa intake. This result is not confounded by a performance effect because the motor task employed during scanning was identical throughout all sessions. In contrast to previous imaging studies in which cortical reorganization in Parkinson's disease was thought to have caused M1 hyperactivation, our data are in accordance with the hypothesis that, in de novo idiopathic hemiparkinsonian syndrome, motor cortex hypoactivation in contralateral M1 and bilateral SMA is caused by a decreased input from the subcortical motor loop, which is reversible by L-dopa.

Effects of food on the pharmacokinetics of levodopa in a dual-release formulation

The objective was to assess the effect of food on the pharmacokinetics of levodopa and 3-O-methyldopa after administration of a new levodopa/benserazide formulation with a dual-release drug delivery profile (Madopar DR). In an open-label, two-way cross-over study, 19 healthy volunteers who had fasted overnight were randomized to receive a single oral dose of levodopa/benserazide (200/50 mg) in the absence or presence of a standardized, high-fat breakfast, administered 30 min before drug administration. The treatment periods (fasting, non-fasting) were preceded by a baseline regimen of levodopa/benserazide (100/25 mg t.i.d. for 6 or 7 days). Blood samples were taken at specific times over a 12-hour period. Plasma concentrations of levodopa and 3-O-methyldopa were determined by high-performance liquid chromatography for pharmacokinetic evaluation. The parameter C(max) of levodopa was significantly lower and t(max) longer under postprandial conditions than under fasting conditions (mean C(max) 1.41 vs. 2.09 mg l(-1); mean t(max) 3.1 vs. 1.0 h). With food, the area under the curve (AUC) of levodopa was equivalent to that following an overnight fast. Compared with volunteers who had fasted, food did not alter t(1/2). Estimates of C(max), t(max) and AUC of 3-O-methyldopa under non-fasting conditions were not significantly different from those under fasting conditions. In conclusion, food decreases the rate of levodopa absorption, but had no effect on the systemic exposure to levodopa and the degree of 3-O-methyldopa formation. Standardization of levodopa/benserazide administration with respect to meal times is recommended.

Quantitative analysis of memantine in human plasma by gas chromatography/negative ion chemical ionization/mass spectrometry

A sensitive and specific method for the determination of memantine in human plasma is presented. Memantine was extracted from plasma and derivatized to the pentafluorobenzoyl derivative in a one-step procedure avoiding any sample concentration steps. Amantadine was used as an internal standard. The compounds were measured by gas chromatography/negative ion chemical ionization mass spectrometry without any further processing. Using this detection mode, the fragment ions at m/z 353 and 325 were obtained at high relative abundance. Calibration graphs were linear over the range 0.117-30 ng ml(-1). At the limit of quantification (LOQ), the inter-assay precision was 2.00% and the intra-assay variability was 3.22%. The accuracy at the LOQ showed deviations of -1.42% (intra-assay) and -2.47% (inter-assay). The method is rugged, rapid and robust and was applied to the batch determination of memantine during pharmacokinetic profiling of the drug.

Levodopa pharmacokinetics and motor performance during activities of daily living in patients with Parkinson's disease on individual drug combinations

Pharmacokinetics and pharmacodynamics of levodopa were evaluated at a high-resolution level in a heterogeneous group of 10 patients with idiopathic Parkinson's disease during their normal daily activity. A physician and a nurse spent 10 hours with each patient from the first morning dose of levodopa during daily activities at home and at work. Plasma samples were obtained every 20 minutes for analysis of levodopa and 3-O-methyldopa by high-performance liquid chromatography. To assess clinical response, mobility was rated on every test occasion by patients and by investigators. Food and fluid intake and physical activity were also monitored. There was a large intra- and interindividual variability in the pharmacokinetics of levodopa regardless of the different drug combinations used. Mean plasma levodopa concentration ranged between 0.45 to 7.07 microg/mL and peak concentrations between 0.95 to 13.75 microg/mL. In 44 of 58 dosing events, an oral dose of levodopa was related to a peak in plasma concentration. Assessment of the clinical effects was more sensitive when given by patients than when given by the investigators. The fluctuations of the levodopa concentration in plasma had a clear effect on the clinical parameters assessed, even during early disease stages. Variation in levodopa concentration is the determining factor for motor fluctuations also in patients on clinically optimized combinations with dopamine agonists and enzyme inhibitors.

Influence of layer position on in vitro and in vivo release of levodopa methyl ester and carbidopa from three-layer matrix tablets

A versatile oral controlled release system for the simultaneous delivery of levodopa methyl ester and carbidopa, consisting of a three-layer matrix tablet, has been studied and developed. Each individual layer of the matrix exhibited a different release mechanism, i.e. the first layer was swellable (S), the second one was erodible (E) and the third one was disintegrating (D). The three layers have been assembled in the monolithic matrix in different relative positions. It was found that in the monolith the three layers could interact, producing in vitro release profiles depending on their relative position. The monoliths having the configurations DSE and SDE were administered to human volunteers in order to determine the plasma profiles. The pharmacokinetic data showed a significant difference between the early time plasma curves: the monolith DSE, having the fast release profile, gave rise to a rapid appearance of a high levodopa plasma level, whereas the slower releasing monolith SDE produced a smoothed plasma concentration profile.

Body weight influences pharmacokinetics of levodopa in Parkinson's disease

Changes in body weight may induce substantial variations in peripheral pharmacokinetics of drugs, but the relation between body weight and levodopa (LD) pharmacokinetics has never been investigated in Parkinson's disease. To address this issue, we conducted a pharmacokinetic study with 164 patients with sporadic Parkinson's disease. Patients underwent an oral acute LD test with 250 mg of LD, and pharmacokinetic variables were assessed at baseline and at 30, 60, 120, and 240 minutes after LD administration. Plasmatic-LD areas under the curve and body weight were significantly and inversely correlated as well as the elimination of the half-life of LD and body weight. In our sample, women were significantly lighter and had a significantly greater area under the curve than men. Moreover, a greater percentage of women showed LD peak-dose dyskinesias compared with men. Our findings suggest that lighter patients with Parkinson's disease probably receive a greater cumulative dosage of LD per kilogram of body weight during long-term treatment, because in clinical practice, LD is administered without any adjustment of the dose to body weight. This could explain gender differences for the development of LD-induced peak-dose dyskinesias observed during the course of the disease.

The determination of biperiden in plasma using gas chromatography mass spectrometry: pharmacokinetics after intramuscular administration to guinea pigs

A gas chromatographic-mass spectrometric (GC-MS) method has been developed for the analysis of the biperiden from plasma. The method utilizes 290 microl of plasma and a simple hexane extraction/clean-up procedure. Standard curves were linear over the range of 1.9-250 ng/mL. The range of correlation coefficients for the individual standard curves was 0.9984-0.9999; the largest coefficient of variation expressed as a percentage (% CV) was 11.5%. Precision and accuracy were examined by assessing between-day and within-day variability. For between-day precision, the % CVs ranged from 2.86 to 5.17%. Accuracy as expressed by percentage error ranging from -2.16 to 5.83%. The study for within-day precision demonstrated % CVs from 0.95 to 5.55% with accuracy from -3.37 to 2.45%. Applicability of the method was demonstrated by examining the pharmacokinetics of intramuscular (i.m.) biperiden as an anticonvulsant treatment in a guinea pig model for organophosphate (OP)-induced seizure activity. Mean pharmacokinetic parameter estimates were similar to literature values; selected mean pharmacokinetic parameter estimates were: apparent volume of distribution, 13.9 L/kg; half-life of elimination, 93 min; time to maximal plasma concentration, 27.4 min; and maximal plasma concentration, 32.22 eta g/mL. The time to maximal plasma concentration was found to be similar to the onset time for terminating OP-induced seizure activity in guinea pigs receiving biperiden as an anticonvulsant treatment. The studies indicate that the method affords the required precision, accuracy and sensitivity to assay biperiden at the doses utilized for these pharmacokinetic studies after i.m. administration to guinea pigs.