Pharmacokinetics of levodopa

Effect of levodopa-carbidopa intestinal gel on dyskinesia in advanced Parkinson's disease patients

OBJECTIVE

The purpose of this study was to assess the effect of levodopa-carbidopa intestinal gel (carbidopa-levodopa enteral suspension) in advanced Parkinson's disease patients with troublesome dyskinesia.

METHODS

Post hoc analyses of patient data from a 12-week, randomized, double-blind study and a 54-week open-label study were performed. Efficacy was assessed in the subgroup of patients defined by ≥1 hour of "on" time with troublesome dyskinesia at baseline as recorded in Parkinson's disease symptom diaries (double blind: n = 11 levodopa-carbidopa intestinal gel, n = 12 oral levodopa-carbidopa; open label: n = 144 levodopa-carbidopa intestinal gel). The changes in "off" time, "on" time with and without troublesome dyskinesia, and the overall safety and tolerability of levodopa-carbidopa intestinal gel were analyzed.

RESULTS

Although not significantly different from oral levodopa treatment (P > .05) in the double-blind study, levodopa-carbidopa intestinal gel treatment resulted in a reduction from baseline in "on" time with troublesome dyskinesia (mean [standard deviation] hours: baseline = 3.1 [1.7], change from baseline to final = -1.8 [1.8], P = .014), increase in "on" time without troublesome dyskinesia (baseline = 7.4 [2.2], change = 4.4 [3.6], P = .004), and decrease in "off" time (baseline = 5.5 [1.3], change = -2.7 [2.8], P = .015). Similar trends were found in the open-label study. An increase in levodopa-carbidopa intestinal gel dose was not significantly correlated with increased "on" time with troublesome dyskinesia in either study (double blind: r = -.073, P = .842; open label: r = -0.001, P = .992). Adverse events were usually mild to moderate in severity and related to the gastrointestinal procedure.

CONCLUSION

Our exploratory analyses suggest that optimizing levodopa delivery with levodopa-carbidopa intestinal gel may reduce troublesome dyskinesia in advanced Parkinson's disease.

Ex vivo buccal drug delivery of ropinirole hydrochloride in the presence of permeation enhancers: the effect of charge

In the current study, the ex vivo permeation of ropinirole hydrochloride (RH) across porcine buccal mucosa in the presence of three permeation enhancers, namely N-trimethyl chitosan (TMC) (positively charged) a chitosan derivative, sulfobutyl ether-β-cyclodextrin (SBE-β-CD) (negatively charged) and hydroxypropyl-β-cyclodextrin (HP-β-CD) (neutral), was investigated. Buccal permeation studies were conducted using Franz diffusion cells. Cumulative amounts of RH were plotted versus time. The presence of the permeation enhancers significantly increased the transport of the drug across the porcine buccal epithelium compared to its plain congener (RH solution). The rank order effect of the permeation enhancers for the transport of RH across buccal epithelium was TMC ≥ SBE-β-CD > HP-β-CD > RH solution. The presence of TMC increased 1.34-fold the transport of RH across buccal epithelium, whereas an increase of 1.23- and 1.28-fold was reported in the presence of HP-β-CD and SBE-β-CD, respectively. Infrared spectroscopy (IR) was employed to investigate the interaction of permeation enhancers with the epithelial lipids of porcine buccal mucosa corroborating the permeation results. Finally, light microscopy was performed to assess the histological changes in the porcine epithelium. Formation of vacuoles, spongiosis and acantholysis linear detachment and destruction of the epithelium resulted from the presence of the permeation enhancers. The data suggest that all enhancers tested, and particularly TMC, increase the transport of RH across buccal epithelium.

Efficacy and motor complications of original and generic levodopa in Parkinson's disease treatment

BACKGROUND

In general, a generic drug is considered interchangeable with the original formulated drug. In Parkinson's disease (PD), generic drug use remains debated. This study was aimed to investigate whether the generic drug was as effective as the original in improving the symptoms of PD and the prevalence of motor complications.

METHODS

This study was a multicenter cohort study of patients with PD enrolled from three northeast hospitals in Thailand between February 2013 and February 2014. The patients were categorized into original and generic levodopa groups. The clinical characteristics, efficacy, and motor complications were compared between the groups.

RESULTS

There were 400 eligible patients. Of these, 327 patients (81.75%) met the study criteria and were classified as the original levodopa group (200 patients, 61.16%) and the generic levodopa group (127 patients, 38.84%). The average age of all patients with PD was 65 years. The duration of PD and the modified Hoehn-Yahr stages were not different between the groups. The total doses of original and generic levodopa-equivalent doses were significantly different (199.97±127.08 versus 305.58±138.27 mg; P-value <0.001) and the actual doses were 198.10±117.92 versus 308.85±139.40 mg (P-value <0.001). Approximately 80% of patients with PD in both groups had good responses (P-value >0.999), but the development of motor complications was significantly greater in the original than in the generic group.

CONCLUSION

Generic levodopa was effective in improving the symptoms of PD. The prevalence of motor complications in the original compound group, at a lower dose of levodopa equivalent, was higher than in the generic group.

Integrated safety of levodopa-carbidopa intestinal gel from prospective clinical trials

BACKGROUND

Continuous administration of levodopa-carbidopa intestinal gel (carbidopa-levodopa enteral suspension) through a percutaneous endoscopic gastrojejunostomy is a treatment option for advanced Parkinson disease (PD) patients with motor fluctuations resistant to standard oral medications. Safety data from 4 prospective studies were integrated to assess the safety of this therapy.

METHODS

Safety data from 4 studies were summarized using 2 overlapping data sets, permitting the separation of procedure/device-associated (n = 395) from non-procedure/device adverse events (n = 412).

RESULTS

At the data cutoff, median exposure to levodopa-carbidopa intestinal gel was 911 days (range, 1-1980 days) with 963 total patient-years of exposure. Procedure/device adverse events occurred in 300 patients (76%), and serious adverse events occurred in 68 (17%); most frequently reported procedure/device adverse events and serious adverse events were complications of device insertion (41% and 8%, respectively) and abdominal pain (36% and 4%, respectively). Non-procedure/device adverse events occurred in 92% (379), with most frequently reported being insomnia (23%) and falls (23%); 42% (171) had non-procedure/device serious adverse events, with most frequently reported being pneumonia (5%) and PD symptoms (2%). Adverse events led to discontinuation in 17% (72), most frequently because of complication of device insertion (2.4%). There were 34 treatment-emergent deaths (8.3%) in the overlapping data sets, 2 of which (0.5%) were considered "possibly related" to the treatment system.

CONCLUSION

In the largest collection of levodopa-carbidopa intestinal gel safety data from prospective clinical studies, procedure/device events were frequently reported and occasionally life threatening. Most non-procedure/device events were typical for levodopa treatment and an elderly population. These factors combined with high treatment efficacy led to a relatively low discontinuation rate in advanced PD patients.

Carbidopa levodopa enteral suspension

INTRODUCTION

The search for consistent, effective treatments in Parkinson's disease (PD) is ongoing. The importance of continuous dopaminergic stimulation (CDS) is understood to underlie best medical therapy for PD by providing closer replication of physiological patterns of dopamine release in healthy brains.

AREAS COVERED

An overview of interventions to improve motor fluctuations in PD is presented. Significant improvements in off-time are achieved by providing continuous therapy using targeted deep brain stimulation (DBS), subcutaneous apomorphine infusion and carbidopa/levodopa enteral suspension (Duopa). Duopa is a newly approved treatment in the US for advanced PD that delivers levodopa pumped to the intestinal tract through a percutaneous gastrostomy with jejunum tube extension (PEG-J tube). Trials with carbidopa/levodopa enteral suspension show improvement in motor fluctuations, reduction in plasma levodopa variation and improvement in overall "on" time compared with oral immediate release formulation of carbidopa/levodopa.

EXPERT OPINION

The degree of improvement in number of off hours per day on carbidopa/levodopa enteral suspension infusion rivals that seen with DBS and apomorphine infusion and makes this new treatment a valuable option in advanced fluctuating PD patients, especially those who are neither candidates for DBS or who do not have access to apomorphine infusion therapy or who have failed either or both therapies.

PLGA/DPPC/trimethylchitosan spray-dried microparticles for the nasal delivery of ropinirole hydrochloride: in vitro, ex vivo and cytocompatibility assessment

In the present study we investigated polymer-lipid microparticles loaded with ropinirole hydrochloride (RH) for nasal delivery. RH microparticles were further evaluated by means of scanning electron microscopy (SEM), ζ-potential measurements, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). In vitro release studies were performed in simulated nasal electrolyte solution (SNES) pH5.5 at 35°C. Ex vivo permeation studies were conducted across sheep nasal mucosa. Cytocompatibility was tested in cultured human airway epithelial cells (Calu-3). SEM studies revealed spheroid microparticles in the range of 2.09μm to 2.41μm. The presence of trimethylchitosan (TMC) induced a slight shift towards less negative ζ-potential values. Surface chemistry (XPS) revealed the presence of dipalmitoylphospatidylcholine (DPPC) and poly(lactic-co-glycolic acid) (PLGA) onto microparticles' surface, further corroborating the FT-IR and XRD findings. In vitro release studies showed that the microparticle composition can partly modulate the release of RH. Ex vivo studies demonstrated a 2.35-folded enhancement of RH permeation when RH was co-formulated with TMC of low molecular weight, compared to the control. All formulations tested were found to be non-toxic to cells. The results suggest that polymer-lipid microparticles may be a promising carrier for the nasal delivery of RH.

Influence of Dopaminergic Medication on Conditioned Pain Modulation in Parkinson's Disease Patients

Background

Pain is highly prevalent in patients with Parkinson’s disease (PD), but little is known about the underlying pathophysiological mechanisms. The susceptibility to pain is known to depend on ascending and descending pathways. Because parts of the descending pain inhibitory system involve dopaminergic pathways, dysregulations in dopaminergic transmission might contribute to altered pain processing in PD. Deficits in endogenous pain inhibition can be assessed using conditioned pain modulation (CPM) paradigms.

Methods

Applying such a paradigm, we investigated i) whether CPM responses differ between PD patients and healthy controls, ii) whether they are influenced by dopaminergic medication and iii) whether there are effects of disease-specific factors. 25 patients with idiopathic PD and 30 healthy age- and gender-matched controls underwent an established CPM paradigm combining heat pain test stimuli at the forearm and the cold pressor task on the contralateral foot as the conditioning stimulus. PD patients were tested under dopaminergic medication and after at least 12 hours of medication withdrawal.

Results

No significant differences between CPM responses of PD patients and healthy controls or between PD patients “on” and “off” medication were found. These findings suggest (i) that CPM is insensitive to dopaminergic modulations and (ii) that PD is not related to general deficits in descending pain inhibition beyond the known age-related decline. However, at a trend level, we found differences between PD subtypes (akinetic-rigid, tremor-dominant, mixed) with the strongest impairment of pain inhibition in the akinetic-rigid subtype.

Conclusions

There were no significant differences between CPM responses of patients compared to healthy controls or between patients “on” and “off” medication. Differences between PD subtypes at a trend level point towards different pathophysiological mechanisms underlying the three PD subtypes which warrant further investigation and potentially differential therapeutic strategies in the future.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

L-Dopa Pharmacokinetic Profile with Effervescent Melevodopa/Carbidopa versus Standard-Release Levodopa/Carbidopa Tablets in Parkinson's Disease: A Randomised Study

Objectives. To characterize the pharmacokinetic profile of levodopa (L-dopa) and carbidopa after repeated doses of the effervescent tablet of melevodopa/carbidopa (V1512; Sirio) compared with standard-release L-dopa/carbidopa in patients with fluctuating Parkinson's disease. Few studies assessed the pharmacokinetics of carbidopa to date. Methods. This was a single-centre, randomized, double-blind, double-dummy, two-period crossover study. Patients received V1512 (melevodopa 100 mg/carbidopa 25 mg) or L-dopa 100 mg/carbidopa 25 mg, 7 doses over 24 hours (Cohort 1), 4 doses over 12 hours (Cohort 2), or 2 doses over 12 hours in combination with entacapone 200 mg (Cohort 3). Pharmacokinetic parameters included area under the plasma-concentration time curve (AUC), maximum plasma concentration (C_max), and time to C_max (t_max). Results. Twenty-five patients received at least one dose of study medication. L-dopa absorption tended to be quicker and pharmacokinetic parameters less variable after V1512 versus L-dopa/carbidopa, both over time and between patients. Accumulation of L-dopa in plasma was less noticeable with V1512. Carbidopa exposure and interpatient variability was lower when V1512 or L-dopa/carbidopa was given in combination with entacapone. Both treatments were well tolerated. Conclusions. V1512 provides a more reliable L-dopa pharmacokinetic profile versus standard-release L-dopa/carbidopa, with less drug accumulation and less variability. This trial is registered with ClinicalTrials.gov NCT00491998.

Drug therapy for Parkinson’s disease: An update

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder, affecting about 1% of the population above the age of 65. PD is characterized by a selective degeneration of the dopaminergic neurons of the substantia nigra pars compacta. This results in a marked loss of striatal dopamine and the development of the characteristic features of the disease, i.e., bradykinesia, rest tremor, rigidity, gait abnormalities and postural instability. Other types of neurons/neurotransmitters are also involved in PD, including cholinergic, serotonergic, glutamatergic, adenosine, and GABAergic neurotransmission which might have relevance to the motor, non-motor, neuropsychiatric and cognitive disturbances that occur in the course of the disease. The treatment of PD relies on replacement therapy with levodopa (L-dopa), the precursor of dopamine, in combination with a peripheral decarboxylase inhibitor (carbidopa or benserazide). The effect of L-dopa, however, declines over time together with the development of motor complications especially dyskinesia in a significant proportion of patients within 5 years of therapy. Other drugs include dopamine-receptor-agonists, catechol-O-methyltransferase inhibitors, monoamine oxidase type B (MAO-B) inhibitors, anticholinergics and adjuvant therapy with the antiviral drug and the N-methyl-D-aspartate glutamate receptor antagonist amantadine. Although, these medications can result in substantial improvements in parkinsonian symptoms, especially during the early stages of the disease, they are often not successful in advanced disease. Moreover, dopaminergic cell death continues over time, emphasizing the need for neuroprotective or neuroregenerative therapies. In recent years, research has focused on non-dopaminergic approach such as the use of A_2A receptor antagonists: istradefylline and preladenant or the calcium channel antagonist isradipine. Safinamide is a selective and reversible inhibitor of MAO-B, a glutamate receptor inhibitor as well as sodium and calcium channel blocker. Minocycline and pioglitazone are other agents which have been shown to prevent dopaminergic nigral cell loss in animal models of PD. There is also an evidence to suggest a benefit from iron chelation therapy with deferiprone and from the use of antioxidants or mitochondrial function enhancers such as creatine, alpha-lipoic acid, l-carnitine, and coenzyme Q10.

Medication adherence in patients with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, after Alzheimer's disease, affecting the elderly worldwide. Current therapy for PD is largely based on prescription of drugs that act as either dopamine precursors, dopamine agonists or agents that inhibit key enzymes in the dopamine catabolic pathways. Most of these drugs are administered in tablet or capsule form and can involve multiple daily doses in complex dosing regimens, which contributes to sub-optimal compliance amongst patients. There is evidence to suggest that non-compliance with medications results in perceived poor response to therapy and may ultimately increase direct and indirect health care costs. Medication compliance in PD assumes a particularly important role, given that PD is a progressive, debilitating condition, and once medication is instituted for ameliorating the symptoms of PD, it is lifelong. We included nine research studies in our review of the medical literature, which report the prevalence of significant medication non-compliance in PD, using standard definitions, varies between 10 and 67%. This variation partly reflects differences in defining what clinically significant medication adherence is, the methods used to estimate the scale of the problem and the underlying population heterogeneity. Nevertheless, medication adherence is related to health costs and to the quality of life of patients affected by PD and, indirectly, their carers. Educating patients and their carers is one method of improving patient adherence to therapy. Simplifying drug regimens can also aid in this effort.

Pharmacological strategies for the management of levodopa-induced dyskinesia in patients with Parkinson's disease

L-Dopa-induced dyskinesias (LID) are the most common adverse effects of long-term dopaminergic therapy in Parkinson's disease (PD). However, the exact mechanisms underlying dyskinesia are still unclear. For a long time, nigrostriatal degeneration and pulsatile stimulation of striatal postsynaptic receptors have been highlighted as the key factors for the development of LID. In recent years, PD models have revealed a wide range of non-dopaminergic neurotransmitter systems involved in pre- and postsynaptic changes and thereby contributing to the pathophysiology of LID. In the current review, we focus on therapeutic LID targets, mainly based on agents acting on dopaminergic, glutamatergic, serotoninergic, adrenergic, and cholinergic systems. Despite a large number of clinical trials, currently only amantadine and, to a lesser extent, clozapine are being used as effective strategies in the treatment of LID in clinical settings. Thus, in the second part of the article, we review the placebo-controlled trials on LID treatment in order to disentangle the changing scenario of drug development. Promising results include the extension of L-dopa action without inducing LID of the novel monoamine oxidase B- and glutamate-release inhibitor safinamide; however, this had no obvious effect on existing LID. Others, like the metabotropic glutamate-receptor antagonist AFQ056, showed promising results in some of the studies; however, confirmation is still lacking. Thus, to date, strategies of continuous dopaminergic stimulation seem the most promising to prevent or ameliorate LID. The success of future therapeutic strategies once moderate to severe LID occur will depend on the translation from preclinical experimental models into clinical practice in a bidirectional process.

A randomised clinical trial to evaluate the effects of Plantago ovata husk in Parkinson patients: changes in levodopa pharmacokinetics and biochemical parameters

Background

Plantago ovata husk therapy could be used in patients with Parkinson disease to reduce the symptoms of gastrointestinal disorders, but it is important to know whether this compound modifies levodopa pharmacokinetics. The maintenance of constant plasma concentrations of levodopa abolishes the clinical fluctuations in parkinsonian patients. The aim of this randomised clinical trial was to establish the influence of the fiber Plantago ovata husk in the pharmacokinetics of levodopa when administered to Parkinson patients well controlled by their oral medication.

Methods

To evaluate the effects of this fiber on several biochemical parameters. 18 volunteers participated in the study and received alternatively two treatments (Plantago ovata husk or placebo) with their usual levodopa/carbidopa oral dose. On days 0 (initial situation), 14 and 35 of the study, blood samples were taken to assess levodopa pharmacokinetics and to determine biochemical parameters.

Results

Levodopa C_max was very similar in the initial situation (603.2 ng/ml) and after placebo administration (612.0 ng/ml), being slightly lower (547.8 ng/ml) when Plantago ovata husk was given. AUC was very similar in the three groups: initial situation.- 62.87 μg.min/ml, fiber treatment.- 64.47 μg.min/ml and placebo treatment.- 65.10 μg.min/ml. Fiber reduced significantly the number of peaks observed in the levodopa concentrations, maintaining concentrations more stable. No significant differences were found in total cholesterol, LDL-cholesterol and triglycerides with the administration of Plantago ovata husk.

Conclusions

Plantago ovata husk administration caused a smoothing and homogenization of levodopa absorption, providing more stable concentrations and final higher levels, resulting in a great benefit for patients.

Trial registration

EudraCT2006-000491-33

Preventive effect of rikkunshito on gastric motor function inhibited by L-dopa in rats

We previously reported that ghrelin prevented l-dopa (LD)-induced inhibition of gastric emptying (GE) of a non-nutrient solution in rats. Parkinson's disease treatment involves the combined administration of l-dopa with the enzyme l-amino acid decarboxylase inhibitor, carbidopa (CD) to reduce peripheral formation of dopamine. We investigated the effect LD/CD given orogastrically (og) on GE of a non-nutrient or nutrient meal and whether og pretreatment with rikkunshito, a kampo medicine clinically used to treat gastroparesis, influenced LD/CD effect on GE and postprandial antral and duodenal motility in conscious rats. LD/CD (20/2 mgkg(-1)) decreased significantly GE to 26.3 ± 6.0% compared to 61.2 ± 3.2% in og vehicle monitored 20-min after a non-nutrient meal and to 41.9 ± 5.8% compared to 72.9 ± 5.2% in og vehicle monitored 60 min after a nutrient meal. Rikkunshito (0.5 or 1.0 g kg(-1)) reduced the LD/CD (20/2 mg kg(-1)) inhibition of GE of non-nutrient meal (36.9 ± 7.4% and 46.6 ± 4.8% respectively vs. 12.1 ± 7.4% in og vehicle plus LD/CD) while having no effect alone (56.6 ± 8.5%). The ghrelin antagonist, [d-Lys(3)]-GHRP-6 (1 mg kg(-1)) injected intraperitoneally partially reversed rikkunshito preventive effect on LD/CD-inhibited GE. Rikkunshito (1.0 g kg(-1)) blocked LD/CD (20/2 mg kg(-1))-induced delayed GE of a nutrient meal and the reduction of postprandial antral motility. In 6-hydroxydopamine-induced Parkinson's disease rat model, rikkunshito (1.0 g kg(-1), og) also prevented LD/CD-inhibited gastric emptying of a nutrient meal and enhanced fasting plasma levels of acylated ghrelin. These data indicate that oral rikkunshito alleviates the delayed GE induced by LD/CD in naïve and PD rat model in part through ghrelin-related mechanisms.

Pharmaceutical quality of seven generic Levodopa/Benserazide products compared with original Madopar® / Prolopa®

Background

By definition, a generic product is considered interchangeable with the innovator brand product. Controversy exists about interchangeability, and attention is predominantly directed to contaminants. In particular for chronic, degenerative conditions such as in Parkinson’s disease (PD) generic substitution remains debated among physicians, patients and pharmacists. The objective of this study was to compare the pharmaceutical quality of seven generic levodopa/benserazide hydrochloride combination products marketed in Germany with the original product (Madopar® / Prolopa® 125, Roche, Switzerland) in order to evaluate the potential impact of Madopar® generics versus branded products for PD patients and clinicians.

Methods

Madopar® / Prolopa® 125 tablets and capsules were used as reference material. The generic products tested (all 100 mg/25 mg formulations) included four tablet and three capsule formulations. Colour, appearance of powder (capsules), disintegration and dissolution, mass of tablets and fill mass of capsules, content, identity and amounts of impurities were assessed along with standard physical and chemical laboratory tests developed and routinely practiced at Roche facilities. Results were compared to the original “shelf-life” specifications in use by Roche.

Results

Each of the seven generic products had one or two parameters outside the specifications. Deviations for the active ingredients ranged from +8.4% (benserazide) to −7.6% (levodopa) in two tablet formulations. Degradation products were measured in marked excess (+26.5%) in one capsule formulation. Disintegration time and dissolution for levodopa and benserazide hydrochloride at 30 min were within specifications for all seven generic samples analysed, however with some outliers.

Conclusions

Deviations for the active ingredients may go unnoticed by a new user of the generic product, but may entail clinical consequences when switching from original to generic during a long-term therapy. Degradation products may pose a safety concern. Our results should prompt caution when prescribing a generic of Madopar®/Prolopa®, and also invite to further investigations in view of a more comprehensive approach, both pharmaceutical and clinical.

Rhythm-specific modulation of the sensorimotor network in drug-naive patients with Parkinson's disease by levodopa

Brain activity during rest is characterized by slow (0.01-0.1 Hz) fluctuations of blood oxygenation level-dependent functional magnetic resonance imaging signals. These fluctuations are organized as functional connectivity networks called resting-state networks, anatomically corresponding to specific neuronal circuits. As Parkinson's disease is mainly characterized by a dysfunction of the sensorimotor pathways, which can be influenced by levodopa administration, the present study investigated the functional connectivity changes within the sensorimotor resting-state network in drug-naïve patients with Parkinson's disease after acute levodopa administration. Using a double-blind placebo-controlled design, resting-state functional magnetic resonance imaging was carried out in 20 drug-naïve patients with Parkinson's disease, immediately before and 60 min after, oral administration of either levodopa or placebo. Control resting-state functional magnetic resonance imaging data were recorded in 18 age- and sex-matched healthy volunteers. Independent component analysis was performed to extract resting-state network maps and associated time-course spectral features. At the anatomical level, levodopa enhanced the sensorimotor network functional connectivity in the supplementary motor area, a region where drug-naïve patients with Parkinson's disease exhibited reduced signal fluctuations compared with untreated patients. At the spectral frequency level, levodopa stimulated these fluctuations in a selective frequency band of the sensorimotor network. The reported effects induced by levodopa on sensorimotor network topological and spectral features confirm that the sensorimotor system is a target of acute levodopa administration in drug-naïve patients with Parkinson's disease. Moreover, while the regional changes in supplementary motor area reflect the functional improvement in motor function, the rhythm-specific modulation induced by the dopamine precursor discloses a novel aspect of pharmacological stimulation in Parkinson's disease, adding further insight to the comprehension of levodopa action.

Effects of L-dopa during auditory instrumental learning in humans

The dopaminergic neurotransmitter system is critically involved in promoting plasticity in auditory cortex. We combined functional magnetic resonance imaging (fMRI) and a pharmacological manipulation to investigate dopaminergic modulation of neural activity in auditory cortex during instrumental learning. Volunteers either received 100 mg L-dopa (Madopar) or placebo in an appetitive, differential instrumental conditioning paradigm, which involved learning that a specific category of frequency modulated tones predicts a monetary reward when fast responses were made in a subsequent reaction time task. The other category of frequency modulated tones was not related to a reward. Our behavioral data provides evidence that dopaminergic stimulation differentially impacts on the speed of instrumental responding in rewarded and unrewarded trials. L-dopa increased neural BOLD activity in left auditory cortex to tones in rewarded and unrewarded trials. This increase was related to plasma L-dopa levels and learning rate. Our data thus provides evidence for dopaminergic modulation of neural activity in auditory cortex, which occurs for both auditory stimuli related to a later reward and those not related to a reward.

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.

BL-1023 improves behavior and neuronal survival in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-intoxicated mice

The therapeutic potential of BL-1023, a chemical combination of L-3,4-dihydroxyphenylalanine (L-DOPA) and gamma-aminobutyric acid (GABA), was investigated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxicated mice. Such animals exhibit nigrostriatal degeneration, characteristic of human Parkinson's disease. Drug was administered during and after the development of MPTP-induced nigrostriatal lesions followed by measures of motor function and behavior, surviving nigrostriatal dopaminergic neurons and termini, and striatal dopamine levels. When administered after lesion development, BL-1023 improved motor function of MPTP-mice as measured by rotarod, total floor and vertical plane movements, and stereotypic movements in open field activity tests compared to MPTP-mice without treatment. This also paralleled modest nigral dopaminergic neuronal protection. Such significant improvements in motor function, behaviors, and dopaminergic neuronal numbers were not seen when BL-1023 was administered during MPTP-induced lesion development. The data demonstrate select abilities of BL-1023 to increase dopaminergic neuronal survival and improve motor function in MPTP-mice.