Levodopa in the treatment of Parkinson's disease: a consensus meeting

Clinical Report on an Implant-Supported Overdenture in a Parkinson's Patient

Speaking, chewing, and swallowing difficulties can result from Parkinson's disease (PD), which frequently affects the oro-pharyngeal muscles. The reduction in food and hydration intake that is unavoidable leads to a worsening of neurological symptoms. Patients with Parkinson's disease experience significant challenges when adjusting to wearing entire dentures. Each of these problems presents a considerable challenge for the doctor in terms of prosthodontic rehabilitation. This case study describes how a patient with Parkinson's disease was able to employ flexible removable partial dentures supported by implants to replace both their full and partial set of missing teeth. A well-made prosthesis will help the patient with their psychological, functional, and aesthetic impairments.

Comparative Effectiveness of Carbidopa/Levodopa Enteral Suspension and Deep Brain Stimulation on Pill Burden Reduction in Medicare Fee-for-Service Patients with Advanced Parkinson's Disease

INTRODUCTION

Complex polypharmacy regimens to manage persistent motor fluctuations result in significant pill burden for patients with advanced Parkinson's disease (APD). This study evaluated the effectiveness of carbidopa/levodopa enteral suspension (CLES) and deep brain stimulation (DBS) on reducing pill burden in APD patients.

METHODS

We utilized 100% Medicare fee-for-service claims from 2014 to 2018 linked to CLES Patient Support Program (PSP) data. CLES initiators (CLES-I) were propensity matched 1:1 with patients enrolled in PSP who did not initiate treatment (CLES-NI) (N = 188) or undergo DBS, and 1:3 with patients who received DBS (N = 204, N = 612). Average daily pill burden and levodopa equivalent daily dosage (LEDD) were measured at baseline, 0-6 months and 7-12 months follow-up.

RESULTS

CLES-I and CLES-NI had higher pill burden than DBS patients at baseline. However, at 6 months post-treatment, CLES-I had significantly fewer pills/day than CLES-NI (4.7 versus 11.4, p < 0.05) and DBS (4.8 versus 7.4, p < 0.05). A significant reduction in pill burden was observed at 0-6 months (46.3%) and 7-12 months (68.3%) follow-up for CLES-I (p < 0.001) versus increased burden for CLES-NI (+10.5%, p < 0.05 and +8.2%, p > 0.05) and insignificant reductions for DBS (-3.9% and -6.1%, p > 0.05). Mean adjusted pill burden showed 57.3% fewer pills at 0-6 months and 74.1% at 7-12 months among CLES-I compared with CLES-NI, and 49.6% and 70.1% reduction compared with DBS. CLES-I showed a decrease in LEDD at 7-12 months compared with baseline (935 to 237 mg) and to CLES-NI (237 mg versus 1112 mg) and DBS patients (236 mg versus 594 mg).

CONCLUSION

CLES led to a significant reduction in pill burden and oral LEDD compared with CLES-NI and DBS patients. Pill burden reduction could be considered a treatment goal for patients with APD challenged by complex polypharmacy regimens that interfere with activities of daily living and quality of life.

Pharmacokinetics, Pharmacodynamics, and Tolerability of Opicapone in Healthy Chinese and Caucasian Subjects: An Open-Label, Single-Center, Phase 1 Study

INTRODUCTION

This study evaluated the pharmacokinetics (PK) and pharmacodynamics (PD) of single and multiple doses of opicapone (OPC) in healthy Chinese and Caucasian subjects.

METHODS

In this open-label, single-center, phase 1 study, eligible Chinese subjects received one of three OPC doses (25, 50, or 100 mg), and Caucasian subjects received either 25 or 50 mg of OPC. All subjects were administered a single dose of OPC, whereas subjects in the 50-mg OPC group continued to receive once-daily doses of 50 mg OPC for 10 days. The primary endpoint was to evaluate and compare the plasma concentrations and PK parameters of OPC and its main metabolite, and erythrocyte-soluble catechol-O-methyltransferase (S-COMT) activity in Chinese subjects with that of Caucasian subjects. The secondary endpoint was to evaluate the safety of OPC in Chinese subjects. The estimated results for geometric mean ratios (GMRs) were evaluated with the standard bioequivalence (BE) limits between 80% and 125% to evaluate the ethnic differences. All statistical analyses were performed using SAS version 9.4.

RESULTS

In total, 70 subjects (45 Chinese, 25 Caucasian) were enrolled; the majority of them were male (85.7%). The plasma exposure of both OPC and BIA 9-1103 increased in an approximately dose-proportional manner in both populations. Maximum S-COMT inhibition ranged from 79% to 95% after a single dose and was about 94% after a 10-day once-daily regimen in both populations. The point estimates of GMRs (Chinese/Caucasian) and 90% CI, except C_max in 25-mg and 50-mg OPC groups, for PK and PD parameters were within 80% to 125%. Furthermore, no new risks or safety concerns associated with OPC were identified, indicating a tolerable safety profile in healthy Chinese subjects.

CONCLUSION

Ethnicity had no significant impact on PK and PD parameters after single or multiple doses of OPC, and OPC was safe and tolerable in healthy Chinese subjects.

TRIAL REGISTRATION

ChiCTR number, CTR20192230.

Biomaterial Strategies for Restorative Therapies in Parkinson's Disease

Parkinson's disease (PD) is a progressive neurological disorder, in which dopaminergic midbrain neurons degenerate, leading to dopamine depletion that is associated with neuronal death. In this Review, we initially describe the pathogenesis of PD and established therapies that unfortunately only delay progression of the disease. With a rapidly escalating incidence in PD, there is an urgent need to develop new therapies that not only halt progression but even reverse degeneration. Biomaterials are playing critical roles in these new therapies which include controlled and site-specific delivery of neurotrophins, increased engraftment of implanted neural stem cells, and redirection of endogenous stem cell populations away from their niche to encourage reparative mechanisms. This Review will therefore cover important design features of biomaterials used in regenerative medicine and tissue engineering strategies targeted at PD.

The Long-Term Impact of Levodopa/Carbidopa Intestinal Gel on 'Off'-time in Patients with Advanced Parkinson's Disease: A Systematic Review

INTRODUCTION

Levodopa/carbidopa intestinal gel (LCIG; carbidopa/levodopa enteral suspension) has been widely used and studied for the treatment of motor fluctuations in levodopa-responsive patients with advanced Parkinson's disease (PD) when other treatments have not given satisfactory results. Reduction in 'off'-time is a common primary endpoint in studies of LCIG, and it is important to assess the durability of this response. This systematic literature review was conducted to qualitatively summarise the data on the long-term effects of LCIG therapy on 'off'-time.

METHODS

Studies were identified by searching PubMed, EMBASE and Ovid on 30 September 2019. Studies were included if they reported on patients with PD, had a sample size of ≥ 10, LCIG was an active intervention and 'off'-time was reported for ≥ 12 months after initiation of LCIG treatment. Randomised clinical trials, retrospective and prospective observational studies, and other interventional studies were included for selection. Data were collected on: 'off'-time (at pre-specified time periods and the end of follow-up), study characteristics, Unified Parkinson's Disease Rating Scale (UPDRS) II, III and IV total scores, dyskinesia duration, quality of life scores, non-motor symptoms and safety outcomes.

RESULTS

Twenty-seven studies were included in this review. The improvement in 'off'-time observed shortly after initiating LCIG was maintained and was statistically significant at the end of follow-up in 24 of 27 studies. 'Off'-time was reduced from baseline to end of follow-up by 38-84% and was accompanied by a clinically meaningful improvement in quality of life. Stratified analysis of 'off'-time demonstrated mean relative reductions of 47-82% at 3-6 months and up to 83% reduction at 3-5 years of follow-up. Most studies reported significant improvements in activities of daily living and motor complications. Most frequent adverse events were related to the procedure or the device.

CONCLUSION

In one of the largest qualitative syntheses of published LCIG studies, LCIG treatment was observed to provide a durable effect in reducing 'off'-time.

INFOGRAPHIC

Video Abstract.

Effects of Aging on Levo-Dihydroxyphenylalanine- Induced Dyskinesia in a Rat Model of Parkinson's Disease

Background

It remains unclear why patients with young-onset Parkinson's disease more often develop levo-dihydroxyphenylalanine (L-dopa)-induced dyskinesia (LID) and have a more severe form than patients with old-onset Parkinson's disease. Previous studies using animal models have failed to show young-onset Parkinson's disease enhances LID.

Objectives

To evaluate the association of age at dopaminergic denervation (onset age) and initiation of L-dopa treatment (treatment age) with LID development in model rats.

Methods

We established rat models of young- and old-lesioned Parkinson's disease (6-hydroxydopamine lesions at 10 and 88 weeks of age, respectively). Dopaminergic denervation was confirmed by the rotational behavior test using apomorphine. Rats in the young-lesioned group were allocated to either L-dopa treatment at a young or old age, or saline treatment. Rats in the old-lesioned group were allocated to either L-dopa treatment or saline group. We evaluated L-dopa-induced abnormal involuntary movements during the 14-day treatment period. We also examined preprodynorphin mRNA expression in the striatum (a neurochemical hallmark of LID) and the volume of the medial globus pallidus (a pathological hallmark of LID).

Results

LID-like behavior was enhanced in L-dopa-treated young-lesioned rats compared with L-dopa-treated old-lesioned rats. Preprodynorphin mRNA expression was higher in L-dopa-treated young-lesioned rats than in in L-dopa-treated old-lesioned rats. The volume of the medial globus pallidus was greater in L-dopa-treated young-lesioned rats than in L-dopa-treated old-lesioned rats. Treatment age did not affect LID-like behavior or the degree of medial globus pallidus hypertrophy in the young-lesioned model.

Conclusion

Both dopaminergic denervation and L-dopa initiation at a young age contributed to the development of LID; however, the former may be a more important factor.

Impact of carbidopa-levodopa enteral suspension on quality of life and activities of daily living in patients with advanced Parkinson's disease: Results from a pooled meta-analysis

INTRODUCTION

To estimate the impact of carbidopa/levodopa enteral suspension (CLES) on key patient-centered outcomes in patients with advanced Parkinson's disease (PD).

METHODS

A comprehensive literature review identified relevant studies, from which data were meta-analyzed over 3-month intervals up to 24 months. Patient-centered outcomes of interest included mean (95% CI) changes from baseline (Δ) in quality of life (QoL), measured using PD-specific (PDQ-8, PDQ-39) and generic (EQ-5D) instruments; activities of daily living (ADL), measured in On and Off states using UPDRS Part II; and motor symptoms (i.e., Off time/day and motor examination [measured in On and Off states using UPDRS Part III]).

RESULTS

The pooled meta-analysis included data from 26 studies evaluating 1556 patients on CLES. At 3 months, all outcomes showed significant improvement: QoL (ΔPDQ-39 = -10.26 [-11.54, -8.97], ΔEQ-5D_VAS = 15.42 [12.58, 18.26]); ADL (ΔUPDRS II_ON = -4.32 [-5.63, -3.01]); motor symptoms (ΔOff time hours/day = -3.48 [-4.15, -2.82], ΔUPDRS III_ON = -6.20 [-9.88, -2.51]). At 24 months, there were statistically significant mean improvements in QoL (ΔPDQ-39 = -7.74 [-12.40, -3.07], ΔEQ-5D_VAS = 11.18 [6.90, 15.45]) and ADL (ΔUPDRS II_OFF = -3.88 [-5.34, -2.42]), and Off time (-4.21 [-5.16, -3.26] hours/day).

CONCLUSIONS

Impact of CLES on significantly reducing Off time/day was observed to be rapid and durable (i.e., remained consistent across 24 months). Most QoL and ADL measures showed a consistent pattern of improvement with initiation of treatment and remained significantly improved from baseline at 24 months.

Use of a medication-based algorithm to identify advanced Parkinson's disease in administrative claims data: Associations with claims-based indicators of disease severity

Introduction

Lack of a gold standard definition for advanced Parkinson's Disease (APD), coupled with absence of disease severity information in diagnostic codes, hinders use of large administrative databases for conducting population health and comparative effectiveness studies.

Methods

Using pharmacy claims data, we created an algorithm to identify APD: any 30-day average levodopa equivalent dose (LED) >1000 mg/day. Using 2013 100% U.S. Medicare claims, we applied this algorithm and used multivariate logistic regression to examine associations between assigned APD status and claims-based indicators of PD severity (any deep brain stimulation, fall, hallucinations, walker, wheelchair, specialty bed, dementia diagnosis, skilled nursing facility, hospice), adjusting for sociodemographic, clinical, and treatment characteristics. Levodopa >1000 mg/day, levodopa >800 mg/day and LED >800 mg/day were used in sensitivity analysis.

Results

In our sample (N = 144,703), 20% were assigned APD status based on the LED >1000 mg/day cut-off. This group had significantly higher odds of having each claims-based indicator, compared with those assigned mild-moderate PD status. Odds ratios were highest for indicators for any DBS (OR: 2.96; 95% CI:2.75–3.19) and specialty bed (OR:2.15, 95% CI: 1.99–2.32) and lowest for fall (OR:1.27; 95% CI:1.20–1.34) and dementia diagnosis (OR:1.21; 95% CI:1.18–1.25). Results based on alternative approaches were similar.

Conclusions

Medicare patients classified as having APD via a pharmacy claims-based algorithm had higher odds of having claims-based clinical markers of APD, compared with patients categorized as having mild-moderate PD. This proxy strategy could facilitate future claims-based studies and warrants further refinement and validation using medical records or other clinical sources.

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Prescription claims can be used to calculate average daily levodopa-equivalent dose.

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An algorithm (LED >1000 mg/day) was used to identify advanced Parkinson's in claims.

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20% of people with Parkinson's disease in a Medicare sample aged 65+ met this definition.

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The remaining 80% of the sample was classified as having mild/moderate disease.

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The advanced group had higher odds of having clinical markers of advanced disease.

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

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

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.

Population pharmacokinetics of levodopa in subjects with advanced Parkinson's disease: levodopa-carbidopa intestinal gel infusion vs. oral tablets

AIMS

Levodopa-carbidopa intestinal gel (LCIG) provides continuous levodopa-carbidopa delivery through intrajejunal infusion. This study characterized the population pharmacokinetics of levodopa following a 16 h jejunal infusion of LCIG or frequent oral administration of levodopa-carbidopa tablets (LC-oral) in subjects with advanced Parkinson's disease (PD).

METHODS

A non-linear mixed-effects model of levodopa pharmacokinetics was developed using serial plasma concentrations from an LCIG phase 1 study and a phase 3 double-blind, double-dummy study of the efficacy and safety of LCIG compared with LC-oral in advanced PD patients (n = 68 for model development; 45 on LCIG and 23 on LC-oral). The final model was internally evaluated using stochastic simulations and bootstrap and externally evaluated using sparse pharmacokinetic data from 311 subjects treated in a long term safety study of LCIG.

RESULTS

The final model was a two compartment model with a transit compartment for absorption, first order elimination, bioavailability for LCIG (97%; confidence interval = 95% to 98%) relative to LC-oral, different first order transit absorption rate constants (LCIG = 9.2 h(-1) vs. LC-oral = 2.4 h(-1) ; corresponding mean absorption time of 7 min for LCIG vs. 25 min for LC-oral) and different residual (intra-subject) variability for LCIG (15% proportional error, 0.3 μg ml(-1) additive error) vs. LC-oral (29% proportional error, 0.59 μg ml(-1) additive error). Estimated oral clearance and steady-state volume of distribution for levodopa were 24.8 l h(-1) and 131 l, respectively.

CONCLUSIONS

LCIG administration results in faster absorption, comparable levodopa bioavailability and significantly reduced intra-subject variability in levodopa concentrations relative to LC-oral administration.

Levodopa: effect on cell death and the natural history of Parkinson's disease

This review article considers the question of whether or not levodopa is toxic in Parkinson's disease (PD). l-dopa is the most effective symptomatic treatment for PD and has provided benefit for millions of patients. However, there has been a longstanding concern that l-dopa might be toxic and accelerate neuronal degeneration and clinical progression as a consequence of reactive oxygen species generated by the drug's oxidative metabolism. In vitro, l-dopa can induce degeneration of dopaminergic neurons, but it is not clear that the effects of the drug on cultured dopamine neurons reflect what happens in the PD brain. In vivo, l-dopa has not been demonstrated to have toxic effects on dopamine neurons in normal, dopamine-lesioned, or oxidatively stressed animal models, but none of these models precisely replicates the PD condition. Clinical trials have tested the effect of l-dopa on clinical progression and have not demonstrated any findings indicative of toxicity. However, the symptomatic and long-duration effects of the drug could mask ongoing neuronal degeneration. Furthermore, l-dopa induces a greater decline in imaging measures of dopaminergic function than placebo or dopamine agonists, consistent with toxicity. Pathological studies have not demonstrated evidence of accelerated loss of dopamine neurons, but prospective and properly controlled studies with stereological unbiased counting have not been performed. Thus, although there is no hard evidence to suggest that l-dopa is toxic in PD patients, the issue has not been fully resolved. It is generally recommended that physicians continue to use l-dopa, but in the lowest dose that provides satisfactory clinical control.

Cerebrospinal fluid α-synuclein in the differential diagnosis of parkinsonian syndromes

ABSTRACT: 

Aim: To evaluate the diagnostic value of the level of α-synuclein, DJ-1, and Alzheimer's disease markers in the cerebrospinal fluid (CSF) in patients with parkinsonian syndromes. Materials & methods: We measured α-synuclein, DJ-1 and Alzheimer's disease markers by quantitative immunoassays in 122 CSF samples from patients with Parkinson's disease (PD; n = 38), dementia with Lewy bodies (n = 20), multiple-system atrophy (n = 18), progressive supranuclear palsy (n = 28), corticobasal degeneration (n = 7), unspecified atypical parkinsonian disorders (n = 5) and healthy controls (n = 6). Results: The level of α-synuclein was significantly decreased in CSF from PD patients. For the total tau/α-synuclein ratio, we obtained an area under the curve of 0.80 of the receiver operating characteristics curve for the PD diagnosis. With a cut-off of 1.33, the tau/α-synuclein ratio had 93% diagnostic specificity at 75% sensitivity for PD. Conclusion: CSF α-synuclein measurement may be useful in the differential diagnosis of PD versus other parkinsonian syndromes. CSF α-synuclein is found at low levels in the CSF and requires specifically adjusted assays to be measured.

Multiple treatments with L-3,4-dihydroxyphenylalanine modulate dopamine biosynthesis and neurotoxicity through the protein kinase A-transient extracellular signal-regulated kinase and exchange protein activation by cyclic AMP-sustained extracellular signal-regulated kinase signaling pathways

Multiple treatments with L-3,4-dihydroxyphenylalanine (L-DOPA; 20 µM) induce neurite-like outgrowth and reduce dopamine biosynthesis in rat adrenal pheochromocytoma (PC) 12 cells. We therefore investigated the effects of multiple treatments with L-DOPA (MT-LD) on cell survival and death over a duration of 6 days by using PC12 cells and embryonic rat midbrain primary cell cultures. MT-LD (10 and 20 µM) decreased cell viability, and both types of cells advanced to the differentiation process at 4-6 days. MT-LD induced cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) phosphorylation and exchange protein activation by cAMP (Epac) expression at 1-3 days, which led to transient extracellular signal-regulated kinase (ERK1/2) phosphorylation in both cells. In these states, MT-LD activated cAMP-response element binding protein (CREB; Ser133) and tyrosine hydroxylase (Ser40) phosphorylation in PC12 cells, which led to an increase in intracellular dopamine levels. In contrast, MT-LD induced prolonged Epac expression at 4-5 days in both cells, which led to sustained ERK1/2 phosphorylation. In these states, the dopamine levels were decreased in PC12 cells. In addition, MT-LD induced c-Jun N-terminal kinase1/2 phosphorylation and cleaved caspase-3 expression at 4-6 days in both cells. These results suggest that MT-LD maintains cell survival via PKA-transient ERK1/2 activation, which stimulates dopamine biosynthesis. In contrast, at the later time period, MT-LD induces differentiation via both prolonged Epac and sustained ERK1/2 activation, which subsequently leads to the cell death process. Our data demonstrate that L-DOPA can cause neurotoxicity by modulating the Epac-ERK pathways in neuronal and PC12 cells.

Excessive Sensitivity to Uncertain Visual Input in L-DOPA-Induced Dyskinesias in Parkinson's Disease: Further Implications for Cerebellar Involvement

When faced with visual uncertainty during motor performance, humans rely more on predictive forward models and proprioception and attribute lesser importance to the ambiguous visual feedback. Though disrupted predictive control is typical of patients with cerebellar disease, sensorimotor deficits associated with the involuntary and often unconscious nature of l-DOPA-induced dyskinesias in Parkinson’s disease (PD) suggests dyskinetic subjects may also demonstrate impaired predictive motor control.

Methods: We investigated the motor performance of 9 dyskinetic and 10 non-dyskinetic PD subjects on and off l-DOPA, and of 10 age-matched control subjects, during a large-amplitude, overlearned, visually guided tracking task. Ambiguous visual feedback was introduced by adding “jitter” to a moving target that followed a Lissajous pattern. Root mean square (RMS) tracking error was calculated, and ANOVA, robust multivariate linear regression, and linear dynamical system analyses were used to determine the contribution of speed and ambiguity to tracking performance.

Results: Increasing target ambiguity and speed contributed significantly more to the RMS error of dyskinetic subjects off medication. l-DOPA improved the RMS tracking performance of both PD groups. At higher speeds, controls and PDs without dyskinesia were able to effectively de-weight ambiguous visual information.

Conclusion: PDs’ visually guided motor performance degrades with visual jitter and speed of movement to a greater degree compared to age-matched controls. However, there are fundamental differences in PDs with and without dyskinesia: subjects without dyskinesia are generally slow, and less responsive to dynamic changes in motor task requirements, but in PDs with dyskinesia, there was a trade-off between overall performance and inappropriate reliance on ambiguous visual feedback. This is likely associated with functional changes in posterior parietal–ponto–cerebellar pathways.

Drug treatment of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease. While its cause remains elusive, much progress has been made regarding its treatment. Available drugs have a good symptomatic effect, but none has yet been shown to slow the progression of the disease in humans. The most efficacious drug is levodopa, but it remains unclear whether the symptomatic benefit is associated with neurotoxic effects and long-term deterioration. The long-term problem associated with levodopa is the appearance of dyskinesias, which is significantly delayed among patients treated with dopamine agonists as initial therapy. Less clear is the role of other drugs in PD, such as monoamine oxidase inhibitors (MAOIs), including selegiline and rasagiline, the putative N-meihyl-o-aspartaie (NMDA) receptor antagonists amantadine and memantine, and the muscarinic receptor blockers. All these may be used as initial therapy and delay the use of dopaminergic drugs, or can be added later to reduce specific symptoms (tremor or dyskinesias). Advanced PD is frequently associated with cognitive decline. To some extent, this can be helped by treatment with cholinesterase inhibitors such as rivastigmine. Similarly, hallucinations and delusions affect PD patients in the advanced stages of their disease. The use of classical neuroleptic drugs in these patients is contraindicated because of their extrapyramidal effects, but atypical drugs, and particularly clozapine, are very helpful. The big void in the therapy of PD lies in the more advanced stages. Several motor symptoms, like postural instability, dysphagia, and dysphonia, as well as dyskinesias, are poorly controlled by existing drugs. New therapies should also be developed against autonomic symptoms, particularly constipation.

Parkinson's disease therapeutics: new developments and challenges since the introduction of levodopa

The demonstration that dopamine loss is the key pathological feature of Parkinson's disease (PD), and the subsequent introduction of levodopa have revolutionalized the field of PD therapeutics. This review will discuss the significant progress that has been made in the development of new pharmacological and surgical tools to treat PD motor symptoms since this major breakthrough in the 1960s. However, we will also highlight some of the challenges the field of PD therapeutics has been struggling with during the past decades. The lack of neuroprotective therapies and the limited treatment strategies for the nonmotor symptoms of the disease (ie, cognitive impairments, autonomic dysfunctions, psychiatric disorders, etc.) are among the most pressing issues to be addressed in the years to come. It appears that the combination of early PD nonmotor symptoms with imaging of the nigrostriatal dopaminergic system offers a promising path toward the identification of PD biomarkers, which, once characterized, will set the stage for efficient use of neuroprotective agents that could slow down and alter the course of the disease.

L-DOPA: a scapegoat for accelerated neurodegeneration in Parkinson's disease?

There is consensus that amelioration of the motor symptoms of Parkinson's disease is most effective with L-DOPA (levodopa). However, this necessary therapeutic step is biased by an enduring belief that L-DOPA is toxic to the remaining substantia nigra dopaminergic neurons by itself, or by specific metabolites such as dopamine. The concept of L-DOPA toxicity originated from pre-clinical studies conducted mainly in cell culture, demonstrating that L-DOPA or its derivatives damage dopaminergic neurons due to oxidative stress and other mechanisms. However, the in vitro data remain controversial as some studies showed neuroprotective, rather than toxic action of the drug. The relevance of this debate needs to be considered in the context of the studies conducted on animals and in clinical trials that do not provide convincing evidence for L-DOPA toxicity in vivo. This review presents the current views on the pathophysiology of Parkinson's disease, focusing on mitochondrial dysfunction and oxidative/proteolytic stress, the factors that can be affected by L-DOPA or its metabolites. We then critically discuss the evidence supporting the two opposing views on the effects of L-DOPA in vitro, as well as the animal and human data. We also address the problem of inadequate experimental models used in these studies. L-DOPA remains the symptomatic 'hero' of Parkinson's disease. Whether it contributes to degeneration of nigral dopaminergic neurons, or is a 'scapegoat' for explaining undesirable or unexpected effects of the treatment, remains a hotly debated topic.

Pros and cons of apomorphine and L-dopa continuous infusion in advanced Parkinson's disease

Motor fluctuations and dyskinesia are common in advanced Parkinson's disease and can be poorly managed by current oral medications. Risk factors include the amount of L-dopa administered, gender and patient age. Continuous duodenal L-dopa or subcutaneous apomorphine infusions are helpful strategies because they can control motor complications by providing continuous dopaminergic drug delivery. Apomorphine subcutaneous infusion provides a motor benefit similar to that of dopamine and is relatively easy to use in advanced PD. However, it commonly requires concomitant administration of oral L-dopa and its long-term use is limited by compliance. Continuous administration of L-dopa/carbidopa by infusion in the duodenum/jejunum is a more complex procedure requiring a gastrostomy for the placement of the infusion tube, but it allows replacement of all oral medications and the achievement of a satisfactory therapeutic response paralleled by a reduction of motor complication severity. It should be noted that although these procedures are effective, most evidence relates to small case series and, particularly in the case of apomorphine, despite its long-term availability, there is a complete lack of randomized blinded studies. In addition, unlike deep brain stimulation, it is unclear which patients are the best candidates for these procedures, making any indirect comparison very complex, given the clinical heterogeneity of reported patients. This has consequences in resource allocation and in estimating cost-benefit ratios for these complex therapies in advanced PD.

How should we treat a patient with early Parkinson's disease?

Parkinson's disease (PD) is characterised by the progressive degeneration of dopaminergic nigro-striatal neurons and severe striatal dopaminergic deficiency, leading to bradykinesia. Levodopa was the first drug used for PD treatment and is still considered the most useful weapon for the control of PD symptoms. However, levodopa treatment induces motor complications, which is considered as a major problem as the disease progresses. Dopamine agonists, catechol-O-methyltransferase inhibitors and monoamine oxidase B inhibitors are some more recently developed drug categories which are expected to have a more favourable effect on motor complications. The choice of the best initial treatment in PD remains a controversial matter. Early therapeutic decisions in PD should balance the need for efficient short-term symptom control against long-term complication profile. The individualisation of the treatment seems to be the key for the best approach of early PD patients.

Oral and infusion levodopa-based strategies for managing motor complications in patients with Parkinson's disease

Levodopa is the most effective treatment for Parkinson's disease (PD) signs and symptoms, and patients invariably will require it during the course of the disease. It also provides benefits in activities of daily living, quality of life and life expectancy. However, after a few years of levodopa treatment the majority of patients will experience motor fluctuations and dyskinesia. Initial use of a dopamine receptor agonist may delay the emergence of motor fluctuations but at the cost of reduced symptomatic control compared with the use of levodopa in some cases. Adequate management of motor fluctuations and dyskinesia is essential to maintaining satisfactory quality of life at the advanced stage of disease. Various levodopa-based strategies are currently available that aim to control motor complications (wearing-off and dyskinesia) in PD and each approach has its own unique benefit and risk profile. Strategies such as dose fragmentation (smaller, more frequent dosing) or the use of orally administered, liquid levodopa formulations or melevodopa can reduce off-time intervals or facilitate absorption. More recently introduced, continuous delivery of dopaminergic medications may represent a more effective approach to treat motor complications in advanced PD and its effect can be perceived from improvement in clinical scales, as well as in health-related items. Indeed, continuous levodopa delivery by duodenal infusion may stabilize and significantly improve motor function as well as patients' quality of life. We propose a treatment algorithm that takes into account all currently available levodopa-based treatment strategies for motor complications in patients with PD.

Apomorphine and levodopa infusion therapies for advanced Parkinson's disease

Continuous infusion of levodopa or apomorphine provide constant dopaminergic stimulations are good alternatives to deep brain stimulation to control motor fluctuations in patients with advanced Parkinson’s disease (PD). Apomorphine provides motor benefit similar to dopamine, but its long-term use is limited by compliance, mostly injection site skin reactions. Administration of levodopa/carbidopa by continuous duodenal infusion allows replacement of all oral medications and permits achievement of a satisfactory therapeutic response paralleled by a reduction in motor complication severity. However, this procedure is more invasive than apomorphine as it requires a percutaneous endoscopic gastrostomy Clinical experience with infusions shows that continuous dopaminergic stimulation of dopaminergic medications reduces dyskinesia and widens the therapeutic window in advanced PD.

Current status of symptomatic medical therapy in Parkinson's disease

Symptomatic medical therapies for Parkinson's disease (PD) have been disease modifying and have led to improvement in daily function, quality of life, and survival. For 40 years, these therapies have been primarily dopaminergic, and currently include the dopamine (DA) precursor levodopa (LD), DA agonists, catechol-O-methyltransferase (COMT) inhibitors, and monoamine oxidase (MAO) inhibitors. The roles of all these classes of agents have evolved, with significant changes occurring since the early 2000s. This article reviews the current literature for each of these classes of drugs, with a focus on efficacy and place in the therapeutic scheme. Levodopa is no longer considered to be toxic and, thus, its early use is not only appropriate but recommended. Ergot agonists are no longer in use, and new agents administered in patch form or subcutaneous injections have been approved. The COMT inhibitor tolcapone, with its significant efficacy, has been reintroduced, and two new MAO inhibitors have been approved. Selected safety issues are discussed, including the incidence of melanoma in relation to LD; pathological gambling and DA agonists; hepatic toxicity of tolcapone; and the tyramine or so-called cheese reaction with MAO B inhibitors. The article closes with a discussion of future directions and new drugs under development.

Unregulated cytosolic dopamine causes neurodegeneration associated with oxidative stress in mice

The role of dopamine as a vulnerability factor and a toxic agent in Parkinson's disease (PD) is still controversial, yet the presumed dopamine toxicity is partly responsible for the "DOPA-sparing" clinical practice that avoids using L-3,4-dihydroxyphenylalanine (L-DOPA), a dopamine precursor, in early PD. There is a lack of studies on animal models that directly isolate dopamine as one determining factor in causing neurodegeneration. To address this, we have generated a novel transgenic mouse model in which striatal neurons are engineered to take up extracellular dopamine without acquiring regulatory mechanisms found in dopamine neurons. These mice developed motor dysfunctions and progressive neurodegeneration in the striatum within weeks. The neurodegeneration was accompanied by oxidative stress, evidenced by substantial oxidative protein modifications and decrease in glutathione. Ultrastructural morphologies of degenerative cells suggest necrotic neurodegeneration. Moreover, L-DOPA accelerated neurodegeneration and worsened motor dysfunction. In contrast, reducing dopamine input to striatum by lesioning the medial forebrain bundle attenuated motor dysfunction. These data suggest that pathology in genetically modified striatal neurons depends on their dopamine supply. These neurons were also supersensitive to neurotoxin. A very low dose of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (5 mg/kg) caused profound neurodegeneration of striatal neurons, but not midbrain dopamine neurons. Our results provide the first in vivo evidence that chronic exposure to unregulated cytosolic dopamine alone is sufficient to cause neurodegeneration. The present study has significant clinical implications, because dopamine replacement therapy is the mainstay of PD treatment. In addition, our model provides an efficient in vivo approach to test therapeutic agents for PD.

Impact of Functional Age on the Use of Dopamine Agonists in Patients With Parkinson Disease

BACKGROUND

Parkinson disease (PD) is primarily a neurodegenerative disorder that affects as many as 1,500,000 people in the United States. It is predominantly a disease of the elderly, and special treatment challenges must be addressed in this patient population.

REVIEW SUMMARY

It has been generally accepted that PD patients over the age of 70 will have a shorter lifespan than younger patients and are at less risk for developing treatment-emergent complications by virtue of their lower exposure to medication over the course of the disease. Consequently, elderly patients are often treated aggressively when motor symptoms start to become disabling. Recent statistics, however, suggest that effective treatments for PD have helped to increase the longevity of PD patients, suggesting that elderly patients may, in fact, have sufficient medication exposure to raise concern over levodopa-induced motor complications. If this is the case, physicians should consider treating their elderly PD patients with dopamine agonists, which have several advantages over levodopa therapy, not the least of which is a lower prevalence of motor complications.

CONCLUSION

Dopamine agonists are safe and effective in elderly patients and offer numerous advantages when used as either monotherapy or adjunctive therapy, particularly in patients requiring long-term treatment.

Pharmacokinetic optimisation in the treatment of Parkinson's disease : an update

Pharmacotherapy for Parkinson's disease is focused on dopaminergic drugs, mainly the dopamine precursor levodopa and dopamine receptor agonists. The elimination half-life (t(1/2)) of levodopa from plasma (in combination with a decarboxylase inhibitor) of about 1.5 hours becomes more influential as the disease progresses. The long-duration of response to levodopa, which is evident in early Parkinson's disease, diminishes and after a few years of treatment motor performance is closely correlated to the fluctuating plasma concentrations of levodopa. Absorption of levodopa in the proximal small intestine depends on gastric emptying, which is erratic and may be slowed in Parkinson's disease. The effects of levodopa on motor function are dependent on gastric emptying in patients in the advanced stages of disease. The current treatment concept is continuous dopaminergic stimulation (CDS). Sustained-release formulations of levodopa may provide more stable plasma concentrations. Oral liquid formulations shorten the time to reach peak concentration and onset of effect but do not affect plasma levodopa variability. The t(1/2) of levodopa can be prolonged by adding a catechol-O-methyltransferase inhibitor (entacapone or tolcapone), which may reduce fluctuations in plasma concentrations, although both peak and trough concentrations are increased with frequent administration. Intravenous and enteral (duodenal/jejunal) infusions of levodopa yield stable plasma levodopa concentrations and motor performance. Enteral infusion is feasible on a long-term basis in patients with severe fluctuations. Among the dopamine receptor agonists the ergot derivatives bromocriptine, cabergoline, dihydroergocryptine and pergolide, and the non-ergot derivatives piribedil, pramipexole and ropinirole, have longer t(1/2) compared with levodopa. Thus, they stimulate dopamine receptors in a less pulsatile manner, yet pharmacokinetic studies of repeated doses of dopamine receptor agonists are few. Optimisation of these drugs is often performed with standardised titration schedules. Apomorphine and lisuride have short t(1/2) and are suitable for subcutaneous infusion, with results similar to those of levodopa infusion. Transdermal administration of dopamine receptor agonists such as rotigotine might be an alternative in the future. In general, initial dopamine receptor agonist monotherapy is associated with poorer motor performance and lower incidence of motor complications compared with levodopa. Buccal administration of the monoamine oxidase-B inhibitor selegiline (deprenyl) provides better absorption and less formation of metabolites compared with standard tablets. To conclude, several new drugs, formulations and routes of administration have been introduced in the treatment of Parkinson's disease during the last decade, mainly with CDS as the aim. CDS can be approached by optimising the use of dopaminergic drugs based on pharmacokinetic data.

Prognosis of Parkinson's disease: Time to stage III, IV, V, and to motor fluctuations

We report a long-term outcome on a large cohort of Japanese patients with Parkinson's disease (PD). A total of 1,768 (793 men, 975 women) consecutive patients visited our clinic from 1 January 1989 to 31 December 2002. Among them, 1,183 patients (531 men, 652 women) came to our clinic within 5 years from the onset of disease and at the Hoehn & Yahr Stage III or less at the first visit. Long-term outcome was evaluated in this subcohort of the patients. We examined the duration to reach Stage III, IV, and V, and the duration to develop wearing off and dyskinesia. Time to reach Stage III was slightly but significantly shorter in women, in that 23.8% of men and 35.3% of women reached Stage III by the end of the 5th year; 49.7% of men and 63.3% of women reached Stage III by the end of the 10th year, and 88.9% of men and 79.9% of women by the end of the 15th year (P < 0.001). Also, durations to develop wearing off and dyskinesia were shorter in women compared to men. These data suggest that the disease progression may be slightly faster for women. Young-onset patients showed significantly longer duration to reach Stage III, IV, and V but shorter duration to develop wearing off and dyskinesia. Not many studies are available in the literature on the long-term outcome of PD, and our data would be useful as a reference.

A new look at levodopa based on the ELLDOPA study

Levodopa has been the gold standard for Parkinson's disease (PD) therapy since it was successfully introduced in 1967. But in the years since then, after recognizing that levodopa often leads to the motor complications of wearing-off and dyskinesias, there have been debates among clinicians as to when levodopa therapy should be started. Delaying therapy was advocated for the purpose of delaying the development of these motor complications. This became more popular as the dopamine agonists became available. Although less potent than levodopa in ameliorating the symptoms of PD, they were much less likely to produce the unwanted motor complications, even though they had their own adverse effects. When it was recognized that dopamine, itself, might be a factor leading to the death of dopaminergic neurons through its contributing to the formation of oxyradicals, a new concern arose, namely that levodopa, through its conversion to brain dopamine, might add to the existing oxidative stress and possibly enhance neurodegeneration of dopaminergic neurons. Though widely debated and without definite evidence, this possibility was sufficient to make some clinicians have further reason to delay the start of levodopa therapy. The ELLDOPA study was created to test this hypothesis. The clinical component of the study failed to find an enhancement of PD symptoms after levodopa was withdrawn following 40 weeks of levodopa therapy. Rather, the clinical results indicated that the symptoms had progressed much less than placebo, and in a dose-response manner. This suggests that levodopa may actually have neuroprotective properties. The uncertainty that a 2-week withdrawal of levodopa may not have entirely eliminated its symptomatic benefit and the discordant results of the neuroimaging component of the ELLDOPA study have created even more uncertainty that levodopa is neuroprotective. A survey of neurologists who treat PD patients showed that the vast majority of these clinicians do not believe levodopa is neuroprotective, and they remain concerned about the drug's likelihood of inducing motor complications. Thus, the ELLDOPA study failed to change the treating pattern of PD, and the clinicians require more convincing evidence of either neuroprotection or neurotoxicity of levodopa before they would alter their treatment approach.

Long term motor complications of levodopa: clinical features, mechanisms, and management strategies

Levodopa is the most effective symptomatic treatment of Parkinson's disease. However, after an initial period of dramatic benefit, several limitations become apparent including, "dopa resistant" motor symptoms (postural abnormalities, freezing episodes, speech impairment), "dopa resistant" non-motor signs (autonomic dysfunction, mood and cognitive impairment, etc), and/or drug related side effects (especially psychosis, motor fluctuations, and dyskinesias). Motor complications include fluctuations, dyskinesias, and dystonias. They can be very disabling and difficult to treat. Therefore, strategies should ideally be developed to prevent them. Though mechanisms underlying motor complications are only partially understood, recent work has revealed the importance of pulsatile stimulation of postsynaptic dopamine receptors and the disease severity. As a result of intermittent stimulation there occurs a cascade of changes in cell signalling leading to upregulation of the N-methyl-D-aspartate subtype of gamma-aminobutryric acid-ergic neurones. Modified preparations of levodopa (controlled release preparations, liquid levodopa), catecholamine-o-methyltransferase inhibitors, dopamine agonists, amantidine, and various neurosurgical approaches have been used in the prevention and/or treatment of motor complications. Current management of motor complications is less than satisfactory. With better understanding of the pathogenetic mechanisms, it is hoped that future therapeutic strategies will provide a safer and targeted treatment.

NMDA receptor antagonists ameliorate the stepping deficits produced by unilateral medial forebrain bundle injections of 6-OHDA in rats

RATIONALE AND OBJECTIVES

To test the hypothesis that excess glutamatergic transmission at NMDA receptors may contribute to the pathogenesis of Parkinson's disease (PD), we examined the effects of various NMDA receptor antagonists on a recently developed rat model of PD.

METHODS

Following unilateral injections of 12 microg 6-OHDA into the medial forebrain bundle of male Long Evans rats, stepping with both front paws was measured separately as the paws were dragged backwards and laterally. The effects of i.p. injections of varying doses of L-dopa, the non-competitive NMDA receptor antagonist dizocilpine [(+)-MK-801], the competitive NMDA receptor antagonist CPP, and combinations of L-dopa and NMDA receptor antagonists were then examined on stepping in three separate groups of rats.

RESULTS

The lesioned rats stepped less often with their contralateral paw than with their ipsilateral paw, and the magnitude of this stepping deficit was positively correlated with the amount of DA depletion in the ipsilateral dorsal striatum. L-dopa (1-25 mg/kg) dose dependently enhanced stepping with the contralateral paw, and 0.15-0.3 mg/kg dizocilpine and 1.5-6.25 mg/kg CPP enhanced stepping with the contralateral paw as much as did 8 mg/kg L-dopa. The combinations of L-dopa and each of the NMDA receptor antagonists did not significantly improve stepping more than either drug alone. Moreover, none of the drugs completely eliminated the stepping deficits, and high doses began to impair stepping with the ipsilateral paw by inducing turning.

CONCLUSIONS

These data indicate that deficits in contralateral stepping are a reliable and sensitive measure of akinesia in unilateral 6-OHDA-lesioned rats, and they support the hypothesis that excess glutamatergic transmission at NMDA receptors may play a role in the expression of PD symptomology.

Levodopa Infusion Therapy in Parkinson Disease

Orally administered levodopa, in combination with a decarboxylase inhibitor, is the gold standard therapy for Parkinson disease (PD). The problems in management of motor fluctuations in the advanced stages of the disorder are due to the close relationship between plasma levodopa levels and availability of dopamine at striatal receptor sites. The fluctuating levodopa concentrations are mainly explained by the fact that levodopa absorption only occurs in the proximal small intestine. The patient's motor function thus depends on gastric emptying, which is erratic and may even be delayed in PD. Oral therapy with sustained-release formulations and COMT inhibitors have not solved the problems satisfactorily. Therefore, infusions of levodopa by intravenous and enteral (duodenal/jejunal) routes of administration have been studied. In this review of the literature on clinically relevant levodopa infusion studies, it is shown that improvements regarding fluctuations in both plasma levodopa levels and motor performance have been repeatedly reported. The results acquired so far suggest that levodopa infusion is a safe and efficacious therapy. Recent drug delivery development and long-term studies have shown that infusion is a clinically feasible alternative to treat advanced PD.

Rationale for current therapies in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects an estimated 1 million people in the US and tens of millions worldwide. Medication therapy has made significant advances and improvements especially over the last 10 years. A number of new treatments and new strategies have emerged and the quality of life for the average sufferer has improved. This review will describe the rationale and strategies for current medical therapies in PD, with special emphasis on the use of antipsychotic agents. Levodopa remains the most efficacious medication for the management of PD. Long-term use of levodopa, however, is associated with the development of motor fluctuations including dyskinesia. Trials with dopamine agonists have demonstrated a delay in the onset of dyskinesia with the use of this therapy. There is also active, ongoing investigation to determine whether a neuroprotective effect may be present with agonist therapy. Anticholinergics have been successfully used to treat tremor as well as sialorrhoea and urinary urgency. Catechol-O-methyltransferase inhibitors increase 'on time', decrease 'off time,' and improve motor scores. Continuous stimulation of dopamine receptors may decrease the fluctations observed with pulsatile delivery of anti-Parkinsonian medications, but this will require more study. Monoamine oxidase-B inhibitors, specifically selegiline, may provide symptomatic improvement; the question as to whether a neuroprotective benefit is present remains unanswered. Amantadine has demonstrated both symptomatic benefit and dyskinesia benefit in some patients. Selective dopamine blockers such as clozaril and quetiapine, have been shown to be effective in the treatment of psychosis. This class of medications is particularly useful as an adjunctive to levodopa and dopamine agonists. Doses of dopaminergic drugs can be escalated to treat Parkinsonian symptoms, whereas selective dopamine blockers can be added to block psychosis. Old management strategies required a reduction in dopaminergic therapy and therefore worsened Parkinsonian symptoms. Even though there have been great advances in the medical options for symptomatic management of PD, there are still many unmet needs for this patient population.

Advances in the pharmacological management of Parkinson disease

Numerous advances have taken place in the pharmacological management of Parkinson disease (PD) in recent years. Some of the more clinically relevant will be discussed in the text that follows. New drugs have been developed to treat or prevent the motor fluctuations and dyskinesias that occur frequently with the continuous use of levodopa. Such drugs include the catechol-O-methyl-transferase (COMT) inhibitors, such as tolcapone and entecapone, and new dopamine (DA) agonists with long half lives such as cabergoline, pramipexole or ropirinole. Also new, atyical, antipsychotics have appeared which have revolutionized the treatment of PD since they allow us to control hallucinations and other psychotic behaviour without worsening of motor function. Finally preliminary reports suggest that cholinesterase inhibitors, such as rivastigmine, can be usefull in the management of cognitive impairment in PD, one of the most difficult clinical problems encountered in the management of this neurodegenerative disorder.

Entacapone is beneficial in both fluctuating and non-fluctuating patients with Parkinson's disease: a randomised, placebo controlled, double blind, six month study

OBJECTIVE

To study the effect of entacapone, a specific peripherally acting catechol-O-methyltransferase (COMT) inhibitor used in combination with levodopa treatment, in cases of Parkinson's disease with both fluctuating and non-fluctuating response to treatment.

METHODS

A randomised, placebo controlled, double blind, six month study was undertaken in 172 fluctuating and 128 non-fluctuating patients. The clinical efficacy and safety of 200 mg entacapone given with each daily levodopa dose was studied. Efficacy was examined using home diaries, the unified Parkinson disease rating scale (UPDRS), and recording of daily levodopa dose.

RESULTS

The primary efficacy variable for fluctuating patients-the proportion of daily ON time-showed a significant increase compared with placebo (p < 0.05). The absolute ON time (mean (SD)) increased from 9.5 (2.5) to 10.8 (2.4) hours (p < 0.01), and the daily OFF time was correspondingly reduced from 7.0 (2.6) to 5.9 (2.5) hours (p < 0.05 v placebo). This improvement was achieved despite a reduction in daily levodopa requirements. The effect was rapidly lost on withdrawal of entacapone. In non-fluctuating patients, the primary efficacy measure was part II of the UPDRS (activities of daily living; ADL). In this group of patients, ADL scores improved in the entacapone group (p < 0.01 v placebo), and there was also a 40 mg reduction in levodopa requirement (p < 0.01 v placebo). Entacapone was well tolerated by both fluctuating and non-fluctuating patients.

CONCLUSIONS

The ability of entacapone to provide additional benefits to levodopa treatment in increasing ON time in fluctuating Parkinson's disease patients was confirmed. A novel finding was that patients without fluctuations also obtained benefit from the addition of entacapone to their levodopa treatment, as evidenced by improved ADL scores and a relatively reduced levodopa requirement.

Parkinson's disease: is the initial treatment established?

Recent studies have suggested that initial dopamine agonist therapy with pramipexole or ropinirole may slow the progression of Parkinson's disease (PD) and also reduce the subsequent risk of levodopa motor complications. This presumed effect on PD progression, however, could be artifactual, resulting from the influence of chronic drug treatment on regulation of dopamine system proteins. With respect to levodopa motor complications, there is no dispute that pramipexole and ropinirole are effective in reducing levodopa dyskinesias and motor fluctuations; however, it is not clear that they must be started early, as opposed to initiation only after the levodopa complications develop. Levodopa therapy has numerous advantages that include greater efficacy, much lesser expense, simpler administration, and a lower frequency of hallucinosis and somnolence. Carbidopa/levodopa, pramipexole, and ropinirole are all appropriate first choices in the treatment of PD.

The increased utilisation of dopamine agonists and the introduction of COMT inhibitors have not reduced levodopa consumption--a nation-wide perspective in Sweden

OBJECTIVE

To study the impact of the new pharmacological treatment strategies in Parkinson's disease by analysis of the sales of dopaminergic drugs in Sweden 1990-2001.

METHODS

Invoice statistics and statistics on prescription sales of dopaminergic drugs 1990-2001 were obtained from the 906 public pharmacies and the 89 hospital pharmacies in Sweden. The Swedish Diagnosis and therapy survey was used to study the diagnosis the drugs were prescribed for.

RESULTS

During the period the sales expressed in DDD/1000 inhabitants and day increased from 1.75 to 1.86 (6%) for levodopa and from 0.04 to 0.27 (575%) for dopamine agonists. The increase in sales of dopamine agonists occurred after 1997 and consisted entirely of the sales of the new agonists, cabergoline, pramipexole and ropinirole. In Swedish crowns the total sales of dopaminergic drugs increased with 126% during the period. The cost for the dopamine agonists was 8% of the total cost for dopaminergic drugs in 1990 and 23% in 2001. The prescription sales figures of levodopa and dopamine agonists for the different Swedish counties in 2001 varied between 1.52 and 2.44 and 0.13 and 0.74 DDD/1000 inhabitants and day, respectively. There was no correlation, whether positive or negative, between the sales of dopamine agonists, levodopa and COMT inhibitors or between the sales and the densities of neurologists.

CONCLUSION

The consumption of levodopa in Sweden continues to increase in spite of a dramatic increase in the utilisation of dopamine agonists and the introduction of COMT-inhibitors.

The contribution of the MPTP-treated primate model to the development of new treatment strategies for Parkinson's disease

Current research into Parkinson's disease (PD) is directed at developing novel agents and strategies for improved symptomatic management. The aim of this research is to provide effective and maintained symptom control throughout the course of the disease without loss of efficacy and without priming the basal ganglia for the onset of dyskinesia. To achieve these objectives, it is important to have relevant animal models of PD in which new pharmacological agents and treatment strategies can be assessed prior to clinical assessment. At present, the most effective experimental model of PD is the methyl phenyl tetrahydropyridine (MPTP)-treated primate. Primates treated with MPTP develop motor disturbances resembling those seen in idiopathic PD, including bradykinesia, rigidity and postural abnormalities. In addition, MPTP-treated primates are responsive to all commonly used antiparkinsonian agents and display treatment-associated motor complications such as dyskinesia, wearing-off and on-off, which occur during the long-term treatment of the illness. This review examines how studies conducted in MPTP-treated primates have contributed to the development of dopaminergic therapies. There is now accumulating evidence that the pulsatile manner in which short-acting agents stimulate striatal dopamine receptors is a key contributing factor to the priming of the basal ganglia for dyskinesia induction. It has been suggested that providing more continuous stimulation of dopamine receptors will avoid the development of motor complications, particularly dyskinesia. So far, the actions of all commonly used antiparkinsonian drugs assessed in MPTP-treated primates have proved to be highly predictive of drug action in PD. These primate studies have demonstrated that long-acting dopamine agonists and levodopa given in combination with a catechol-O-methyl transferase (COMT) inhibitor (to increase its relatively short half-life), induce significantly less dyskinesia than occurs with standard levodopa therapy.

The management of patients with early Parkinson's disease

A major problem in the management of early Parkinson's disease is to choose the first medication to prescribe. This decision should rely on the level of available clinical evidence, largely based, at least for efficacy, on the results of randomised clinical trials. Safety and costs are also crucial to consider. Other factors like for example pathophysiological concepts, individual experience, marketing pressure, socio-economical environment, patients needs and expectations have, however, also their own influence. Levodopa is efficacious and cheap, but induces long-term motor complications. The early use of dopamine agonists is more and more frequently promoted, because large prospective L-dopa-controlled trials demonstrated that this strategy reduces the risk of such long-term complications. Integrating individual clinical expertise to the best available external clinical evidence (evidence-based medicine) is the best strategy in making decisions about the care of individual patients.

Dopaminergic substitution in Parkinson's disease

Motor complications associated with long-term levodopa application, which follow the so-called honeymoon period of well-tolerated levodopa administration and are looked upon as one clinical marker for progression of Parkinson's disease (PD), initiated a long and controversial debate on the putative neurotoxicity of levodopa. Since dopamine agonists (DA) delay onset of motor complications, they support the neuroprotective treatment strategy in PD. Efficacy and tolerability of DA differs in particular due to their affinity to various dopamine receptor subtypes. The accumulating evidence for levodopa-associated homocysteinaemia, which represents a risk factor for increased incidence of vascular disease in PD, supports the strategy of initial DA application and the use of levodopa as an add-on compound in as low a dose as possible in young PD patients.

Emerging therapies in the pharmacological treatment of Parkinson's disease

The pharmacological management of Parkinson's disease is a complex and dynamic task; there is no one 'right' strategy indicating which drugs should be used at a particular stage of the disease. There are now many different drugs belonging to several classes that may be effective, and there are still differences of opinion among leading clinicians about the best course of treatment. This review focuses on drug therapy for the motor impairment in Parkinson's disease. Current and future research directions are summarised by taking inventory of recent and innovative areas of development in the field, representing each category with at least one of its featured treatments. The main research efforts are being directed towards delaying the use of levodopa or finding therapies to be used as adjunct to it, in order to postpone motor complications and, in particular, dyskinesias. One of the recent trends is early employment of dopamine agonists. Additional efforts are being directed towards protecting and restoring dopamine neurons. Novel therapies acting on non-dopaminergic systems are also being researched.

Frontiers in Neuropharmacotherapy Part II: Multiple Sclerosis and Parkinson’s Disease

Disease-modifying agents such as β-interferons and glatiramer acetate have a significant impact on slowing the course of relapsing-remitting multiple sclerosis (MS). Therapeutic guidelines recommend initiating therapy with 1 of the 3 agents shortly after diagnosis of clinically definite MS, but there is insufficient data to specifically select one of the therapies. New research helps differentiate the therapies based on their induction of neutralizing antibodies, optimal dosing, and monitoring strategies. New treatments for secondary progressive MS are also emerging with evidence for the use of interferon β-1b and the approval of mitoxantrone. Future therapies for MS include oral glatiramer acetate and combination therapy.

Levodopa continues to be the standard of care for the treatment of Parkinson’s disease, but the approval of newer therapies that spare the use of levodopa and improve safety profiles are changing the management of the disease. Dopamine agonists such as bromocriptine and pergolide have been used to manage complications of levodopa therapy in patients with advanced disease, but new research supports the use of the more selective dopamine agonists, pramipexole and ropinirole, as monotherapy in early Parkinson’s disease. The combination of a catechol-O-methyltransferase (COMT) inhibitor with levodopa provides a new therapeutic option for treating patients with motor complications in advanced disease.

Pathophysiology of Parkinson's disease: from clinical neurology to basic neuroscience and back

Parkinson's disease (PD) is characterized by motor and nonmotor (cognitive and limbic) deficits. The motor signs of PD include hypokinetic signs such as akinesia/bradykinesia, rigidity and loss of normal postural reflexes, and hyperkinetic signs such as tremor. Dopamine depletion in the striatum is the hallmark of PD and of its animal models, still the pathophysiology of the parkinsonian symptoms and especially of parkinsonian tremor are under debate. The most extreme hypotheses argue about peripheral versus central nervous system origin, intrinsic cellular oscillator versus network oscillators, and basal ganglia-based pathophysiology versus cerebellar-thalamic based pathophysiology. Recent studies support the view that parkinsonian symptoms are most likely due to abnormal synchronous oscillating neuronal activity within the basal ganglia. Peripheral factors do only play a minor role for the generation, maintenance, and modulation of PD tremor and other signs. The most likely candidates producing these neuronal oscillations are the weakly coupled neural networks of the basal ganglia-thalamo-cortical loops. However, the present evidence supports the view that the basal ganglia loops are influenced by other neuronal structures and systems and that the tuning of these loops by cerebello-thalamic mechanisms and by other modulator neurotransmitter systems entrain the abnormal synchronized oscillations. Neurosurgical procedures, such as lesions or high-frequency stimulation of different parts of the loop, might resume the normal unsynchronized activity of the basal ganglia circuitry, and, therefore, ameliorate the clinical symptoms of Parkinson's disease.

Pharmacokinetic-pharmacodynamic relationship of levodopa with and without tolcapone in patients with Parkinson's disease

OBJECTIVE

To investigate the effect of administration of the catechol-Omethyltransferase (COMT) inhibitor tolcapone on the concentration-effect relationship of levodopa in patients with advanced Parkinson's disease and on-off fluctuations.

DESIGN

Nonblind single-group 2-period pharmacokinetic-pharmacodynamic study.

PATIENTS AND PARTICIPANTS

12 patients, mean age 59 years, with idiopathic Parkinson's disease and response fluctuations.

METHODS

The pharmacokinetics [plasma concentrations of levodopa and 3-O-methyldopa (3-OMD)] and motor effects [global score of the Columbia University Rating Scale (CURSsigma)] of levodopa (plus the peripheral decarboxylase inhibitor benserazide 1:4) were determined for 4 consecutive dosage intervals (4 hours each, starting at 8.00am) in 12 patients before (day 1) and during (day 8) coadministration of tolcapone 100 mg 3 times daily for 7 days.

RESULTS

Under tolcapone, exposure to levodopa [area under the plasma concentration-time for the dosage interval (AUCt)] observed for the separate doses increased by 1.6- to 2.2-fold, and peak plasma drug concentrations (Cmax) increased by 1.1 - to 2.1 -fold. 3-OMD concentrations at day 8 were reduced to about 20% of the values at day 1. At baseline (day 1, before the first levodopa dose), CURSsigma averaged 40 +/- 10 points. After the first levodopa dose. CURSsigma declined to 20 +/- 9 points. At day 8. the predose CURSsigma decreased to a final score of 31 +/-13 points, and the maximal decline after the first levodopa dose was to a final score of 16 +/- 8 points. Population analysis (NONMEM) of the concentration-effect relationship of levodopa according to a sigmoidal Emax model and over all dosage intervals did not show differences in levodopa responsiveness with or without tolcapone. The population mean of the 50% effective concentration (EC50) of levodopa was 1350 microg/L with an standard error of the population parameter estimate of 18%: adding tolcapone treatment as a covariate did not significantly change the population fit. Circadian influences on levodopa respon- siveness were not evaluable by the NONMEM model due to overparametrisation, but visual inspection of plotted data did not suggest differences in the concentration-effect relationship between the 4 consecutive dosage intervals on days 1 and 8.

CONCLUSIONS

The gain in clinical improvement with levodopa under tolcapone can be fully explained by tolcapone-induced changes of peripheral levodopa pharmacokinetics. We suggest that this interaction study, performed in patients and using clinical data, excludes any central effects of tolcapone or any inhibiting effect of 3-OMD on levodopa permeation through the blood-brain barrier, which otherwise would have led to a decrease in the EC50 of levodopa.

Parkinson's Disease: Initial Treatment with Levodopa or Dopamine Agonists

The question of whether to use levodopa (LD) or dopamine agonists as initial therapy in Parkinson's disease has been a controversy for nearly 20 years. There are several issues relating to this treatment regimen that may effect ones decision. Review of them results in the following conclusions: LD does not cause the onset of motor fluctuations and dyskinesia; it probably relates to disease progression. Tolerance does not develop with long-term LD therapy. LD is not toxic. LD decreases mortality in Parkinson's disease. Motor fluctuations can occur with dopamine-agonist monotherapy, but the actual frequency is as yet unknown. Dopamine agonists are not neuroprotective. Clinical trials have indicated that LD remains the most potent symptomatic therapeutic agent available. Dopamine agonists do provide some symptomatic relief when used alone in early Parkinson's disease. Standard preparations of LD have the same effect on early disease as controlled release preparations. Dopamine agonists cause less dyskinesia and fluctuations. These conclusions indicate that both drugs are effective symptomatic agents with their own positive and negative aspects. There is no incorrect choice. It is reasonable to start young onset patients (younger than 50 years of age) with an agonist, because they seem to be more prone to develop motor fluctuations and dyskinesia. However, if employment is in jeopardy then LD may be needed. Because agonists cause more hallucinations, freezing, and somnolence, problems of particular relevance to the elderly (older than 70 years), then LD would be the best agent for older onset patients. In general, but particularly for those falling in between these age groups, treatment should be individualized. In this time of cost effectiveness, LD remains the least expensive of these agents.