Levodopa: why the controversy?

Ferroptosis and its potential role in the physiopathology of Parkinson's Disease

Parkinson's Disease (PD) is a common and progressive neurodegenerative disorder characterised by motor impairments as well as non-motor symptoms. While dopamine-based therapies are effective in fighting the symptoms in the early stages of the disease, a lack of neuroprotective drugs means that the disease continues to progress. Along with the traditionally recognised pathological hallmarks of dopaminergic neuronal death and intracellular α-synuclein (α-syn) depositions, iron accumulation, elevated oxidative stress and lipid peroxidation damage are further conspicuous features of PD pathophysiology. However, the underlying mechanisms linking these pathological hallmarks with neurodegeneration still remain unclear. Ferroptosis, a regulated iron dependent cell death pathway involving a lethal accumulation of lipid peroxides, shares several features with PD pathophysiology. Interestingly, α-syn has been functionally linked with the metabolism of both iron and lipid, suggesting a possible interplay between dysregulated α-syn and other PD pathological hallmarks related to ferroptosis. This review will address the importance for understanding these disease mechanisms that could be targeted therapeutically. Anti-ferroptosis molecules are neuroprotective in PD animal models and the anti-ferroptotic iron chelator, deferiprone, slowed disease progression and improved motor function in two independent clinical trials for PD. An ongoing larger multi-centre phase 2 clinical trial will confirm the therapeutic potential of deferiprone and the relevance of ferroptosis in PD. This review addresses the known pathological features of PD in relation to the ferroptosis pathway with therapeutic implications of targeting this cell death pathway.

Exosomes in Parkinson's Disease

Exosomes, nano-sized extracellular vesicles secreted by most cell types, are found in all kinds of biological fluids and tissues, including the central nervous system (CNS). The proposed functions of these vesicles include roles in cell-cell signaling, removal of cellular debris, and transfer of pathogens between cells. Many studies have revealed that exosomes derived from the CNS occur in the cerebrospinal fluid and peripheral body fluids, and their contents are altered during disease, making them an appealing target for biomarker development in Parkinson's disease (PD). Exosomes have been shown to spread toxic α-synuclein (αsyn) between cells and induce apoptosis, which suggests a key mechanism underlying the spread of αsyn aggregates in the brain and the acceleration of pathology in PD. However, potential neuroprotective roles of exosomes in PD have also been reported. On the treatment side, as drug delivery vehicles, exosomes have been used to deliver small interfering RNAs and catalase to the brain, and have shown clear therapeutic effects in a mouse model of PD. These features of exosomes in PD make them extremely interesting from the point of view of developing novel diagnostic and therapeutic approaches.

Neuroprotective and Therapeutic Strategies against Parkinson's Disease: Recent Perspectives

Parkinsonism is a progressive motor disease that affects 1.5 million Americans and is the second most common neurodegenerative disease after Alzheimer’s. Typical neuropathological features of Parkinson’s disease (PD) include degeneration of dopaminergic neurons located in the pars compacta of the substantia nigra that project to the striatum (nigro-striatal pathway) and depositions of cytoplasmic fibrillary inclusions (Lewy bodies) which contain ubiquitin and α-synuclein. The cardinal motor signs of PD are tremors, rigidity, slow movement (bradykinesia), poor balance, and difficulty in walking (Parkinsonian gait). In addition to motor symptoms, non-motor symptoms that include autonomic and psychiatric as well as cognitive impairments are pressing issues that need to be addressed. Several different mechanisms play an important role in generation of Lewy bodies; endoplasmic reticulum (ER) stress induced unfolded proteins, neuroinflammation and eventual loss of dopaminergic neurons in the substantia nigra of mid brain in PD. Moreover, these diverse processes that result in PD make modeling of the disease and evaluation of therapeutics against this devastating disease difficult. Here, we will discuss diverse mechanisms that are involved in PD, neuroprotective and therapeutic strategies currently in clinical trial or in preclinical stages, and impart views about strategies that are promising to mitigate PD pathology.

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.

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.

Levodopa-related wearing-off in Parkinson's disease: identification and management

BACKGROUND

Levodopa is currently the most effective treatment for Parkinson's disease (PD); however, long-term levodopa therapy often results in motor complications, such as motor fluctuations and dyskinesia. The initial complication is commonly wearing-off, which is the re-emergence of motor and non-motor symptoms before the next scheduled levodopa dose.

OBJECTIVE

The purpose of this article was to review published literature that discusses wearing-off, focusing on the role of the healthcare professional, including the primary care physician, in the effective management of wearing-off.

METHODS

An electronic literature search was conducted using MEDLINE and EMBASE to find articles discussing wearing-off and its management using the following keywords: 'Parkinson's disease'; 'wearing-off'; 'levodopa'; 'primary care'.

FINDINGS AND CONCLUSIONS

Current evidence indicates that a consistent delivery of levodopa should improve long-term symptomatic efficacy and may prevent or delay motor complications. A number of therapeutic options are available to optimize therapeutic outcome, including modification of the levodopa dose or dosing schedule,switching to another levodopa formulation and the use of adjunct therapies, such as catechol-O-methyl transferase inhibitors, dopamine agonists and monoamine oxidase-B inhibitors. The management of wearing-off is dependent upon the early identification of symptoms and the initiation of effective treatment. Key issues are the need to educate patients and to facilitate good communication with both primary and secondary healthcare professionals. In most cases, patients with PD initially present to primary healthcare professionals who may refer the patient to a neurologist once disease management becomes more complex. However, in many cases, especially in rural areas where neurologists may not be widely available, the primary healthcare professionals may manage the patient throughout the disease course. Limitations of this review include the restricted search criteria and selected search period.

Treatment of levodopa-induced motor complications

Chronic levodopa treatment for Parkinson's disease patients is frequently associated with the development of motor complications such as end-of-dose wearing-off and dyskinesias. In this review, we provide an overview of the strategies available for dealing with these problems. Medical management includes manipulation of levodopa dosing to establish the optimum treatment schedule, improving levodopa absorption, catechol-O-methyl transferase-inhibition (COMT), Monoamine oxidase-B (MAO-B) inhibition, dopaminergic agonists, amantadine, and continuous dopaminergic infusions. Surgical procedures and particularly deep brain stimulation are also reviewed. It should be noted that none of these treatments has been shown to provide anti-parkinsonian efficacy that is greater than what can be achieved with levodopa. We highlight the importance of initiating therapy with a treatment strategy that reduces the risk that a Parkinson's disease patient will develop motor complications in the first place. Key Words: Advanced PD, dyskinesias, motor fluctuations, levodopa, dopamine agonists, COMT inhibitors, MAO-B inhibitors.

Levodopa/DDCI and entacapone is the preferred treatment for Parkinson's disease patients with motor fluctuations in routine practice: a retrospective, observational analysis of a large French cohort

Levodopa is the gold standard drug for the symptomatic control of Parkinson's disease (PD). However, long-term treatment with conventional formulations [levodopa and a dopa decarboxylase inhibitor (DDCI)], is associated with re-emergence of symptoms because of wearing-off and dyskinesia. Treatment with levodopa/DDCI and entacapone extends the half-life of levodopa, avoiding deep troughs in levodopa plasma levels and providing more continuous delivery of levodopa to the brain. In this open-label, retrospective, observational study we investigated the effects of levodopa/DDCI and entacapone therapy in 800 PD patients with motor fluctuations. Levodopa/DDCI and entacapone treatment was assessed as good/very good in improving motor fluctuations (64%) and activities of daily living (ADL; 62%). The therapeutic utility was considered to be good/very good in 70% of cases. Moreover, there was a reduction in levodopa dose in 20% of patients. Neurologists preferred levodopa/DDCI and entacapone compared with increasing levodopa dosage, dose-fractionation or addition of a dopamine agonist (63%, 29% and 23% of patients respectively). Reasons included achieving more continuous dopaminergic stimulation (40%), reducing motor fluctuations (54%) and improving ADL (41%). This analysis reveals the preference of neurologists for levodopa/DDCI and entacapone over conventional levodopa-modification strategies for the effective treatment of PD motor fluctuations in clinical practice.

When should levodopa therapy be initiated in patients with Parkinson's disease?

Levodopa is available in three forms: immediate-release, orally disintegrating and sustained-release tablets. Levodopa is metabolised in the gastrointestinal tract, kidney and liver by aromatic acid dopa decarboxylase using pyridoxine as a cofactor. Approximately 70-80% of the dose is eliminated in the urine. Central conversion of levodopa to dopamine likely occurs at surviving dopaminergic terminals and at serotonergic and adrenergic nerve terminals that contain decarboxylase. Dopamine is metabolised by catechol-O-methyltransferase and monoamine oxidase. The major metabolites of dopamine are homovanillic acid and dihydroxyphenylacetic acid. Levodopa remains the most efficacious pharmacological treatment for the symptoms of Parkinson's disease (PD). Results of current levodopa trials suggest that treatment with levodopa at the onset of disease provides superior motor and functional control compared with dopamine receptor agonists. Moreover, levodopa is generally better tolerated with a lower incidence of gastrointestinal and neuropsychiatric adverse effects. The debate over the role of levodopa in the treatment of PD is fuelled by the results of in vitro studies that show generation of free radicals by levodopa and its toxic effects on cell cultures. Levodopa has also consistently been shown to produce motor fluctuations (in particular dyskinesias) sooner than has been observed in PD patients, especially younger patients, given dopamine agonists initially. However, the cumulative body of knowledge thus far does not show definitive evidence that levodopa is neurotoxic to parkinsonian patients. In older PD patients with lesser risk of motor fluctuations, levodopa may be used initially, and perhaps solely, in demented PD patients and those at higher risk of developing neuropsychiatric adverse effects. In young parkinsonian patients with mild motor dysfunction, use of levodopa may be delayed or the dosage minimised. However, because of levodopa's superior efficacy, when a rapid and sustained symptomatic improvement is required because of significant motor disability, levodopa may be used as the first-line agent regardless of age.

Patient satisfaction with switching to Stalevo: an open-label evaluation in PD patients experiencing wearing-off (Simcom Study)

OBJECTIVES AND METHODS

This study investigated the ease with which 52 Parkinson's disease patients already receiving adjunct entacapone to traditional levodopa were switched to Stalevo (levodopa/carbidopa/entacapone).

RESULTS

The switch to Stalevo was straightforward for most patients taking standard-release levodopa with 86% of these patients being able to replace their entire regimen without having to change the amount of levodopa taken. The majority of patients (54%, P = 0.162) preferred Stalevo; 31% preferred their prior treatment regimen; 15% had no preference. Patients found Stalevo more simple to dose (94%), more convenient to use (84%), easier to handle (84%), easier to remember (67%) and easier to swallow (59%), compared with their previous medication.

CONCLUSIONS

Stalevo was well tolerated, with a low incidence of adverse events. The study shows that Stalevo is an effective, preferred and well-tolerated means of delivering levodopa/carbidopa/entacapone in one easy-to-use tablet.

Development of a Patient Questionnaire to facilitate recognition of motor and non-motor wearing-off in Parkinson’s disease

We previously reported that the use of a specifically designed Wearing-Off Questionnaire (WOQ) identified symptoms of wearing-off more frequently than standard assessments conducted by movement disorder specialists during a routine office visit. In the previous study we used a WOQ of 32 symptoms; however this tool was not designed for daily use. In this paper we describe the retrospective development of a simpler, 19-symptom WOQ more suitable for routine clinical use.

Present and future drug treatment for Parkinson's disease

Considerable advances made in defining the aetiology, pathogenesis, and pathology of Parkinson's disease (PD) have resulted in the development and rapid expansion of the pharmacopoeia available for treatment. Anticholinergics were used before the introduction of levodopa which is now the drug most commonly used. Dopamine agonists are effective when used alone or as an adjunct to levodopa, while monoamine oxidase B inhibitors improve motor function in early and advanced PD. However, treatment mainly addresses the dopaminergic features of the disease and leaves its progressive course unaffected; the drug treatment available for the management of non-motor symptoms is limited. This article seeks to set current treatment options in context, review emerging and novel drug treatments for PD, and assess the prospects for disease modification. Surgical therapies are not considered.

Hydrosoluble fiber (Plantago ovata husk) and levodopa II: experimental study of the pharmacokinetic interaction in the presence of carbidopa

Levodopa combined with carbidopa constitutes one of the most frequent medication in the treatment of Parkinson's disease. Plantago ovata husk (water-soluble fiber) improves levodopa absorption conditions, but when this drug is administered with carbidopa, fiber could reduce its effectiveness. The purpose of this study is to investigate whether the presence of P. ovata husk modifies in rabbits the bioavailability and other pharmacokinetic parameters of levodopa (20 mg/kg) when administered by the oral route with carbidopa (5 mg/kg). We have also studied whether pharmacokinetic modifications are fiber-dose dependent (100 and 400 mg/kg). When levodopa and carbidopa were administered with 100 mg/kg P. ovata husk, the value of AUC for levodopa diminishes 29.7% (sign, n=6, P<0.05) and Cmax 28.1% (sign, n=6, P<0.05) in relation to the values obtained when these drugs were administered without fiber. If the dose of fiber was 400 mg/kg, the decrease was smaller: 20.4% for AUC (no significant difference) and 24.6% for Cmax (sign, n=6, P<0.05), that may indicate an inhibitory action of AADC by the fiber or any of its partial hydrolysis products. On the other hand, since certain time on, levodopa concentrations are always higher in the groups that receive fiber: 210 min with 100 mg/kg and 150 min with 400 mg/kg. The administration of P. ovata husk with levodopa/carbidopa to patients with Parkinson disease could be beneficial and in particular in those patients who also suffer constipation due to an improvement of levodopa kinetic profile with higher final concentrations, a longer plasma half-life and lower Cmax.

Optimising levodopa therapy for the management of Parkinson’s disease

Levodopa remains unrivalled in providing symptomatic benefit for the treatment of Parkinson's disease (PD). However, wearing-off and dyskinesia have been associated with chronic therapy using traditional levodopa formulations. The onset of these motor complications arises, in part, due to the limited pharmacokinetic profile of traditional levodopa and not as a direct consequence of levodopa per se. Clinical trials addressing these issues have suggested that providing less pulsatile and more continuous dopaminergic stimulation by improving the pharmacokinetic profile of levodopa may overcome the onset of these motor complications. It can, therefore, be suggested that the onset of dyskinesia may be prolonged if levodopa is administered in a more continuous manner by administering it as a combination of levodopa/DDCI and COMT inhibitor.

Contribution of l-3,4-dihydroxyphenylalanine metabolism to the inhibition of gluconeogenesis in rabbit kidney-cortex tubules

The circulating L-3,4-dihydroxyphenylalanine, the drug of choice in the therapy of Parkinson's disease (PD), is efficiently extracted by kidney and converted to dopamine, known to control several renal functions. As: (i) in addition to liver, kidney is an important source of glucose in mammals and (ii) the action of this drug on renal gluconeogenesis has not yet been studied, the aim of the present investigation was to estimate the influence of L-3,4-dihydroxyphenylalanine metabolism on glucose formation in isolated kidney-cortex tubules incubated with various gluconeogenic substrates. The data indicate that a rapid intracellular degradation of L-3,4-dihydroxyphenylalanine and tyramine (at 100 and 200 microM concentrations) is accompanied by 25-40% decrease in glucose production from pyruvate, alanine + glycerol + octanoate and dihydroxyacetone due to augmented generation of hydrogen peroxide via monoamine oxidase B, resulting in a decline of glutathione redox state by 40%. Moreover, following inhibition of monoamine oxidase B by deprenyl or substitution of pyruvate by aspartate + glycerol + octanoate both L-3,4-dihydroxyphenylalanine and tyramine affect neither the rate of gluconeogenesis nor glutathione redox state. In view of: (i) L-3,4-dihydroxyphenylalanine- and tyramine-induced changes in intracellular levels of gluconeogenic intermediates, and (ii) a significant decline of phosphoenolpyruvate carboxykinase activity by 500 microM oxidized glutathione, it is likely that L-3,4-dihydroxyphenylalanine- and tyramine-evoked disturbances in the glutathione redox state might diminish flux through phosphoenolpyruvate carboxykinase and in consequence decrease glucose formation in renal tubules, suggesting a new potential side-action of L-3,4-dihydroxyphenylalanine treatment.

Identification of motor and nonmotor wearing-off in Parkinson's disease: Comparison of a patient questionnaire versus a clinician assessment

This study compares the sensitivity of a Patient Questionnaire versus information gathered by clinicians at a routine clinic visit in recognizing symptoms of wearing-off in early Parkinson's disease (PD). This Patient Questionnaire, containing 32 items representing a wide spectrum of motor and nonmotor wearing-off symptoms, was administered to subjects attending two PD clinics. The Patient Questionnaire results were compared to the information gathered by the clinician from the Unified Parkinson's Disease Rating Scale (UPDRS) Part IV, Question 36 and from a specific Clinical Assessment Question regarding loss of medication efficacy, wearing-off, sleepiness, dyskinesias, psychiatric complications, morning akinesia, other dopaminergic side effects, or none of the above. Examiners were blinded to study hypothesis and survey contents. Three hundred consecutive subjects with PD of <5 years duration were evaluated; the mean subject age was 72 +/- 9.6 years and 60.2% were men. Subjects reporting wearing-off were significantly younger (69.9 vs. 74.7 years) and differed regarding duration of PD symptoms (3.7 vs. 3.1 years). Wearing-off was found in 181 subjects (62.6%) by one or more of the three measures. The most sensitive tool was the Patient Questionnaire, with 165 subjects (57.1%) indicating symptoms of wearing-off. Question 36 of the UPDRS was positive in 127 subjects (43.9%), and the Clinical Assessment Question identified 85 subjects (29.4%) as experiencing wearing-off. All of these results were found to differ significantly. The mean number of wearing-off symptoms reported by the 165 subjects indicating wearing-off on the clinical survey was 6.25, with tremor being the most common motor feature and tiredness the most common nonmotor feature.

Multiple small doses of levodopa plus entacapone produce continuous dopaminergic stimulation and reduce dyskinesia induction in MPTP-treated drug-naïve primates

Long-acting dopamine agonist drugs induce a lower incidence of dyskinesia in MPTP-treated primates and patients with Parkinson's disease compared to pulsatile treatment with levodopa, supporting the concept of continuous dopaminergic stimulation as a means of dyskinesia avoidance. We examined the effects of L-dopa administered with or without the COMT inhibitor entacapone on dyskinesia induction in previously untreated MPTP-treated common marmosets. Administration of L-dopa (12.5 mg/kg p.o.) plus carbidopa twice daily produced fluctuating improvement in motor behavior coupled with dyskinesia. Coadministration with entacapone produced similar patterns of motor improvement and dyskinesia that were not different from that produced by L-dopa alone. Treatment with L-dopa (6.25 mg/kg p.o.) plus carbidopa four times daily reversed motor disability and induced dyskinesia in a manner that was not different from the twice-daily treatment regimens. However, coadministration with entacapone produced more continuous improvement in locomotor activity with less dyskinesia than animals treated with L-dopa four times daily alone. These data support the notion that pulsatile stimulation contributes to the development of dyskinesia and suggests that more frequent dosing of L-dopa plus entacapone may be a useful treatment strategy for patients in the early stages of Parkinson's disease.

Levodopa in the treatment of Parkinson's disease: Current controversies

Levodopa is the most effective symptomatic agent in the treatment of Parkinson's disease (PD) and the "gold standard" against which new agents must be compared. However, there remain two areas of controversy: (1) whether levodopa is toxic, and (2) whether levodopa directly causes motor complications. Levodopa is toxic to cultured dopamine neurons, and this may be a problem in PD where there is evidence of oxidative stress in the nigra. However, there is little firm evidence to suggest that levodopa is toxic in vivo or in PD. Clinical trials have not clarified this situation. Levodopa is also associated with motor complications. Increasing evidence suggests that they are related, at least in part, to the short half-life of the drug (and its potential to induce pulsatile stimulation of dopamine receptors) rather than to specific properties of the molecule. Treatment strategies that provide more continuous stimulation of dopamine receptors provide reduced motor complications in MPTP monkeys and PD patients. These studies raise the possibility that more continuous and physiological delivery of levodopa might reduce the risk of motor complications. Clinical trials to test this hypothesis are underway. We review current evidence relating to these areas of controversy.

Neuroprotection and pharmacotherapy for motor symptoms in Parkinson's disease

Parkinson's disease leads to major disability that impairs the quality of life of patients and leads to increased health-care costs. While there is no proven neuroprotective treatment, more basic-science research and clinical trials are needed to identify drugs that slow or halt the progression of the disorder. The mainstay of symptomatic treatment is levodopa. With long-term use, levodopa causes motor complications including involuntary movements and response fluctuations. These have lead to more cautious prescribing of levodopa. Dopamine agonists can be used as an alternative initial therapy to delay the onset of motor complications but at the expense of more dopaminergic adverse events, poorer control of motor symptoms, and increased cost. Once motor complications have developed, adjuvant therapy with dopamine agonists or entacapone can reduce off time and levodopa dose. Severe fluctuations that are not controlled by oral combination therapy can be controlled with subcutaneous apomorphine injections or infusions.

The Scientific Basis for the Current Treatment of Parkinson's Disease

Parkinson's disease (PD) is an age-related neurodegenerative disease that affects approximately one million people in the United States. The introduction of levodopa revolutionized the treatment for this disorder, but the long-term utility of the drug is limited by motor complications, the development of features such as postural instability and dementia that do not respond to treatment, and continued disease progression. Insights into the organization of the basal ganglia in the normal and PD conditions has permitted the design of new treatment strategies that reduce the risk of developing motor complications. Additionally, increased knowledge of the mechanisms responsible for cell death in PD has permitted the development of putative neuroprotective drugs that might slow or stop disease progression. No drug has yet been established to alter the rate of disease progression, but the rapid pace of research offers reason for optimism.

Efficacy and safety of levodopa with entacapone in Parkinson's disease patients suboptimally controlled with levodopa alone, in daily clinical practice: an international, multicentre, open-label study

The combination of entacapone with levodopa is effective in the treatment of Parkinson's disease (PD), providing significant improvements in 'on' time and Unified Parkinson's Disease Rating Scale (UPDRS) motor and ADL scores in controlled clinical trials. This multicentre, open-label study was designed to further evaluate the effectiveness of levodopa combined with entacapone 200 mg in routine clinical practice. Patients experiencing end-of-dose wearing-off were treated for 8 weeks (treatment phase), with an optional extension phase up to 20 weeks. The primary efficacy parameter was the Investigators' Global Assessment of Change; secondary efficacy parameters included UPDRS, 'off' time (from patient diaries), Patients' Global Assessment of Change, quality of life (QoL), SF-36 Health Assessment Questionnaire and Parkinson's Disease Questionnaire 39 (PDQ-39). Of the 479 patients who entered this study, 427 (89.1%) completed the treatment phase and 374 (78.1%) continued into the extension phase. Based on the Investigators' Assessment of Change, 380 (79.7%) patients showed an improvement with entacapone during the treatment phase. This improvement was maintained into the extension phase, and at Week 20, 301 (82.2%) patients continued to show an improvement. A positive treatment effect with entacapone was also seen with all secondary efficacy parameters, including QoL. Mean change in the total PDQ-39 scores showed improvements from baseline of -4.0 score points to the end of the treatment phase (n=182) and -3.1 score points at the end of the extension phase (n=152). Entacapone in combination with levodopa was generally well tolerated: 40 patients (8.4%) discontinued treatment due to adverse events (AEs) by the end of the extension phase. This study in a daily clinical practice setting confirmed the efficacy of coadministering entacapone with levodopa shown in controlled clinical trials and suggests that the combination is useful in improving the disability and QoL in patients with PD.

Prevention and treatment of motor fluctuations

The symptoms of Parkinson's disease can become increasingly difficult to control as the disease advances, particularly with the development of motor complications, such as end-of-dose wearing-off and dyskinesias, following long-term therapy. At this stage, the patient is frequently referred to a Parkinson's disease specialist for advice on the management of their disease. In this review we provide an overview of the Parkinson's disease specialist's strategies for coping with such problems. This includes strategy to prevent or delay motor fluctuations and the concept of the long duration response. The paper also includes establishing the optimum and most rational levodopa treatment schedule, improving levodopa absorption, use of COMT-inhibition, the addition of oral dopaminergic agonists, and the use of subcutaneous injections or infusions of apomorphine or lisuride. Finally, we highlight the increasing importance of treatment strategies that stimulate dopamine receptors in a more continuous, less pulsatile manner as a way of reducing the risk of developing treatment-associated motor complications.

Limitations of current Parkinson's disease therapy

Levodopa and other dopaminergic medications drastically improve the motor symptoms and quality of life of patients with Parkinson's disease in the early stages of the disease. However, once the "honeymoon" period has waned, usually after a few years of dopaminergic therapy, patients become progressively more disabled despite an ever more complex combination of available antiparkinsonian treatments. Sooner or later, they suffer from "dopa-resistant" motor symptoms (speech impairment, abnormal posture, gait and balance problems), "dopa-resistant" nonmotor signs (autonomic dysfunction, mood and cognitive impairment, sleep problems, pain) and/or drug-related side effects (especially psychosis, motor fluctuations, and dyskinesias). Therefore, the current antiparkinsonian therapy cannot be considered as ideal with regard to both efficacy and safety.