Loss of long-duration response to levodopa over time in PD: implications for wearing-off

Optimizing the selection of Parkinson's disease patients for neuromodulation using the levodopa challenge test

BACKGROUND

In Parkinson's disease (PD), early stages are associated with a good long-duration response and as the disease advances, the short-duration response predominates. The transition between the long-duration and short-duration responses may be an important and measurable intermediate stage. A critical criterion in determining the candidature for neuromodulation is a beneficial response to an 'off-on' levodopa challenge test. This test is usually reserved for those that have already developed marked short-duration response and are candidates for deep brain stimulation (DBS) surgery. However, identifying those that are in transition may allow DBS to be offered earlier.

OBJECTIVE

The objective of the study was to determine if the transition from a long-duration to a short-duration response can be assessed on a levodopa challenge test.

METHODS

An 'off-on" levodopa challenge test was done in sixty-five PD patients divided into four groups based on the disease duration.

RESULTS

OFF motor scores increased in all groups [Mean ± STD; 22.94 ± 8.52, 31.53 ± 9.87, 34.05 ± 9.50, and 33.92 ± 10.15 in groups 1-4, respectively] while a significant response to medication was maintained on 'off-on' testing. The mean levodopa equivalency dose in groups 1 and 2 was significantly less than in groups 3 and 4. This transition occurred between years 7 and 9 of disease duration.

CONCLUSION

Performing a regular levodopa challenge test, when levodopa dose increases substantially, should be considered to determine the ideal time for DBS in patients with Parkinson's disease.

An evaluation of the efficacy and value of CVT-301 for the treatment of Parkinson's disease

Introduction: Levodopa is the most effective drug in the treatment of Parkinson's disease, but its chronic treatment is linked to the occurrence of motor complications with fluctuations of motor performance and dyskinesia. Unpredictable OFF episodes can be severe and disabling and current rescue medications cannot always be used safely. Rescue therapy is characterized by a rapid and predictable ON response and the safety profile of levodopa will represent a major advantage for patients affected by unresponsive OFF episodes.Areas covered: CVT-301 is a new inhaled formulation of LD recently developed as a self-administered treatment for OFF periods. Herein, the pharmacodynamic and pharmacokinetic properties, efficacy, and safety of CVT-301 are reviewed.Expert opinion: CVT-301 may offer several potential advantages including increased systemic bioavailability through pulmonary absorption, rapid onset of action, avoidance of first-pass drug metabolism, and less plasma level variability. It should be noted that the delivery device used has been described as relatively simple to use, but the few steps required to prepare and self-administer the dose can be challenging for PD patients during their OFF state. Additionally, resolution of an OFF episode requires the administration of two capsules of CVT-301, which further complicates the use of the device.

A synthetic kinematic index of trunk displacement conveying the overall motor condition in Parkinson's disease

Parkinson's disease (PD) is characterized by motor impairment, affecting quality of life and increasing fall risk, due to ineffective postural control. To this day, the diagnosis remains based on clinical approach. Similarly, motor evaluation is based on heterogeneous, operator-dependent observational criteria. A synthetic, replicable index to quantify motor impairment is still lacking. Hence, we have designed a new measure of postural stability which assesses the trunk displacement in relation to the center of mass, that we named trunk displacement index (TDI). Twenty-three PD patients and twenty-three healthy controls underwent motor examination through a stereophotogrammetric system. A correlation analysis was performed to assess the relationship of TDI with gait parameters and clinical motor scale (UPDRS-III). The TDI sensitivity was estimated, comparing pre- and post- L-DOPA subclinical dose intake. The TDI showed significant correlations with many gait parameters and with the UPDRS-III. Furthermore, the TDI resulted capable in discriminating between off and on state in PD, whereas gait parameters failed two show any difference between those two conditions. Our results suggest that the TDI may be considered a highly sensitive biomechanical index, reflecting the overall motor condition in PD, and provided of clinical relevance due to the correlation with the clinical evaluation.

Natural history of motor symptoms in Parkinson's disease and the long-duration response to levodopa

The natural pattern of progression of Parkinson’s disease is largely unknown because patients are conventionally followed on treatment. As Parkinson’s disease progresses, the true magnitude of the long-duration response to levodopa remains unknown, because it can only be estimated indirectly in treated patients. We aimed to describe the natural course of motor symptoms by assessing the natural OFF in consecutive Parkinson’s disease patients never exposed to treatment (drug-naïve), and to investigate the effects of daily levodopa on the progression of motor disability in the OFF medication state over a 2-year period. In this prospective naturalistic study in sub-Saharan Africa, 30 Parkinson’s disease patients (age at onset 58 ± 14 years, disease duration 7 ± 4 years) began levodopa monotherapy and were prospectively assessed using the Unified Parkinson’s disease Rating Scale (UPDRS). Data were collected at baseline, at 1-year and 2-years follow-up. First-ever levodopa intake induced a significant improvement in motor symptoms (natural OFF versus ON state UPDRS-III 41.9 ± 15.9 versus 26.8 ± 15.1, respectively; P < 0.001). At 1-year follow-up, OFF state UPDRS-III score after overnight withdrawal of levodopa was considerably lower than natural OFF (26.5 ± 14.9; P < 0 .001). This effect was not modified by disease duration. At the 2-year follow-up, motor signs after overnight OFF (30.2 ± 14.2) were still 30% milder than natural OFF (P = 0.001). The ON state UPDRS-III at the first-ever levodopa challenge was similar to the overnight OFF score at 1-year follow-up and the two conditions were correlated (r = 0.72, P < 0.001). Compared to the natural progression of motor disability, levodopa treatment resulted in a 31% lower annual decline in UPDRS-III scores in the OFF state (3.33 versus 2.30 points/year) with a lower model’s variance explained by disease duration (67% versus 36%). Using the equation regressed on pretreatment data, we predicted the natural OFF at 1-year and 2-year follow-up visits and estimated that the magnitude of the long-duration response to levodopa ranged between 60% and 65% of total motor benefit provided by levodopa, independently of disease duration (P = 0.13). Although levodopa therapy was associated with motor fluctuations, overnight OFF disability during levodopa was invariably less severe than the natural course of the disease, independently of disease duration. The same applies to the yearly decline in UPDRS-III scores in the OFF state. Further research is needed to clarify the mechanisms underlying the long-duration response to levodopa in Parkinson’s disease. Understanding the natural course of Parkinson’s disease and the long-duration response to levodopa may help to develop therapeutic strategies increasing its magnitude to improve patient quality of life and to better interpret the outcome of randomized clinical trials on disease-modifying therapies that still rely on the overnight OFF to define Parkinson’s disease progression.

Therapeutic Strategies to Treat or Prevent Off Episodes in Adults with Parkinson's Disease

Parkinson's disease is a chronic, neurodegenerative disease, which manifests with a mixture of motor, cognitive and behavioural symptoms. Levodopa is the most effective antiparkinsonian treatment to date, although chronic use engenders a mixture of complications in a substantial proportion of patients. Amongst these is the occurrence of episodes of worsening symptoms-'off' phenomena. These episodes can manifest with either motor or non-motor symptoms or a combination of these features and have been found to have profound impacts on patients' quality of life. Although preventative measures are poorly evidenced, avoiding excessive total daily levodopa intake in selected populations that are deemed to be of a higher risk for developing these episodes warrants further exploration. Methods to improve levodopa bioavailability and delivery to the brain are currently available and are of value in addressing these episodes once they have become established. These include modifications to levodopa formulations as well as the use of complimentary agents that improve levodopa bioavailability. The deployment of device-assisted approaches is a further dimension that can be considered in addressing these debilitating episodes. This review summarises the clinical manifestations of 'off' phenomena and the current approaches to treat them. Although we briefly discuss clinical advances on the horizon, the predominant focus is on existing, established treatments.

MRI of Motor and Nonmotor Therapy-Induced Complications in Parkinson's Disease

Levodopa therapy remains the most effective drug for the treatment of Parkinson's disease, and it is associated with the greatest improvement in motor function as assessed by the Unified Parkinson's Disease Rating Scale. Dopamine agonists have also proven their efficacy as monotherapy in early Parkinson's disease but also as adjunct therapy. However, the chronic use of dopaminergic therapy is associated with disabling motor and nonmotor side effects and complications, among which levodopa-induced dyskinesias and impulse control behaviors are the most common. The underlying mechanisms of these disorders are not fully understood. In the last decade, classic neuroimaging methods and more sophisticated techniques, such as analysis of gray-matter structural imaging and functional magnetic resonance imaging, have given access to anatomical and functional abnormalities, respectively, in the brain. This review presents an overview of structural and functional brain changes associated with motor and nonmotor therapy-induced complications in Parkinson's disease. Magnetic resonance imaging may offer structural and/or functional neuroimaging biomarkers that could be used as predictive signs of development, maintenance, and progression of these complications. Neurophysiological tools, such as theta burst stimulation and transcranial magnetic stimulation, might help us to integrate neuroimaging findings and clinical features and could be used as therapeutic options, translating neuroimaging data into clinical practice. © 2020 International Parkinson and Movement Disorder Society.

Clinical and pharmacokinetics equivalence of multiple doses of levodopa benserazide generic formulation vs the originator (Madopar)

AIMS

While several generic preparations of levodopa/carbidopa and levodopa/benserazide (LBD) are currently available, pharmacokinetic (PK) equivalence and therapeutic equivalence studies with levodopa generics are not available in Italy. Lack of data on generic formulations is a critical factor for their limited use in this country and often lead patients to refuse the generic version of the branded drug.

METHODS

An experimental, 2-centre, randomized, double-blind, 2-sequence, noninferiority cross-over study was designed to evaluate both the PK equivalence and clinical equivalence of multiple doses of the generic preparation of LDB, Teva Italia, compared to the originator (Madopar). Forty-three out-patients with a diagnosis of idiopathic Parkinson's disease on LDB, were recruited and randomly assigned to 1 of 2 study sequences: generic-originator or originator-generic. Clinical evaluations were performed at the end of each study period. A PK study with an LDB fixed dose (100 + 25 mg) was performed in a subpopulation of 14 subjects.

RESULTS

Clinical data showed a reduction of 0.49 and 1.54 in the mean UPDRS III scores for the LDB and the originator, respectively. The 95% CIs [-2.21: 0.11] of the mean difference original vs LDB are smaller than the clinically significant difference of 3 UPDRS III points, supporting the conclusion that the treatment with LDB is not inferior to the originator. No statistically significant differences were found with respect to area under the curve to last dose, half-life, maximum concentration, time to maximum concentration and last observed concentration.

CONCLUSION

These findings prove the therapeutic clinical equivalence as well the PK equivalence of the generic LDB and the originator (Madopar).

Touchscreen typing-pattern analysis for detecting fine motor skills decline in early-stage Parkinson's disease

Parkinson’s disease (PD) is a degenerative movement disorder causing progressive disability that severely affects patients’ quality of life. While early treatment can produce significant benefits for patients, the mildness of many early signs combined with the lack of accessible high-frequency monitoring tools may delay clinical diagnosis. To meet this need, user interaction data from consumer technologies have recently been exploited towards unsupervised screening for PD symptoms in daily life. Similarly, this work proposes a method for detecting fine motor skills decline in early PD patients via analysis of patterns emerging from finger interaction with touchscreen smartphones during natural typing. Our approach relies on low-/higher-order statistical features of keystrokes timing and pressure variables, computed from short typing sessions. Features are fed into a two-stage multi-model classification pipeline that reaches a decision on the subject’s status (PD patient/control) by gradually fusing prediction probabilities obtained for individual typing sessions and keystroke variables. This method achieved an AUC = 0.92 and 0.82/0.81 sensitivity/specificity (matched groups of 18 early PD patients/15 controls) with discriminant features plausibly correlating with clinical scores of relevant PD motor symptoms. These findings suggest an improvement over similar approaches, thereby constituting a further step towards unobtrusive early PD detection from routine activities.

The spectrum of "off" in Parkinson's disease: What have we learned over 40 years?

The terms "on" and "off" were used by Marsden and his contemporaries over 40 years ago to describe times when Parkinson's disease patients experienced good motor function ("on") and immobility ("off"). Yet there remains no published consensus definition of "off", leading clinicians and patients to develop individualized impressions of "off" determinations. In this paper, we first discuss the evolution of the terminology and understanding of "off" states since Marsden's time, which now include non-motor as well as motor symptoms. We then review pathophysiology and risk factors for the development of "off" states as well as tools to detect the "off" state, before proposing a practical definition of "off" for consideration. A common, practical definition of the "off" state could improve clinical recognition of "off" symptoms and lead to significant benefit for patients.

Switching L-dopa Therapy from Pulsatile to Pulse Administration Reduces Motor Complications in Parkinson's Disease

OBJECTIVE

To evaluate the severity of wearing-off and dyskinesia in patients with complicated Parkinson disease (PD) after switching L-dopa oral therapy from a "pulsatile" administration, consisting in intermittent multiple daily small doses of the drug, to a "pulse" administration, consisting in standard oral doses given at specific interdose intervals.

METHODS

Thirty-four PD patients with motor complications were monitored twice with standardized waking day motor status evaluations using the Unified Parkinson Disease Rating Scale-Motor Examination (UPDRS-ME) and the Abnormal Involuntary Movement Scale (AIMS) after switching L-dopa administration modality from "pulsatile" to "pulse." To quantify predictable motor fluctuations, a Wearing Off Index was computed based on changes in treatment response magnitude.

RESULTS

On the whole, after switching from "pulsatile" to "pulse" administration, there was a reduction in number of L-dopa daily doses and an increase in the amount of the dosage of the single doses, AIMS maximum score decreased without increasing motor disability. More specifically, in predominant fluctuating patients, there was a significant reduction in UPDRS-ME average score as well as in Wearing Off Index. In predominant dyskinetic patients, there was a significant reduction in average and maximum AIMS scores with no changes in average and maximum UPDRS-ME scores.

CONCLUSIONS

Switching L-dopa therapy from "pulsatile" to "pulse" modality may reduce the severity of wearing-off and dyskinesia in complicated PD.

Parkinson's disease: disturbed vestibular function and levodopa

Evidence indicates Levodopa effects central postural control. As electrophysiological postural control biomarkers, sensory oto-acoustic features were extracted from Electrovestibulography (EVestG) data to identify 20 healthy age and gender matched individuals as Controls from 20 PD subjects before (PDlowmed) and 18 after (PDmed) morning doses of Levodopa. EVestG data was collected using a single tilt stimulus applied in the pitch plane. The extracted features were based on the measured firing pattern, interval histogram and the shape of the average field potential response. An unbiased cross validated classification accuracy of 88%, 88% and 79% was achieved using combinations of 2 features for separating PDlowmed from control, control from PD (combined PDlowmed and PDmed), and PDlowmed from PDmed groups respectively. One feature showed significant correlations (p<0.05) with the Modified Hoehn and Yahr PD staging scale. The results indicate disturbed vestibular function is observed in both the PDmed and PDlowmed conditions, and these are separable. The implication is that Levodopa may also affect peripheral as well as central postural control.

Cortico-striatal-thalamic network functional connectivity in hemiparkinsonism

Cortico-striatal-thalamic network functional connectivity (FC) and its relationship with levodopa (L-dopa) were investigated in 69 patients with hemiparkinsonism (25 drug-naïve [n-PD] and 44 under stable/optimized dopaminergic treatment [t-PD]) and 27 controls. Relative to controls, n-PD patients showed an increased FC between the left and the right basal ganglia, and a decreased connectivity of the affected caudate nucleus and thalamus with the ipsilateral frontal and insular cortices. Compared with both controls and n-PD patients, t-PD patients showed a decreased FC among the striatal and thalamic regions, and an increased FC between the striatum and temporal cortex, and between the thalamus and several sensorimotor, parietal, temporal, and occipital regions. In both n-PD and t-PD, patients with more severe motor disability had an increased striatal and/or thalamic FC with temporal, parietal, occipital, and cerebellar regions. Cortico-striatal-thalamic functional abnormalities occur in patients with hemiparkinsonism, antecede the onset of the motor symptoms on the opposite body side and are modulated by L-dopa. In patients with hemiparkinsonism, L-dopa is likely to facilitate a compensation of functional abnormalities possibly through an increased thalamic FC.

The role of neuroplasticity in dopaminergic therapy for Parkinson disease

Dopamine replacement is a mainstay of therapeutic strategies for Parkinson disease (PD). The motor response to therapy involves an immediate improvement in motor function, known as the short-duration response (SDR), followed by a long-duration response (LDR) that develops more slowly, over weeks. Here, we review evidence in patients and animal models suggesting that dopamine-dependent corticostriatal plasticity, and retention of such plasticity in the absence of dopamine, are the mechanisms underlying the LDR. Conversely, experience-dependent aberrant plasticity that develops slowly under reduced dopamine levels could contribute substantially to PD motor symptoms before initiation of dopamine replacement therapy. We place these findings in the context of the role of dopamine in basal ganglia function and corticostriatal plasticity, and provide a new framework suggesting that therapies that enhance the LDR could be more effective than those targeting the SDR. We further propose that changes in neuroplasticity constitute a form of disease modification that is distinct from prevention of degeneration, and could be responsible for some of the unexplained disease-modifying effects of certain therapies. Understanding such plasticity could provide novel therapeutic approaches that combine rehabilitation and pharmacotherapy for treatment of neurological and psychiatric disorders involving basal ganglia dysfunction.

The role of the long-duration response to levodopa in Parkinson's disease

The long-duration response (LDR) to levodopa is an important component of the therapeutic response to the drug in Parkinson's disease (PD). Some characteristics are peculiar: it is independent from peripheral pharmacokinetics of levodopa, but it is dependent on the intervals between doses and on the size of each dose. Once the LDR fully develops, it is stable and maximal. After stopping treatment, the decay rate is inversely related to the severity of PD; when the LDR decreases over time, the patients present a fluctuating motor response. Therapeutic strategies based on the development and maintenance of the LDR should be sought to maximize the clinical benefit induced by levodopa and to avoid the appearance of motor complications.

Preservation of function in Parkinson's disease: what's learning got to do with it?

Dopamine denervation gives rise to abnormal corticostriatal plasticity; however, its role in the symptoms and progression of Parkinson's disease (PD) has not been articulated or incorporated into current clinical models. The 'integrative selective gain' framework proposed here integrates dopaminergic mechanisms known to modulate basal ganglia throughput into a single conceptual framework: (1) synaptic weights, the neural instantiation of accumulated experience and skill modulated by dopamine-dependent plasticity and (2) system gain, the operating parameters of the basal ganglia, modulated by dopamine's on-line effects on cell excitability, glutamatergic transmission and the balance between facilitatory and inhibitory pathways. Within this framework and based on recent work, a hypothesis is presented that prior synaptic weights and established skills can facilitate motor performance and preserve function despite diminished dopamine; however, dopamine denervation induces aberrant corticostriatal plasticity that degrades established synaptic weights and replaces them with inappropriate, inhibitory learning that inverts the function of the basal ganglia resulting in 'anti-optimization' of motor performance. Consequently, mitigating aberrant corticostriatal plasticity represents an important therapeutic objective, as reflected in the long-duration response to levodopa, reinterpreted here as the correction of aberrant learning. It is proposed that viewing aberrant corticostriatal plasticity and learning as a provisional endophenotype of PD would facilitate investigation of this hypothesis.

Exercise protects against MPTP-induced neurotoxicity in mice

Exercise has been shown to be potently neuroprotective in several neurodegenerative models, including 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) model of Parkinson's disease (PD). In order to determine the critical duration of exercise necessary for DA neuroprotection, mice were allowed to run for either 1, 2 or 3months prior to treatment with saline or MPTP. Quantification of DA neurons in the SNpc show that mice allowed to run unrestricted for 1 or 2months lost significant numbers of neurons following MPTP administration as compared to saline treated mice; however, 3months of exercise provided complete protection against MPTP-induced neurotoxicity. To determine the critical intensity of exercise for DA neuroprotection, mice were restricted in their running to either 1/3 or 2/3 that of the full running group for 3months prior to treatment with saline or MPTP. Quantification of DA neurons in the SNpc show that mice whose running was restricted lost significant numbers of DA neurons due to MPTP toxicity; however, the 2/3 running group demonstrated partial protection. Neurochemical analyses of DA and its metabolites DOPAC and HVA show that exercise also functionally protects neurons from MPTP-induced neurotoxicity. Proteomic analysis of SN and STR tissues indicates that 3months of exercise induces changes in proteins related to energy regulation, cellular metabolism, the cytoskeleton, and intracellular signaling events. Taken together, these data indicate that exercise potently protects DA neurons from acute MPTP toxicity, suggesting that this simple lifestyle element may also confer significant protection against developing PD in humans.

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.

Motor complications in Parkinson disease: Clinical manifestations and management

Long-term dopaminomimetic therapy, not limited to levodopa, is complicated by the emergence of variations of motor response in a majority of Parkinson disease (PD) patients. These variations can occur in different forms, as early wearing off during the initial stage of motor complications, dyskinesias in the intermediate stage, and complex fluctuations in the advanced stage. Considered to be a major source of disability in advanced PD patients, recognition of these complications is critical in order to develop different strategies designed not only to treat these problems when they develop, but also to prevent troublesome complications associated with potential risk factors. In this article, authors classify a wide clinical spectrum of motor complications into different stages as the disease progresses through the treatment. A number of strategies are proposed in order to manage these complications as well as to avoid them. Better understanding of these potential complications will result in better management of these problems and lessen the disability associated with advanced PD.

COMT inhibition with tolcapone in the treatment algorithm of patients with Parkinson's disease (PD): relevance for motor and non-motor features

Levodopa is the most effective treatment in Parkinson's disease and the association with COMT inhibitors widens its plasma bioavailability and effectiveness. Tolcapone is a potent COMT inhibitor whose utilization in PD is limited due to safety concerns on liver toxicity. However, recent data indicate that if liver function is actively monitored, tolerability is no worse than other currently available therapies. By contrast, administration of tolcapone is associated with significant clinical improvement and benefit involves also non-motor features. In this review we discuss the rationale for the use of tolcapone in association with levodopa and other treatments in PD, and we provide an indirect comparison of current strategies to reduce "off" time. We propose that future guidelines include a trial with tolcapone in all PD patients who continue to complain about motor fluctuations despite treatment with entacapone and/or MAO-B inhibitors. Moreover, we suggest that tolcapone should be considered before surgical or infusional strategies are applied.

Constant dopaminergic stimulation by transdermal delivery of dopaminergic drugs: a new treatment paradigm in Parkinson's disease

Current dopaminergic therapies for the treatment of Parkinson's disease are associated with the development of long-term motor complications. Abnormal pulsatile stimulation of dopamine receptors is thought to underlie the development of motor complications. There is thus a need for therapies that mimic the normal physiological state more closely by resulting in constant dopaminergic stimulation (CDS). Several studies support the hypothesis that CDS can reverse levodopa-induced motor complications. Other potential benefits of CDS include alleviating nocturnal disturbances, minimizing daytime sleepiness, avoiding priming for motor fluctuations and dyskinesia, preventing the development of gastrointestinal dysfunction and reducing the risk of developing psychosis or behavioural disturbances. Continuous infusion of dopaminergic therapies is impractical for the routine treatment of large numbers of patients. Although catechol-O-methyltransferase inhibitors or sustained-release preparations of levodopa may be beneficial, they do not entirely eliminate pulsatile stimulation of dopamine receptors. A new dopamine agonist (rotigotine), delivered over 24 h by a once-daily transdermal patch, has been investigated in several clinical trials. Continuous delivery of rotigotine has been shown to provide 'true' CDS in animal models. The potential of true CDS therapy to prevent or reduce long-term motor and non-motor complications requires investigation in appropriately designed clinical trials.

High-frequency stimulation of the subthalamic nucleus prolongs the increase in striatal dopamine induced by acute l-3,4-dihydroxyphenylalanine in dopaminergic denervated rats

High-frequency stimulation of the subthalamic nucleus (STN-HFS) is a powerful approach for treating the motor symptoms of Parkinson's disease (PD). It results in clinical improvement in patients with PD, further reducing the l-3,4-dihydroxyphenylalanine (L-DOPA) requirement and thus L-DOPA-induced dyskinesia. However, it remains unclear how STN-HFS modifies the response to L-DOPA. We investigated the effect of STN-HFS on striatal extracellular concentrations of dopamine and its metabolites following acute L-DOPA administration in intact or partially dopaminergic denervated (DA-PL) rats. L-DOPA treatment significantly increased striatal dopamine levels in intact and DA-PL animals, with the maximal effect observed 1 h after L-DOPA injection. This increase was more pronounced in DA-PL rats (ipsilateral to the lesion) than in intact animals. It remained fairly stable 1 h after the maximal effect of L-DOPA and then decreased towards basal values. STN-HFS in intact rats had no effect on the maximal L-DOPA-induced increase in striatal extracellular dopamine concentration or the return to basal values, the profiles observed being similar to those for non-stimulated intact animals. Conversely, STN-HFS amplified the L-DOPA-induced increase in striatal dopamine levels during the stimulation period (1 h) in DA-PL rats and this increase was sustained throughout the post-stimulation period (2.5 h), without the return to basal levels observed in stimulated intact and non-stimulated rats. These new neurochemical data suggest that STN-HFS interferes with L-DOPA effects, probably synergically, by stabilizing dopamine levels in the striatum and shed light on the mechanisms of STN-HFS in PD.

The levodopa wearing-off phenomenon in Parkinson’s disease: pharmacokinetic considerations

Levodopa is the most efficacious treatment in the management of Parkinson's disease. Unfortunately, chronic use of traditional levodopa/dopa decarboxylase inhibitor formulations is associated with the development of complications, such as wearing-off and dyskinesia. In an attempt to avoid these complications, some physicians delay the introduction of levodopa or employ levodopa-sparing strategies; however, these strategies are frequently suboptimal for patients. As most patients require the superior efficacy of levodopa during the course of their disease, an appreciation of the changing response to levodopa over time and an understanding of the pharmacokinetic principles underlying the development of complications such as wearing-off is essential in the long-term management of the patient.

Longitudinal study of the motor response to levodopa in Parkinson's disease

In this prospective study of 34 patients with Parkinson's disease, measurements of the short duration levodopa motor response have been performed in defined off states at 3 yearly intervals over a mean period of 11.4 years from the point of commencement of levodopa treatment. Twenty-two patients were still available for study; 10 had died and 2 were lost to follow-up. The levodopa motor response amplitude increases over the first 5 years of treatment, and thereafter, on and off scores worsen in parallel with conservation of the response. Patients who developed motor fluctuations within the first 5 years of treatment had, on average, a stronger response to levodopa with significantly better on phase motor function (P = 0.003). Although the proportion of "midline" motor disability (affecting gait, balance, and cranial motor function) increases with time, these deficits do not actually become unresponsive to levodopa. Patients who developed dementia had a significantly more rapid decline in motor function. The latest graph of serial scores for the whole cohort shows an upward curving or exponential increase in motor disability after the first decade of treatment. Applying a notional untreated disability line to this graph--an estimate of the disability that would have accrued if drugs had never been given--we suggest that the long-duration response to levodopa eventually runs down with disease progression.

Pharmacokinetic and Pharmacodynamic Changes During the First Four Years of Levodopa Treatment in Parkinson’s Disease

The purpose of this analysis is to describe how levodopa pharmacokinetic and pharmacodynamic parameters change over the first 4 years of long-term levodopa treatment in patients with Parkinson's disease. Twenty previously untreated Parkinsonian patients were admitted to the general clinical research center (GCRC) for 4 days at the beginning of long-term levodopa therapy and 6, 12, 24 and 48 months later. On each GCRC admission, patients received a 2 hr IV infusion of levodopa on day 1 and day 4 with no oral levodopa between the infusions. After the first GCRC admission patients were treated with oral levodopa dosed for optimal control of Parkinsonism. Motor function was measured by finger tapping rate. A pharmacokinetic-pharmacodynamic model incorporating 3 effect compartments was used to fit the individual plasma levodopa concentrations and tapping rates. Motor function before the first levodopa infusion (E0(1)) improved over the first 20 months and subsequently returned to the initial baseline at the start of the study. A similar pattern was seen in motor function before the second infusion (E0(2)) after the 3 days levodopa withdrawal, with a decline predicted to fall below the initial baseline at the start of the study by 6 years. Eight patients showed an increase in maximum tapping rate with levodopa (E(max)) approaching a steady state after 16 months. Ten patients showed an increase in E(max) with a peak at 31 months. One patient showed a linear decrease and another patient did not change over the 48 months. Longitudinal progress models were used to describe the time course of pharmacokinetic and pharmacodynamic parameters over 4 years. Peak treatment benefit, defined as the difference between E(max) and E0(1) or E0(2) (D(max)1 or D(max)2), increased with time particularly after the 3-day levodopa withdrawal. Deterioration of pre-dose motor function (E0) as disease progresses coupled with a greater amplitude of response due to levodopa (D(max)) could be a key factor contributing to motor fluctuations associated with long-term levodopa treatment.

Movement time and aging: a normative study in healthy subjects with the "Movement Time Analyzer"

BACKGROUND AND AIMS

Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders characterized by bradykinesia, tremor at rest, and rigidity. Movement Time (MT) has been investigated in PD to evaluate bradykinesia and its levodopa-induced modifications. The Movement Time Analyzer (MTA) is a simple, objective and reliable instrument to study MT, but no normative study has been reported to date.

METHODS

In a sample of normal subjects (n = 68), we studied MT detected by MTA in order to assess normative values, so that the MTA could be used to evaluate patients with PD in daily clinical practice.

RESULTS

In normal subjects, MT progressively increased with aging, and was slower on the non-dominant side than on the dominant side. No differences were found between men or women.

CONCLUSION

Our data provide further information about normative values on MT detected by MTA, and indicate that age and handedness are the main variables influencing motor task performance.

The effects of chronic L-DOPA therapy on pharmacodynamic parameters in a rat model of motor response fluctuations

Chronic L-3,4-dihydroxyphenylalanine (L-DOPA) therapy in Parkinson's disease (PD) is complicated by motor response fluctuations and dyskinesia. The relative contributions of disease severity and chronic L-DOPA therapy to the development of motor fluctuation are not well defined clinically. Experimental studies have been limited partly because models for the antiparkinsonian effects on akinesia have not been employed. Therefore, we employed a model of akinesia using forepaw adjusting steps that have been well characterized to reflect the effect of lesions and the antiparkinsonian effect of dopaminergic drugs and transplants. We administered L-DOPA (12.5 mg/kg) intermittently for 4 weeks to rats with severe nigrostriatal lesions produced by injecting 6-hydroxydopamine into the medial forebrain bundle. The peak magnitude responses to L-DOPA increased after treatment compared to the pretreatment baseline. The latency to peak response to L-DOPA became shorter and reversed after the discontinuation of treatment. The duration of response showed minor changes. The pattern of changes in response to apomorphine was similar to that of L-DOPA except that the peak magnitude did not increase despite chronic L-DOPA treatment. The changes in D1 and D2 receptor binding did not correlate with behavioral changes. In summary, long-term intermittent L-DOPA treatment resulted in priming of antiparkinsonian effects on improving akinesia in a rat model of severe PD. These observed changes do not mirror all aspects of motor response fluctuations in advanced PD patients and suggest differential contributions of dopaminergic treatment and lesion severity to motor complication patterns.

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.

Apomorphine infusion and the long-duration response to levodopa in advanced Parkinson's disease

The authors investigated the long-duration response to levodopa in advanced Parkinson's disease. Eight patients with advanced Parkinson's disease disabled by severe ON/OFF fluctuations treated by chronic daytime subcutaneous apomorphine infusion with supplemental oral levodopa were studied. On day 1, oral levodopa was withdrawn at 4:00 pm and on the following morning subcutaneous apomorphine infusion was continued at the same rate without levodopa therapy. While receiving apomorphine alone, seven of the eight patients turned ON, and their usual dyskinesias returned. The ON phase persisted for 60 to 100 minutes (mean, 185.7 minutes) but then, despite continued, constant-rate apomorphine infusion to stabilize plasma levels, switched to an OFF phase. The authors conclude that the clinical effect of apomorphine is sustained by levodopa long-duration response. This effect is probably the result of postsynaptic mechanisms. In patients with advanced Parkinson's disease, the long-duration response to levodopa is present although slightly diminished.

Response to levodopa in parkinsonian patients with bilateral subthalamic nucleus stimulation

The response to levodopa changes over time in Parkinson's disease, probably due to alterations in the dopaminergic system, progression of the disease and pulsatile oral intake of the drug. Bilateral high-frequency stimulation of the subthalamic nucleus (STN) allows a large reduction or the complete cessation of levodopa intake in patients with advanced Parkinson's disease. We studied variation in the motor short-duration response (SDR) during a levodopa challenge in bilaterally STN-stimulated patients. Twenty-eight consecutive patients with a mean duration of Parkinson's disease of 16.6 +/- 6.0 years at the time of surgery were enrolled. Fourteen patients were evaluated both before STN stimulation and 3 months after surgery (group 1) whereas the other 14 patients were assessed before implantation and after a mean of 3 years of STN stimulation (group 2). After drug withdrawal for one night, the hand-tapping test (TT) was carried out every 15 min, together with evaluation of dyskinesias using a modified Goetz scale. The Unified Parkinson's Disease Rating Scale (UPDRS) motor score was assessed every 30 min. In operated patients, STN stimulation was stopped 15 min before starting the clinical evaluations. A suprathreshold oral levodopa dose was given after one motor evaluation and two TTs. The clinical evaluation was carried out until the TT score returned to the baseline. In group 1, six patients continued without levodopa after surgery and the other eight received a daily mean dose of 337 mg; in group 2, seven patients continued without levodopa and the other seven received a daily mean dose of 386 mg. The main change in the levodopa SDR was a significant reduction in levodopa-induced dyskinesias in both groups. In those patients of group 1 who did not receive levodopa after surgery, the motor UPDRS magnitude decreased and the 'on' UPDRS motor score worsened. In group 2, the results were similar, but in the patients who continued to receive levodopa after surgery the TT magnitude increased. On the whole, chronic bilateral STN stimulation tended to decrease the magnitude of the levodopa SDR without changing the duration and latency of the response. These results suggest that continuous STN stimulation induces long-term plastic changes of the dopaminergic system, with slow and partial desensitization. In addition, the persistence of levodopa intake after surgery might hinder this beneficial process.

Evolution of the response to levodopa during the first 4 years of therapy

The short-duration response, long-duration response, and dyskinetic response to levodopa change during long-term levodopa therapy. How these responses evolve, and which changes contribute to the emergence of motor fluctuations, remain unclear. We studied 18 subjects with Parkinson's disease before they began levodopa therapy and after 6, 12, 24, and 48 months of long-term levodopa therapy. The responses to 2-hour levodopa infusions after overnight and after 3 days of levodopa withdrawal were studied from 6 months onward. The mean magnitude of the short-duration response and the long-duration response measured after overnight without antiparkinsonian medications did not change during the 4 years. However, after 3 days without levodopa, it was apparent that the short-duration-response magnitude was progressively increasing (p < 0.0001) and that the long-duration response was decaying more rapidly (p = 0.0004). The short-duration-response magnitude at 4 years was inversely related to the long-duration-response magnitude (p = 0.022), suggesting that the long-duration response was one determinant of the short-duration-response magnitude. Dyskinesia increased progressively in severity during the study (p = 0.013). The duration of the short-duration response and dyskinesia did not change during the 4 years. Subject reports of motor fluctuations tended to be associated with a large short-duration response (p = 0.054). We suggest that a larger long-duration response, rather than a shortened one, is more important to the development of fluctuations. Improving the baseline or practical-off motor function to reduce the magnitude of the short-duration response may be a strategy to treat fluctuations.

Motor response to apomorphine in patients with Parkinson's disease with long-duration response to levodopa

The authors studied the motor response to apomorphine before and 1 year after levodopa therapy in 12 patients with Parkinson's disease. At the 1-year evaluation, the basal tapping score, recorded after a 12-hour levodopa withdrawal, was higher compared with the test performed while patients were de novo, indicating the presence of a long-duration response to levodopa. The amplitude (net increase) of the motor response to apomorphine was similar before and during levodopa therapy. However, because of the better baseline, the maximal tapping score was higher during levodopa therapy. The duration and the latency of the motor response to apomorphine did not change. The presence of a short-duration response to apomorphine, in the presence of a long-duration response to levodopa, may imply that either different compartment (i.e., postsynaptic versus presynaptic) or transduction pathways are involved in such responses.

Parkinson's disease therapy: tailoring choices for early and late disease, young and old patients

Advances in the understanding of basal ganglia circuitry and its altered function in disease states such as Parkinson's disease (PD), coupled with new insights into the mechanisms of cell death and new findings from therapeutic clinical trials, are being translated into clinical practice. Although levodopa (L-Dopa) remains the most effective drug in the symptomatic treatment of PD, the emergence of side effects, particularly motor fluctuations and dyskinesias, limits its usefulness. Therefore, many parkinsonologists now advocate therapeutic strategies designed to delay the onset of L-Dopa therapy to delay the onset of L-Dopa-related motor complications. The therapeutic approach to PD, however, must be individualized and based on factors such as age of the patient, stage of the disease, and degree of interference of the symptoms with social and occupational functioning, associated symptoms such as cognitive impairment, and response to treatment. This review summarizes the current therapeutic strategies, but it is important to emphasize that the treatment recommendations must be tailored to the needs of individual patients.

The long-duration response to L-dopa in the treatment of early PD

OBJECTIVE

To investigate the long-duration response (LDR) to L-dopa resulting from different regimens of L-dopa.

BACKGROUND

In clinical practice, L-dopa is usually administered without considering the LDR due to the drug. Moreover, it has not been established whether in early PD a multiple daily intake of small doses of L-dopa may induce a sustained LDR.

METHODS

Twenty-four patients with early PD underwent a double-blind, crossover trial, comparing three different 15-day treatment periods with L-dopa: treatment A (250 mg every 24 hours); treatment B (250 mg every 8 hours); and treatment C (125 mg every 8 hours). After completion, 20 patients underwent a subsequent open-label randomized trial with prolonged treatments (250 mg every 24 hours or 125 mg every 8 hours) up to 3 months. LDR was measured at the end of each treatment.

RESULTS

All patients achieved a sustained LDR after treatments A and B, whereas only 17% of patients reached a sustained LDR after treatment C. Overall, the LDRs resulting from treatments A and B had similar magnitude and were larger than the LDR deriving from treatment C. After 3 months of prolonged treatments, only three of 10 patients treated with 125 mg every 8 hours increased their LDR, whereas all 10 patients treated with 250 mg every 24 hours had a maximal and stable LDR.

CONCLUSIONS

Sustained LDR to L-dopa is dependent on the amount of the single doses of the drug. A regimen scheduling small, divided doses during the day, as done in clinical practice, is a questionable therapy for the achievement of a sustained LDR.

Role of dopamine in learning and memory: implications for the treatment of cognitive dysfunction in patients with Parkinson's disease

Along with dementia, Parkinson's disease (PD) is associated with subtle but widespread cognitive impairment even in the absence of clinically apparent cognitive decline. Many of the deficits are reminiscent of those observed in patients with lesions of the prefrontal cortex, that is, failure in executive function that involves skills required for anticipation, planning, initiation and monitoring of goal-directed behaviours. This paper reviews the dopaminergic brain circuitry, and preclinical and clinical evidence supporting the regulation of prefrontal cortex activity by dopamine, and the role of dopamine in cognitive impairment in patients with PD. It addresses the need to integrate these facts and the findings of positive, neutral or detrimental frontal cognitive response to dopaminergic drugs in PD which should be viewed mainly in the context of methodological differences for subject selection. The cognitive effect of levodopa does not much depend on a neuropsychological specificity of the drug, the years of evolution of the disease or the severity of the motor signs. Instead, it may be a function of the level of dopamine depletion in different parts of the basal ganglia and prefrontal cortex. Consequently, dopaminergic agents may enhance cognitive functions in some patients and impair them in others. De novo patients tend to improve during the first year of treatment; stable responders to oral levodopa tend to show no changes; and wearing-off responders tend to deteriorate with acute levodopa challenge. Enhancement and impairment of cognitive function with dopaminergic treatment is incomplete and task-specific, suggesting the need to integrate the above dopamine facts with other neurotransmitter systems findings in PD. Meanwhile, such cognitive dissociation can be useful in refining the definition of the cognitive deficit in PD patients without dementia and emphasising the need to develop new and specific strategies for treatment.