Levodopa Infusion Therapy in Parkinson Disease

Differential Amperometric Microneedle Biosensor for Wearable Levodopa Monitoring of Parkinson's Disease

Levodopa (L-Dopa) is considered to be one of the most effective therapies available for Parkinson's disease (PD) treatment. The therapeutic window of L-Dopa is narrow due to its short half-life, and long-time L-Dopa treatment will cause some side effects such as dyskinesias, psychosis, and orthostatic hypotension. Therefore, it is of great significance to monitor the dynamic concentration of L-Dopa for PD patients with wearable biosensors to reduce the risk of complications. However, the high concentration of interferents in the body brings great challenges to the in vivo monitoring of L-Dopa. To address this issue, we proposed a minimal-invasive L-Dopa biosensor based on a flexible differential microneedle array (FDMA). One working electrode responded to L-Dopa and interfering substances, while the other working electrode only responded to electroactive interferences. The differential current response of these two electrodes was related to the concentration of L-Dopa by eliminating the common mode interference. The differential structure provided the sensor with excellent anti-interference performance and improved the sensor's accuracy. This novel flexible microneedle sensor exhibited favorable analytical performance of a wide linear dynamic range (0-20 μM), high sensitivity (12.618 nA μM^-1 cm^-2) as well as long-term stability (two weeks). Ultimately, the L-Dopa sensor displayed a fast response to in vivo L-Dopa dynamically with considerable anti-interference ability. All these attractive performances indicated the feasibility of this FDMA for minimal invasive and continuous monitoring of L-Dopa dynamic concentration for Parkinson's disease.

A post hoc comparison of levodopa-carbidopa intestinal gel daytime monotherapy vs polytherapy safety and efficacy in patients with advanced Parkinson's disease: Results from 6 phase 3/3b open-label studies

Introduction

As Parkinson's disease (PD) progresses, the number/frequency of PD medications tend to increase, which is correlated with decreased patient compliance and suboptimal control of PD symptoms. We investigated efficacy and safety of levodopa-carbidopa intestinal gel (LCIG) daytime monotherapy (with or without nighttime oral levodopa-carbidopa) compared with polytherapy (LCIG with ≥1 adjunctive PD therapy) in advanced PD patients.

Methods

This post hoc descriptive study compared LCIG stable daytime monotherapy with LCIG stable polytherapy in all six phase 3/3b open-label studies from both US and international sites; because of study design variability, pooling data for comparison was not appropriate. Efficacy assessments included PD diary data (mean change from baseline in “Off” time and “On” time with or without troublesome dyskinesia), mean Unified PD Rating Scale scores (Parts II and III), and 39-item Parkinson's Disease Questionnaire (PDQ-39) summary index. Adverse events were also assessed.

Results

Overall, LCIG daytime monotherapy and polytherapy demonstrated similar efficacy/safety profiles in advanced PD patients, regardless of treatment duration or population. LCIG monotherapy vs. polytherapy groups experienced similar mean decreases in “Off” time (4.6 vs. 4.1 h/day) and similar increases in “On” time without troublesome dyskinesia (4.6 vs. 4.1 h/day). In most studies, PDQ-39 summary index scores were reduced from baseline by ≥5 points, regardless of patient population or study duration. Adverse events not related to the procedure/device were similar in both groups.

Conclusion

Our data suggest that, for appropriate patients, LCIG monotherapy can provide a more simplified treatment option with similar efficacy and safety.

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Advanced Parkinson's disease (PD) often requires a large number of medications

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Levodopa-carbidopa intestinal gel (LCIG) is administered continuously

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LCIG monotherapy vs. polytherapy was assessed in six phase 3/3b studies

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LCIG monotherapy and polytherapy had similar efficacy and safety profiles

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LCIG monotherapy may provide a more simplified treatment option for advanced PD

Single-Dose Pharmacokinetics and Pharmacodynamics of IPX203 in Patients With Advanced Parkinson Disease: A Comparison With Immediate-Release Carbidopa-Levodopa and With Extended-Release Carbidopa-Levodopa Capsules

Objective

IPX203 is an investigational oral extended-release capsule formulation of carbidopa-levodopa (CD-LD). The aim of this study was to characterize the single-dose pharmacodynamics, pharmacokinetics, and safety of IPX203 in subjects with advanced Parkinson disease compared with immediate-release (IR) CD-LD and extended-release CD-LD (Rytary).

Methods

This was a randomized, open-label, rater-blinded, multicenter, single-dose crossover study. Blinded clinicians assessed subject's motor state and Movement Disorders Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III scores for up to 10 hours postdose. Duration of effect was determined using improvement thresholds in the MDS-UPDRS part III.

Results

Levodopa concentrations increased rapidly and similarly across all 3 treatments and were sustained for a longer duration after IPX203 dosing. All treatments exhibited a rapid onset of pharmacodynamic effect, whereas IPX203 had a significantly longer duration of effect based on MDS-UPDRS part III scores compared with IR CD-LD (P < 0.0001) and Rytary (P ≤ 0.0290). IPX203 had a 2.7-hour advantage over IR CD-LD (P < 0.0001) and a 0.9-hour advantage over Rytary in “off” time (P = 0.023) and in “good on” time (2.6 hours more than IR CD-LD, P < 0.0001; 0.9 hours more than Rytary, P = 0.0259) as measured by the Investigator Assessment of Subject's Motor State. Subjects were 77% more likely to require rescue following IR CD-LD treatment compared with IPX203 (hazard ratio, 0.23; P < 0.0001). More subjects reported treatment-emergent adverse effects during IR CD-LD (28.0%) and IPX203 (19.2%) than during Rytary (8.0%) treatment.

Conclusions

Compared with Rytary and IR CD-LD, IPX203 had a longer pharmacodynamic effect consistent with LD pharmacokinetics for the 3 treatments. The safety and tolerability of IPX203 were similar to those of IR CD-LD and Rytary.

Development of new levodopa treatment strategies in Parkinson's disease-from bedside to bench to bedside

This review will illustrate the process of moving from an idea through preclinical research and Galenic developments into clinical investigations and finally to approval by regulatory agencies within the European Union. The two new treatment strategies described, levodopa/carbidopa intestinal gel and levodopa/carbidopa microtablets, for advanced Parkinson's disease, have been developed in collaborative research within departments at Uppsala University. With this historical approach, reference priority is given to reports considered to be of special importance for this more than two decades long process 'from bedside to bench to bedside'.

Clinical Pharmacokinetics of IPX066: Evaluation of Dose Proportionality and Effect of Food in Healthy Volunteers

Objectives

IPX066 is an oral, extended-release capsule formulation of carbidopa-levodopa (CD-LD) available in 4 strengths. The goals of this investigation were to assess the dose proportionality of IPX066 and to study the effects of a high-fat, high-calorie meal and of sprinkling the capsule contents on applesauce on the pharmacokinetics of IPX066 in healthy volunteers.

Methods

Three open-label studies were conducted. In the first study, subjects received 1 capsule of each IPX066 strength (23.75–95, 36.25–145, 48.75–195, and 61.25–245 mg of CD-LD). In the second study, subjects received 1 and 2 capsules of IPX066 245-mg LD under fasting conditions. In the third study, subjects received 2 capsules of IPX066 245-mg LD under 3 conditions: fasting; following a high-fat, high-calorie breakfast; and with the capsule contents sprinkled on applesauce under fasting conditions.

Results

Peak plasma concentrations (C_max) and systemic exposure (AUC_t, AUC_inf) for LD and CD increased dose-proportionally over the range of the IPX066 capsule strengths. Comparison of 1 and 2 IPX066 245-mg LD capsules showed dose-proportional pharmacokinetics for C_max and AUC_t. Sprinkling the capsule contents on applesauce did not affect the pharmacokinetics. A high-fat, high-calorie meal delayed the initial increase in LD concentration by approximately 1 to 2 hours, reduced C_max by 21%, and increased AUC_inf by 13% compared with the fasted state.

Conclusions

IPX066 shows dose-proportional pharmacokinetics. Sprinkling the capsule contents on applesauce does not affect the pharmacokinetics; a high-fat, high-calorie meal delayed absorption by 1 to 2 hours, slightly reduced C_max, and slightly increased extent of absorption.

Jejunal Infusion of levodopa-carbidopa intestinal gel versus oral administration of levodopa-carbidopa tablets in japanese subjects with advanced Parkinson's disease: pharmacokinetics and pilot efficacy and safety

Background and Objective

Oral levodopa-carbidopa (LC-oral) treatment in advanced Parkinson’s disease (PD) is associated with motor complications due to large fluctuations in levodopa plasma concentrations. Levodopa–carbidopa intestinal gel (LCIG) provides individualized continuous levodopa–carbidopa delivery through intrajejunal infusion. This study evaluated the pharmacokinetics, safety, and efficacy of LCIG relative to LC-oral in Japanese subjects with advanced PD.

Methods

Subjects with advanced PD were converted from their anti-PD medications to individually optimized doses of LC-oral (10:1 levodopa:carbidopa ratio) for 28 days (baseline; period 1) followed by switching to intrajejunal infusion of LCIG (4:1 ratio) for 21 days (period 2). Pharmacokinetics, adverse events (AEs), and efficacy were assessed.

Results

Eight patients were enrolled. Six received LCIG and four reported at least one AE [most common: fall (33.3 %), dyskinesia (33.3 %)]; one discontinued due to an AE. The average daily dose was 1230/123 and 1370/342 mg levodopa/carbidopa for LC-oral and LCIG, respectively, at the end of each period. The degree of fluctuation and intra-subject variability of levodopa plasma concentrations were 5.5- and 4-fold lower, respectively, with LCIG than with LC-oral. Levodopa bioavailability was 99 % for LCIG relative to LC-oral. Compared with baseline, LCIG decreased “Off” time (2.68 h, P = 0.002) and increased “On” time without troublesome dyskinesia (2.35 h, P = 0.006) in the PD Diary^©. With the small sample size, no statistically significant changes were seen on other efficacy endpoints.

Conclusions

In Japanese subjects with advanced PD, LCIG resulted in an improved pharmacokinetic profile that appeared to be associated with reduced motor complications compared with LC-oral. These results extend previous findings in mainly Caucasian populations.

Gastroretentive carbidopa/levodopa, DM-1992, for the treatment of advanced Parkinson's disease

OBJECTIVES

This study was undertaken to compare efficacy, tolerability, and pharmacokinetics of DM-1992, an extended-release formulation of carbidopa/levodopa (CD/L-dopa) with immediate-release (IR) CD/L-dopa in patients with advanced Parkinson's disease.

METHODS

This randomized, open-label, crossover study included a 3-d baseline and two 10-d treatment periods. Patients with daily OFF time of 2.5 h or more taking 400 mg or more L-dopa/d in four or more divided doses were titrated to stable regimens of DM-1992 2 times per day or CD/L-dopa IR 3 times to 8 times per day. Patients were allowed to take rescue CD/L-dopa as needed. Using home diaries, patients recorded OFF time and ON time with or without troublesome dyskinesia during baseline and treatment days 7 through 9. During 12-h clinic visits on day 10, plasma samples were collected for pharmacokinetics, and motor performance was assessed hourly.

RESULTS

Thirty-four patients were enrolled; mean baseline L-dopa dosage was 968 mg/d. After titration, CD/L-dopa IR was dosed 4.8 times per day and DM-1992, 2 times per day. Rescue CD/L-dopa IR was given 1.3 times during the DM-1992 arm and 0.2 times during the CD/L-dopa IR arm. The reduction from baseline in % OFF time was greater for DM-1992 compared with CD/L-dopa IR (-5.52% vs. +1.33%; P = 0.0471). At steady-state, compared with CD/L-dopa IR, DM-1992 exhibited a smoother plasma L-dopa concentration profile mostly because of a significantly higher (day 10) predose L-dopa concentration, associated with enhanced motor performance. Although more patients taking DM-1992 had one or more adverse events (AEs) than CD/L-dopa IR patients (35% vs. 15%), no pattern to the AEs was seen, nor any resulting discontinuations.

CONCLUSIONS

DM-1992 was associated with a reduction in %OFF time compared with CD/L-dopa IR despite a reduced dosing frequency. Although the open-label study design and the greater number of rescue doses during the DM-1992 arm call for caution in interpreting the results, the elevated predose plasma L-dopa concentration (12 h after DM-1992 administration) lends objective support to our findings, suggesting that phase 3 studies are warranted.

Pharmacokinetics of levodopa, carbidopa, and 3-O-methyldopa following 16-hour jejunal infusion of levodopa-carbidopa intestinal gel in advanced Parkinson's disease patients

Motor complications of Parkinson's disease (PD) are a consequence of pulsatile dopaminergic stimulation from standard oral levodopa therapy. Levodopa-carbidopa intestinal gel (LCIG) is infused continuously via an intrajejunal percutaneous gastrostomy tube. This was the first study designed to characterize the full pharmacokinetic profiles of levodopa, carbidopa, and levodopa metabolite, 3-O-methyldopa (3-OMD) with 16-h LCIG infusion. Nineteen advanced PD patients (mean age, 65 years) who were on LCIG therapy for ≥30 days were enrolled. Patients received their individualized LCIG infusion doses, and serial pharmacokinetic samples were collected. Eighteen patients completed the study; 19 were assessed for safety. Mean (SD) total levodopa and carbidopa doses were 1,580 (403) and 395 (101) mg, respectively. Mean (SD) C(avg) (μg/mL) were 2.9 (0.84) for levodopa, 17.1 (4.99) for 3-OMD, and 0.22 (0.08) for carbidopa. The degree of fluctuation [defined as (C(max)-C(min))/C(avg)] in levodopa, 3-OMD, and carbidopa plasma concentrations was very low (0.52, 0.21, and 0.96, respectively) during hours 2-16 of infusion. Accordingly, the within-subject coefficients of variation in levodopa, 3-OMD, and carbidopa concentrations were low (13%, 6%, and 19%, respectively). Three patients (16%) reported ≥1 treatment-emergent adverse event; none were considered severe. Continuous intrajejunal LCIG infusion maintained stable plasma levodopa levels over 16 h. Consistent exposure has been shown to reduce motor and nonmotor complications associated with oral medications. LCIG was well tolerated, consistent with previous reports.

Pharmacokinetics and pharmacodynamics of gastroretentive delivery of levodopa/carbidopa in patients with Parkinson disease

OBJECTIVE

To investigate, in patients with Parkinson disease, the pharmacokinetics and pharmacodynamics of levodopa/carbidopa delivered via 3 different extended-release (ER) tablet formulations.

METHODS

This was a randomized, crossover study in patients with stable idiopathic Parkinson disease comparing a conventional ER tablet (C-ER) administered orally 3 times daily with 2 levodopa/carbidopa gastroretentive ER formulations administered orally twice daily, one with an immediate release (IR) component (IR/ER) and one without (ER). Blood samples were collected for pharmacokinetic (PK) analysis, and a finger-tapping test was performed to assess pharmacodynamics. Tolerability was evaluated by monitoring adverse events and measuring vital signs. PK modeling was performed to estimate steady-state levodopa concentrations.

RESULTS

Fourteen patients completed the study. Compared with C-ER, both gastroretentive ER tablets significantly extended the first maximum time (6.0 vs 2.5 h; P < 0.025) and had smoother plasma concentration-time profiles while achieving a similar maximum plasma concentration and area under the curve. The IR/ER formulation exhibited a significantly longer duration of concentration above the presumed efficacious threshold of 300 ng/mL (21 vs 18 h; P = 0.0027) compared with C-ER. PK modeling predicts a steady-state levodopa peak/trough ratio of 4 for both IR/ER and ER formulations and a ratio of 21 for C-ER. Furthermore, superior response in the finger tapping test was observed for the IR/ER and ER formulations compared with the C-ER formulation.

CONCLUSIONS

This study demonstrated that the gastroretentive ER formulations achieved more constant plasma levodopa concentrations and better pharmacodynamics with reduced dose frequency, potentially reducing the on-off phenomena that have been associated with fluctuations in plasma levodopa concentrations.

Interim analysis of long-term intraduodenal levodopa infusion in advanced Parkinson disease

BACKGROUND

This interim 12-month analysis is a part of an open-label, observational, prospective study on health outcomes and cost impact of levodopa/carbidopa intestinal gel (LCIG, Duodopa) in Parkinson disease (PD). The specific aim was to investigate clinical and health-related quality of life (HRQoL) effects in routine care.

METHODS

Unified PD rating scale (UPDRS) was the primary efficacy measurement. PD QoL questionnaire 39 (PDQ-39) assessed HRQoL. Subjects were assessed at baseline, ≥3 months after surgery, and then every 3 months.

RESULTS

Twenty-seven treatment-naïve subjects when started with LCIG showed a decrease in UPDRS score that was statistically significant throughout the year: UPDRS total score (mean ± SD), baseline = 52.1 ± 16.1, N = 27, month 0 (first visit; at least 3 months after permanent LCIG) = 43.1 ± 16.7, N = 27, P = 0.003; month 12 = 42.5 ± 22.6, n = 25, P = 0.017. PDQ-39 results also showed a tendency for improvement: PDQ-39 (mean ± SD), baseline = 33.6 ± 10.8, N = 27, month 0 = 27.1 ± 11.8, N = 27, P = 0.001; 12 months = 28.8 ± 12.8, n = 23, P = 0.126.

CONCLUSIONS

LCIG provides functional improvement beginning at first visit that is sustained for 12 months.

Facing the unique challenges of dyskinesias in Parkinson’s disease

Dyskinesia is among the most challenging complications of levodopa and dopaminergic drug therapy in advanced Parkinson’s disease. This symptom has a negative impact on the quality of life of patients with Parkinson’s disease and is hard to manage. Current advances in our understanding of the diverse phenomenology and complicated pathophysiology of dyskinesia have led to a number of novel strategies aimed at better control of this complication. Further insight has been gained from focusing on the characteristics of the rating scale used for assessment of dyskinesia and from the inherent susceptibility of dyskinesia to placebo effect. Here, we will briefly review the phenomenology, pathophysiology and the treatment of dyskinesia in Parkinson’s disease.

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.

The effect of striatal dopaminergic grafts on the neuronal activity in the substantia nigra pars reticulata and subthalamic nucleus in hemiparkinsonian rats

The electrophysiological correlates of parkinsonism in the basal ganglia have been well studied in patients with Parkinson's disease and animal models. Separately, striatal dopaminergic cell transplantation has shown promise in ameliorating parkinsonian motor symptoms. However, the effect of dopaminergic grafts on basal ganglia electrophysiology has not thoroughly been investigated. In this study, we transplanted murine foetal ventral mesencephalic cells into rats rendered hemiparkinsonian by 6-hydroxydopamine injection. Three months after transplantation, extracellular and local field potential recordings were taken under urethane anaesthesia from the substantia nigra pars reticulata and subthalamic nucleus along with cortical electroencephalograms and were compared to recordings from normal and hemiparkinsonian controls. Recordings from cortical slow-wave activity and global activation states were analysed separately. Rats with histologically confirmed xenografts showed behavioural improvement measured by counting apomorphine-induced rotations and with the extended body axis test. Firing rates in both nuclei were not significantly different between control and grafted groups. However, burst firing patterns in both nuclei in the slow-wave activity state were significantly reduced (P < 0.05) in rats with large surviving grafts, compared to hemiparkinsonian controls. The neuronal firing entropies and oscillations in both nuclei were restored to normal levels in the large-graft group. Electroencephalogram spike-triggered averages also showed normalization in the slow-wave activity state (P < 0.05). These results suggest that local continuous dopaminergic stimulation exerts a normalizing effect on the downstream parkinsonian basal ganglia firing patterns. This novel finding is relevant to future preclinical and clinical investigations of cell transplantation and the development of next-generation therapies for Parkinson's disease that ameliorate pathophysiological neural activity and provide optimal recovery of function.

Therapeutic options for continuous dopaminergic stimulation in Parkinson's disease

Treatment of Parkinson's disease aims to replace dopaminergic transmission at striatal synapses. In the normal state, nigral neurons fire continuously, exposing striatal dopamine receptors to relatively constant levels of dopamine. In the disease state, periodic dosing and the short half-life of antiparkinsonian drugs leads to more intermittent stimulation. Abnormal pulsatile stimulation of striatal dopamine receptors may lead to dysregulation of genes and proteins in downstream neurons and consequently, alterations in neuronal firing patterns. This may ultimately lead to motor complications. In order to prevent the development of motor complications a therapy that provides continuous dopaminergic stimulation as observed in the normal state would be ideal. Different routes of administration of levodopa and other dopaminergic drugs have been tried to achieve continuous dopaminergic stimulation (CDS). This review discusses the various methods available to achieve this goal with particular emphasis on duodenal dopa administration.

Pharmacokinetics of levodopa/carbidopa delivered from gastric-retentive extended-release formulations in patients with Parkinson's disease

The investigators conducted a single-dose pharmacokinetic (PK) study of levodopa/carbidopa delivered from novel gastric-retentive extended-release (ER) tablets versus a comparator ER tablet (M-ER) in patients with Parkinson's disease. Two levodopa/carbidopa (200 mg/50 mg) gastric-retentive ER formulations (4 hours and 6 hours) and M-ER were administered orally with food. Blood samples were collected for up to 24 hours post dose to determine levodopa and carbidopa concentrations. Tolerability was assessed by monitoring adverse events and measuring vital signs. PK modeling was conducted to estimate the release characteristics for future gastric-retentive ER formulations to achieve a less fluctuating plasma concentration profiles. Compared with M-ER, both gastric-retentive ER formulations exhibited a longer time to reach a lower maximal plasma concentration for levodopa and carbidopa. The 4-hour formulation demonstrated a similar area under the concentration-time curve compared with M-ER, whereas the 6-hour formulation demonstrated a lower area under the concentration-time curve. All formulations were well tolerated. Modeling suggests that a gastric-retentive ER formulation with a longer release duration administered twice daily may achieve a less fluctuating levodopa concentration profile than M-ER administered 3 times daily. This study demonstrates that gastric-retentive ER dosage forms may reduce dose frequency while minimizing the plasma peak-to-trough fluctuation and consequently reduce motor fluctuation in patients with Parkinson's disease.

Involvement of the serotonin system in L-dopa-induced dyskinesias

The ability of L-dopa to relieve the motor impairments in Parkinson's disease patients declines over time, and side-effects, such as dyskinesias, appear--limiting the use of the drug in the advanced stage of the disease. Serotonergic neurons are able to convert L-dopa to dopamine and to store this neurotransmitter in synaptic vesicles. This peculiarity might be very important in the advanced disease, when most of the dopaminergic neurons have degenerated. Indeed, an increasing body of evidence points to dopamine released as a false neurotransmitter from the serotonin terminals as the main pre-synaptic determinant of L-dopa-induced dyskinesias in animal models of Parkinson's disease. These findings make the serotonin system an intriguing target for anti-dyskinetic therapies.

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.

Levodopa-induced dyskinesias

Levodopa-induced dyskinesias (LID) are common and difficult to treat. This review focuses on three issues related to LID: clinical features, classification and rating, pathophysiology and pathogenesis, and management. The three primary clinical syndromes are OFF-period dystonia, peak-dose dyskinesia, and diphasic dyskinesia. Several other forms also occur, making the evaluation and choice of treatment complicated. A core component of the pathophysiology of LID is overactivity of the direct striatal output pathway. This pathway provides a direct GABAergic connection by which the striatum inhibits the output regions of the basal ganglia, i.e., the internal globus pallidus and the substantia nigra pars reticulata. Altering dopaminergic dosing and timing can abate dyskinesias, but usually impact the control of parkinsonism. Putative therapies to reduce the problem of dyskinesias could focus on the glutamatergic, GABAergic, alpha2 adrenergic, serotonergic (5HT1A, 5HT2A), opioid, histamine H3, adenosine A2A receptors, the monoamine transport or cannabinoid CB1 receptors systems. The only currently available drug with an evidence-based recommendation on efficacy for dyskinesia is amantadine. Therapy goals include the prevention of dyskinesia and treatment of dyskinesias that are troublesome clinically. New rating measures to assess severity and disability related to dyskinesia are in the process of development and clinimetric testing.

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.

Dopamine dysregulation of movement control in L-DOPA-induced dyskinesia

The nigrostriatal dopamine (DA) system has an essential role in the selection and control of movement sequences, and its degeneration causes the characteristic motor symptoms of Parkinson's disease. Parkinsonian motor symptoms are alleviated by L-DOPA, but this treatment induces motor fluctuations and dyskinesias (abnormal involuntary movements). Clinical and experimental findings indicate that the motor complications of L-DOPA pharmacotherapy are triggered by transient and large changes in extracellular DA levels. The disruption of presynaptic DA homeostasis sets in motion a cascade of postsynaptic alterations, which prime the brain for a complicated motor response to dopaminomimetic treatment. L-DOPA-induced dyskinesia provides a paradigm to study how the dysregulation of DA release and clearance results in maladaptive neuroplasticity sustaining abnormal patterns of movement.

Duodenal levodopa infusion for the treatment of Parkinson’s disease

Motor fluctuations are a common problem in the long-term management of Parkinson's disease (PD), resulting in disability and impaired quality of life. The relatively short serum half-life (approximately 90 min) of oral levodopa/carbidopa and its erratic absorption due to delayed and inconsistent gastric emptying (a non-motor feature of PD) are thought to be important factors in the development of motor fluctuations. Continuous infusion of levodopa/carbidopa directly into the small intestine of PD patients results in marked reduction of motor fluctuations by reducing plasma levodopa variability by an order of magnitude over oral therapy. Previously, the use of long-term intraduodenal infusion of levodopa/carbidopa was limited by the relatively large volumes of infusate necessitated by the low solvency of levodopa. The development of a micronized levodopa (20 mg/ml) and carbidopa (5 mg/ml) suspension utilizing a methylcellulose gel provides the high levodopa concentration and physical and chemical stability necessary for long-term enteral therapy. Clinical evidence indicates that a marked reduction of motor fluctuations and dyskinesias can be achieved and maintained by intraduodenal administration of this suspension. This article reviews the published data describing the efficacy and safety of duodenal levodopa, and discusses its current and potential role in meeting the needs of PD patients.

Advances in the treatment of Parkinson's disease

Parkinson's disease (PD) affects one in every 100 persons above the age of 65 years, making it the second most common neurodegenerative disease after Alzheimer's disease. PD is a disease of the central nervous system that leads to severe difficulties with body motions. The currently available therapies aim to improve the functional capacity of the patient for as long as possible; however they do not modify the progression of the neurodegenerative process. The need for newer and more effective agents is consequently receiving a great deal of attention and consequently being subjected to extensive research. This review concisely compiles the limitations of currently available therapies and the most recent research regarding neuroprotective agents, antioxidants, stem cell research, vaccines and various surgical techniques available and being developed for the management of PD.

Enteral levodopa/carbidopa gel infusion for the treatment of motor fluctuations and dyskinesias in advanced Parkinson's disease

Pharmacotherapy designed to alleviate the symptoms of Parkinson's disease is focused on the stimulation of striatal dopamine receptors. The ideal pharmacological treatment would involve continuous dopaminergic stimulation. Currently, the most effective pharmacotherapy available is levodopa delivered orally; however, its short plasma half-life in combination with erratic gastric emptying and intestinal absorption makes dopaminergic stimulation pulsatile. Motor fluctuations and dyskinesias develop with time as a consequence and can become disabling. A gel formulation of levodopa/carbidopa has been developed for enteral (duodenal or jejunal) infusion via a portable pump. The infusion provides smooth plasma levodopa levels, more continuous dopaminergic stimulation and effective treatment of motor complications.

Dystonia in Parkinson’s disease

Dystonia can occasionally be found in idiopathic Parkinson's disease. It is very uncommon in untreated patients and is more frequently seen as a complication of its treatment. In this review, the various types of dystonia occurring in PD, the differential diagnosis with other parkinsonian syndromes associated with dystonia and treatments available are revised. Dystonia unrelated to treatment can be typical (blepharospasm, torticollis), atypical (parkinsonian writer's cramp, camptocormia, anismus), or occurring in earlyonset Parkinson disease (the so-called kinesigenic foot dystonia, considered a hallmark of early-onset Parkinson's disease). Early and prominent dystonia in untreated patients with parkinsonism should raise the suspicion of other entities other than Parkinson's disease, such as progressive supranuclear palsy, multiple system atrophy or corticobasal degeneration. In patients on chronic dopaminergic treatment, peak-dose dystonia, diphasic dystonia and off-dystonia can be seen. The later constitutes the major dystonic feature of chronic levodopa therapy, and a wide variety of strategies are available to manage this complication. Among them, deep brain stimulation of the subthalamic nucleus has proved to be the most effective one. Dystonic reactions (mainly involving oculomotor cranial nerves and limbs) in operated patients (especially carriers of deep brain stimulation (DBS) devices) are increasingly being reported, constituting a new type of dystonia in patients with Parkinson's disease: dystonia linked to surgical treatment.

Review of the therapeutic management of Parkinson's disease. Report of a joint task force of the European Federation of Neurological Societies (EFNS) and the Movement Disorder Society-European Section (MDS-ES). Part II: late (complicated) Parkinson's disease

To provide evidence-based recommendations for the management of late (complicated) Parkinson's disease (PD), based on a review of the literature. Complicated PD refers to patients suffering from the classical motor syndrome of PD along with other motor or non-motor complications, either disease-related (e.g. freezing) or treatment-related (e.g. dyskinesias or hallucinations). MEDLINE, Cochrane Library and INAHTA database literature searches were conducted. National guidelines were requested from all EFNS societies. Non-European guidelines were searched for using MEDLINE. Part II of the guidelines deals with treatment of motor and neuropsychiatric complications and autonomic disturbances. For each topic, a list of therapeutic interventions is provided, including classification of evidence. Following this, recommendations for management are given, alongside ratings of efficacy. Classifications of evidence and ratings of efficacy are made according to EFNS guidance. In cases where there is insufficient scientific evidence, a consensus statement ('good practice point') is made.

Post- versus presynaptic plasticity in L-DOPA-induced dyskinesia

L-3,4-dihydroxyphenylalanine (L-DOPA) remains the most efficacious drug for the treatment of Parkinson's disease (PD), but causes adverse effects that limit its utility. L-DOPA-induced dyskinesia (abnormal involuntary movements) is a significant clinical problem that attracts growing scientific interest. Current notions attribute the development of dyskinesia to two main factors, viz. the loss of nigrostriatal dopamine (DA) projections and the maladaptive changes produced by L-DOPA at sites postsynaptic to the nigrostriatal neuron. Basic research in the past 15 years has placed a lot of emphasis on the postsynaptic plasticity associated with dyskinesia, but recent experimental work shows that also some presynaptic factors, involving the regulation of L-DOPA/DA release and metabolism in the brain, may show plasticity during treatment. This review summarizes significant studies of L-DOPA-induced dyskinesia in patients and animal models, and outlines directions for future experiments addressing mechanisms of presynaptic plasticity. These investigations may uncover clues to the varying susceptibility to L-DOPA-induced dyskinesia among PD patients, paving the way for tailor-made treatments.

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.

Impact of gastric emptying on levodopa pharmacokinetics in Parkinson disease patients

Adjunction of the catechol-O-methyltransferase (COMT) inhibitor entacapone (EN) to levodopa/carbidopa (LD/CD) improves motor symptoms in patients with Parkinson disease (PD) by a prolonged elimination of LD. But it is not known whether EN addition influences gastric emptying and thus LD pharmacokinetics and pharmacodynamics. Objectives were to simultaneously determine plasma LD elimination, gastric emptying, and clinical response after a single intake of the same LD dosage as LD/CD--or as (LD/CD/EN) formulation on 2 consecutive days. In both groups, PD patients with delayed gastric emptying had significant lower LD plasma concentrations. Addition of EN did not influence gastric emptying but significantly improved motor response, which was not different for patients with delayed gastric emptying. However, with and without EN adjunction gastric emptying distinctly contributes to the variability of plasma LD bioavailability. This may impact LD delivery to the brain and thus motor response in PD patients. Therefore, fine tuning of LD application, which considers gastric emptying, becomes more and more essential in advanced PD stages with a reduced striatal neuronal dopamine capacity, which is responsible for maintenance of motor response in early PD patients.