Repeated administration of piribedil induces less dyskinesia than L-dopa in MPTP-treated common marmosets: a behavioural and biochemical investigation

Comparison of the effectiveness, safety, and costs of anti-Parkinson drugs: A multiple-center retrospective study

AIMS

This study aimed to systematically compare the effectiveness, safety, and costs of different anti-Parkinson drugs (APDs).

METHODS

This is a multi-center study that retrospectively analyzed the data of 8420 outpatients with PD from 2014 to 2019 across 30 tertiary hospitals in China. The effectiveness was evaluated by changes in total dosages of APDs, normalized by levodopa equivalent dose (LED) and presented as ΔLEDs; levodopa equivalent dose cost (LEDc) represented the daily cost of APDs; and newly added diagnostics were represented as APDs-related adverse events.

RESULTS

A total of 384 patients with eligible medical records for three consecutive years were enrolled. Patients treated with carbidopa/levodopa or levodopa/benserazide had significantly lower mean ΔLEDs than other groups (p < 0.01), followed by pramipexole and selegiline. The piribedil group had the highest ΔLEDs, with mean differences of 112.56-355.04 mg compared to other groups (p < 0.01). Meanwhile, LEDc in the levodopa/benserazide, carbidopa/levodopa, and piribedil groups were significantly lower than those in pramipexole or selegiline groups ($0.088-0.135/day for levodopa/benserazide; $0.070-0.126/day for carbidopa/levodopa; $0.112-0.138/day for piribedil; $0.290-0.332/day for pramipexole; $0.229-0.544/day for selegiline; p < 0.01). Patients with piribedil had more adverse events, with an incidence rate of 35.7%, followed by levodopa/benserazide (25.6%), selegiline (23.5%), carbidopa/levodopa (23.3%), and pramipexole (16.4%). Pramipexole showed a lower incidence rate of adverse events than piribedil, including neuropsychiatric symptoms (p = 0.006), headache/dizziness (p = 0.016), and gastrointestinal symptoms (p = 0.031).

CONCLUSIONS

Carbidopa/levodopa or levodopa/benserazide might exhibit better clinical improvement with less medical cost, while piribedil presented less clinical improvement but a higher risk of headache/dizziness, gastrointestinal, and neuropsychiatric symptoms.

Investigation of the Pharmaceutical Care in One Elderly Parkinson's Disease Patient with Psychotic Symptoms

A 66-year-old male patient with a 10-year course of Parkinson's disease (PD) was admitted for hallucination lasting a half a month. After treatment with levodopa/carbidopa, selegiline, and piribedil, the patient's motor symptoms were improved while no significant effects were observed on psychotic symptoms. A clinical pharmacist analyzed the pharmacologic and pharmacokinetic characteristics of selegiline and piribedil, summarized the scheme of PD with psychotic symptoms in the literature, and discovered that selegiline might potentiate psychotic side effects of piribedil, while the use of levodopa/carbidopa cannot be ruled out either. Finally, the clinical pharmacist proposed to reduce the dosage of levodopa/carbidopa, increase the dosage of selegiline and quetiapine, and discontinue piribedil. The clinician accepted this suggestion. After the adjustment of medication, the patient's motor symptoms were absolutely improved and the psychotic symptoms were notably improved. This case study suggests that long-term treatment with levodopa/carbidopa and piribedil, along with the progression of the disease itself, could contribute to the emergence of psychotic symptoms in PD. Additionally, selegiline could potentiate psychotic side effects of piribedil. Neurology clinical pharmacists should work alongside neurology clinicians at the bedside to optimize pharmacotherapy, improve patient safety, and contribute to scholarly efforts.

The effect of Banisteriopsis caapi (B. caapi) on the motor deficits in the MPTP-treated common marmoset model of Parkinson's disease

Banisteriopsis caapi (B. caapi) contains harmine, harmaline, and tetrahydroharmine, has monoamine oxidase inhibitory activity, and has reported antiparkinsonian activity in humans when imbibed as a tea; however, its effects are poorly documented. For this reason, motor function was assessed in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated common marmosets following administration of B. caapi extract (28.4-113.6 mg/kg; po), harmine (0.1 and 0.3 mg/kg; sc), and selegiline (10 mg/kg; sc), alone or with a submaximal dose of L-3,4-dihydroxyphenylalanine (L-DOPA; 4-7 mg/kg). L-DOPA reversed motor disability, increased locomotor activity, and induced moderate dyskinesia. B. caapi did not increase locomotor activity or induce dyskinesia but at 56.8 and 113.6 mg/kg improved motor disability. The L-DOPA response was unaltered by co-administration of B. caapi. Harmine (0.1 and 0.3 mg/kg) produced a mild improvement in motor disability without affecting locomotor activity or dyskinesia but had no effect on the L-DOPA-induced antiparkinsonian response. Selegiline (10 mg/kg) alone improved motor function to the same extent as L-DOPA, but with only mild dyskinesia, and did not alter the response to L-DOPA, although dyskinesia was reduced. The findings suggest that B. caapi alone has a mild antiparkinsonian effect but does not enhance the L-DOPA response or reduce dyskinesia.

Adverse effects produced by different drugs used in the treatment of Parkinson's disease: A mixed treatment comparison

OBJECTIVE

This mixed treatment comparison is used to compare the adverse effects of eleven different drugs used to treat Parkinson's disease (PD). The drugs that we compare include the following: ropinirole, rasagiline, rotigotine, entacapone, apomorphine, pramipexole, sumanirole, bromocriptine, piribedil, pergolide, and levodopa.

METHODS

PubMed, EMBASE, and Cochrane Library were searched from the inception to December 2015. Our analysis combines the evidences of direct comparison and indirect comparison between various literatures. We evaluated the merging odds ratios (OR) value and surface under the cumulative ranking curves (SUCRA) of each of the drugs and used this as a mode of comparison.

RESULTS

Twenty-four randomized controlled trials (RCTs) were included in this study. Our results demonstrated that the incidence of adverse reactions of ropinirole, rotigotine, entacapone, and sumanirole were obviously higher in terms of nausea compared to the placebo. Ropinirole produced the highest incidence rates of dyskinesia side effects, whereas pramipexole was significantly higher in terms of patients' hallucination. In addition, the SUCRA values of all the drugs showed that the incidence of adverse reaction of pergolide was relatively high (nausea: 83.5%; hallucination: 79.8%); for dyskinesia and somnolence, the incidence of ropinirole was higher (dyskinesia: 80.5%; somnolence: 69.4%); the incidence of adverse reaction of piribedil was higher on PD in terms of dizziness (67.0%); and the incidence of bromocriptine was relatively high in terms of constipation (62.3%).

CONCLUSIONS

This mixed treatment comparison showed that the drugs ropinirole, bromocriptine, and piribedil produced the highest incidence rates of nausea, dyskinesia, hallucination, dizziness, constipation, and somnolence symptoms. Thus, we conclude that as these three drugs produced the most frequent symptoms, they are not recommended for the treatment of patients with Parkinson's disease.

Piribedil for the Treatment of Motor and Non-motor Symptoms of Parkinson Disease

Dopamine agonists are well-established symptomatic medications for treating early and advanced Parkinson disease (PD). Piribedil was one of the first agonists to be marketed (1969) and is widely used as an extended-release oral formulation in European, Latin-American, and Asian countries. Piribedil acts as a non-ergot partial dopamine D2/D3-selective agonist, blocks alpha2-adrenoreceptors and has minimal effects on serotoninergic, cholinergic, and histaminergic receptors. Animal models support the efficacy of piribedil to improve parkinsonian motor symptoms with a lower propensity than levodopa to induce dyskinesia. In PD patients, randomized double-blind studies show that piribedil (150-300 mg/day, three times daily) is superior to placebo in improving motor disability in early PD patients. Based on such evidence, piribedil was considered in the last Movement Disorder Society Evidence-Based Medicine review as "efficacious" and "clinically useful" for the symptomatic treatment of PD, either as monotherapy or in conjunction with levodopa, in non-fluctuating early PD patients. This effect appears comparable to what is known from other D2 agonists. However, randomized controlled trials are not available to assess the effect of piribedil in managing levodopa-induced motor complications. Pilot clinical studies suggest that piribedil may improve non-motor symptoms, such as apathy, but confirmatory trials are needed. The tolerability and safety profile of piribedil fits with that of the class of dopaminergic agonists. As for other non-ergot agonists, pneumo-pulmonary, retroperitoneal, and valvular fibrotic side effects are not a concern with piribedil. The original combination of piribedil D2 dopaminergic and alpha-2 adrenergic properties deserve further investigations to better understand its antiparkinsonian profile.

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

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

Dopamine receptor agonists for Parkinson's disease

INTRODUCTION

Prolonged administration of l-3,4-dihydroxyphenylalanine (l-DOPA) for Parkinson's disease (PD) is hampered by motor complications related to the progressive incapacity of residual nigrostriatal neurons to properly utilize the drug. Direct stimulation of dopaminergic (DAergic) receptors with specific compounds (DA agonists) has, therefore, become an additional therapeutic tool for PD.

AREAS COVERED

DA agonists have considerable anti-parkinsonian symptomatic efficacy, although they are less potent than l-DOPA. This review summarizes pre-clinical and clinical data on DA agonists and their role in treating PD. Specific focus was put on second-generation, first-line non-ergolinic DA agonists and their motor, non-motor and putative neuroprotective effects. The anti-parkinsonian potential of recently developed DA agonists that reached Phase II and III clinical trials was also addressed.

EXPERT OPINION

DA agonists can be useful along the whole natural course of PD, as monotherapy in the initial phase or combined with l-DOPA in advanced PD. Extended-release formulations have been developed for second-generation DA agonists, which are better appreciated by patients. Neuroprotective properties have been proposed for DA agonists, based on pre-clinical studies, but never convincingly demonstrated in patients. New DA agonists, with better symptomatic efficacy and devoid of the side effects that characterize current compounds, are needed.

Modeling Parkinson's disease in primates: The MPTP model

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) primate models of Parkinson's disease (PD) reproduce most, although not all, of the clinical and pathological hallmarks of PD. The present contribution presents the possibilities offered by the MPTP monkey models of PD to readers with minimal knowledge of PD, emphasizing the diversity of species, route and regimen of administration, symptoms and pathological features. Readers would eventually find out that there is not a single MPTP monkey model of PD but instead MPTP monkey models of PD, each addressing a specific experimental need.

New approaches to therapy

L-DOPA-induced dyskinesia (LID) is a major complication of the treatment of Parkinson's disease (PD). LID comprises two major components, the priming process responsible for its onset and the expression of involuntary movements that underlies its clinical manifestation. The mechanisms responsible for these components are partially understood and their biochemical basis is being unraveled but avoidance and treatment remain an issue. In this chapter, we review what is known about the involvement of dopaminergic systems in LID and the way in which dopaminergic therapy can be used to avoid the onset of LID or to reverse or suppress involuntary movements once these have been established. The involvement of specific dopamine receptor subtypes, continuous dopaminergic stimulation (CDS) and continuous drug delivery (CDD) is reviewed. However, a major role is emerging in the avoidance and suppression of LID through the use of nondopaminergic mechanisms and we consider the present and future use of glutamatergic drugs, serotoninergic agents, adenosine antagonists and others as a means of improving therapy. There is compelling basic science supporting a role for nondopaminergic approaches to LID but at the moment the translational benefit to PD is not being achieved as predicted. There needs to be further consideration of why this is the case and how in future, both experimental models of dyskinesia and clinical trial design can be optimized to ensure success.

Plasma neuropeptide Y: a biomarker for symptom severity in chronic fatigue syndrome

BACKGROUND

Chronic fatigue syndrome (CFS) is a complex, multi-symptom illness with a multisystem pathogenesis involving alterations in the nervous, endocrine and immune systems.Abnormalities in stress responses have been identified as potential triggers or mediators of CFS symptoms. This study focused on the stress mediator neuropeptide Y (NPY). We hypothesized that NPY would be a useful biomarker for CFS.

METHODS

The CFS patients (n = 93) were from the Chronic Fatigue and Related Disorders Clinic at the University of Miami and met the 1994 case definition of Fukuda and colleagues. Healthy sedentary controls (n = 100)) were from NIH or VA funded studies. Another fatiguing, multi-symptom illness, Gulf War Illness (GWI), was also compared to CFS. We measured NPY in plasma using a radioimmunoassay (RIA). Psychometric measures, available for a subset of CFS patients included: Perceived Stress Scale, Profile of Mood States, ATQ Positive & Negative Self-Talk Scores, the COPE, the Beck Depression Inventory, Fatigue Symptom Inventory, Cognitive Capacity Screening Examination, Medical Outcomes Survey Short Form-36, and the Quality of Life Scale.

RESULTS

Plasma NPY was elevated in CFS subjects, compared to controls (p = .000) and to GWI cases (p = .000). Receiver operating characteristics (ROC) curve analyses indicated that the predictive ability of plasma NPY to distinguish CFS patients from healthy controls and from GWI was significantly better than chance alone. In 42 patients with CFS, plasma NPY had significant correlations (<0.05) with perceived stress, depression, anger/hostility, confusion, negative thoughts, positive thoughts, general health, and cognitive status. In each case the correlation (+ or -) was in the anticipated direction.

CONCLUSIONS

This study is the first in the CFS literature to report that plasma NPY is elevated compared to healthy controls and to a fatigued comparison group, GWI patients. The significant correlations of NPY with stress, negative mood, general health, depression and cognitive function strongly suggest that this peptide be considered as a biomarker to distinguish subsets of CFS.

From the MPTP-treated primate to the treatment of motor complications in Parkinson's disease

The MPTP-treated primate has proved to be a highly predictive model of the effects of dopaminergic drugs in the symptomatic treatment of Parkinson's disease (PD) and for the avoidance of motor complications. Using MPTP-treated primates, new dopaminergic therapies have been devised alongside novel treatment strategies and novel routes of administration while providing knowledge on how to use dopaminergic drugs in a manner that avoids the onset of motor complications. The use of MPTP-treated primates led to the concept of continuous dopaminergic stimulation (CDS) and the early introduction of dopamine receptor agonists as monotherapy for PD for the prevention of dyskinesia. However, CDS does not explain the differences in dyskinesia induction that exist between L-dopa and dopamine receptor agonists, and a more rationale approach to therapy involves continuous drug delivery (CDD). CDD has been explored in the MPTP-treated primate and this review focuses on some of the evidence showing that the delivery of dopaminergic drugs in PD is key to the avoidance of dyskinesia while maintaining therapeutic efficacy. Other types of motor complication, such as "wearing off" and "on-off" remain to be explored in MPTP-treated primates and the model has yet to be used to examine non-motor components of PD. Despite having been employed for almost 25 years, the MPTP-treated primate has many potential uses in the future that will further improve the treatment of PD.

From the cell to the clinic: a comparative review of the partial D₂/D₃receptor agonist and α2-adrenoceptor antagonist, piribedil, in the treatment of Parkinson's disease

Though L-3,4-dihydroxyphenylalanine (L-DOPA) is universally employed for alleviation of motor dysfunction in Parkinson's disease (PD), it is poorly-effective against co-morbid symptoms like cognitive impairment and depression. Further, it elicits dyskinesia, its pharmacokinetics are highly variable, and efficacy wanes upon long-term administration. Accordingly, "dopaminergic agonists" are increasingly employed both as adjuncts to L-DOPA and as monotherapy. While all recognize dopamine D(2) receptors, they display contrasting patterns of interaction with other classes of monoaminergic receptor. For example, pramipexole and ropinirole are high efficacy agonists at D(2) and D(3) receptors, while pergolide recognizes D(1), D(2) and D(3) receptors and a broad suite of serotonergic receptors. Interestingly, several antiparkinson drugs display modest efficacy at D(2) receptors. Of these, piribedil displays the unique cellular signature of: 1), signal-specific partial agonist actions at dopamine D(2)and D(3) receptors; 2), antagonist properties at α(2)-adrenoceptors and 3), minimal interaction with serotonergic receptors. Dopamine-deprived striatal D(2) receptors are supersensitive in PD, so partial agonism is sufficient for relief of motor dysfunction while limiting undesirable effects due to "over-dosage" of "normosensitive" D(2) receptors elsewhere. Further, α(2)-adrenoceptor antagonism reinforces adrenergic, dopaminergic and cholinergic transmission to favourably influence motor function, cognition, mood and the integrity of dopaminergic neurones. In reviewing the above issues, the present paper focuses on the distinctive cellular, preclinical and therapeutic profile of piribedil, comparisons to pramipexole, ropinirole and pergolide, and the core triad of symptoms that characterises PD-motor dysfunction, depressed mood and cognitive impairment. The article concludes by highlighting perspectives for clarifying the mechanisms of action of piribedil and other antiparkinson agents, and for optimizing their clinical exploitation.

Functional models of Parkinson's disease: a valuable tool in the development of novel therapies

Functional models of Parkinson's disease (PD) have led to effective treatment for the motor symptoms. Toxin-based models, such as the 6-hydroxydopamine-lesioned rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primate, have resulted in novel dopaminergic therapies and new therapeutic strategies. They have also been used to study processes underlying motor complications, particularly dyskinesia, and for developing pharmacological approaches to dyskinesia avoidance and suppression. Symptomatic models of PD based on nigrostriatal degeneration have a high degree of predictability of clinical effect of dopaminergic drugs on motor symptoms in humans. However, the effects of nondopaminergic drugs in these models do not translate effectively into clinical efficacy. Newer experimental models of PD have attempted to reproduce the pathogenic process and to involve all areas of the brain pathologically affected in humans. In addition, models showing progressive neuronal death have been sought but so far unsuccessfully. Pathogenic modeling has been attempted using a range of toxins, as well as through the use of transgenic models of gene defects in familial PD and mutant rodent strains. However, there are still no accepted progressive models of PD that mimic the processes known to occur during cell death and that result in the motor deficits, pathology, biochemistry, and drug responsiveness as seen in humans. Nevertheless, functional models of PD have led to many advances in treating the motor symptoms of the disorder, and we have been fortunate to have them available. They are an important reason the treatment of PD is so much better compared with treatments for related illnesses.

Comparative effects of the dopaminergic agonists piribedil and bromocriptine in three different memory paradigms in rodents

The potential memory-enhancing properties of two dopamine agonists currently used in patients with Parkinson's disease, piribedil (1, 10 mg/kg/day, subcutaneously) and bromocriptine (5 mg/kg/day, subcutaneously), were evaluated in three experiments. Although piribedil (10 mg/kg) and bromocriptine equally enhanced spontaneous object recognition in young adult rats (experiment A), only piribedil displayed beneficial effects against aging-related memory impairments in two radial-maze experiments in mice. First (experiment B), a two-stage paradigm of spatial discrimination was used to assess relational/declarative memory in aged mice; piribedil (1 and 10 mg/kg) selectively and significantly improved the performances of aged mice in the critical tests for relational/declarative memory, whereas bromocriptine had no effect. Second, in a novel working memory task (experiment C), vehicle- or bromocriptine-treated aged mice displayed, compared with (vehicle) younger controls, a severe and persistent deficit in short-term retention of successive arm-visits, performing close to chance whichever the retention interval. Performances of piribedil (10 mg/kg) group remarkably improved across testing-days and reached young adults' level. The restoration of specific mnemonic impairments, in aged mice, highlights the memory-enhancing properties of piribedil. The efficacy of this drug in treating cognitive impairment of Parkinson's disease should now be assessed in more specific models.This work was published in an abstract form: ECNP Abstracts, 2005 (P8060 & P8065).

Decreased expression of l-dopa-induced dyskinesia by switching to ropinirole in MPTP-treated common marmosets

Current concepts suggest that pulsatile stimulation of dopamine receptors following L-dopa administration leads to priming for dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates, while continuous dopaminergic stimulation with long-acting dopamine agonists does not. We investigated whether L-dopa-induced dyskinesia is reduced by switching to a dopamine agonist. MPTP-treated marmosets received chronic treatment with L-dopa or ropinirole in doses producing equivalent motor activity and reversal of motor deficits. Administration of L-dopa led to the rapid onset of moderate to severe dyskinesia, whereas ropinirole produced only mild dyskinesia. Animals initially treated with L-dopa were switched to an equivalent dose of ropinirole and those treated with ropinirole were switched to an equivalent dose of L-dopa for 56 days. L-dopa-primed animals that were switched to ropinirole showed a trend towards a reduction of dyskinesia intensity, whereas animals initially treated with ropinirole and switched to L-dopa showed a trend toward increased dyskinesia intensity. A subsequent, acute L-dopa challenge reversed motor deficits and induced intense dyskinesia in both groups. This suggests that L-dopa leads to the priming and expression of dyskinesia, but that expression is not maintained when switching to a long-acting dopamine agonist. In contrast, dopamine agonists may prime for dyskinesia, but do not lead to its full expression.

The dopamine agonist piribedil with L-DOPA improves attentional dysfunction: relevance for Parkinson's disease

Cognitive deficits are often associated with motor symptoms in Parkinson's disease. This study investigates the ability of piribedil ([(methylenedioxy-3,4 benzyl)-4 pyperazinyl-1]-2 pyrimidine), a D(2)/D(3) dopamine (DA) receptor agonist with antagonist activity at alpha(2A)-adrenoceptors, to restore motor and attentional deficits in nigrostriatal 6-hydroxydopamine-lesioned rats. Subjects were trained to depress a lever, detect a stimulus occurring after variable foreperiods, and release the lever quickly afterward. Striatal DA depletions produce deficits in the timing of foreperiods and prolong reaction times. Although a subchronic treatment with piribedil (0.1-2 mg/kg) is not effective, a dose of 0.3 mg/kg administered for 3 weeks significantly reverses the akinetic deficits produced by the striatal dopamine depletion and progressively improves attentional deficits. When coadministered with the dopamine prodrug l-3,4-dihydroxyphenylalanine (l-DOPA) (3 mg/kg), piribedil (0.3 mg/kg) promotes a rapid and full recovery of preoperative performance. These results suggest that administration of l-DOPA in combination with piribedil in a chronic treatment as either initial or supplemental therapy for Parkinson's disease might improve cognitive functions while reducing the risk for motor complications.

Switching from Levodopa to the Long-acting Dopamine D2/D3 Agonist Piribedil Reduces the Expression of Dyskinesia While Maintaining Effective Motor Activity in MPTP-treated Primates

BACKGROUND

The control of motor complications following dopaminergic medication in late-stage Parkinson disease remains problematic.

OBJECTIVE

We now investigate the potential of oral administration of the long-acting dopamine D2/D3 agonist piribedil to decrease the expression of dyskinesia induced by prior exposure to levodopa in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates.

METHODS

MPTP-treated common marmosets were treated with equieffective doses of levodopa (10.0-12.5 mg/kg PO, twice daily) or piribedil (3.0-4.0 mg/kg PO, once daily) for 30 days and then switched to the alternative treatment for a further 35 days.

RESULTS

Levodopa administration markedly improved motor function, but dyskinesia rapidly appeared and intensified as treatment progressed. Administration of piribedil produced a similar reversal of MPTP-induced motor deficits but with comparatively mild dyskinesia. On switching from levodopa to piribedil, the intensity of dyskinesia decreased without altering the improvement in motor deficits. However, on switching from piribedil to levodopa, the rapid increase in dyskinesia despite the improvement in motor function being maintained suggests that piribedil also primes for but does not markedly express dyskinesia.

CONCLUSION

The study confirms the low dyskinesia expression resulting from piribedil treatment compared with an equieffective dose of levodopa. Importantly, the results show that switching from levodopa to piribedil rapidly results in a sustained decrease in dyskinesia intensity.

Early piribedil monotherapy of Parkinson's disease: A planned seven-month report of the REGAIN study

Piribedil is a D2 dopamine agonist, which has been shown to improve symptoms of Parkinson's disease (PD) when combined with L-dopa. The objective of this study was to compare the efficacy of piribedil monotherapy to placebo in patients with early PD over a 7-month period. Four hundred and five early PD patients were randomized (double-blind) to piribedil (150-300 mg/day) or placebo. L-dopa open-label supplementation was permitted. Unified Parkinson Disease Rating Scale part III (UPDRS III) score as the last observation on monotherapy over 7 months was the primary outcome measure. Secondary outcomes were proportion of responders (UPDRS III improvement > 30%), patients remaining on monotherapy after 7 months, UPDRS III subscores, and UPDRS II. UPDRS III improved on piribedil (-4.9 points) versus a worsening on placebo (2.6 points; estimated effect = 7.26 points; 95% CI = 5.38-9.14; P < 0.0001). The proportion of responders was significantly higher for piribedil (42%) than for placebo (14%) (OR = 4.69; 95% CI = 2.82-7.80; P < 0.001). Piribedil significantly improved several UPDRS III subscores. UPDRS II improved on piribedil by -1.2 points, while it deteriorated by 1.5 points on placebo (estimated effect = 2.71; 95% CI = 1.8-3.62; P < 0.0001). The proportion of patients remaining on monotherapy after 7 months was greater in the piribedil group (OR = 3.72; 95% CI = 2.26-6.11; P < 0.001). Safety was consistent with that reported for other dopamine agonists, gastrointestinal side effects being the most common (22% of patients in piribedil group vs. 14% on placebo). Piribedil is effective and safe as early PD therapy.

The Parkinson-Control study: A 1-year randomized, double-blind trial comparing piribedil (150 mg/day) with bromocriptine (25 mg/day) in early combination with levodopa in Parkinson's disease

Dopamine agonists have been recommended as early treatment for Parkinson's disease (PD), alone or combined with levodopa. Piribedil is a non-ergot selective D(2)/D(3) agonist with alpha(2) antagonist properties shown to be effective in the treatment of PD. This 12-month international, randomized, double-blind trial aimed to assess the efficacy of piribedil 150 mg versus bromocriptine 25 mg, in early combination with levodopa in Stage I to III PD patients. Motor efficacy was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS III, Items 18-31) as improvement from baseline. Response rate was defined as a 30% improvement. Among the 425 randomly assigned patients, 178 were also included in a substudy on cognitive follow-up evaluated by a dysexecutive syndrome oriented battery. A relevant improvement in UPDRS III over the 12-month study duration was observed both in the piribedil and bromocriptine groups (-7.9 +/- 9.7 points from baseline versus -8.0 +/- 9.5; not significant [n.s.]) with a response rate of 58.4% and 55.3% (n.s.), respectively. Piribedil and bromocriptine resulted in similar improvement on all UPDRS III subscores. Piribedil patients required less levodopa dose increase than those on bromocriptine. Cognitive performance remained generally unchanged in both groups, with a significant effect of piribedil limited to the Wisconsin Card Sorting Test. An overall good tolerability of piribedil was observed. Early combination of piribedil 150 mg with levodopa resulted in significant long-term improvement of all motor symptoms in PD patients insufficiently controlled by levodopa alone. Taking into account both efficacy and acceptability in the long-term, piribedil proved in this bromocriptine controlled study to be an effective and safe treatment for PD.

Enhanced striatal opioid receptor-mediated G-protein activation in L-DOPA-treated dyskinetic monkeys

Long-term l-3,4-dihydroxyphenylalanine (L-DOPA) treatment in Parkinson's disease leads to dyskinesias in the majority of patients. The underlying molecular mechanisms for L-DOPA-induced dyskinesias (LIDs) are currently unclear. However, the findings that there are alterations in opioid peptide mRNA and protein expression and that opioid ligands modulate dyskinesias suggest that the opioid system may be involved. To further understand its role in dyskinesias, we mapped opioid receptor-stimulated G-protein activation using [35S]guanylyl-5'-O-(gamma-thio)-triphosphate ([35S]GTPgammaS) autoradiography in the basal ganglia of normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned squirrel monkeys administered water or L-DOPA. Subtype-selective opioid receptor G-protein coupling was investigated using the mu-opioid agonist [D-Ala, N-Me-Phe, Gly-ol]-enkephalin, delta-agonist SNC80 and kappa-agonist U50488H. Our data show that mu-opioid receptor-mediated G-protein activation is significantly enhanced in the basal ganglia and cortex of L-DOPA-treated dyskinetic monkeys, whereas delta- and kappa-receptor-induced increases were limited to only a few regions. A similar pattern of enhancement was observed in both MPTP-lesioned and unlesioned animals with LIDs suggesting the effect was not simply due to a compromised nigrostriatal system. Opioid receptor G-protein coupling was not enhanced in non-dyskinetic L-DOPA-treated animals, or lesioned monkeys not given L-DOPA. The increases in opioid-stimulated [35S]GTPgammaS binding are directly correlated with dyskinesias. The present data demonstrate an enhanced subtype-selective opioid-receptor G-protein coupling in the basal ganglia of monkeys with LIDs. The positive correlation with LIDs suggests this may represent an intracellular signaling mechanism underlying these movement abnormalities.

Levetiracetam Interferes With the l-Dopa Priming Process in MPTP-Lesioned Drug-Naive Marmosets

OBJECTIVE

Levetiracetam (LEV; Keppra, UCB Pharma) has been shown to reduce established l-3,4 dihydroxyphenylalanine (l-dopa)-induced dyskinesia. This study investigated whether LEV can modify induction of dyskinesia by l-dopa or the process of priming.

METHODS

Drug-naive MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) -lesioned marmosets were treated for 21 days with l-dopa/LEV or l-dopa alone. Subsequently, the animals were left untreated for 1 week and then both groups were challenged with a single dose of l-dopa alone on day 29. Behavior was assessed by automated activity counts and by post hoc analysis of videotapes using validated rating scales.

RESULTS

LEV had no significant effect on the appearance of dyskinesia when administered de novo in combination with l-dopa. However, after a week of drug holiday, the 2 groups exhibited a different response to an acute l-dopa challenge. Thus, animals previously treated with l-dopa alone exhibited a similar level of dyskinesia to that seen on day 21 of the repeated treatment phase of the study. However, animals previously treated with l-dopa/LEV demonstrated significantly reduced dyskinesia compared with day 21 of the repeated treatment phase of the study.

CONCLUSIONS

LEV does not modify the onset of dyskinesia following de novo treatment with l-dopa. However, concomitant treatment with l-dopa/LEV reduces the level of dyskinesia induced by l-dopa following a drug holiday. Thus, prior treatment with LEV appears to modify the mechanisms responsible for the maintenance of l-dopa-induced dyskinesia.

Piribedil as an adjunct to levodopa in advanced Parkinson's disease: the Asian experience

Data on the efficacy and tolerability of piribedil in Asians are scarce. Forty-nine Filipino PD patients with motor fluctuations were enrolled in an 8-week trial of piribedil of up to 150 mg/day. Mean improvement was 48% for the motor UPDRS scores (tremor showed greatest change), and 43% for activities of daily living. Mean daily levodopa dose decreased by 17%, and mean duration of effect of levodopa increased by 1.3 h (45%). Most common side effects were hallucinations (20%), dyskinesias (20%), dizziness (8%), and sleepiness (6%). This trial shows that piribedil is effective and well-tolerated by Asian patients with advanced PD at least with short-term use.

3,4-methylenedioxymethamphetamine (ecstasy) inhibits dyskinesia expression and normalizes motor activity in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primates

Ecstasy [3,4-methylenedioxymethamphetamine (MDMA)] was shown to prolong the action of L-3,4-dihydroxyphenylalanine (L-DOPA) while suppressing dyskinesia in a single patient with Parkinson's disease (PD). The clinical basis of this effect of MDMA is unknown but may relate to its actions on either dopaminergic or serotoninergic systems in brain. In normal, drug-naive common marmosets, MDMA administration suppressed motor activity and exploratory behavior. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated, L-DOPA-primed common marmosets, MDMA transiently relieved motor disability but over a period of 60 min worsened motor symptoms. When given in conjunction with L-DOPA, however, MDMA markedly decreased dyskinesia by reducing chorea and to a lesser extent dystonia and decreased locomotor activity to the level observed in normal animals. MDMA similarly alleviated dyskinesia induced by the selective dopamine D2/3 agonist pramipexole. The actions of MDMA appeared to be mediated through 5-HT mechanisms because its effects were fully blocked by the selective serotonin reuptake inhibitor fluvoxamine. Furthermore, the effect of MDMA on L-DOPA-induced motor activity and dyskinesia was partially inhibited by 5-HT1a/b antagonists. The ability of MDMA to inhibit dyskinesia results from its broad spectrum of action on 5-HT systems. Serotoninergic receptors appear to play an important modulatory role in l-DOPA-induced dyskinesia, and this study may provide a framework for the use of serotoninergic agents in the treatment of L-DOPA-induced dyskinesia.

Recent developments in the pharmacological treatment of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder associated with the loss of dopaminergic neurons in the substantia nigra. The decline of dopamine leads to motor dysfunctions manifested as tremor, rigidity and bradykinesia. The pharmacological treatment of choice for the past 30 years has primarily been the dopamine precursor levodopa. Although it is the most effective treatment available, it is clear that other drugs are needed in order to sustain a therapeutic benefit and to alleviate fluctuations in mobility (i.e., motor fluctuations). Furthermore, there is some evidence that levodopa may hasten the occurrence of motor fluctuations and involuntary movements called dyskinesias. Hence, many clinicians delay the use of levodopa and employ the use of other symptomatic treatments including monoamine oxidase type B (MAO-B) inhibitors and dopamine agonists as first-line therapy in de novo patients. Regardless of treatment, the disease continues to progress as there is still no obvious means of altering disease progression (i.e., no neuroprotective therapy), to restore loss of dopamine (i.e., no restorative therapy) or prevent the disease (i.e. preventative therapy). With disease progression, polypharmacy is common and often employs a combination of antiparkinsonian agents. There have been some key advances in treatment with the advent of MAO-B inhibitors, dopamine agonists and catechol-O-methyltransferase inhibitors; however, the arsenal of drug treatment remains limited. As the mechanism of PD is further elucidated, novel drug treatments will continue to emerge in the areas of preventative, restorative or symptomatic therapy. Despite the purpose of treatment, the ideal pharmacological drug for PD will include the presence of a safe side-effect profile, a simple dosing schedule, the ability to provide symptomatic relief and the potential to alter disease progression. The purpose of this article is to examine upcoming antiparkinsonian drugs in clinical trials based on their pharmacology, safety and efficacy.

Piribedil enhances frontocortical and hippocampal release of acetylcholine in freely moving rats by blockade of alpha 2A-adrenoceptors: a dialysis comparison to talipexole and quinelorane in the absence of acetylcholinesterase inhibitors

In a dialysis procedure not requiring perfusate addition of acetylcholinesterase inhibitors to "boost" basal levels of acetylcholine (ACh), the influence of the antiparkinson agent piribedil upon levels of ACh in frontal cortex and dorsal hippocampus of freely moving rats was compared with those of other antiparkinson drugs and selective ligands at alpha(2)-adrenoceptors (ARs). Suggesting a tonic, inhibitory influence of alpha(2A)-ARs upon cholinergic transmission, the alpha(2)-AR agonist 5-bromo-6-[2-imidazolin-2-yl-amino]-quinoxaline tartrate (UK14,304), and the preferential alpha(2A)-AR agonist guanabenz reduced levels of ACh. They were elevated by the antagonists 2(2-methoxy-1,4 benzodioxan-2-yl)-2-imidazoline HCl (RX821002) and atipamezole and by the preferential alpha(2A)-AR antagonist 2-(2H-(1-methyl-1,3-dihydroisoindole)methyl)-4,5-dihydroimidazole (BRL44008). In contrast, trans-2,3,9,13b-tetrahydro-1,2-dimethyl-1H-dibenz[c,f]imidazo[1,5-a]azepine (BRL41992) and prazosin, preferential alpha(2B/2C)-AR antagonists, were inactive. The dopaminergic agonist and antiparkinson agent piribedil, which behaves as an antagonist at alpha(2)-ARs, dose dependently increased extracellular levels of ACh. This action was absent upon pretreatment with a maximally effective dose of RX821002. On the other hand, a further dopaminergic agonist and antiparkinson agent, talipexole, which possesses agonist properties at alpha(2)-ARs, dose dependently reduced levels of ACh. This action was also blocked by RX821002. In contrast to piribedil and talipexole, quinelorane, which interacts with dopaminergic receptors but not alpha(2)-ARs, failed to affect ACh levels. Finally, in analogy to the frontal cortex, piribedil likewise elicited a dose-dependent increase in extracellular levels of ACh in the dorsal hippocampus. In conclusion, in distinction to talipexole and quinelorane, and reflecting its antagonist properties at alpha(2A)-ARs, piribedil reinforces cholinergic transmission in the frontal cortex and dorsal hippocampus of freely moving rats. These actions may be related to its facilitatory influence upon cognitive function.