Dopamine agonists

Future Directions for Developing Non-dopaminergic Strategies for the Treatment of Parkinson's Disease

The symptomatic treatment of Parkinson's disease (PD) has been dominated by the use of dopaminergic medication, but significant unmet need remains, much of which is related to non-motor symptoms and the involvement of non-dopaminergic transmitter systems. As such, little has changed in the past decades that has led to milestone advances in therapy and significantly improved treatment paradigms and patient outcomes, particularly in relation to symptoms unresponsive to levodopa. This review has looked at how pharmacological approaches to treatment are likely to develop in the near and distant future and will focus on two areas: 1) novel non-dopaminergic pharmacological strategies to control motor symptoms; and 2) novel non-dopaminergic approaches for the treatment of non-motor symptoms. The overall objective of this review is to use a 'crystal ball' approach to the future of drug discovery in PD and move away from the more traditional dopamine-based treatments. Here, we discuss promising non-dopaminergic and 'dirty drugs' that have the potential to become new key players in the field of Parkinson's disease treatment.

Apomorphine for Parkinson's disease: pharmacologic and clinical considerations

INTRODUCTION

In Parkinson's disease, dopamine depletion in the basal ganglia leads to symptoms including bradykinesia, gait abnormalities, and cognitive impairment. Even with treatment, the disease course leads to decreases in the amount of dopamine produced and released into the synapse. As dopamine production falls and the treatment course is insufficient to match the metabolic supply and demand, acute 'off' periods develop that cause reemergence of symptoms. Apomorphine is used to reverse these 'off' periods and restore function in patients with Parkinson's. This review will provide clinicians a concise article to read to learn more about apomorphine and its appropriate utilization.

AREAS COVERED

The research discussed is focused on the history, pharmacokinetics, and mechanism of action of Apomorphine. Its utilization as a treatment for Parkinson's Disease and its comparison to currently utilized drugs is also discussed in this review. We focused on articles published on PubMed and Google Scholar within the last 10 years, but in some instances had to go as far back as 1951 to include early articles published about apomorphine.

EXPERT OPINION

The expert opinion section focuses on the ways in which apomorphine could be administered in the future to better promote utilization and increase tolerability.

Novel therapeutic interventions for combating Parkinson's disease and prospects of Nose-to-Brain drug delivery

Parkinson disease (PD) is a progressive neurodegenerative disorder prevalent mainly in geriatric population. While, L-DOPA remains one of the major choices for the therapeutic management of PD, various motor and non-motor manifestations complicate the management of PD. In the last two decades, exhaustive research has been carried out to explore novel therapeutic approaches for mitigating motor and non-motor symptoms of PD. These approaches majorly include receptor-based, anti-inflammatory, stem-cell and nucleic acid based. The major limitations of existing therapeutic interventions (of commonly oral route) are low efficacy due to low brain bioavailability and associated side effects. Nanotechnology has been exploited and has gained wide attention in the recent years as an approach for enhancement of bioavailability of various small molecule drugs in the brain. To address the challenges associated with PD therapy, nose-to-brain delivery utilizing nanomedicine-based approaches has been found to be encouraging in published evidence. Therefore, the present work summarises the major challenges and limitations with antiparkinsonian drugs, novel therapeutic interventions, and scope of nanomedicine-based nose-to-brain delivery in addressing the current challenges of antiparkinsonian therapy. The manuscript tries to sensitize the researchers for designing brain-targeted nanomedicine loaded with natural/synthetic scaffolds, biosimilars, and nucleic acids that can bypass the first-pass effect for the effective management of PD.

A critical review of apomorphine hydrochloride sublingual film for the treatment of Parkinson's disease 'OFF' episodes

Introduction: Parkinson's disease (PD) is a neurodegenerative disorder defined by its motor features. Levodopa therapy is the gold standard therapy, but over time, response is impeded by the development of motor fluctuations, including 'off' episodes where PD symptoms reemerge. Sublingual apomorphine offers a new, novel, and effective therapy developed for treatment of 'off' episodes. Areas covered: Apomorphine is an old dopamine agonist developed as a subcutaneous injectable rescue therapy for 'off' periods in PD that was approved in the United States in 2004. We will discuss its history, chemistry and clinical use. We will also cover the recent development and approval of sublingual apomorphine film that offers a novel formulation and provides effective treatment for 'off' episodes including results of the phase 3 randomized, double-blinded, placebo-controlled study. Oral mucosal side effects, which were mild to moderate and reversible in most patients experiencing them, will be discussed. Expert opinion: The new sublingual apomorphine is safe and effective for relief of 'off' periods that impact quality of life. Its ease of use will be beneficial to those with needle phobia and device challenges with currently available injectable and inhaled therapeutics. Side effect profile is an improvement from previous attempts at sublingual formulation.

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 use of monoamine pharmacological agents in the treatment of sexual dysfunction: evidence in the literature

INTRODUCTION

The monoamine neurotransmitters serotonin, dopamine, and norepinephrine play an important role in many medical and psychological conditions, including sexual responsiveness and behavior. Pharmacological agents that modulate monoamines may help alleviate sexual dysfunction.

AIMS

To provide an overview of pharmacological agents that modulate monoamines and their use in the treatment of sexual dysfunction.

METHODS

EMBASE and PubMed search for articles published between 1950 and 2010 using key words "sexual dysfunction,""monoamines,""monoaminergic receptors," and "generic names for pharmacological agents."

MAIN OUTCOME MEASURES

To assess the literature evaluating the efficacy of monoamine pharmacologic agents used in the treatment of sexual dysfunction.

RESULTS

The literature primarily cites the use of monoaminergic agents to treat sexual side effects from serotonergic reuptake inhibitors (SSRIs), with bupropion, buspirone and ropinirole providing the most convincing evidence. Controlled trials have shown that bupropion improves overall sexual dysfunction, but not frequency of sexual activity in depressed and nondepressed patients. Nefazodone and apomorphine have been used to treat sexual dysfunction, but their use is limited by significant side effect and safety profiles. New research on pharmacologic agents with subtype selectivity at dopaminergic and serotonergic receptors and those that possess dual mechanisms of action are being investigated.

CONCLUSION

There has been tremendous progress over the past 50 years in understanding the role of monoamines in sexual function and the effect of pharmacologic agents which stimulate or antagonize monoaminergic receptors on sexual dysfunction. Nevertheless, large, double-blind, placebo-controlled studies evaluating the efficacy of currently available agents in populations without comorbid disorders are limited, preventing adequate interpretation of data. Continued research on sexual function and specific receptor subtypes will result in the development of more selective pharmacologic agents with the goal of increasing efficacy without the dose-limiting side effects of nonselective agents.

Current status of symptomatic medical therapy in Parkinson's disease

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

Disruption of prepulse inhibition of the startle reflex by the preferential D(3) agonist ropinirole in healthy males

RATIONALE

Emerging evidence from agonist-antagonist studies suggests a role for the dopamine D(3) receptor subtype in the regulation of PPI in animals, but such evidence is lacking for human subjects.

OBJECTIVES

This study examines the effect of the preferential D(3) agonist ropinirole on PPI in humans.

METHODS

PPI was tested in 12 healthy men in three sessions associated with ropinirole 0.25 mg, ropinirole 0.5 mg, or placebo according to a balanced, crossover, double-blind design. Two prepulses (75- and 85-dB white noise bursts) and two lead intervals (50 and 80 ms) were employed.

RESULTS

Ropinirole 0.5 mg significantly reduced prepulse inhibition (PPI) with both prepulses at the 80-ms lead intervals. There was no effect of treatment on startle amplitude and habituation.

CONCLUSIONS

These results suggest a role for the dopamine D(3) receptor in the mediation of human PPI, although a contribution from ropinirole's agonistic activity at the D(2) receptor cannot be entirely excluded. Firm conclusions on the role of the D(3) receptor in the modulation of human PPI can only be drawn with the use of genetic approaches or more selective ligands for this receptor.

Apomorphine in the treatment of Parkinson's disease

Motor fluctuations, refractory to conventional medical management, are one of the most troubling aspects of Parkinson's disease. Apomorphine is a dopaminergic agent that has been known to the medical community for more than a century, but has only recently been developed to treat such motor fluctuations. In this article, the authors review the historical background, structure, mechanism of action, pharmacologic properties, clinical trials, indications and side effects, as well as avenues of further research, of apomorphine.

Effect of Prolactin and Bromocriptine on the Population of Prostate Neuroendocrine Cells from Intact and Cyproterone Acetate-Treated Rats: Stereological and Immunohistochemical Study

This work deals with the quantification of serotonin-immunoreactive prostate neuroendocrine cells (NECs) in rats exposed to prolactin in normal, cyproterone acetate-exposed, and bromocriptine-exposed animals to establish the possible influence of prolactin with or without androgenic blockade on this cell population. Thirty male peripubertal Sprague-Dawley rats were grouped as controls (CT) and those treated with cyproterone acetate (CA), cyproterone acetate plus prolactin, cyproterone acetate plus bromocriptine, prolactin (PL), and bromocriptine (BC). The volume of ductal epithelium (Vep) and total number (NSER) of the NECs serotonin-immunoreactive were measured. NECs were detected in the periurethral ducts. Compared to CT, Vep was increased in PL and BC and NSER was decreased in CA and increased in the prolactin or bromocriptine groups. The androgenic blockade decreases NSER in rat prostate; PL induces in normal and cyproterone acetate-treated rats the increase of NSER; and BC exerts a local effect over the prostate similar to that described for PL.

Pergolide: multiple-dose pharmacokinetics in patients with mild to moderate Parkinson disease

The primary objective of this study was to describe the pharmacokinetics of oral pergolide in patients with mild to moderate Parkinson disease using a new high-performance liquid chromatography-tandem mass spectrometry assay. A secondary objective was to investigate the relationship between plasma concentrations and efficacy. Fourteen patients with a diagnosis of Parkinson disease completed this multicenter, open-label, dose-escalating study. Pergolide was administered for 58 days, using increasing daily doses from 0.05 mg daily up to 1 mg three times daily and then tapering the dose. The steady-state pharmacokinetic profile and motor score were determined at dose levels of 0.25, 0.5, and 1 mg three times a day and during elimination after the last dose. Pergolide was absorbed with a median time to maximum concentration of 2 to 3 hours across the dose range. Systemic exposure appeared to increase proportionally with dose over the range of 0.25 to 1 mg three times daily within a patient, but there was a large variability in exposures between patients (interpatient coefficients of variation were 56.4% for the area under the curve). Pergolide was widely distributed (volume of distribution, approximately 14,000 L) and was eliminated with a mean half-life of 21 hours. Motor scores improved as both peak plasma pergolide concentrations and exposure increased. No unexpected safety concerns were identified. Pergolide is absorbed relatively quickly into the systemic circulation, has a large apparent volume of distribution, and has a relatively long half-life (mean, 21 hours). This prolonged half-life is of particular interest, given the current hypothesis that more continuous dopaminergic receptor stimulation may reduce motor complications in patients with Parkinson disease.

The effects of dopamine agonists on prepulse inhibition in healthy men depend on baseline PPI values

RATIONALE AND OBJECTIVES

Dopamine (DA) agonists reliably disrupt prepulse inhibition (PPI) of the startle reflex in animals but less so in humans despite cross-species similarities in the neural regulation of PPI. This study examines whether individual variation in baseline PPI may account for the inconsistencies in DA agonist-induced PPI disruption in humans.

METHODS

Baseline PPI measures were obtained from 32 healthy adult men. Subjects were subsequently tested in three sessions after ingestion of placebo or active drug in a balanced double-blind design. Seventeen subjects were given 0.05 and 0.1 mg of pergolide (a direct DA agonist) and 15 subjects were given 100 and 200 mg of amantadine (an indirect DA agonist). In each treatment group, subjects were assigned to "high" and "low" PPI subgroups based on the median split of their baseline PPI.

RESULTS

Amantadine and pergolide disrupted PPI in high- but not in low-PPI subjects. In contrast, low-PPI subjects showed a trend towards PPI facilitation especially with pergolide.

CONCLUSIONS

Our results suggest that baseline PPI is an important determinant of the effect of DA agonists on PPI.

Pergolide Mesylate, a Dopaminergic Receptor Agonist, Applied With l-DOPA Enhances Serum Antioxidant Enzyme Activity in Parkinson Disease

The aim of this study was to compare patients with Parkinson disease (PD) patients treated with pergolide mesylate (PM), a dopaminergic receptor agonist, together with L-DOPA and those these treated with L-DOPA alone on the concentration of free radicals (FR), glutathione, and the activity of superoxide dismutase (SOD) and catalase in the serum. The study was carried out using 16 age-matched control subjects, 16 PD patients treated with L-DOPA at a dose of 1 to 1.5 g daily, and 16 PD patients treated with L-DOPA 1 to 1.5 g daily with PM 0.75 to 1.25 mg daily. The mean duration of treatment of PD was 6 years (range, 2-8 years) with l-DOPA, and 2 years with PM + L-DOPA or L-DOPA alone. Although there was no significant difference in lipid peroxidation products among the 3 groups, patients treated with L-DOPA showed high levels of FR as determined by dichlorofluorescein. Although catalase and SOD activities were elevated in both groups of PD patients, additional treatment with PM further enhanced catalase activity compared with those treated with l-DOPA alone. Interestingly, patients treated with PM + L-DOPA showed a significantly increased level of glutathione compared with those treated with L-DOPA alone. Collectively, these data suggest that PM + L-DOPA is a more efficient therapy in maintaining an antioxidative defense in PD patients compared with treatment with L-DOPA alone.

Neuroprotective effects of the novel D3/D2 receptor agonist and antiparkinson agent, S32504, in vitro against 1-methyl-4-phenylpyridinium (MPP+) and in vivo against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): a comparison to ropinirole

The novel naphtoxazine derivative and preferential D(3) vs D(2) receptor agonist, S32504, restores perturbed motor function in rodent and primate models of antiparkinsonian activity with a potency superior to those of two further, preferential D(3) receptor agonists, pramipexole and ropinirole. However, potential neuroprotective properties of S32054 have not, to date, been evaluated. Herein, employing several measures of cellular integrity, we demonstrate that S32504 robustly, concentration-dependently and completely protects terminally differentiated SH-SY5Y cells against 1-methyl-4-phenylpyridinium (MPP+)-induced cell death in vitro. Further, S32504 was substantially more potent than pramipexole and ropinirole, the latter of which was neurotoxic at high concentrations. In vivo, subchronic treatment with low (0.25 mg/kg) and high (2.5 mg/kg) doses of S32504 prior to and during treatment of mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, MPTP, provided complete protection against MPTP-induced tyrosine hydroxylase immunoreactive (TH-IR) neuronal death in the substantia nigra pars compacta and ventral tegmental area. A high dose of ropinirole (2.5 mg/kg) provided some protection but statistical significance was not attained, and a low dose (0.25 mg/kg) was ineffective. Neither drug afforded protection against the MPTP-induced loss of DA fibers in the striatum, as measured by TH-IR and dopamine transporter immunoreactive fiber counts. In conclusion, the novel naphotoxazine and dopaminergic agonist, S32504, robustly protects dopaminergic neurones against the neurotoxic effects of MPP(+) and MPTP in in vitro and in vivo models, respectively. The underlying mechanisms and therapeutic pertinence of these actions will be of interest to further evaluate in view of its potent actions in behavioral models of antiparkinson activity.

Pramipexole and pergolide in the treatment of depression in Parkinson's disease: a national multicentre prospective randomized study

An 8-month multicentre prospective randomized study aimed at comparing the effects of dopamine receptor agonists pramipexole (PPX; Mirapexin) and pergolide (PRG; Permax) as add-on to L-dopa therapy on depression [Montgomery and Asberg Depression Rating Scale (MADRS)] in 41 non-demented patients (25 men, 16 women) suffering from both mild or moderate depression and advanced Parkinson's disease (PD). The assessment was performed by a blinded independent observer. Motor symptoms (UPDRS III), motor complications (UPDRS IV), activities of daily living (UPDRS II and VI) and depressive symptoms as measured by Self - Rating Depression Scale by Zung were evaluated in an open-label design. The average value of Zung scores decreased significantly in both groups with no statistical difference between both groups. A significant decrease in the average value of MADRS scores was present only in the PPX group. The average UPDRS scores decreased significantly with no statistical difference between both groups at the comparable average total daily dose of both preparations. In both cases, the total daily dose of L-dopa decreased significantly but the decrease was statistically more pronounced in the PRG group. Our results demonstrate the antidepressant effect of PPX in patients with PD while we can't make any conclusions with regard to antidepressant effect of PRG.

Loss of response to levodopa in Parkinson's disease and co-occurrence with dementia: role of D3 and not D2 receptors

Previous data suggest a relationship between the loss of response to levodopa in Parkinson's disease (PD) patients with the co-occurrence of dementia, but the role of alterations in the dopamine system has not been explored. We measured the extent of striatal DA loss and changes in striatal DA D(2) and D(3) receptors in postmortem striatum of PD patients who historically had or had not lost their clinical response to dopaminergic drugs and/or had an additional diagnosis of dementia. Clinical evaluation and retrospective chart reviews for PD and dementia, and neuropathological diagnoses were obtained. All PD cases (+/-dementia), regardless of response to dopaminergic drugs, exhibited a significant and similar degree and pattern of loss of tyrosine hydroxylase immunocytochemistry and DA transporter binding in striatum, and loss of tyrosine hydroxylase-immunoreactive neurons and brain-derived neurotrophic-immunoreactive neurons from the ventral midbrain. D(2) receptor concentrations were modestly elevated in the rostral striatum of all the PD cases (+/-dementia), whether or not they continued to respond to dopaminergic drugs. In contrast, loss of D(3) receptor concentration correlated with loss of response to dopaminergic drugs, independent of the presence or absence of dementia. A maintained response to dopaminergic drugs correlated with an elevation of D(3) receptors. Dementia with PD was highly correlated with a loss of response to dopaminergic drugs, and was also correlated with reduced D(3) receptors. The alterations in D(3) receptor concentrations were greatest in the nucleus accumbens, caudal striatum, and globus pallidus. Thus, loss of dopamine D(3) receptors may be a more important contributing factor to a loss of response to dopaminergic drugs than changes in the D(2) receptor.

Benefit-risk considerations in the treatment of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is a relatively recently characterised syndrome with clinical and pathological features that distinguish it from classical Alzheimer's disease. These characteristics include more rapid decline, spontaneous features of parkinsonism, visual hallucinations and fluctuating cognition. This article reviews the clinical syndrome of DLB and the agents used to treat its cognitive, motor and behavioural manifestations. Benefit-risk issues regarding the treatment of DLB are discussed based upon limited randomised, controlled clinical trials with some speculative conclusions being drawn from case reports and case series. We conclude that patients with DLB may respond better to cholinesterase inhibitors than patients with Alzheimer's disease on both cognitive and behavioural measures. Cholinesterase inhibitor therapy may result in reduced caregiver burden and less time institutionalised. These agents are well tolerated with the majority of adverse effects being gastrointestinal in nature. Although neuropsychiatric manifestations are numerous in patients with DLB, antipsychotics should be used infrequently and with caution, although atypical antipsychotics are better tolerated than conventional antipsychotics. Physicians should exhibit caution when prescribing these agents because of the increased risk of extrapyramidal adverse effects. Limited data suggest that the use of levodopa or other dopaminergic agents may be of benefit for the treatment of the parkinsonism that is associated with DLB. However, the increased risk of hallucinations and neuropsychiatric symptoms may negate the potential benefits of increased mobility. There is insufficient evidence to draw conclusions about the use of antidepressants; however, selective serotonin reuptake inhibitors may be of benefit.

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

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

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

Open-label pilot study of bupropion plus bromocriptine for treatment of cocaine dependence

Combinations of medications are often used in neuropsychiatry to enhance treatment efficacy. This 8-week, open-label study tested the combination of bupropion (< or =300 mg) and bromocriptine (< or =7.5 mg) daily in 34 cocaine-dependent (DSM-IIIR) outpatients also receiving weekly individual counseling. The first 18 subjects spent one week at maximum dose; the next 16 spent three weeks. Both groups showed significant reductions in self-reported cocaine use, with no significant change in proportion of urine toxicology tests positive for cocaine. There were no significant differences in outcome between groups. These results suggest that the combination of bupropion and bromocriptine is safe in cocaine addicts, but provide ambiguous evidence of its efficacy.

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

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

The long-term safety and efficacy of pramipexole in advanced Parkinson's disease

Objective: To assess the long-term safety and efficacy of pramipexole in advanced Parkinson's disease over a four year time period.Methods: This study is an open-label extension trial of pramipexole for Parkinson's disease open to patients completing a double-blind placebo controlled safety and efficacy trial of this drug. Three hundred and six patients entered the trial. These patients had moderate to severe PD (stage II-IV Hoehn and Yahr during off time) and were experiencing motor fluctuations. Patients were titrated over a six week period and then entered a maintenance phase which lasted up to 50 months. Patients were evaluated every 3 months using the Unified Parkinson's Disease Rating Scale (UPDRS II, III and IV) and modified Schwab and England scale (S/E).Results: Sixty-four percent (197) of the 306 patients who entered this study completed it. Patients showed steady improvement over the 6 week ascending dose interval when pramipexole was reintroduced into the trial as the open-label study medication. Over the duration of the trial patients slowly returned to their baseline levels. This was true for all measures evaluated except for the UPDRS part IV. On UPDRS part IV patients remained below their baseline score which indicated an improvement for the duration of the study. Patterns similar to the overall scores were seen when the individual components of the UPDRS scale part II for "on" and "off" periods and part III were evaluated. However tremor during "on" periods showed improvement over baseline for the duration of the trial. The most common adverse events secondary to pramipexole occurring in greater than 10% of patients included dyskinesias, asymptomatic orthostatic hypotension, dizziness, insomnia, and hallucinations.Conclusion: Pramipexole was well tolerated for up to 4 years. Pramipexole treatment appeared to show continued efficacy in the treatment of Parkinson's disease for 3 years in this open-label descriptive study. After 3 years there was a gradual return to baseline motor states perhaps suggesting progression of Parkinson's disease.

Treatment of Parkinson's disease

The aim of current treatment of Parkinson's disease is to ameliorate the symptoms while seeking to lessen the potential development of late levodopa complications. To this end, there is ample evidence that the early use of dopamine agonists is beneficial in younger Parkinsonian patients but monotherapy with dopamine agonists is for only a select few. Nonergot dopamine agonists offer the potential for fewer side effects. Lower dose levodopa therapy delays the onset and reduces severity of dyskinesia and end of dose failure. However levodopa remains the treatment of choice in Parkinson's disease and should not be restricted unnecessarily in patients with disability. There is no evidence that levodopa is toxic to dopaminergic neurons in people with Parkinson's disease. As yet, no drugs are of proven neuroprotective value. Dopamine agonists, catechol-o-methyltransferase inhibitors, amantadine and apomorphine have differing but beneficial roles in the management of levodopa side effects. Ablative surgery and deep brain stimulation of thalamus, globus pallidus and subthalamic nucleus are increasingly available but choice of procedure depends not just on patient symptomatology, but also on local experience and results. Ideally, deep brain stimulation is the treatment of choice as it offers less morbidity than bilateral ablative surgery, the possibility of postoperative adjustments and the potential for reversibility if better treatments become available.

Clinical pharmacokinetics of ropinirole

Ropinirole is a selective non-ergoline dopamine D2 receptor agonist indicated for use in treating Parkinson's disease. When taken as oral tablets, ropinirole is rapidly and almost completely absorbed, and it is extensively distributed from the vascular compartment. The bioavailability is approximately 50%. Ropinirole shows low plasma protein binding. The drug is inactivated by metabolism in the liver, and none of the major circulating metabolites have pharmacological activity. The principal metabolic enzyme is the cytochrome P450 (CYP) isoenzyme CYP1A2. Ropinirole shows approximately linear pharmacokinetics when given as single or repeated doses, and is eliminated with a half-life of approximately 6 hours. Population pharmacokinetics have demonstrated that gender, mild or moderate renal impairment, Parkinson's disease stage and concomitant illnesses or the use of several common concomitant medications have no effect on the pharmacokinetics of ropinirole. Clearance is slower for patients older than 65 years compared with those who are younger, and in women taking hormone replacement therapy compared with those who are not. The CYP1A2 inhibitor ciprofloxacin produced increases in the plasma concentrations of ropinirole when these 2 drugs were coadministered, but no interaction was seen with theophylline which, like ropinirole, is also a substrate for CYP1A2. There is no obvious plasma concentration-effect relationship for ropinirole.

The initial treatment of Parkinson's disease should begin with levodopa

For over two decades controversy has surrounded the initial choice of therapeutic agent for patients with early symptomatic Parkinson's disease. Whether levodopa or dopamine receptor agonist monotherapy in these patients is more efficacious and/or results in fewer long-term complications of dopaminergic therapy such as motor fluctuations, dyskinesias, or psychiatric disorders is unresolved. This article examines the evidence related to levodopa-sparing strategies and levodopa-induced toxicity in Parkinson's disease. At this time, there is little evidence to support levodopa-sparing strategies or to suggest that levodopa is toxic and harmful to patients with Parkinson's disease.