A "combined" levodopa test as a useful method for evaluating the efficacy of dopamine agonists: application to pergolide and bromocriptine

Restoring pars intermedia dopamine concentrations and tyrosine hydroxylase expression levels with pergolide: evidence from horses with pituitary pars intermedia dysfunction

Background

Pituitary pars intermedia dysfunction (PPID) develops slowly in aged horses as degeneration of hypothalamic dopaminergic neurons leads to proliferation of pars intermedia (PI) melanotropes through hyperplasia and adenoma formation. Dopamine (DA) concentrations and tyrosine hydroxylase (TH) immunoreactivity are markedly reduced in PI tissue of PPID-affected equids and treatment with the DA receptor agonist pergolide results in notable clinical improvement. Thus, we hypothesized that pergolide treatment of PPID-affected horses would result in greater DA and TH levels in PI tissue collected from PPID-affected horses versus untreated PPID-affected horses.

To test this hypothesis, pituitary glands were removed from 18 horses: four untreated PPID-affected horses, four aged and four young horses without signs of PPID, and six PPID-affected horses that had been treated with pergolide at 2 µg/kg orally once daily for 6 months. DA concentrations and TH expression levels in PI tissues were determined by high performance liquid chromatography with electrochemical detection and Western blot analyses, respectively.

Results

DA and TH levels were lowest in PI collected from untreated PPID-affected horses while levels in the pergolide treated horses were similar to those of aged horses without signs of PPID.

Conclusions

These findings provide evidence of restoration of DA and TH levels following treatment with pergolide. Equine PPID is a potential animal model of dopaminergic neurodegeneration, which could provide insight into human neurodegenerative diseases.

Orodispersible sublingual piribedil to abort OFF episodes: a single dose placebo-controlled, randomized, double-blind, cross-over study

S90049, a novel sublingual formulation of the non-ergoline D(2)-D(3) agonist piribedil, has a pharmacokinetic profile promising to provide rapid relief on motor signs in Parkinson's disease (PD). We assessed the efficacy and safety of S90049 in aborting OFF episodes responding to subcutaneous apomorphine in PD patients with motor fluctuations. This was a single-dose double-blind double-placebo 3 x 3 cross-over study. Optimal tested doses were determined during a previous open-label titration phase (S90049 median dose: 60 mg, apomorphine: 5 mg). Primary endpoint was the maximal change versus baseline in UPDRS motor score (Delta UPDRS III) assessed after drug administration following an overnight withdrawal of antiparkinsonian medications. Thirty patients (age: 60 +/- 8 years, PD duration: 12 +/- 6 years, UPDRS III OFF: 37 +/- 15) participated. S90049 was superior to placebo on Delta UPDRS III (-13 +/- 12 versus -7 +/- 9 respectively; estimated difference -5.2, 95% Confidence Interval (CI)[-10.4;0.05], P = 0.05). This was also true for secondary outcomes: number of patients switching from OFF to ON (17 on S90049 vs. 8 on placebo, P = 0.03), time to turn ON (P = 0.013) and duration of the ON phase (P = 0.03). In the 17 patients who switched ON on S90049, Delta UPDRS III was similar on S90049 (-21.2 +/- 10.1) and apomorphine (-23.6 +/- 14.1) (estimated difference: 4.0 95% CI [-2.9;10.9]). S90049 was well tolerated: no serious or unexpected adverse event occurred. A single dose of up to 60 mg of S90049 given sublingually was superior to placebo in improving UPDRS III and aborting a practical OFF in patients with advanced PD. Testing greater doses might improve response rate.

Effects of a dopamine agonist on the pharmacodynamics of levodopa in Parkinson disease

BACKGROUND

Treatment of Parkinson disease commonly includes levodopa and dopamine agonists; however, the interaction of these 2 drugs is poorly understood.

OBJECTIVE

To examine the effects of a dopamine agonist on the motor response to levodopa.

DESIGN

Double-blind, randomized, placebo-controlled, crossover clinical trial.

SETTING

Ambulatory academic referral center. Patients Thirteen patients with idiopathic Parkinson disease taking levodopa and experiencing motor fluctuations and dyskinesia.

INTERVENTIONS

Eligible individuals were randomly assigned to receive pramipexole dihydrochloride or placebo for 4 weeks followed by a 2-hour intravenous levodopa infusion on consecutive days at 2 rates and with blinded assessments. They were then crossed over to the alternate oral therapy for 4 weeks followed by levodopa infusion and reassessment.

MAIN OUTCOME MEASURES

Change in finger-tapping speed, measured using the area under the curve (AUC) for finger taps per minute across time; peak finger-tapping speed; duration of response; time to "ON" (defined as a 10% increase in finger-tapping speed above baseline); walking speed; and dyskinesia AUC.

RESULTS

Pramipexole with levodopa infusion increased finger-tapping speed beyond the change in baseline by a mean (SE) of 170 (47.2) per minute x minutes (P = .006) and more than doubled the AUC for finger-tapping speed. Pramipexole increased peak finger-tapping speed by a mean (SE) of 18 (8.5) taps per minute (P = .02) and improved mean (SE) walking speed (15.9 [0.70] vs 18.9 [0.70] seconds, P = .004). Pramipexole prolonged duration of response after levodopa infusion and shortened time to ON. Pramipexole increased mean (SE) baseline dyskinesia scores (26.0 [5.85] vs 12.1 [5.85] points, P = .05) and peak dyskinesia scores with levodopa infusion.

CONCLUSIONS

Pramipexole augmented the motor response to levodopa beyond a simple additive effect and increased the severity of levodopa-induced dyskinesia. When considering a combination of these therapies, an appropriate balance should be maintained regarding gain of motor function vs worsening of dyskinesia. Trial Registration clinicaltrials.gov Identifier: NCT00666653.

Medical treatment of Parkinson disease

The cardinal characteristics of Parkinson disease (PD) include resting tremor, rigidity, and bradykinesia. Patients may also develop autonomic dysfunction, cognitive changes, psychiatric symptoms, sensory complaints, and sleep disturbances. The treatment of motor and non-motor symptoms of Parkinson disease is addressed in this article.

Medical management of levodopa-associated motor complications in patients with Parkinson's disease

Parkinson's disease is a neurodegenerative disorder that affects approximately 1% of people over the age of 60 years. Levodopa is standard, and often initial, therapy for patients with this condition; however, with continued treatment and as the disease progresses, up to 80% of patients experience 'wearing-off' symptoms, dyskinesias and other motor complications. These levodopa-associated problems may become disabling and profoundly affect quality of life. Medications commonly used to manage these symptoms include monoamine oxidase type B (MAO-B) inhibitors, catechol-O-methyltransferase (COMT) inhibitors, the NMDA receptor antagonist amantadine and dopamine receptor agonists. Agents that block MAO-B, such as rasagiline and selegiline, are used as both initial and adjunctive therapy in patients with Parkinson's disease. These medications increase concentrations of dopamine in the brain by blocking its reuptake from the synaptic cleft, a mechanism that can slow motor decline, increase 'on' time and improve symptoms of Parkinson's disease. Adverse events with these agents can include confusion, hallucination and orthostatic hypotension. MAO-B inhibition may elicit drug-drug interactions if administered with TCAs, SSRIs or SNRIs. Conventional oral selegiline is associated with potentially harmful plasma concentrations of three major amphetamine metabolites, although metabolite concentrations are significantly lower with a new orally disintegrating tablet (ODT) selegiline formulation. Selegiline ODT is also absorbed more efficiently and shows less pharmacokinetic variability than conventional oral selegiline.COMT mediates peripheral catabolism of levodopa. Therefore, agents that block COMT, such as tolcapone and entacapone, increase the elimination half-life of levodopa. Given adjunctively with levodopa, COMT inhibitors can decrease 'off' time and increase 'on' time, as well as lower the daily levodopa dose. Although more potent than entacapone, tolcapone requires monitoring for hepatotoxicity. Amantadine is a noncompetitive NMDA receptor antagonist shown to lower dyskinesia scores and improve motor complications in patients with Parkinson's disease when given adjunctively with levodopa. Dopamine agonists, also used as initial and adjunctive therapy in Parkinson's disease, improve motor response and decrease 'off' time purportedly through direct stimulation of dopamine receptors. Current dopamine agonists include bromocriptine, pergolide, cabergoline, lisuride, apomorphine, pramipexole, ropinirole and rotigotine. Although effective, this class of medications can be associated with cardiovascular and psychiatric adverse effects that can limit their utility. All medications used to manage levodopa-associated motor complications in patients with Parkinson's disease have had differing degrees of success. Although head-to-head comparisons of drugs within classes are rare, some differences have emerged related to effects on motor fluctuations, dyskinesias and on/off times, as well as to adverse effects. When choosing a drug to treat levodopa-induced complications, it is important to consider the risks and benefits of the different classes and of the specific agents within each class, given the different efficacy and safety profiles of each.

Comparing dopamine agonists in Parkinsonʼs disease

Dopamine agonists are effective in the management of both advanced and early-stage Parkinson's disease. Unfortunately, randomized head-to-head comparative studies between the many different dopamine agonists now available are sparse. Indirect comparisons of dopamine agonists show that ergot derivatives, such as pergolide and cabergoline, are as effective as non-ergot derivatives, such as ropinirole and pramipexole, in ameliorating Parkinson's disease symptoms in patients in early or advanced stages of the condition. As far as safety and tolerability are concerned, no significant differences between dopamine agonists are found. However, some specific adverse events, such as somnolence and sleep attacks, seem less frequent in monotherapy studies with pergolide than in those with the non-ergot dopamine agonists; however, because of the lack of direct-comparison studies this cannot be proved conclusively. Randomized, controlled comparative studies between dopamine agonists are necessary to verify any possible differences in their effectiveness and tolerability in the treatment of Parkinson's disease.

Cost-effectiveness of pergolide compared to bromocriptine in the treatment of Parkinson's disease: a decision-analytic model

OBJECTIVE

To develop a decision-analytic model to assess the cost-effectiveness of pergolide versus bromocriptine in the treatment of Parkinson's disease (PD).

METHODS

A Markov decision-analytic model is used to examine cost-effectiveness. The model ran for 20 cycles of 6 months' duration, and the patients progress through six stages: Hoehn-Yahr stages 1-5 and death. The transitional probabilities for each stage are derived from a 12-year longitudinal study of patients with PD. The costs in the model are derived from an expert panel containing six Australian neurologists. A review of the randomized controlled trials comparing the efficacy and safety of pergolide versus bromocriptine was undertaken. Five studies were identified, with four showing that pergolide offers superior efficacy when compared to bromocriptine. The Mizuno et al. (1995) study was the largest of the controlled trials and also measured patient Hoehn-Yahr status before and after treatment. This was identified as the most appropriate source of relative efficacy data for the model. The model examined various scenarios based on alternate durations of superior clinical benefit with pergolide compared to bromocriptine. The main analysis assumed that patients in each arm of the model would have identical Hoehn-Yahr status by the fifth year. Sensitivity analysis was used to determine cost-effectiveness in the case where the therapeutic benefit was of a shorter duration.

RESULTS

The Mizuno study indicates that an additional 19.09% of patients improved by at least one stage on pergolide over bromocriptine, with an odds ratio of 2.26 (p < .01). The total health care cost per patient over the 10-year period was $46,323 in the pergolide treatment arm and $47,351 in the bromocriptine treatment arm, an incremental saving of $1028. Patients also spent extra time in Hoehn-Yahr stages 1, 2, and 3. In sensitivity analyses, when the benefit from pergolide expired between 6 months and 5 years after treatment cessation, cost savings ranged from $68 to $2535.

CONCLUSION

Pergolide is cost saving and more efficacious than bromocriptine, and is therefore cost-effective.

The early treatment of Parkinson's disease: levodopa, dopamine agonists or both

Much has been written about the pharmacologic management of Parkinson's disease (PD) because of an expanding arsenal of antiparkinson drugs and our quest to alter the natural history of disease. Choice of initial therapy may prove fundamental to a treatment strategy that maximizes symptomatic control while minimizing the chances for long-term complications such as motor fluctuations and dyskinesias. Dopamine agonists (DA) have assumed a primary role in the early therapy of PD because of their antiparkinson effectiveness and low propensity to induce fluctuations and dyskinesias. Four available DA in the United States and an array of recent studies supporting their utility in early PD have shaped current PD management. Moreover, DA have neuroprotective properties in vivo. Nevertheless, levodopa remains the most effective drug for symptomatic control in PD. There is conflicting evidence regarding the putative neurotoxicity of levodopa and the mechanisms for levodopa-related motor fluctuations are not entirely known. Clinicians must therefore weigh the available evidence as they initiate therapy in PD. Clearly, both DA and levodopa will remain essential components of the early management of PD.

Diurnal motor variations to repeated doses of levodopa in Parkinson's disease

Patients with Parkinson's disease (PD) in long-term levodopa therapy often complain of worsening of motor symptoms in the afternoon and evening. The pathophysiology of this phenomenon is not known. We evaluated the motor response to repeated doses of levodopa during a 12-hour period in 52 parkinsonian patients (19 de novo, 20 stable, and 13 wearing-off). On the day of the study, all patients received standard doses of levodopa/carbidopa at 8:00 a.m., 12:00 noon, and 4:00 p.m. Motor measurements such as tapping test, walking time, and tremor score, and blood samples for levodopa and 3-O-methyldopa (3OMD) plasma analysis, were performed hourly. Mean motor scores and pharmacokinetic data, evaluated for a period of 3 hours after each levodopa dose, were compared. In de novo patients, we did not observe diurnal changes in motor score, whereas a progressive daytime worsening was visible in stable and wearing-off patients. No significant difference in levodopa pharmacokinetics after each levodopa dose was observed within each patient group, whereas 3OMD plasma levels significant increased with repeated levodopa administrations. However, no significant correlation between motor scores and 3OMD plasma levels was observed, suggesting that the diminishing motor response to afternoon and evening doses of levodopa in patients in long-term levodopa therapy does not relate to the pharmacokinetics of the drug. It is possible that this phenomenon may be an expression of the occurrence of tolerance to repeated doses of levodopa.

Motor fluctuations in Parkinson's disease: pathophysiology and treatment

At the initial stages of Parkinson's disease (PD), levodopa (LD) is able to reduce most motor symptoms and to significantly improve the patient's quality of life. However, in the vast majority of patients with prolonged LD usage, some decline in efficacy occurs and motor complications eventually begin to appear. These complications consist not only of daily fluctuations in the voluntary motor performance often accompanied by involuntary movements, but also of fluctuations in cognitive, autonomic, and sensory functions. Several recent studies on LD complications in PD have led to a better understanding of their pathophysiology and of the possible therapeutic interventions, and a summary of these findings is presented in this review. Different observations now suggest that postsynaptic pharmacodynamic factors play a major role in determining fluctuations in PD. Two explanations are given: chronic intermittent dopaminergic therapy may lead to postsynaptic receptor downregulation in PD; or, receptor changes in the striatum may occur independently of treatment as a result of structural adaptation of the postsynaptic dopaminergic system to the progressive decline of the nigrostriatal pathway. The hypothesis of reversible postsynaptic changes as the main mechanism underlying a fluctuating response to LD lends itself to a possible pharmacological manipulation of the dopaminergic response to reverse, or even avoid, motor fluctuations (initial monotherapy with dopamine agonists and early combination LD/dopamine agonists). The role of peripheral pharmacokinetics factors is also critical and the use of controlled release LD formulations, of monoamine oxidase (MAO)-B and of catechol-O-methyltransferase (COMT) inhibitors may all, to a different degree, improve such phenomena. In the last decade, there has been a resurgence in surgical therapies in advanced PD, due to higher levels of accuracy and safety provided by the new surgical devices, and to a more precise localization of the target areas allowed by the neurophysiological mapping techniques. The surgical procedures currently used in advanced PD are stereotactic brain lesions (internal globus pallidus and subthalamic nucleus), chronic brain stimulation (of the same nuclei) and striatal grafting of dopamine-producing cells. All these procedures have already shown their efficacy in the management of severe fluctuations in PD, but their indications, and relative advantages and disadvantages, are still the subject of considerable debate and controversy.