Amantadine and levodopa in the treatment of Parkinson's disease

Safety review of current pharmacotherapies for levodopa-treated patients with Parkinson's disease

INTRODUCTION

Levodopa remains the gold standard for treatment of Parkinson's disease (PD). Patients develop complications with disease progression, necessitating adjunctive therapy to control fluctuations in motor and non-motor symptoms and dyskinesia. Knowledge of medication safety and tolerability is critical to ascertain the benefit-risk ratio and select an adjunctive therapy that provides the highest chance for medication adherence. Posing a challenge are the sheer abundance of options, stemming from the development of several new drugs in recent years, as well as differences in commercial drug availability worldwide.

AREAS COVERED

This review evaluates the efficacy, safety, and tolerability of current US FDA-approved pharmacotherapies for levodopa-treated PD patients, including dopamine agonists, monoamine oxidase type-B inhibitors, catechol-O-methyltransferase inhibitors, the N-methyl-D-aspartate receptor antagonist amantadine, and the adenosine receptor antagonist istradefylline. Data were taken from pivotal phase III randomized controlled and post-surveillance studies, when available, that directly led to FDA-approval.

EXPERT OPINION

No strong evidence exists to support use of a specific adjunctive treatment for improving Off time. Only one medication has demonstrated improvement in dyskinesia in levodopa-treated PD patients; however, every patient cannot tolerate it and therefore adjunctive therapy should be tailored to an individual's symptoms and risk for specific adverse effects.

Andrade LA, Ferraz HB, Barbosa ER, Rieder CRDM, da Silva DJ, Chien HF, Capato T, Rosso AL, Souza Lima CF, Bezerra JMF, Nicaretta D, Povoas Barsottini OG, Godeiro-Júnior C, Broseghini Barcelos L, Gisbert Cury R, Spitz M, Azevedo Silva SMC, Della Colletta MV. Guidelines for Parkinson’s disease treatment: consensus from the Movement Disorders Scientific Department of the Brazilian Academy of Neurology - motor symptoms

ABSTRACT The treatment of Parkinson's disease (PD) is challenging, especially since it is considered highly individualized. The Brazilian Academy of Neurology has recognized the need to disseminate knowledge about the management of PD treatment, adapting the best evidence to the Brazilian reality. Thus, the main published treatment guidelines were reviewed based on the recommendations of group from the Movement Disorders Scientific Department of the Brazilian Academy of Neurology.

NMDA receptors in clinical neurology: excitatory times ahead

Since the N-methyl-D-aspartate receptor (NMDAR) subunits were cloned less than two decades ago, a substantial amount of research has been invested into understanding their physiological function in the healthy CNS. Research has also been directed at their pathological roles in various neurological diseases, including disorders resulting from acute excitotoxic insults (eg, ischaemic stroke, traumatic brain injury), diseases due to chronic neurodegeneration (eg, Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis), disorders arising from sensitisation of neurons (eg, epilepsy, neuropathic pain), and neurodevelopmental disorders associated with NMDAR hypofunction (eg, schizophrenia). Selective NMDAR antagonists have not produced positive results in clinical trials. However, there are other NMDAR-targeted therapies used in current practice that are effective for treating some neurological disorders. In this Review, we describe the evidence for the use of these therapies and provide an overview of drugs being investigated in clinical trials. We also discuss new NMDAR-targeted strategies in clinical neurology.

Amantadine in Parkinson's disease

BACKGROUND

Although levodopa is the most common drug prescribed to relieve the symptoms of Parkinson's disease it is associated with motor and psychiatric side-effects. Consequently, interest has turned to alternative drugs with improved side-effect profiles to replace or augment levodopa. Amantadine, originally used as an antiviral drug, has been shown to improve the symptoms of Parkinson's disease.

OBJECTIVES

To compare the efficacy and safety of amantadine therapy (monotherapy or adjuvant therapy) versus placebo in treating people with Parkinson's disease.

SEARCH STRATEGY

Electronic searches of The Cochrane Controlled Trials Register (The Cochrane Library Issue 3, 2001), MEDLINE (1966-2001), EMBASE (1974-2001), SCISEARCH (1974-2001), BIOSIS (1993-2001), GEROLIT (1979-2001), OLDMEDLINE (1957-1965), LILACS (1982-2001), MedCarib (17th Century - 2001), PASCAL (1973-2001), JICST-EPLUS (1985-2001), RUSSMED (1973-2001), DISSERTATION ABSTRACTS (2000-2001), SIGLE (1980-2001), ISI-ISTP (1990-2001), Aslib Index to Theses (2001), Clinicaltrials.gov (2001), metaRegister of Controlled Trials (2001), NIDRR (2001) and NRR (2001) were conducted. Grey literature was hand searched and the reference lists of identified studies and reviews examined. The manufacturers of amantadine were contacted.

SELECTION CRITERIA

Randomised controlled trials comparing amantadine with placebo in the treatment of patients with a clinical diagnosis of idiopathic Parkinson's disease.

DATA COLLECTION AND ANALYSIS

Data was abstracted independently by NC and KD onto standardised forms and disagreements were resolved by discussion.

MAIN RESULTS

Six randomised controlled trials were found comparing amantadine monotherapy or adjuvant therapy with placebo in the treatment of idiopathic Parkinson's disease. Five examined amantadine as adjuvant therapy with optimal levels of levodopa or anticholinergics and one examined amantadine as an adjuvant therapy with minimum tolerated levels of anticholinergics or as a monotherapy. Five were double-blind cross-over studies and one was a double-blind parallel group study. In total they examined 215 patients. The parallel group study allowed the randomisation codes to be broken and allowed patients in the placebo group to then receive amantadine. This could have led to bias. One study did not present the results of the placebo arm of the trial, hence we could not determine the difference between the two treatment groups. Two cross-over studies presented the results of the combined data from both treatment and placebo arms. The risk of carry-over effect into the second arm meant that these results could not be analysed. The final two studies presented at least some of their data from the end of the first arm of the trials. However only means were given, without standard deviations, so we could not determine the statistical significance of any difference between the amantadine and placebo groups. Although the authors did report on the side-effects from amantadine (such as livido recticularis, dry mouth and blurred vision), they state that none of them were severe.

REVIEWER'S CONCLUSIONS

A considerable amount of evidence on the effectiveness of amantadine has accrued from non-controlled trials, often in patients with Parkinsonian conditions other than idiopathic Parkinson's disease. However, rigorous analysis of the six randomised controlled trials of amantadine reveals insufficient evidence of its efficacy and safety in the treatment of idiopathic Parkinson's disease.

Parkinson's disease: Cogentin with Sinemet, a better response

1. A randomized, placebo controlled, double-blind cross-over study was conducted to evaluate the clinical efficacy of the anticholinergic agent, benztropine mesylate (CogentinR) in 29 patients with mild to moderate, idiopathic Parkinson disease. 2. Patients were maintained on a stable, therapeutically optimal dosage and schedule of levadopa-carbidopa (Sinemet) throughout the study. 3. Both the neurologist's and the patient's global assessments of treatment efficacy indicated that Sinemet plus benztropine mesylate resulted in significantly greater improvement than Sinemet plus placebo. 4. Qualitative and quantitative evaluations of relevant neurologic functions showed small, but statistically significant improvements for rigidity, finger tapping speed and activities of daily living in patients during the Sinemet plus benztropine mesylate treatment period. 5. At the completion of the study 16 patients chose to continue taking benztropine mesylate as an adjuvant to Sinemet. 6. No important adverse side effects occurred during the study.

Human neurologic function and the aging process

Sixty-one normal men whose ages ranged from 20 to 80 years were evaluated on two occasions by means of a comprehensive series of 128 instrumented tests of neurologic function. The tests measured cognition, vision, strength, steadiness, reactions, speed, coordination, fatigue, gait, station, sensations, and tasks of daily living. The reliability of each test measured was determined, and any measure found unreliable (r less than or equal to 0.41) was not further analyzed. Significant age-related linear decreases were found for almost all neurologic functions. The declines over the age span varied from less than 10 percent to more than 90 percent for different functions. For the upper extremities, the largest declines (greater than 50 percent) were in hand-force steadiness, speed of hand-arm movements, and vibration sense; for the lower extremities, the largest declines were in one-legged balance with eyes closed and in vibration sense. For 13 of 14 tests in which significant dominant body-side effects were found, larger re-testing 7-10 days later, the subjects improved their scores by more than 5 percent on only 17 tests, 9 of which concerned the activities of daily living. No significant differential learning effects were found across age groups. The results point to the importance of developing a data bank on age-based neurologic function so that therapeutic effects can be evaluated in terms of age- and sex-matched normal functioning.