Pharmacogenetics of antiparkinsonian drug treatment: a systematic review

Causes and factors related to dopamine agonist withdrawal in Parkinson's disease

BACKGROUND

Although dopamine agonists (DAs) are useful in Parkinson's disease (PD), they are not frequently used in elderly patients due to adverse effects. However, there is a lack of evidence because few elderly PD patients are enrolled in clinical trials.

AIMS OF THE STUDY

The aims of this study were to analyze the reasons of DA withdrawal (DAW) in a group of PD patients in clinical practice and to identify the related factors. Specifically, we studied the effect of age, comorbidity, and polypharmacy as potential risk factors for DAW.

METHODS

A retrospective chart review of the follow-up (from May, 2012 to March, 2015) of a subgroup of PD patients receiving a DA (n = 68; 60.3% males, 69.3 ± 9.2 years old) from a cohort (n = 150) previously studied in detail in 2012 was used to identify predictive factors of DAW.

RESULTS

The DAW percentage was 18.2% (12/66; follow-up of 690.2 ± 232.6 days). DAW causes were cognitive impairment (3), reduction therapy (3), hallucinations (2), dyskinesia (2), and excessive diurnal somnolence (2). Only a higher levodopa daily dose (HR 1.003; 95% CI 1.001-1.006; P = 0.044) was an independent predictor of DAW after adjustment for other explanatory variables.

CONCLUSIONS

The frequency of DAW was low. Advanced age alone is not a contraindication to the administration of DAs.

[A current view on dopamine receptor agonists in the treatment of Parkinson's disease]

Dopamine receptor agonists (DRA) is a widely used group of antiparkinsonian drugs. The article presents short results: related to the mechanism of the stimulation of different types of dopamine receptors. The advantages of this group of drugs compared to levodopa medications as well as the studies of DRA in vitro and in vivo are described. Multiple studies demonstrate an important role of DRA in the treatment of Parkinson's disease (PD): a good control of motor symptoms, the possibility of monotherapy in the early stages of disease, the reduced risk of motor complications compared to start therapy with levodopa and decrease in the duration of "OFF-period" and UPDRS scores as well as the possibility to reduce the dose of levodopa in case of combined treatment with levodopa containing preparations. Pramipexole has demonstrated the efficacy in the treatment of persistent tremor and depression in double-blind placebo-controlled trials. A significant improvement of quality of life index has been shown in PD patients treated with these drugs. Side-effects often limited the use of DRA in clinical practice. The data on the dose equivalence of different DRA are recommended to use if it is necessary to switch from one DRA to another.

Pharmacogenetics of drug response in Parkinson's disease

Parkinson's disease (PD) is a debilitating, demoralizing and financially devastating condition affecting 1% of population at the age of 60 years. Thus, very important issue to address is individual therapy optimization. Recent results have shown evidence that variable efficacy of treatment and risk of motor and mental complications could have genetic origin. Significant roles in that process play (pharmaco)genomic/genetic studies of PD. Variability in genes coding for drug-metabolizing enzymes, drug receptors and proteins involved in drug pathway signaling is an important factor determining inter-individual variability in drug responses. Interpersonal differences in drug responses are clearly documented although individualized treatment of PD is not widely known. Treatment with antiparkinsonian drugs is associated with the development of complications, such as L-DOPA-induced dyskinesia (LID), hallucinations and excessive daytime sleepiness. Carriers of specific genetic polymorphisms are particularly susceptible to development of some of these drug adverse effects. Pharmacogenomics aims to understand the relationship between genetic factors and inter-individual variations in drug responses, and to translate this information in therapy tailored to individual patient genetics. Relatively few efforts have been made to investigate the role of pharmacogenetics in the individual response to anti-PD drugs. Thus, many genetic variations and polymorphisms in myriad of different proteins can influence individual response to anti-PD drugs.

DRD2 haplotype is associated with dyskinesia induced by levodopa therapy in Parkinson's disease patients

AIM

Dyskinesia and motor fluctuation are frequent and serious complications of chronic levodopa therapy in patients with Parkinson's disease. Since genetic factors could play a role in determining the occurrence of these problems, the aim of the present study was to investigate whether possible functional polymorphisms among DRD2 and ANKK1 genes are associated with the risk of developing dyskinesia and motor fluctuations in Parkinson's disease patients.

PATIENTS & METHODS

One hundred and ninety nine patients in treatment with levodopa were genotyped for the -141CIns/Del, rs2283265, rs1076560, C957T, TaqIA and rs2734849 polymorphisms at the DRD2/ANKK1 gene region.

RESULTS

Carriers of the TTCTA haplotype showed an increased risk for the presence of dyskinesia (p = 0.007; 1.538 [95% CI: 1.126-2.101]).

CONCLUSION

Our data suggest an influence of the DRD2/ANKK1 gene region on levodopa-induced dyskinesia.

Pharmacological treatment and the prospect of pharmacogenetics in Parkinson's disease

Parkinson disease (PD) is a progressive movement disorder marked by tremor, rigidity, bradykinesia and postural instability. Levodopa (l-dopa), usually combined with a peripheral dopa decarboxylase inhibitor, has been proved to provide the best symptomatic benefit for PD. However, its long-term efficacy is limited because of motor complications and drug-induced dyskinesia. Dopamine agonists, catechol-O-methyltransferase inhibitors and monoamine oxidase-B inhibitors are anti-parkinsonian (anti-PD) drugs that have been found to further improve the potency of l-dopa and prevent the onset of motor complications. However, as PD is a progressive disorder, all the drugs used for its therapy, manifest reduced efficacy and adverse effects with time. Research on the field of pharmacogenetics has pointed out that the genetic variability of each individual determines to a large extent the inter-individual variability in response to anti-PD drugs. Clinicogenetic trials show that drug efficacy or toxicity or susceptibility to side effects are features governed by genetic principles. This article is a review of the present pharmacological treatment of PD and current pharmacogenetic data for PD.

An update expert opinion on management and research strategies in Parkinson's disease psychosis

INTRODUCTION

Psychosis, a frequent complication in Parkinson's disease (PD), contributes significantly to morbidity, mortality, nursing-home placement and quality of life. Medication side effects, issues of trial design and negative outcomes have limited clinical advances of new treatments for PD psychosis. Evidence-based medicine maintains clozapine as the most effective antipsychotic in PD without motor worsening, despite risk of agranulocytosis. Safe, effective treatments that improve psychosis without exacerbating parkinsonism are urgently needed.

AREAS COVERED

This article reviews the: i) phenomenology of PD psychosis, ii) pharmacological rationale for antipsychotics in PD; iii) clinical trials of antipsychotics in PD; iv) novel research strategies such as neuroimaging, genetics and animal models; and v) associated challenges in studying and treating PD psychosis. Preparation of this review included an extensive literature search using PubMed.

EXPERT OPINION

Management of PD psychosis is complex. Challenges pertaining to study design, rating scales, subject recruitment and completion have limited PD psychosis treatment trials. Novel research strategies focus on nondopaminergic systems and incorporate neuroimaging, genetic associations and animal models. These strategies also have challenges but have the potential to enhance our understanding of PD psychosis and advance the development of agents that can ultimately be tested in well-designed, randomized, controlled trials.

Clinical and pharmacogenetic determinants for the discontinuation of non-ergoline dopamine agonists in Parkinson's disease

Objective

To identify determinants for the discontinuation of non-ergoline dopamine agonist (DA) treatment in patients with Parkinson’s disease (PD) and to identify genetic determinants in genes encoding dopamine receptor (DR)D2 and DRD3 in a exploratory analysis.

Methods

Patients included were first-time users of the non-ergoline DA ropinirole or pramipexole who had been diagnosed with PD before 2005. Treatment discontinuation was defined as a gap of 180 days or more between two refills of the DA. Non-genetic determinants for discontinuation were studied in the overall population, and genetic determinants [DRD2 141C Ins/Del, DRD2 (CA)_n STR, DRD2 TaqIA, DRD3 MscI single nucleotide polymorphism (SNP) and DRD3 MspI SNP] were studied in a subgroup. Cox proportional hazard analysis was used to estimate the hazard ratios (HR) for the discontinuation of non-ergoline DA treatment.

Results

The study population comprised 90 patients. Apomorphine use was associated with non-ergoline DA discontinuation, although the apomorphine group consisted only of three patients [HR 6.26; 95% confidence interval (CI) 1.85–21.2]. Daily levodopa dosages between 500 and 1000 mg were positively associated with discontinuation (HR 2.31; 95% CI 1.08–4.93). Included in the exploratory pharmacogenetic analysis were 38 patients. The absence of a 15× DRD2 CA repeat allele was significantly related with a decreased discontinuation of non-ergoline treatment (HR 0.23; 95% CI 0.07–0.81). The DRD3 MspI polymorphism showed a non-significant allele dose effect, suggestive of a causal relationship.

Conclusion

This study identified apomorphine use and levodopa dosages between 500 and 1000 mg as non-genetic and the 15× DRD2 CA repeat allele as genetic determinants for the discontinuation of non-ergoline DA treatment in patients with PD. More research is needed to replicate these findings.

New thoughts on thought disorders in Parkinson's disease: review of current research strategies and challenges

Psychosis is a frequent nonmotor complication in Parkinson's disease (PD), characterized by a broad phenomenology and likely due to a variety of intrinsic (i.e., PD-related) and extrinsic factors. Safe and effective therapies are greatly needed as PD psychosis contributes significantly to morbidity, mortality, nursing home placement, and quality of life. Novel research strategies focused on understanding the pharmacology and pathophysiology of PD psychosis, utilizing translational research including animal models, genetics, and neuroimaging, and even looking beyond the dopamine system may further therapeutic advances. This review discusses new research strategies regarding the neurobiology and treatment of PD psychosis and several associated challenges.

Generic versus branded pharmacotherapy in Parkinson's disease: does it matter? A review

There is an ongoing debate about generic drug use for a multitude of conditions including epilepsy, psychosis, hypertension, post-organ transplantation, and several infectious diseases. Most of the concerns involve drugs with narrow therapeutic indices. There is a heightened attention to health care costs and macroeconomic policy as well as microeconomic business decisions that may impact the use of generic drugs. The issues surrounding generic substitution for chronic degenerative conditions such as in Parkinson's disease (PD) continue to be controversial subjects for physicians, pharmacists, patients, Medicare/governmental insurance programs, and for private insurance companies. The United States Food and Drug Administration (FDA) requires that generic drugs meet a standard for bioequivalence prior to market approval, but this may not translate to therapeutic efficacy or to overall patient tolerance. In this review we will address issues related to the use of generics versus branded drugs in PD, and the potential impact substitution of generics may have on patients and on clinicians. Having proper documentation may help in deciding the appropriate usage of these drugs in PD. Medicare, governmental run health care systems, and third party insurance companies should in a complex disease such as PD, allow physicians and patients the chance to properly document the superiority of brand versus generic approaches. Currently, in the U.S, and in many countries around the world, there is no obligation for payers to respect these types of patient specific bedside trials, and there has been no standardization of the process.

Association of the DRD2 and DRD3 polymorphisms with response to pramipexole in Parkinson's disease patients

OBJECTIVE

To evaluate the impact of the DRD2 TaqIA and DRD3 Ser9Gly polymorphisms on the efficacy of pramipexole in treating patients with Parkinson's disease (PD).

METHODS

Thirty patients with PD prospectively received pramipexole 0.25 mg three times daily for 2 months. Unified Parkinson Disease Rating Scale (UPDRS) assessments were conducted at baseline and 2 months after treatment initiation. Improvement by 20% or more in the total score on the UPDRS was considered to indicate responsiveness. The PCR-restriction fragment length polymorphism analysis was used to analyze the DRD2 Taq1A and DRD3 Ser9Gly genotype.

RESULTS

The DRD2 Taq1A allele frequencies were A141.7 (A1) and 58.3% (A2), and the DRD3 Ser9Gly allele frequencies were 68.3 (Ser) and 31.7% (Gly). When the subjects were grouped by the DRD3 Ser9Gly polymorphism, the response rates for pramipexole treatment were significantly higher in the Ser/Ser group (60%) than in the group containing the Gly allele (13%). There was a significant association between the DRD3 Ser9Gly polymorphism and response rate to pramipexole in PD patients (P = 0.024). When the subjects were grouped by the DRD2 Taq1A polymorphism, there were no significant differences among the three Taq1A genotypes.

CONCLUSIONS

DRD3 Ser9Gly polymorphisms are significantly associated with the therapeutic efficacy of pramipexole in Chinese patients with PD. A large-scale and multi-dose group study in patients with PD is necessary for evaluating the impact of the genetic polymorphisms of the dopamine receptor on the therapeutic effects of pramipexole.

Discontinuation of ropinirole and pramipexole in patients with Parkinson's disease: clinical practice versus clinical trials

OBJECTIVE

To compare characteristics and incidence of discontinuation of Parkinson's disease (PD) patients starting ropinirole or pramipexole in clinical practice with data from randomised controlled clinical trials (RCTs).

METHODS

Included in the retrospective clinical-practice cohort were first-time users of ropinirole or pramipexole diagnosed with PD before 2005. Baseline characteristics and incidence of discontinuation were compared between the clinical-practice cohort and RCTs. Treatment discontinuation was defined as more than 180 days between two refills of ropinirole or pramipexole. The incidence of discontinuation in RCTs was based on the reported rate of discontinuation for any cause.

RESULTS

Included were 45 patients who started with ropinirole and 59 patients who started with pramipexole. Treatment was discontinued within 3 years in 51% (ropinirole) and 60% (pramipexole) of the patients. Ten RCTs with ropinirole and 12 with pramipexole were identified. Baseline characteristics did not differ between the clinical-practice cohort and RCTs. RCTs reported discontinuation rates comparable with those at the same timepoint in the clinical practice until 1 year of follow-up.

CONCLUSION

This study shows that the overall incidence of discontinuation of ropinirole and pramipexole between the patients in our clinical-practice cohort and patients in the RCTs was comparable for the short term. However for the long term, discontinuation in practice is possibly higher.

Molecular pathways and genetic aspects of Parkinson's disease: from bench to bedside

Idiopathic Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by dopaminergic neuronal loss within the substantia nigra. The incidence and prevalence of PD is rising with an increasing aging population. PD is a slowly progressive condition and patients can develop debilitating motor and functional impairment. Current research has implicated oxidative stress, alpha-synucleinopathy and dysfunction of the ubiquitin-proteasome system in the pathogenesis of PD. A number of gene mutations have also been linked to the development of PD. The elucidation of these new molecular pathways has increased our knowledge of PD pathophysiology. This article reviews important molecular mechanisms and genetic causes implicated in the pathogenesis of PD, which has led to new areas of therapeutic drug research.