Catechol-O-methyltransferase inhibitors versus active comparators for levodopa-induced complications in Parkinson's disease

Priority setting partnership to identify the top 10 research priorities for the management of Parkinson's disease

OBJECTIVES

This priority setting partnership was commissioned by Parkinson's UK to encourage people with direct and personal experience of the condition to work together to identify and prioritise the top 10 evidential uncertainties that impact on everyday clinical practice for the management of Parkinson's disease (PD).

SETTING

The UK.

PARTICIPANTS

Anyone with experience of PD including: people with Parkinson's (PwP), carers, family and friends, healthcare and social care professionals. Non-clinical researchers and employees of pharmaceutical or medical devices companies were excluded. 1000 participants (60% PwP) provided ideas on research uncertainties, 475 (72% PwP) initially prioritised them and 27 (37% PwP) stakeholders agreed a final top 10.

METHODS

Using a modified nominal group technique, participants were surveyed to identify what issues for the management of PD needed research. Unique research questions unanswered by current evidence were identified and participants were asked to identify their top 10 research priorities from this list. The top 26 uncertainties were presented to a consensus meeting with key stakeholders to agree the top 10 research priorities.

RESULTS

1000 participants provided 4100 responses, which contained 94 unique unanswered research questions that were initially prioritised by 475 participants. A consensus meeting with 27 stakeholders agreed the top 10 research priorities. The overarching research aspiration was an effective cure for PD. The top 10 research priorities for PD management included the need to address motor symptoms (balance and falls, and fine motor control), non-motor symptoms (sleep and urinary dysfunction), mental health issues (stress and anxiety, dementia and mild cognitive impairments), side effects of medications (dyskinesia) and the need to develop interventions specific to the phenotypes of PD and better monitoring methods.

CONCLUSIONS

These research priorities identify crucial gaps in the existing evidence to address everyday practicalities in the management of the complexities of PD.

Network neighbors of drug targets contribute to drug side-effect similarity

In pharmacology, it is essential to identify the molecular mechanisms of drug action in order to understand adverse side effects. These adverse side effects have been used to infer whether two drugs share a target protein. However, side-effect similarity of drugs could also be caused by their target proteins being close in a molecular network, which as such could cause similar downstream effects. In this study, we investigated the proportion of side-effect similarities that is due to targets that are close in the network compared to shared drug targets. We found that only a minor fraction of side-effect similarities (5.8 %) are caused by drugs targeting proteins close in the network, compared to side-effect similarities caused by overlapping drug targets (64%). Moreover, these targets that cause similar side effects are more often in a linear part of the network, having two or less interactions, than drug targets in general. Based on the examples, we gained novel insight into the molecular mechanisms of side effects associated with several drug targets. Looking forward, such analyses will be extremely useful in the process of drug development to better understand adverse side effects.

A double-blind, randomized, placebo and active-controlled study of nebicapone for the treatment of motor fluctuations in Parkinson's disease

To determine the efficacy, safety and tolerability of nebicapone, a new catechol-O-methyltransferase inhibitor for the treatment of motor fluctuations in Parkinson's disease (PD), we conducted a multicenter, randomized, 8-week double-blind, placebo- and active-controlled, parallel-group study comparing nebicapone 50 mg, 100 mg, or 150 mg, entacapone 200 mg (active control) or placebo administered concomitantly with levodopa/carbidopa or levodopa/benserazide. Two hundred and fifty-two PD patients with motor fluctuations treated with levodopa/carbidopa or levodopa/benserazide (4-8 daily doses) were enrolled and 250 patients were eligible for intention-to-treat (ITT) analysis on the basis of having at least one efficacy assessment. The primary endpoint was 8-week change from baseline in absolute "Off" time duration noted in self-scoring diaries. At 8 weeks of treatment the mean daily "Off" time decreased significantly compared to placebo for nebicapone 150 mg (-106 min; 95%CI: -192; -21) and entacapone 200 mg (-81 min; 95%CI: -142; -19). The decrease in "Off" time with nebicapone 50 mg or 100 mg did not reach statistical significance. Treatment-emergent adverse events were reported by 32% to 49% of patients in any treatment group, with no observed dose relationship in the nebicapone groups. Clinically relevant elevations in aspartate transaminase (AST) and/or alanine transaminase (ALT) were observed in 4 of 46 patients with the nebicapone 150 mg dose. The results of this study show that nebicapone 150 mg is efficacious for the treatment of motor fluctuations in PD patients. However, the risk of increasing liver transaminases and its clinically relevance deserves further evaluation.

COMT inhibition with tolcapone in the treatment algorithm of patients with Parkinson's disease (PD): relevance for motor and non-motor features

Levodopa is the most effective treatment in Parkinson's disease and the association with COMT inhibitors widens its plasma bioavailability and effectiveness. Tolcapone is a potent COMT inhibitor whose utilization in PD is limited due to safety concerns on liver toxicity. However, recent data indicate that if liver function is actively monitored, tolerability is no worse than other currently available therapies. By contrast, administration of tolcapone is associated with significant clinical improvement and benefit involves also non-motor features. In this review we discuss the rationale for the use of tolcapone in association with levodopa and other treatments in PD, and we provide an indirect comparison of current strategies to reduce "off" time. We propose that future guidelines include a trial with tolcapone in all PD patients who continue to complain about motor fluctuations despite treatment with entacapone and/or MAO-B inhibitors. Moreover, we suggest that tolcapone should be considered before surgical or infusional strategies are applied.

Neuroprotection and pharmacotherapy for motor symptoms in Parkinson's disease

Parkinson's disease leads to major disability that impairs the quality of life of patients and leads to increased health-care costs. While there is no proven neuroprotective treatment, more basic-science research and clinical trials are needed to identify drugs that slow or halt the progression of the disorder. The mainstay of symptomatic treatment is levodopa. With long-term use, levodopa causes motor complications including involuntary movements and response fluctuations. These have lead to more cautious prescribing of levodopa. Dopamine agonists can be used as an alternative initial therapy to delay the onset of motor complications but at the expense of more dopaminergic adverse events, poorer control of motor symptoms, and increased cost. Once motor complications have developed, adjuvant therapy with dopamine agonists or entacapone can reduce off time and levodopa dose. Severe fluctuations that are not controlled by oral combination therapy can be controlled with subcutaneous apomorphine injections or infusions.