Infusion Therapies in the Treatment of Parkinson’s Disease

INTRODUCTION

Levodopa is the most effective therapy in treating Parkinson’s disease (PD) [1–3]. However, as the disease progresses, loss of striatal dopamine nerve terminals and diminished dopamine buffering capacity occurs [2–5]. Delayed gastric emptying associated with dysautonomia may also alter plasma levodopa bioavailability and contribute to an unpredictable response to oral therapy [6–8]. As a result, motor and/or non-motor fluctuations can occur in which patients alternate between good clinical efficacy (“On” time) and inadequate clinical efficacy (“Off” time) [3]. Levodopa-related fluctuations in PD are associated with non-physiological, discontinuous, or pulsatile stimulation of striatal dopamine receptors and can lead to unwanted motor symptoms known as dyskinesias [3, 9].

Dopamine agonists, catechol-O-methyltransferase inhibitors, and monoamine oxidase-B inhibitors can be added to treatment regimens to prolong oral levodopa efficacy, reduce “Off” time, and improve motor disability [1, 6]. However, polypharmacy and numerous doses may result in reduced treatment adherence [10] and additional side effects [1, 3, 11].

Infusion and surgical therapies offer an alternative to oral medication for patients with advanced PD (aPD) if symptoms are inadequately controlled [12–15], and recent European Academy of Neurology/Movement Disorder Society guidelines indicate alternative therapies can be considered for aPD with fluctuations not sufficiently managed with oral treatments [16]. Invasive surgical therapy, such as deep brain stimulation is an alternative intervention that has been extensively studied in patients with aPD with fluctuations and is recommended as a potential therapeutic option for patients with aPD [16]; however, deep brain stimulation is outside of the scope of this review. The present review provides an up-to-date overview of the efficacy of infusion therapies in patients with aPD, focuses on tools to identify patients who may benefit from these therapies, and provides considerations around optimal use of these therapies.

OVERVIEW OF EXISTING INFUSION THERAPIES

OVERVIEW OF EMERGING INFUSION THERAPIES

Additional infusion therapies such as once a week subcutaneous infusion of dopamine agonists or agents such as exenatide are under development and investigation while intracerebral infusion of trophic factors such as glial cell-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) have been examined.

Foslevodopa/foscarbidopa (previously known and referred to as ABBV-951) is a new soluble formulation of carbidopa and levodopa prodrugs delivered as a 24-hour/day continuous subcutaneous infusion by an infusion set connected to a portable pump [52–54]. On delivery to the body, foslevodopa/foscarbidopa is rapidly converted to the pharmacologically active levodopa/carbidopa via alkaline phosphatases, quickly reaching and maintaining steady-state therapeutic levels of plasma levodopa [52]. Foslevodopa/foscarbidopa has the potential to offer an efficacious and minimally invasive alternative therapy for patients with aPD and is undergoing approval by the FDA. Most AEs reported were non-serious and mild or moderate in severity [52–54]. Data from the pivotal study on the efficacy of 24-hour/day foslevodopa/foscarbidopa at week 12 revealed a significant (p = 0.0083) increase in hours of “On” time without troublesome dyskinesia and “Off” time compared to oral immediate-release levodopa-carbidopa [54].

ND0612 is a liquid formulation of levodopa-carbidopa delivered subcutaneously by a similar pump system as CSAI [55]. Patients may receive the infusion either continuously (24 hours) or during waking hours only [56]. ND0612 has an adequate safety profile and most patients treated with ND0612 have reported mild to moderate AEs [57]. Continuous administration of ND0612 elevated and sustained plasma levodopa to therapeutic levels, and 28-day intervention significantly improved motor symptoms from baseline to post-treatment in patients with aPD (“Off” time: p <  0.01; “On” time with dyskinesia: p <  0.001) [55, 56].

Infudopa is another soluble combination of levodopa and carbidopa that may be administered via intravenous injection, short-term intravenous infusion, and long-term subcutaneous infusion [58]. In a phase 1 clinical trial, patients presented with elevated and stable levels of plasma levodopa after a 16-hour subcutaneous infusion of infudopa [59]. Limited data on tolerability are available, but in the few patients who received subcutaneous infudopa infusion and presented with AEs, these events were mild to moderate [59, 60].

IDENTIFYING PATIENTS WITH ADVANCED PARKINSON’S DISEASE WHO MAY BENEFIT FROM INFUSION THERAPY

A large multicenter observational study— OBSERVE-PD (OBSERVational, cross-sEctional PD)— acquired data from 2615 patients with PD in 18 countries and reported that only 43.6% of patients who met the criteria for aPD and were eligible for advanced treatment, were actually receiving it [61]. Although timely intervention with advanced treatment may result in better outcomes and improved QoL [13, 62, 63], international consensus on definitive diagnostic criteria for aPD and identification of patients who may benefit from advanced treatment is an unmet need in clinical practice [61, 64].

Some progress has been made on defining aPD. In 2018, a Delphi-panel approach was utilized to gain consensus from 17 leading movement disorders specialists on 15 clinical indicators for suspected aPD and seven eligibility criteria for device-aided therapies, considering motor and non-motor symptoms and functional impairments [62]. A retrospective analysis of the clinical indicators of aPD and device-aided therapy eligibility found all indicators demonstrated high clinical screening accuracy for identifying patients with aPD and determining those who were eligible to receive advanced treatment [65]. Further, OBSERVE-PD reported a moderate correlation (K = 0.430; 95% confidence interval 0.406–0.473) between physician’s judgment and the 2018 consensus criteria in 2615 patients [61]. Specific indicators of aPD included taking at least five oral levodopa doses per day, at least 2 hours of “Off” time per day, and at least 1 hour per day with troublesome dyskinesia, giving rise to the “5-2-1” criteria [62, 66]. A post-hoc analysis of data from a multicountry observational study of patients (N = 4714) with physician-identified aPD found that 33% of patients met the 5-2-1 screening criteria, with greater than 75% concordance between clinician judgment and the 5-2-1 criteria [66].

The MANAGE-PD (Making Informed Decision to Aid Timely Management of Parkinson’s Disease) tool, based on the Delphi consensus [62], is another instrument to help physicians identify patients who are not receiving adequate symptom control and may benefit from advanced treatment [67]. MANAGE-PD accounts for the impact of motor symptoms and non-motor symptoms and classifies patients into three categories regarding their current treatment regimen: 1) controlled with current therapy, 2) inadequately controlled with current therapy but may benefit from non– device-aided optimization, and 3) inadequately controlled with current treatment but may benefit from device-aided therapy [67]. The agreement between MANAGE-PD outcomes and ratings from PD specialists (as assessed by intra-class correlation coefficient) suggests that MANAGE-PD is a valid tool and complements physicians’ decision-making related to treatment optimization [67].

CONSIDERATIONS AROUND OPTIMAL USE OF INFUSION THERAPY

Key areas for a successful infusion therapy include effective patient education; meticulous patient care and comprehensive assessments; interprofessional communication; and collaboration between patients, their caregivers, and knowledgeable and competent nurses [68].

While proper timing of infusion therapy is crucial for aPD treatment success, treatment also poses a challenge because of the numerous factors that influence the choice of therapy— including local availability and the differences among treatment centers, ranging from clinical experience to reimbursement [69]. The general recommendation is to initiate therapy before major disability occurs. For this reason, it is advised to start discussing advanced treatment with patients early in the disease course, preferably when motor fluctuations start to occur but are still manageable with modifications of oral dopaminergic therapy [69].

As initiation of infusion therapy is a highly individualized decision and often requires joint decision-making, patients and their caregivers are encouraged to actively participate in the process. Patient participation in decision-making concerning therapy positively correlates with patient satisfaction and adherence, and contributes to positive outcomes [70]. Joint decision-making involves assessing patients’ and their families’ expectations for the treatment, educating them about realistic treatment outcomes and symptoms that are more likely to improve, answering their questions, and giving the patient an active role in the process [70]. Unfortunately, many patients with aPD are reluctant to change their therapy regimen despite fulfilling the criteria for “advanced” therapies [61]. In one study nearly 38% of patients eligible for device-aided treatments reported no plan to use it, citing “needing more time to decide” (39%) and “refusal” (25%) as the two main reasons the eligible patients did not plan for advanced therapy [61]. A consensus guidance document was published on the “Navigate PD” pan-European educational program, which was developed to supplement existing guidelines, and provides insight on the many nuances of infusion therapy and patient management [13]. Considering emerging infusion therapies in the near future, treatment options for patients with aPD may expand to efficacious non-surgical subcutaneous therapy for controlling fluctuations [54].

Education on the most frequent AEs and common reasons for discontinuing each therapeutic option are also important aspects for patients and caregivers to consider in the decision-making process (Table 4) [70]. Patients and their families should be educated on caregiver burden and the resources that are available to them [71–73]. The lack of a caregiver may represent a challenge for patients considering infusion therapy, although this is somewhat dependent on local care facilities and services available [69, 74].

Multidisciplinary teams that include the treating neurologist, a PD nurse specialist, geriatrician, physical therapist, occupational therapist, speech therapist, nutritionist, and psychologist may improve treatment success, enhance QoL and ADL, provide strategies to support mental health, and ensure optimal nutrition [75, 76]. Positive outcomes require the commitment of all parties involved— patient, care provider, treating neurologist, and PD nurse specialist— who are crucial in complementing the therapeutic efforts of the rest of the team [70, 75]. PD nurse specialists play a key role in assisting patients and caregivers with their needs, as well as providing individual support, education, access to services, and coordination of care [77]. In this regard, PD nurse specialists can be a bridge of communication between the treating neurologist and the patient, helping improve therapy adherence [78]. By supporting individuals throughout all disease stages, PD nurse specialists can also contribute to the timely initiation of advanced care planning discussions, resulting in increased treatment initiation and reduced treatment discontinuations [70, 79]. Use of telemedicine may facilitate the communication between medical providers and patients, reduce commute time to attend in-person visits, and facilitate the implementation of home-based multidisciplinary care [80].

The literature on aftercare programs for patients with PD, and their influence on long-term adherence to infusion therapy, and on caregivers’ burden, is scarce. Studies have analyzed the reasons patients discontinue infusion therapies and found important factors that can increase therapeutic adherence and long-term benefits of infusion therapy. These include clinician experience in selecting and treating patients with aPD, the presence of a well-trained caregiver, and the availability of a proper aftercare system [81–83].

CONCLUSIONS

This review summarizes the benefits of infusion therapy in patients with aPD and outlines considerations around its optimal use. Although a lack of consensus around the identification of aPD represents an ongoing challenge, and advanced treatments are underused in aPD, new tools or simple criteria have been proposed to assist clinicians in advanced disease staging and patient classification for infusion therapy eligibility. Several studies show that patient and physician acceptance of infusion therapies may become less of a barrier with appropriate multidisciplinary management and proper patient education, especially with the key contributions made by PD nurse specialists.