Continuous Dopaminergic Stimulation Research Articles

Effects of Continuous Dopaminergic Stimulation on Parkinson's Disease Gait: A Longitudinal Prospective Study with Levodopa Intestinal Gel Infusion.

Gait issues, including reduced speed, stride length and freezing of gait (FoG), are disabling in advanced phases of Parkinson's disease (PD), and their treatment is challenging. Levodopa/carbidopa intestinal gel (LCIG) can improve these symptoms in PD patients with suboptimal control of motor fluctuations, but it is unclear if continuous dopaminergic stimulation can further improve gait issues, independently from reducing Off-time. To analyze before (T0) and after 3 (T1) and 6 (T2) months of LCIG initiation: a) the objective improvement of gait and balance; b) the improvement of FoG severity; c) the improvement of motor complications and their correlation with changes in gait parameters and FoG severity. This prospective, longitudinal 6-months study analyzed quantitative gait parameters using wearable inertial sensors, FoG with the New Freezing of Gait Questionnaire (NFoG-Q), and motor complications, as per the MDS-UPDRS part IV scores. Gait speed and stride length increased and duration of Timed up and Go and of sit-to-stand transition was significantly reduced comparing T0 with T2, but not between T0-T1. NFoG-Q score decreased significantly from 19.3±4.6 (T0) to 11.8±7.9 (T1) and 8.4±7.6 (T2) (T1-T0 p = 0.018; T2-T0 p < 0.001). Improvement of MDS-UPDRS-IV (T0-T2, p = 0.002, T0-T1 p = 0.024) was not correlated with improvement of gait parameters and NFoG-Q from T0 to T2. LEDD did not change significantly after LCIG initiation. Continuous dopaminergic stimulation provided by LCIG infusion progressively ameliorates gait and alleviates FoG in PD patients over time, independently from improvement of motor fluctuations and without increase of daily dosage of dopaminergic therapy.

Effectiveness of Continuous Dopaminergic Therapies in Parkinson’s Disease: A Review of L-DOPA Pharmacokinetics/Pharmacodynamics

Background: Parkinson’s disease (PD) is characterized by striatal dopamine deficiency. Since dopamine cannot cross the digestive and blood-brain barriers, its precursor, levodopa (L-DOPA), remains the mainstay of treatment. However, the significant pharmacokinetic (Pk) and pharmacodynamic (Pd) limitations of L-DOPA, combined with the severity of PD, may trigger motor and non-motor complications, for which continuous dopaminergic delivery therapies have been developed. Objective: The aim of this study was to review the literature on the Pk/Pd limitations of L-DOPA and how current treatments of continuous dopaminergic administration ameliorate these problems, in order to identify the need for new therapeutic avenues. Methods: A comprehensive literature search was carried out using PubMed and 75 articles were initially extracted. Following independent screening by two reviewers and consideration of eligibility, 10 articles were chosen for further analysis. Information concerning the Pk/Pd of L-DOPA was classified for each article. Results: Pk/Pd problems notably include: (i) restricted digestive and cerebral absorption; (ii) unnecessary peripheral distribution; (iii) short half-life; (iv) age- and PD-induced decline of central aromatic L-amino acid decarboxylase; (v) misdistribution in many cells; and (vii) pulsatile stimulation of dopaminergic receptors. Current treatments only slightly ameliorate some of these problems. Conclusions: Many Pk/Pd constraints are not resolved by existing continuous dopaminergic delivery therapies. This highlights the significant gap between these treatments and the ideal of continuous dopaminergic stimulation.

Levodopa-Carbidopa-Entacapone Intestinal Gel in Advanced Parkinson Disease: A Multicenter Real-Life Experience.

For Parkinson disease (PD) patients who have been diagnosed with advanced disease that can no longer be effectively controlled with optimized oral or transdermal medications, a range of device-aided therapies (DAT) are available, comprising either deep brain stimulation or infusion therapies providing continuous dopaminergic stimulation. Levodopa-entacapone-carbidopa intestinal gel (LECIG) infusion is the latest DAT for advanced PD (APD) that was approved in Romania in 2021. What is the experience to date in real-world clinical practice in Romania regarding the efficacy and tolerability of LECIG in APD? A retrospective evaluation of 74 APD patients treated with LECIG at 12 specialized APD centers in Romania. Demographic data and various clinical parameters were recorded, including Mini Mental State Evaluation score or Montreal Cognitive Assessment Test score. Levodopa-equivalent daily dose and the administered doses of levodopa and other PD medications were evaluated at baseline and after starting LECIG treatment. The efficacy of LECIG in reducing daily hours of off time, motor fluctuations, and dyskinesias were assessed. Any percutaneous endoscopic gastrojejunostomy system or device complications after starting LECIG treatment were noted. At baseline, patients were taking oral levodopa for a mean of 5.3 times per day, with a high proportion also taking concomitant add-on therapies (dopamine agonists, 86%, monoamine oxidase type-B inhibitors, 53%; catechol-O-methyltransferase inhibitors, 64%). LECIG treatment significantly reduced daily off time versus baseline from 5.7 h/d to 1.7 hours per day ( P < 0.01). Duration and severity of dyskinesias was also significantly reduced versus baseline, and improvements were observed in Hoehn and Yahr Scale scores. LECIG treatment also allowed a significant reduction in the use of concomitant oral medications. These findings suggest that LECIG treatment is an effective DAT option in APD that can simplify the treatment regimen.

A study of the genotoxicity, fertility and early embryonic development toxicity of rotigotine behenate extended-release microspheres.

Continuous dopaminergic stimulation (CDS) has become an important strategy for the development of drugs to treat Parkinson's disease (PD). Rotigotine behenate extended-release microspheres (RBEM) for injection represent a new treatment regime for CDS and are undergoing clinical trials. In this study, we aimed to investigate the effect of RBEM on genotoxicity, fertility and early embryonic development. We used the Ames test, Chinese hamster lung (CHL) cell chromosome aberration test and the mouse bone marrow micronucleus test, to evaluate the genotoxicity of RBEM. These tests were all negative, thus indicating that RBEM did not induce genotoxicity. In reproduction toxicity testing in male rats on obvious findings following intramuscular administration (i.m.) of RBEM at up to 540 mg/kg (P > 0.5), when female rats were administered with RBEM in the dose range of 60 to 540 mg/kg given (i.m.), there were clear effects on fertility and early embryonic development. These results indicated that RBEM could induce toxicity in female rats and exert effect on fertility and early embryonic development stage.

The effect of rasagiline on swallowing function in Parkinson's disease

Dysphagia, a potentially fatal symptom of Parkinson's disease, is characterized by frequent silent aspiration, a risk factor for aspiration pneumonia. The transdermal dopamine agonist rotigotine alleviates dysphagia in patients with Parkinson's disease and is more effective than oral levodopa, suggesting the importance of continuous dopaminergic stimulation during swallowing. Rasagiline is a monoamine oxidase B (MAOB) inhibitor that facilitates continuous dopaminergic stimulation. We hypothesized that MAOB inhibition by rasagiline would be effective in improving swallowing function in patients with early- and mid-to late-stage Parkinson's disease. To this end, we performed an analytical observational study to determine the effects of rasagiline (1 mg/day) on swallowing function using videofluoroscopic swallowing study. This open-label, evaluator-blinded study enrolled 32 patients with Parkinson's disease, among whom 19 were drug-naïve and 13 were receiving add-on therapy. Our results showed that rasagiline significantly improved all swallowing measures during the oral and pharyngeal phases, including oral transit time and pharyngeal transit time, in all enrolled patients. Similar results were found in drug-naïve and mid-to late-stage patients, with no intergroup differences. In conclusion, drugs capable of continuous dopaminergic stimulation may effectively improve swallowing function in patients with Parkinson's disease, with similar effects in early- and mid-to late-stage Parkinson's disease. This study has been the first to show that rasagiline significantly improves swallowing function in mid-to late-stage patients receiving add-on therapy.

A video-atlas of levodopa-induced dyskinesia in Parkinson's disease: terminology matters.

Dyskinesia is a common complication of long-term levodopa therapy in patients with Parkinson's disease (PD), which often worsens the quality of life. It is usually dose-dependent and emerges possibly due to pulsatile stimulation of dopamine receptors. Delineating the pattern of dyskinesia is crucial for determining the most effective therapeutic approach, a task that often presents challenges for numerous neurologists. This article comprehensively describes various patterns of dyskinesia in PD patients and features video demonstration of some of the common forms of dyskinesia. We have used a real case scenario as an example to lead the discussion on the phenomenology, distinguishing features, and management of various types of dyskinesia. A comprehensive literature search was conducted in PubMed using "dyskinesia" as a keyword. The prototype case with videos highlights the differentiating features of dyskinesia along with the treatment strategies. A wide range of descriptive rubrics have been used for certain dyskinesia which are described in detail in this article. The newer types of dyskinesia associated with continuous dopaminergic stimulation in patients with advanced PD and their implications have been described. As there are distinct ways of managing various types of dyskinesia, understanding the phenomenology and chronology of dyskinesia is vital for the optimal management of dyskinetic PD patients. We suggest that dyskinesia should be classified broadly into peak-dose dyskinesia (PDD), biphasic dyskinesia (BD), and OFF-period dystonia. The occurrence of low-dose dyskinesia and complex dyskinesia of continuous dopaminergic treatments should be known to specialists and will require additional studies.

Should continuous dopaminergic stimulation be a standard of care in advanced Parkinson's disease?

The standard of care is a term that refers to the level of care, skill, and treatment that a healthcare provider should offer to a patient based on the current scientific evidence and the level of medical knowledge available in the field. For Parkinson's disease (PD), the standard care is mostly considered to be oral treatment with dopaminergic drugs, particularly levodopa which remains the 'gold standard'. However, effective management with levodopa during the later stages of the disease becomes increasingly challenging due to the ongoing neurodegenerative process, the consequences of its pulsatile dopaminergic stimulation, and the gastrointestinal barriers to effective drug absorption. As a result, the concept of applying continuous dopaminergic stimulation has emerged with infusion therapies (continuous subcutaneous apomorphine, levodopa-carbidopa intestinal gel, and levodopa-entacapone-carbidopa intestinal gel infusion). These therapies seek to provide continuous stimulation of striatal dopamine receptors that is efficient not only in alleviating clinical symptoms, but also in delaying, reducing, and possibly preventing the onset of levodopa-related motor (fluctuations, dyskinesia) and non-motor complications; and they are also associated with clinically relevant side effects. Clinical studies and real-life experience support the notion that infusion therapies should be accepted as part of the standard of care for patients with advanced PD who have refractory, severe, and disabling motor complications that affect their quality of life. However, they should be considered based on the needs of individualized patients and the access to these advanced therapies needs to be made more accessible to the general PD population.

Access to device-aided therapies in advanced Parkinson's disease: navigating clinician biases, patient preference, and prognostic uncertainty.

Device-aided therapies (DAT), which include deep brain stimulation and pump-based continuous dopaminergic stimulation with either levodopa or apomorphine, are among the major advances in the clinical management of Parkinson's disease (PD). Although DAT are being increasingly offered earlier in the disease course, their classical indication remains advanced PD. Theoretically, every patient should be offered transition to DAT when faced with refractory motor and nonmotor fluctuations and functional decline. Worldwide clinical reality is far from these ideal, and, therefore, question the "real-world" equal opportunity of access to DAT for PD patients with advanced PD-even within a single health care system. Differences in access to care, referral pattern (timing and frequency), as well as physician biases (unconscious/implicit or conscious/explicit bias), and patients' preferences or health-seeking behaviour are to be considered. Compared to DBS, little information is available concerning infusion therapies, as well as neurologists' and patients' attitudes towards them. This viewpoint aims to be thought-provoking and to assist clinicians in moving through the process of DAT selection, by including in their decision algorithm their own biases, patient perspective, ethical concerns as well as the current unknowns surrounding PD prognosis and DAT-related long-term side effects for a given patient.

The effects of safinamide on dysphagia in Parkinson's disease.

Dysphagia is a potentially fatal symptom of Parkinson's disease (PD) and is characterized by frequent silent aspiration, a risk factor for aspiration pneumonia. The transdermal dopamine agonist rotigotine alleviates dysphagia in patients with PD and is more effective than oral levodopa, suggesting the importance of continuous dopaminergic stimulation (CDS) in swallowing. Safinamide is a monoamine oxidase B (MAOB) inhibitor that facilitates CDS. In this retrospective open-label evaluator-blinded research, swallowing functions in nine patients with PD were examined using a video fluoroscopic swallowing study (VFSS) before and after treatment with 50 mg of oral safinamide. The VFSS results showed that safinamide significantly improved some swallowing measures during oral and pharyngeal phases, including oral transit time and pharyngeal transit time, without worsening of any measures. Notably, improvements in lip closure, an oral phase component, seemed to be most attributable to improvements in oral phase scores. In conclusion, a medicine for CDS may effectively improve swallowing functions in patients with PD. This is the first study to show that the MAOB inhibitor safinamide partly but significantly improves swallowing function in patients with PD.

Tailoring Motor Fluctuation Treatment: Beyond Levodopa Dose Adjustment

Susan Fox opened this satellite symposium at the 8th European Academy of Neurology (EAN) Congress with an overview of the concept of motor fluctuations (MF) in Parkinson’s disease (PD). She emphasised that levodopa remains the gold standard therapy for PD. However, MFs are one of the critical complications of levodopa therapy that affect many patients with advancing PD and, when diagnosed, represent a challenge in patient management. Alternative options are, therefore, needed to provide continuous dopaminergic stimulation while maximising the levodopa benefit. Despite different options, Angelo Antonini showed that neurologists often prefer to adjust levodopa dose rather than add an adjunctive agent. Market research confirms that, in patients with PD, the levodopa dose is adjusted in around 80% of patients, while only 20% have adjunct therapy as a first-line option. Adjusting the levodopa dose, either by increasing or fractionating the dose, or both, remains a valid, tried-and-tested option, although it has limitations. Joaquim Ferreira presented emerging evidence from a Phase II clinical trial, suggesting a potential benefit of adding opicapone 50 mg compared with 100 mg levodopa to treat patients with PD and end-of-dose fluctuations. This symposium aimed to present the effect of opicapone with relatively low total daily doses of levodopa; an option that may not have been traditionally considered by neurologists who are used to adjusting levodopa as a first-line response.

Continuous dopaminergic stimulation counteracts L-DOPA-induced overactivity of Ca2+ in 6-OHDA-lesioned rats.

In the clinical treatment of Parkinson's disease (PD), the emergence of L-DOPA-induced dyskinesia (LID) and other motor symptoms remains a restrictive factor for the use of levodopa (L-DOPA). Our objective was to test the effect of continuous dopaminergic stimulation (CDS) on LID and the mechanism of its effect on the calcium (Ca2+) signaling pathway. 6-OHDA (6-hydroxydopamine)-treated rats were administered 1% CMC-Na, L-DOPA, rotigotine behenate (RGTB), and L-DOPA + RGTB, respectively, for 28days. During the treatment, the abnormal involuntary movement (AIM) scores were conducted on days 1, 5, 10, 14, 19, 23 and 28 after the first dose. Subsequently, the number of tyrosine hydroxylase (TH)-positive neurons was detected by immunohistochemistry. Additionally, the changes in Ca2+ were detected using a laser confocal technique, and the related proteins, such as neuronal NOS (nNOS), BAX, BCL2, CaMKII, P-CaMKII, and PSD-95, were measured by Western blot. Transmission electron microscopy (TEM) was used to investigate the changes in synaptic structure. The data showed that CDS reduced the AIM scores, increased the expression of TH in the substantia nigra (SN), decreased the expression of nNOS and BAX/BCL2ratio in the striatum, reduced the Ca2+ influx induced by L-DOPA and inhibited the Ca2+ signaling pathways of dopamine neurons in the striatum. Moreover, the overactivity of synapses induced by L-DOPA was inhibited by CDS. These data further support the hypothesis that continuous delivery of a dopamine agonist reduces the risk of LID induction. Moreover, RGTB could be a promising treatment for PD by simulating CDS.

Parkinson's Disease with Intolerable Painful Dystonia: Classification and Therapeutic Choices of Pain in Parkinson' Disease

Disabling painful dystonia is one of the most burdensome symptoms that a patient with Parkinson's disease (PD) experiences. How do we treat disabling painful dystonia in PD? In this review, classification and mechanisms of pain and their management in PD especially for dystonia-related pain are described. Moreover, painful bilateral dystonic foot spasm is also an important development to be considered in the early stage of the disease. Recent classification of pain in PD does not involve this symptom, partly because this symptom is relatively unobserved due to early initiation of treatment in PD patients. Treatment options for dystonia-related pain are diverse and are necessarily contingent on the cause of dystonia in PD. Reducing L-dopa and other drugs is useful for patients with on-dystonia and dyskinesia-related pain in PD. Increasing L-dopa and other drugs are better for early morning dystonia and off-period dystonia-related pain in PD. Finally, as severe and troublesome painful dystonia is often challenging to treat, continuous dopaminergic stimulation such as treatment with levodopa-carbidopa intestinal gel is considered effective for these symptoms.

Continuous Dopaminergic Stimulation Improves Cortical Maladaptive Changes in Advanced Parkinson's Disease.

With the progression of Parkinson's disease (PD), pulsatile treatment with oral levodopa causes maladaptive changes within basal ganglia-thalamo-cortical circuits, which are clinically expressed as motor fluctuations and dyskinesias. At the level of the motor cortex, these changes may be detected using transcranial magnetic stimulation (TMS), as abnormal corticospinal and intracortical excitability and absent response to plasticity protocols. We investigated the effect of continuous dopaminergic stimulation on cortical maladaptive changes related to oral levodopa treatment. Twenty patients with advanced PD were tested using TMS within 1 week before and again 6 months after the introduction of levodopa-carbidopa intestinal gel. We measured resting and active motor thresholds, input/output curve, short interval intracortical inhibition curve, cortical silent period, and response to intermittent theta burst stimulation. Patients were clinically assessed with Part III and Part IV of the Movement Disorders Society Unified Parkinson's Disease Rating Scale. Six months after the introduction of levodopa-carbidopa intestinal gel, motor fluctuations scores (P = 0.001) and dyskinesias scores (P < 0.001) were reduced. Resting and active motor threshold (P=0.012 and P = 0.015) and x-intercept of input/output curve (P=0.005) were also decreased, while short-interval intracortical inhibition and response to intermittent theta bust stimulation were improved (P=0.026 and P=0.031, respectively). Changes in these parameters correlated with clinical improvement. In patients with advanced PD, switching from intermittent to continuous levodopa delivery increased corticospinal excitability and improved deficient intracortical inhibition and abnormal motor cortex plasticity, along with amelioration of motor fluctuations and dyskinesias. Continuous dopaminergic stimulation ameliorates maladaptive changes inflicted by chronic pulsatile dopaminergic stimulation. © 2022 International Parkinson and Movement Disorder Society.

Cabergoline, a long-acting dopamine agonist, attenuates L-dopa-induced dyskinesia without L-dopa sparing in a rat model of Parkinson’s disease

Intermittent administration of L-dopa in Parkinson’s disease is associated with L-dopa-induced dyskinesia (LID). Long-acting dopamine agonists may reduce the risk of LID by continuous dopaminergic stimulation. We examined the LID-like behavior, preprodynorphin messenger ribonucleic acid (mRNA) expression in the striatum (a neurochemical LID hallmark), and the volume of the entopeduncular nucleus (a pathological LID hallmark) in Parkinson’s disease rat models that were treated with L-dopa and cabergoline. Cabergoline co-treatment with L-dopa reduced LID, striatal preprodynorphin mRNA expression, and hypertrophy of the entopeduncular nucleus, indicating that cabergoline has an anti-LID effect independent of the L-dopa-sparing effect.

Levodopa-entacapone-carbidopa intestinal gel infusion in advanced Parkinson's disease: real-world experience and practical guidance.

As Parkinson’s disease (PD) progresses, treatment needs to be adapted to maintain symptom control. Once patients develop advanced PD, an optimised regimen of oral and transdermal medications may no longer provide adequate relief of OFF periods and motor complications can emerge. At this point, patients may wish to consider a device-aided therapy (DAT) that provides continuous dopaminergic stimulation to help overcome these issues. Levodopa–entacapone–carbidopa intestinal gel (LECIG) infusion is a recently developed DAT option. The aim of this article is twofold: (1) to give an overview of the pharmacokinetics of LECIG infusion and clinical experience to date of its use in patients with advanced PD, including real-world data and patient-reported outcomes from a cohort of patients treated in Sweden, the first country where it was introduced, and (2) based on that information to provide practical guidance for healthcare teams starting patients on LECIG infusion, whether they are transitioning from oral medications or from other DATs, including recommendations for stepwise dosing calculation and titration. In terms of clinical efficacy, LECIG infusion has been shown to have a similar effect on motor function to standard levodopa–carbidopa intestinal gel (LCIG) infusion but, due to the presence of entacapone in LECIG, the bioavailability of levodopa is increased such that lower overall levodopa doses can be given to achieve therapeutically effective plasma concentrations. From a practical standpoint, LECIG infusion is delivered using a smaller cartridge and pump system than LCIG infusion. In addition, for patients previously treated with LCIG infusion who have an existing percutaneous endoscopic transgastric jejunostomy (PEG-J) system, this is compatible with the LECIG infusion system. As it is a relatively new product, the long-term efficacy and safety of LECIG infusion remain to be established; however, real-world data will continue to be collected and analysed to provide this information and help inform future clinical decisions.

Праміпексол пролонгованого вивільнення — нові можливості тривалої дофамінергічної стимуляції при хворобі Паркінсона

Найважливішим підходом до дофамінергічної стимуляції при хворобі Паркінсона (ХП) є застосування агоністів дофамінових рецепторів (АДР). Порівняно з препаратами леводопи АДР характеризуються меншим ризиком розвитку лікарських дискінезій і моторних флуктуацій, відсутністю необхідності метаболізації в головному мозку й встановленим в експерименті нейропротективним потенціалом. Одним з найбільш ефективних препаратів цієї групи є праміпексол — синтетичне похідне бензотіазолу (тетрагідробензотіазол). Праміпексол є потужним агоністом D2-рецепторів з максимальною спорідненістю до підтипу D3-рецепторів. Стимуляція D2-рецепторів базальних гангліїв забезпечує ефект препарату щодо рухових проявів захворювання, у той час як стимуляція D3-рецепторів лімбічної системи зменшує немотор-ні прояви, у тому числі позитивно впливає на нейропсихологічний статус і зменшує ступінь вираженості депресивного синдрому у хворих із ХП. Ефективність праміпексолу доведена численними дослідженнями як на ранніх стадіях ХП — як монотерапії, так і на розгорнутих стадіях — у поєднанні з препаратами леводопи. Із розвитком захворювання схема його лікування ускладнюється за рахунок збільшення кількості прийнятих препаратів і кратності їх прийому. Це неминуче створює проблему недостатньої прихильності пацієнтів до лікування. У зв’язку з цим розроблена нова лікарська форма праміпексолу — праміпексол пролонгованої дії, що забезпечує його тривале вивільнення й допускає одноразовий прийом протягом дня. Це не тільки робить лікування хворого більш зручним, але й покращує прихильність пацієнтів до лікування, підвищує довгострокову ефективність терапії. Крім того, при повільному вивільненні праміпексолу протягом доби досягається більш стабільна його концентрація в крові, що може забезпечити кращу переносимість і ефективний контроль симптомів захворювання протягом усього дня (як у денний, так і в нічний час).

Biphasic (Subtherapeutic) Levodopa-Induced Respiratory Dysfunction in Parkinson Disease.

To evaluate 3 cases illustrating a rarely recognized phenotype of Parkinson disease (PD), namely, biphasic levodopa-induced respiratory dysfunction manifesting as dyspnea. To appreciate the nature of the fluctuations of respiratory function in response to levodopa, we measured changes in respiratory muscle control before and after the best therapeutic response to levodopa in 3 PD patients with fluctuating dyspnea. Episodes of breathlessness were accompanied by shallow tachypnea and reduced respiratory muscle control, as measured by maximal expiratory pressure, peak cough flow, and forced expiratory volume in 1 second. The spectrum of respiratory dysfunction in PD includes a biphasic reduced respiratory muscle control accompanying periods when the effect of levodopa is subtherapeutic. This biphasic levodopa-related complication represents a rarely recognized nonmotor phenomenon in PD. Management requires increasing the levodopa dose, shortening the interdose interval, or implementing a program of continuous dopaminergic stimulation.

L-DOPA products for continuous dopaminergic stimulation

L-DOPA products for continuous dopaminergic stimulation

Continuous Dopaminergic Stimulation as a Treatment for Parkinson's Disease: Current Status and Future Opportunities

Levodopa-induced motor complications remain an important source of disability for many patients with Parkinson's disease. Substantial laboratory evidence indicates that motor complications relate to the nonphysiological restoration of brain dopamine with intermittent doses of standard oral levodopa. Dopamine levels are normally maintained at a relatively constant level, even following a dose of levodopa. However, in the Parkinsonian state, where dopamine terminals have degenerated with a loss of their buffering capacity, intermittent doses of levodopa lead to dramatic peak and trough fluctuations in striatal dopamine levels. This results in pulsatile stimulation of dopamine receptors, molecular changes in striatal neurons, physiological changes in pallidal neurons, and ultimately the development of motor complications. These observations led to the hypothesis that continuous delivery of levodopa might be associated with a reduced risk of motor complications. This concept is known as continuous dopamine stimulation (CDS). Preliminary studies in animal models and patients with Parkinson's disease supported this hypothesis, suggesting a reduced risk of both motor fluctuations and dyskinesias. The present review considers the scientific advances and the more definitive clinical trials testing this concept that have taken place during the past decade and considers ongoing experimental studies and future opportunities. © 2020 International Parkinson and Movement Disorder Society.

Infusion Therapies for Parkinson's Disease.

Advanced Parkinson's disease (APD) is marked by significant motor and non-motor complications affecting the patient's quality of life. Optimization of standard oral therapies (SOT) at some point fails to provide adequate relief. Among the available device-aided therapies, infusion therapies (IT) work on the rationale that continuous striatal dopaminergic stimulation can significantly reduce the motor fluctuations and smoothen the treatment response. This review serves to familiarize readers with available IT for APD with a focus on motor and non-motor effects, and safety. Several recent longitudinal studies have demonstrated a reduction in OFF and an equivalent increase in ON time with the use of levodopa-carbidopa intestinal gel infusion (LCIG). Additionally, the benefit is noted on dyskinesia and non-motor symptoms. Similarly, backed by long-term clinical experience and open-label studies, a recent double-blind trial validates the efficacy of continuous subcutaneous apomorphine infusion (CSAI). Both IT are accompanied by a high rate of mild to moderate adverse events (AE) that can influence patient selection and clinical utility. While device and procedure-related AE are common for LCIG, infusion site reactions dominate the CSAI AE. IT are a viable and superior alternative for APD over SOT. Both therapies provide meaningful improvement of the motor fluctuations with a positive impact on the quality of life.