Gender and pramipexole effects on levodopa pharmacokinetics and pharmacodynamics

The role of autophagy in Parkinson's disease: a gender difference overview

Recent studies have demonstrated dysregulation of the autophagy pathway in patients with Parkinson's disease (PD) and in animal models of PD, highlighting its emerging role in disease. In particular, several studies indicate that autophagy, which is an essential degradative process for the damaged protein homeostasis and the management of cell balance, can manifest significant variations according to gender. While some evidence suggests increased autophagic activation in men with PD, women may have distinct regulatory patterns. In this review, we examined the existing literature on gender differences in PD-associated autophagic processes, focusing on the autophagy related proteins (ATGs) and leucine rich repeat kinase 2 (LRRK2) genes. Also, this review would suggest that an in-depth understanding of these gender differences in autophagic processes could open new perspectives for personalized therapeutic strategies, promoting more effective and targeted management of PD.

Exploring gender differences in pharmacokinetics of central nervous system related medicines based on a systematic review approach

Due to the inevitable differences in physiological and/or genetic factors between genders, the possibility that differences in pharmacokinetics between genders may occur when exposed to the same dose of the same drug is subject to reasonable inference and suspicion. Nevertheless, a significant number of medicines still rely on empirical usage and uniform clinical application without consideration of inter-individual diversity factors. In particular, in the pharmacokinetic diversity of medicines related to central nervous system (CNS) activity, consideration of gender factors and access to comparative analysis are very limited. The purpose of this study was to conduct an integrated analysis and review of differences in pharmacokinetics between genders that have not been specifically reported to date for medicines related to CNS effects, which are a group of drugs with relatively significant concerns about systemic side effects. This study was accessible through extensive data collection and analyzes using a web-based scientific literature search engine of pharmacokinetic results of CNS-related drugs performed on humans, taking gender into account. As a result, significant differences in pharmacokinetics between genders were identified for many drugs related to CNS. And most of the pharmacokinetic differences between genders suggested a higher in vivo exposure in females. This study suggests that consideration of gender factors cannot be ignored and will be an important point of interest in the precision medicine application of CNS-related medicines.

To restrict or not to restrict? Practical considerations for optimizing dietary protein interactions on levodopa absorption in Parkinson's disease

Administration of levodopa for Parkinson's disease (PD) has remained the most effective therapy for symptom management despite being in use for over 50 years. Advancing disease and age, changing tolerability and gastrointestinal (GI) dysfunction may result in change in dietary habits and body weight, as well as unpredictable motor fluctuations and dyskinesias. Dietary proteins which convert into amino acids after digestion are implicated as major factors that inhibit levodopa absorption. For people living with PD (PwP) who experience motor fluctuations, low protein diets (LPD) and protein redistribution diets (PRD) may be effective and are often recommended as a non-pharmacologic approach for improving levodopa bioavailability. However, there is a lack of consensus on a standard definition of these diets and appropriate treatment algorithms for usage. This may be due to the paucity of high-level evidence of LPD and PRD in PwP and whether all or specific subgroups of patients would benefit from these strategies. Managing diet and protein intake with proper education and monitoring may reduce complications associated with these diets such as dyskinesias and unintentional weight loss. Additionally, alterations to medications and GI function may alter levodopa pharmacokinetics. In this narrative review we focus on 1) mechanisms of dietary protein and levodopa absorption in the intestine and blood brain barrier, 2) dietetic approaches to manage protein and levodopa interactions and 3) practical issues for treating PwP as well as future directions to be considered.

Sex Is the Main Determinant of Levodopa Clinical Pharmacokinetics: Evidence from a Large Series of Levodopa Therapeutic Monitoring

BACKGROUND

Different studies, mostly with limited cohorts, have suggested the effects of patients' characteristics on levodopa (LD) pharmacokinetics.

OBJECTIVE

We primarily aimed at investigating in a large population the relationship between patients' features and LD kinetic variables, to assess the main demographic and clinical predictors of LD clinical pharmacokinetics.

METHODS

The study was retrospective, based on data collected from subjects with parkinsonism on chronic LD undergoing LD therapeutic monitoring (TM). LD TM includes serial quantitative motor tests and blood samples to measure plasma drug concentrations after each subject's chronically taken first-morning LD dose intake.

RESULTS

Five hundred patients, 308 males (61.6%), mean (SD) age of 65 (10.1) years were included. Parkinsonian symptoms and LD therapy lasted 5.5 (4.5) and 3.4 (3.9) years, respectively. MDS-UPDRS part III "off" score was 28.8 (15.2). LD dose was 348.2 (187.1) mg/day. From multiple linear regression analysis, test dose, sex, type of LD decarboxylase inhibitor, weight and MDS-UPDRS part III score were linear predictors of both LD peak plasma concentration (Cmax) (R2 = 0.52) and area under the 3-h plasma concentration-time curve (AUC) (R2 = 0.71), while age was a further predictor only for AUC. Besides test dose, sex was the strongest independent contributing variable to LD AUC, which resulted 27% higher in females compared to males.

CONCLUSION

This is the largest collection of data on the relationship between demographic and clinical-therapeutic variables and LD kinetics in patients with parkinsonian symptoms. As a main clinically practical finding, women might require a 25% reduced weight-normalized LD dose compared with men to achieve the same LD bioavailability.

Sex and gender differences in movement disorders: Parkinson's disease, essential tremor, dystonia and chorea

Sex and gender-based differences in epidemiology, clinical features and therapeutical responses are emerging in several movement disorders, even though they are still not widely recognized. In this chapter, we summarize the most relevant evidence concerning these differences in Parkinson's disease, essential tremor, dystonia and chorea. Indeed, both sex-related biological (hormonal levels fluctuations) and gender-related variables (socio-cultural and environmental factors) may differently impact symptoms manifestation and severity, phenotype and disease progression of movement disorders on men and women. Moreover, sex differences in treatment responses should be taken into account in any therapeutical planning. Physicians need to be aware of these major differences between men and women that will eventually have a major impact on better tailoring prevention, treatment, or even delaying progression of the most common movement disorders.

Gender Differences in Levodopa Pharmacokinetics in Levodopa-Naïve Patients With Parkinson's Disease

Background

Levodopa (LD) is the most effective drug in the treatment of Parkinson’s disease (PD). Unfortunately, prolonged use of LD leads to complications, mainly motor/non-motor fluctuations (MNMF) and dyskinesias (DYS). Women seem more prone to develop such LD-related complications. Nonetheless, there is a paucity of prospective studies examining gender-related predictors of MNMF and DYS. Among several factors, which concur with a very complex scenario, changes in LD pharmacokinetics influence the drug’s effectiveness. The present study aimed to assess gender-related differences in LD pharmacokinetics in patients with PD at their first-ever intake of LD.

Materials and Methods

This is a multicentric study enrolling patients with PD, who were LD-naïve and received a single dose of LD/benserazide (100/25 mg) formulation. All participants gave their written informed consent, and the study was approved by the local Ethics Committees. To measure plasma LD concentrations and pharmacokinetic parameters (AUC, Cmax, Tmax, t_1/2), fasting blood samples were collected before drug intake and then at 8-time points until 260 min. LD concentrations were measured by ultra-high-performance liquid chromatography coupled with mass spectrometry (UHPLC-MS). Multiple linear regression analyses were performed to identify the predictors of the parameters.

Results

Thirty-five patients (16 women and 19 men) were consecutively enrolled. Area under curve (AUC) and maximum plasma concentration (Cmax) were significantly higher in women than men (p = 0.0006 and p = 0.0014, respectively). No statistically significant difference was found regarding Tmax and t_1/2. Multiple linear regression analyses revealed that female sex (β = 1.559116, 95% CI 0.8314479 2.286785; p < 0.0001) and body mass index (BMI) (β = −0.0970631, 95% CI −0.1733004 −0.0208258; p = 0.014) significantly predicted AUC. Only female sex significantly predicted Cmax (β = 1,582.499, 95% CI 731.581 2,433.417; p = 0.001). Moreover, only BMI significantly predicted t_1/2 (β = 0.0756267, 95% CI 0.0143407 0.1369126; p = 0.017). Stratifying by gender, BMI was confirmed to significantly predict t_1/2 in women (β = 0.1300486, 95% CI 0.0172322 0.242865; p = 0.027), but not in men.

Conclusion

This study provides novel insights on gender differences in LD pharmacokinetics, possibly contributing to the later development of motor complications and dyskinesia in PD.

Safety considerations when using non-ergot dopamine agonists to treat Parkinson's disease

INTRODUCTION

Nonergot dopamine agonists (NEDA) represent an excellent treatment option for Parkinson's disease (PD) patients, in both early and advanced stages of the disease. The post-marketing phase of NEDA has highlighted, though, the occurrence of important long-term adverse events.

AREAS COVERED

This review reports recent updates on NEDA adverse events, analyzing neurobiological bases and risk factors of these complications. A literature search has been performed using Medline and reviewing the bibliographies of selected articles.

EXPERT OPINION

NEDA represents a very important option in the treatment of PD. Criticisms on their use can be overcome through a better knowledge of these molecules and of the risk factors for adverse events which allow specialists to prevent the occurrence of undesired complications and consent a tailor-based approach. Abbreviations: PD: Parkinson's disease, DA: dopamine agonists, NEDA: non-ergot dopamine agonists, ICD: impulse control disorders, DAWS: dopamine agonist withdrawal syndrome, CYP: Cytochrome P, PK: pharmacokinetic, AUC: area under the curve, HRT: hormone replacement therapy, AV: atrioventricular, HF: heart failure, OH: orthostatic hypotension, RBD: REM behavior disorders, PDP: Parkinson's disease psychosis, DRT: dopamine replacement therapy, DDS: dopamine dysregulation syndrome, MMSE: Mini-Mental state examination, EDS: excessive daytime somnolence.

Female, aging, difference formulations of DCI, or lower body weight increases AUC4hr of levodopa in patients with Parkinson's disease

INTRODUCTION

There is considerable intra- and inter-individual variability in the pharmacokinetics (PK) of levodopa after oral administration. Inter-individual variability in levodopa PK has also been demonstrated in fasting single-dose studies. We examined the factors that affect levodopa PK in patients with Parkinson's disease (PD) and quantified the intensity of their respective effects.

METHODS

We studied 220 patients who underwent PK assessment after administration of 1 tablet of levodopa/DOPA decarboxylase inhibitor (DCI) combination, which contained 10 mg carbidopa/100 mg levodopa or 25 mg benserazide/100 mg levodopa. PK was evaluated using non-compartmental analysis.

RESULTS

In total, 220 PD patients (including 112 men) were studied. The mean age (±standard deviation) and mean disease duration was 68.1 ± 8.9 and 7.7 ± 5.8 years, respectively. The Cmax of levodopa was 9.0 ± 4.0 ng/mL, Tmax was 41.4 ± 40.2 min, and area under the blood concentration-time curve up to 4 h (AUC_4hr) was 12.3 ± 3.7 ng/mL*4hr. Factors affecting AUC_4hr were analyzed using multiple linear regression models. Age (1.1 ± 0.23 per +10 years, p = 3.1E-8), sex (2.2 ± 0.5 for female, p = 1.9E-5), DCI (1.4 ± 0.4 for benserazide, p = 0.0028), and body weight (-0.77 ± 0.22 per +10 kg, p = 5.4E-4) were significantly related to AUC_4hr, while disease duration, dyskinesia status, and eGFR were not related to AUC_4hr and Cmax.

CONCLUSION

Female, aging, difference formulations of DCI, or lower body weight independently contributes to increased AUC_4hr of levodopa in Japanese patients with PD in this study.

Comparative examination of levodopa pharmacokinetics during simultaneous administration with lactoferrin in healthy subjects and the relationship between lipids and COMT inhibitory activity in vitro

Background: Lactoferrin (bLF) is an iron-binding multifunctional protein that is abundant in milk. In mice, it inhibits catechol-O-methyltransferase (COMT) activity and increases blood levodopa levels. However, the clinical effects are unknown.Objective: The objective of this study was to determine the effect of bLF on the kinetics of levodopa in blood.Design: The effects of the concomitant administration of a combined formulation of levodopa and an aromatic amino acid decarboxylase inhibitor and bLF on the concentration of levodopa in blood and its metabolism were assessed in eight healthy subjects. In addition, we analyzed the association with clinical factors and evaluated whether clinical factors affected the COMT inhibitory activity of bLF in vitro.Results: Although not statistically significant, the peak plasma concentration (C_max) of levodopa increased by 18.5%. From the results of the stratified analysis of total cholesterol, a relationship with ΔC_max was predicted. Therefore, bLF was reacted with cholesterol in the presence of lecithin and sodium deoxycholate in vitro to evaluate COMT inhibitory activity, and an increase in inhibitory activity was observed. By contrast, the ester compound cholesteryl oleate had no effect. The inhibitory activity of free fatty acids, which are known to interact with bLF, was also enhanced.Conclusion: The COMT inhibitory activity of bLF is not effective in elevating blood levodopa levels. However, in humans with high lipid levels, such as cholesterol, interactions may enhance the inhibitory effect, resulting in the enhanced absorption of levodopa.Trial registration: ID, UMIN000026787, registered 30 March 2017; URL, https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000030749Trial registration: UMIN Japan identifier: UMIN000026787.

Sex-Dependent Improvement in Survival of Parkinson's Disease Patients

Background

Advances in the treatment of Parkinson's disease (PD) and changes in general life expectancy may have improved survival in patients with PD.

Objective

The objective of this study was to investigate recent trends in PD mortality.

Methods

In total, 1521 patients with PD in local and national registries were followed for 11 years (2006-2016) from diagnosis until exit date or death, and the causes of death were recorded.

Results

The survival of men with PD improved during the follow-up period, but no change was observed in women (2-year postdiagnosis survival in men, 79.0%-86.3%, P = 0.03; 2-year postdiagnosis survival in women, 82.8%-87.5%, P = 0.42). Pneumonia was the most common immediate cause of death.

Discussion

The survival of men with PD has improved in Finland without a similar change in women. Because changes in treatment likely affect both sexes similarly, the results may reflect the decreasing sex gap in life expectancy. This phenomenon will likely increase the already high male-to-female prevalence ratio of PD.

Safety of Levodopa-Carbidopa Intestinal Gel Treatment in Patients with Advanced Parkinson's Disease Receiving ≥2000 mg Daily Dose of Levodopa

Background

Levodopa-carbidopa intestinal gel (LCIG) provides continuous levodopa administration and clinical benefits to patients with advanced Parkinson's disease (PD). This report evaluates long-term safety and efficacy of high-dose LCIG in PD patients.

Methods

Data were collected from several prospective, phase III clinical studies and an observational registry. The phase III program (N = 412) included four multicenter studies: a 12-week, randomized, double-blind study and three open-label studies extending ≥12 months. GLORIA (N = 412) included four multicenter studies: a 12-week, randomized, double-blind study and three open-label studies extending ≥12 months. GLORIA (.

Results

A total of 72 of 412 (17.5%) patients required dosages ≥2000 mg/day LCIG in the phase III program and 47 of 375 (12.5%) patients in GLORIA. Baseline demographics and disease severity were similar between dosage groups with more men in the high-dosage group. Compared with the <2000 mg/day dosage group, patients requiring ≥2000 mg/day LCIG had higher rates of AEs/ADRs including polyneuropathy; improvements in "Off" time and discontinuations due to AEs were similar between dosage groups and lower for discontinuations due to ADRs reported in GLORIA.

Conclusions

Patients who require ≥2000 mg/day LCIG exhibited a safety profile comparable to the established safety/tolerability of LCIG with similar clinical improvements. Higher AEs were noted but within what is accepted for LCIG. Continuous administration of LCIG is beneficial to advanced PD patients who require very high doses of levodopa.

Sex differences in movement disorders

In a range of neurological conditions, including movement disorders, sex-related differences are emerging not only in brain anatomy and function, but also in pathogenesis, clinical features and response to treatment. In Parkinson disease (PD), for example, oestrogens can influence the severity of motor symptoms, whereas elevation of androgens can exacerbate tic disorders. Nevertheless, the real impact of sex differences in movement disorders remains under-recognized. In this article, we provide an up-to-date review of sex-related differences in PD and the most common hyperkinetic movement disorders, namely, essential tremor, dystonia, Huntington disease and other chorea syndromes, and Tourette syndrome and other chronic tic disorders. We highlight the most relevant clinical aspects of movement disorders that differ between men and women. Increased recognition of these differences and their impact on patient care could aid the development of tailored approaches to the management of movement disorders and enable the optimization of preclinical research and clinical studies.

Amisulpride and l-DOPA modulate subcortical brain nuclei connectivity in resting-state pharmacologic magnetic resonance imaging

The precise understanding of the dopaminergic (DA) system and its pharmacological modifications is crucial for diagnosis and treatment of neuropsychiatric disorders, as well as for understanding basic processes, such as motivation and reward. We probed the functional connectivity (FC) of subcortical nuclei related to the DA system according to seed regions defined according to an atlas of subcortical nuclei. We conducted a large pharmaco‐fMRI study using a double‐blind, placebo‐controlled design, where we examined the effect of l‐DOPA, a dopamine precursor, and amisulpride, a D2/D3‐receptor antagonist on resting‐state FC in 45 healthy young adults using a cross‐over design. We examined the FC of subcortical nuclei with connection to the reward system and their reaction to opposing pharmacological probing. Amisulpride increased FC from the putamen to the precuneus and from ventral striatum to precentral gyrus. l‐DOPA increased FC from the ventral tegmental area (VTA) to the insula/operculum and between ventral striatum and ventrolateral prefrontal cortex and it disrupted ventral striatal and dorsal caudate FC with the medial prefrontal cortex. In an exploratory analysis, we demonstrated that higher self‐rated impulsivity goes together with a significant increase in VTA‐mid‐cingulate gyrus FC during l‐DOPA‐challenge. Therefore, our DA challenge modulated distinct large‐scale subcortical connectivity networks. A dopamine‐boost can increase midbrain DA nuclei connectivity to the cortex. The involvement of the VTA‐cingulum connectivity in dependence of impulsivity has implications for diagnosis and therapy in disorders like ADHD.

Comparison of Parkinson's Disease Patients' Characteristics by Indication for Deep Brain Stimulation: Men Are More Likely to Have DBS for Tremor

Background

We investigated whether the characteristics of Parkinson’s disease (PD) patients differ based on the primary indication for deep brain stimulation (DBS).

Methods

We reviewed data for 149 consecutive PD patients who underwent DBS at the University of Virginia. Patients were categorized based on primary surgical indication, and clinical characteristics were compared between groups.

Results

Twenty-nine (93.5%) of 31 PD patients who underwent DBS for medication refractory tremor were men, and 66 (62.3%) of 106 PD patients who underwent DBS for motor fluctuations were men (p = 0.001). Other primary indications for DBS were tremor and fluctuations (n = 5), medication intolerance (n = 5), and dystonia (n = 2).

Discussion

Patients who underwent DBS for medication refractory tremor were predominantly men, while patients who had DBS for motor fluctuations approximated the gender distribution of PD. Possible explanations are that men with PD are more likely to develop medication refractory tremor or undergo surgery for medication refractory tremor in PD compared to women.

Pharmacokinetics of Rytary®, An Extended-Release Capsule Formulation of Carbidopa-Levodopa

Parkinson's disease (PD) is a chronic progressive neurological disorder characterized by resting tremor, rigidity, bradykinesia, gait disturbance, and postural instability. Levodopa, the precursor to dopamine, coadministered with carbidopa or benserazide, aromatic amino acid decarboxylase inhibitors, is the most effective and widely used therapeutic agent in the treatment of PD. With continued levodopa treatment, a majority of patients develop motor complications such as dyskinesia and motor 'on-off' fluctuations, which are, in part, related to the fluctuations in plasma concentrations of levodopa. A new extended-release (ER) carbidopa-levodopa capsule product (also referred to as IPX066) was developed and approved in the US as Rytary^® and in the EU as Numient^®. The capsule formulation is designed to provide an initial rapid absorption of levodopa comparable to immediate-release (IR) carbidopa-levodopa, and to subsequently provide stable levodopa concentrations with reduced peak-to-trough excursions in plasma concentrations in order to reduce motor fluctuations associated with pulsatile stimulation of dopamine receptors and to minimize dyskinesia. Phase III studies of this ER carbidopa-levodopa capsule formulation in patients with PD have shown a significant reduction in 'off' time compared with IR carbidopa-levodopa and carbidopa-levodopa-entacapone. We present a review of the clinical pharmacokinetics and pharmacodynamics of this ER product of carbidopa-levodopa in healthy subjects and in patients with PD.

Gender differences in Parkinson's disease: A clinical perspective

Available data indicate that there are gender differences in many features of Parkinson's disease (PD). Precise identification of the gender differences is important to tailor treatment, predict outcomes, and meet other individual and social needs in women and men with PD. The aim of this study was to review the available clinical data on gender differences in PD. Original articles and meta-analyses published between 1990 and 2016 systematically exploring gender differences in PD were reviewed. There is slight male preponderance in incidence and prevalence of PD. PD starts earlier in men. Women tend to be more prone to develop tremor-dominant PD but are less rigid than men. Motor improvement after deep brain stimulation is equal in both sexes, but women tend to show better improvement in activities of daily living. Furthermore, women with PD show better results on tests for general cognitive abilities, outperform men in verbal cognitive tasks, show more pain symptoms, and score higher on depression scales. It seems, however, that the differences in cognition, mood, and pain perception are not disease specific as similar gender differences can be found in healthy subjects and in other neurological conditions. Despite PD being the most frequently studied movement disorder, studies investigating gender differences in PD are still scarce with most of the studies being cross-sectional. Good-quality, prospective, longitudinal studies analyzing gender differences in PD and comparing them to matched healthy controls are needed in order to properly address the issues of gender differences in PD.

Dose-Response Analysis of the Effect of Carbidopa-Levodopa Extended-Release Capsules (IPX066) in Levodopa-Naive Patients With Parkinson Disease

Parkinson disease is an age-related disorder of the central nervous system principally due to loss of dopamine-producing cells in the midbrain. Levodopa, in combination with carbidopa, is widely regarded as an effective treatment for the symptoms of Parkinson disease. A dose-response relationship is established for carbidopa-levodopa extended-release capsules (IPX066) in levodopa-naive Parkinson disease patients using a disease progression model. Unified Parkinson Disease Rating Scale (UPDRS) part II plus part III scores from 171 North American patients treated with placebo or IPX066 for approximately 30 weeks from a double-blind, parallel-group, dose-ranging study were used to develop the pharmacodynamic model. The model comprised 3 components: a linear function describing disease progression, a component describing placebo (or nonlevodopa) effects, and a component to describe the effect of levodopa. Natural disease progression in early Parkinson disease as measured by UPDRS was 11.6 units/year and faster in patients with more severe disease (Hoehn-Yahr stage 3). Maximum placebo/nonlevodopa response was 23.0% of baseline UPDRS. Maximum levodopa effect from IPX066 was 76.7% of baseline UPDRS, and the ED50 was 450 mg levodopa. Equilibration half-life for the effect compartment was 62.8 days. Increasing age increased and being female decreased equilibration half-life. The quantitative model allowed description of the entire time course of response to clinical trial intervention.

The Human Experience with Intravenous Levodopa

Objective: To compile a comprehensive summary of published human experience with levodopa given intravenously, with a focus on information required by regulatory agencies.

Background: While safe intravenous (IV) use of levodopa has been documented for over 50 years, regulatory supervision for pharmaceuticals given by a route other than that approved by the U.S. Food and Drug Administration (FDA) has become increasingly cautious. If delivering a drug by an alternate route raises the risk of adverse events, an investigational new drug (IND) application is required, including a comprehensive review of toxicity data.

Methods: Over 200 articles referring to IV levodopa were examined for details of administration, pharmacokinetics, benefit, and side effects.

Results: We identified 142 original reports describing IVLD use in humans, beginning with psychiatric research in 1959–1960 before the development of peripheral decarboxylase inhibitors. At least 2760 subjects have received IV levodopa, and reported outcomes include parkinsonian signs, sleep variables, hormone levels, hemodynamics, CSF amino acid composition, regional cerebral blood flow, cognition, perception and complex behavior. Mean pharmacokinetic variables were summarized for 49 healthy subjects and 190 with Parkinson's disease. Side effects were those expected from clinical experience with oral levodopa and dopamine agonists. No articles reported deaths or induction of psychosis.

Conclusion: At least 2760 patients have received IV levodopa with a safety profile comparable to that seen with oral administration.

Population pharmacokinetics of levodopa in subjects with advanced Parkinson's disease: levodopa-carbidopa intestinal gel infusion vs. oral tablets

AIMS

Levodopa-carbidopa intestinal gel (LCIG) provides continuous levodopa-carbidopa delivery through intrajejunal infusion. This study characterized the population pharmacokinetics of levodopa following a 16 h jejunal infusion of LCIG or frequent oral administration of levodopa-carbidopa tablets (LC-oral) in subjects with advanced Parkinson's disease (PD).

METHODS

A non-linear mixed-effects model of levodopa pharmacokinetics was developed using serial plasma concentrations from an LCIG phase 1 study and a phase 3 double-blind, double-dummy study of the efficacy and safety of LCIG compared with LC-oral in advanced PD patients (n = 68 for model development; 45 on LCIG and 23 on LC-oral). The final model was internally evaluated using stochastic simulations and bootstrap and externally evaluated using sparse pharmacokinetic data from 311 subjects treated in a long term safety study of LCIG.

RESULTS

The final model was a two compartment model with a transit compartment for absorption, first order elimination, bioavailability for LCIG (97%; confidence interval = 95% to 98%) relative to LC-oral, different first order transit absorption rate constants (LCIG = 9.2 h(-1) vs. LC-oral = 2.4 h(-1) ; corresponding mean absorption time of 7 min for LCIG vs. 25 min for LC-oral) and different residual (intra-subject) variability for LCIG (15% proportional error, 0.3 μg ml(-1) additive error) vs. LC-oral (29% proportional error, 0.59 μg ml(-1) additive error). Estimated oral clearance and steady-state volume of distribution for levodopa were 24.8 l h(-1) and 131 l, respectively.

CONCLUSIONS

LCIG administration results in faster absorption, comparable levodopa bioavailability and significantly reduced intra-subject variability in levodopa concentrations relative to LC-oral administration.

Orthostatic stability with intravenous levodopa

Intravenous levodopa has been used in a multitude of research studies due to its more predictable pharmacokinetics compared to the oral form, which is used frequently as a treatment for Parkinson's disease (PD). Levodopa is the precursor for dopamine, and intravenous dopamine would strongly affect vascular tone, but peripheral decarboxylase inhibitors are intended to block such effects. Pulse and blood pressure, with orthostatic changes, were recorded before and after intravenous levodopa or placebo-after oral carbidopa-in 13 adults with a chronic tic disorder and 16 tic-free adult control subjects. Levodopa caused no statistically or clinically significant changes in blood pressure or pulse. These data add to previous data that support the safety of i.v. levodopa when given with adequate peripheral inhibition of DOPA decarboxylase.

Sex-Related Prognostic Predictors for Parkinson Disease Undergoing Subthalamic Stimulation

BACKGROUND

A few reports have addressed the sex-related efficacy of deep brain stimulation (DBS) in the subthalamic nucleus (STN) to treat advanced Parkinson disease (PD). The present study evaluates the sex-related prognostic factors for STN-DBS outcomes.

METHODS

Seventy-two consecutive patients (48 men and 24 women) were reviewed retrospectively. Changes in the Unified PD Rating Scale scores were compared between men and women in the 6-month drug-off/DBS-on state relative to the preoperative drug-off baseline. A multivariate linear regression model was used to identify the preoperative factors predictive of motor improvements after surgery.

RESULTS

Before surgery, the male and female patient groups were comparable in clinical severity, except the women were associated with slightly inferior cognition (P < 0.05) and a relatively better response to levodopa (LD) (P < 0.05) than the men. Both sexes showed similar clinical improvements after STN-DBS therapy. In men, preoperative lower LD requirement and higher motor dysfunction, particularly tremor (adjusted R(2) = 0.613, P < 0.001), as well as greater improvement in tremor and rigidity after LD therapy (adjusted R(2) = 0.232, P = 0.001) were favorable predictors of surgical outcomes. Women achieved a significant improvement if they performed well in activities of daily living even with higher baseline motor scores (adjusted R(2) = 0.620, P < 0.001), or exhibited improvements in akinesia disability after preoperative LD therapy (adjusted R(2) = 0.305, P = 0.003).

CONCLUSIONS

STN-DBS therapy is equally beneficial for both sexes. Sex-related differences exist with regard to favorable prognostic predictors for early surgical outcomes.

Biological factors underlying sex differences in neurological disorders

The prevalence, age of onset, pathophysiology, and symptomatology of many neurological and neuropsychiatric conditions differ significantly between males and females. Females suffer more from mood disorders such as depression and anxiety, whereas males are more susceptible to deficits in the dopamine system including Parkinson's disease (PD), attention-deficit hyperactivity disorder (ADHD), schizophrenia, and autism spectrum disorders (ASD). Until recently, these sex differences have been explained solely by the neuroprotective actions of sex hormones in females. Emerging evidence however indicates that the sex chromosome genes (i.e. X- and Y-linked genes) also contribute to brain sex differences. In particular, the Y-chromosome gene, SRY (Sex-determining Region on the Y chromosome) is an interesting candidate as it is expressed in dopamine-abundant brain regions, where it regulates dopamine biosynthesis and dopamine-mediated functions such as voluntary movement in males. Furthermore, SRY expression is dysregulated in a toxin-induced model of PD, suggesting a role for SRY in the pathogenesis of dopamine cells. Taken together, these studies highlight the importance of understanding the interplay between sex-specific hormones and sex-specific genes in healthy and diseased brain. In particular, better understanding of regulation and function of SRY in the male brain could provide entirely novel and important insights into genetic factors involved in the susceptibility of men to neurological disorders, as well as development of novel sex-specific therapies.

Safety of IPX066 , an extended release carbidopa-levodopa formulation, for the treatment of Parkinson's disease

INTRODUCTION

Levodopa (LD) is the most effective treatment for Parkinson's disease (PD). However, chronic use of LD commonly results in the development of motor complications, including wearing off and dyskinesia. The presumption that the short serum half-life of LD is associated with the development of motor complications has raised the need to develop treatments with increased durations of stable LD concentrations.

AREAS COVERED

We conducted a PubMed search for IPX066 articles and also reviewed abstracts from meetings that included this topic. IPX066 is a newly developed formulation of extended release carbidopa-LD (CD-LD) with a one to four ratio of CD to LD, that was approved by the FDA in January 2015 for the treatment of PD, post-encephalitic parkinsonism, and parkinsonism that may follow carbon monoxide or manganese intoxication. It will be marketed by the trade name Rytary®. A Phase III clinical trial showed that IPX066 is efficacious in improving motor symptoms in early PD patients. In advanced PD patients with motor fluctuations, IPX066 reduced off time and increased on time without troublesome dyskinesia compared to CD-LD immediate release and CD-LD with entacapone. IPX066 had an acceptable safety profile. Adverse events of IPX066 from the different trials are presented.

EXPERT OPINION

IPX066 will probably have a role in the treatment of advanced PD with motor fluctuations. IPX066 could also be used initially when LD therapy is prescribed, but the question of whether this usage could reduce or prevent the development of motor complications is yet to be answered.

The "gender factor" in wearing-off among patients with Parkinson's disease: a post hoc analysis of DEEP study

Background. The early detection of wearing-off in Parkinson disease (DEEP) observational study demonstrated that women with Parkinson's disease (PD) carry an increased risk (80.1%) for wearing-off (WO). This post hoc analysis of DEEP study evaluates gender differences on WO and associated phenomena. Methods. Patients on dopaminergic treatment for ≥1 year were included in this multicenter observational cross-sectional study. In a single visit, WO was diagnosed based on neurologist assessment as well as the use of the 19-item wearing-off questionnaire (WOQ-19); WO was defined for scores ≥2. Post hoc analyses were conducted to investigate gender difference for demographic and clinical features with respect to WO. Results. Of 617 patients enrolled, 236 were women and 381 were men. Prevalence of WO was higher among women, according to both neurologists' judgment (61.9% versus 53.8%, P = 0.045) and the WOQ-19 analysis (72.5% versus 64.0%, P = 0.034). In patients with WO (WOQ-19), women experienced ≥1 motor symptom in 72.5% versus 64.0% in men and ≥1 nonmotor symptom in 44.5% versus 36.7%, in men. Conclusions. Our results suggest WO as more common among women, for both motor and nonmotor symptoms. Prospective studies are warranted to investigate this potential gender-effect.

The benefits of pramipexole selection in the treatment of Parkinson's disease

Levodopa administration as a gold standard in Parkinson's disease (PD) treatment is very valuable, however, long-term administration may cause some motor complications such as abnormal unintended movements and shortening response to each dose (wearing off phenomenon). Dopamine agonists were developed to reduce duration of immobile off periods and dependence to levodopa for improving motor impairments (Clarke et al., Cochrane Libr 1:1-23, 2000). Pramipexole is one of these nonergot dopamine agonists with high relative in vitro specificity and full intrinsic activity at D2 subfamily of dopamine receptors, with a higher binding affinity to D3 than to D4 or D2 receptor subtypes (Piercey, Clin Neuropharmacol 21:141-151, 1998). It can be advantageously administered as monotherapy or adjunctive therapy to levodopa to decrease side effects and increase effectiveness in both early and advanced PD treatment.

Pramipexole in the treatment of Parkinson’s disease: new developments

The nonergot dopamine agonist pramipexole is an efficient and safe drug for the treatment of Parkinson's disease. Clinicians may favor pramipexole over other dopamine agonists because of its suggested higher tolerability with respect to peripheral dopaminergic side effects. Importantly, nonergot dopamine agonists such as pramipexole may not cause restrictive valvular heart disease and may therefore represent the first choice in patients with valvular lesions under treatment with ergot dopamine agonists. However, particular caution has to be exercised in younger Parkinson's disease patients with a shorter disease duration regarding the occurrence of sudden onset of sleep. In light of cost-effectiveness and quality-of-life issues, its final significance for the initial treatment of patients with early Parkinson's disease remains to be determined.

IPX066: a new intermediate-and extended-release carbidopa-levodopa formulation

Carbidopa-levodopa (CD-LD) is the mainstay of treatment for Parkinson's disease (PD), yet most patients with advanced PD develop motor fluctuations with time when treated with CD-LD. Development of longer-acting CD-LD formulations is a major goal for reducing motor fluctuations in advanced PD. IPX066 is a new formulation of CD-LD that contains both an immediate-release and a sustained-release levodopa component, which is currently under review by the US FDA. Recent clinical trials have demonstrated improved effectiveness of IPX066 compared with other CD-LD formulations in advanced PD, with a reduction in 'off' time of approximately 37%. While it has also been shown to be effective in early PD compared with placebo, its role in early PD compared with other available medications for PD is unclear at this time.

Pharmacokinetics and pharmacodynamics of gastroretentive delivery of levodopa/carbidopa in patients with Parkinson disease

OBJECTIVE

To investigate, in patients with Parkinson disease, the pharmacokinetics and pharmacodynamics of levodopa/carbidopa delivered via 3 different extended-release (ER) tablet formulations.

METHODS

This was a randomized, crossover study in patients with stable idiopathic Parkinson disease comparing a conventional ER tablet (C-ER) administered orally 3 times daily with 2 levodopa/carbidopa gastroretentive ER formulations administered orally twice daily, one with an immediate release (IR) component (IR/ER) and one without (ER). Blood samples were collected for pharmacokinetic (PK) analysis, and a finger-tapping test was performed to assess pharmacodynamics. Tolerability was evaluated by monitoring adverse events and measuring vital signs. PK modeling was performed to estimate steady-state levodopa concentrations.

RESULTS

Fourteen patients completed the study. Compared with C-ER, both gastroretentive ER tablets significantly extended the first maximum time (6.0 vs 2.5 h; P < 0.025) and had smoother plasma concentration-time profiles while achieving a similar maximum plasma concentration and area under the curve. The IR/ER formulation exhibited a significantly longer duration of concentration above the presumed efficacious threshold of 300 ng/mL (21 vs 18 h; P = 0.0027) compared with C-ER. PK modeling predicts a steady-state levodopa peak/trough ratio of 4 for both IR/ER and ER formulations and a ratio of 21 for C-ER. Furthermore, superior response in the finger tapping test was observed for the IR/ER and ER formulations compared with the C-ER formulation.

CONCLUSIONS

This study demonstrated that the gastroretentive ER formulations achieved more constant plasma levodopa concentrations and better pharmacodynamics with reduced dose frequency, potentially reducing the on-off phenomena that have been associated with fluctuations in plasma levodopa concentrations.

Differential effects of age on human striatal adenosine A₁ and A(2A) receptors

The aim of this study was to investigate the effect of age on the distribution of adenosine A₁ receptors (A₁Rs) and adenosine A(2A) receptors (A(2A)Rs) in the striatum of healthy subjects using PET imaging with 8-dicyclopropylmethyl-1-[¹¹C]methyl-3-propylxanthine ([¹¹C]MPDX) and [7-methyl-¹¹C]-(E)-8-(3,4,5-trimethoxystyryl)-1,3,7-trimethylxanthine ([¹¹C]TMSX), respectively. We recruited 8 young (22.0 ± 1.7 years) and 10 elderly (65.4 ± 7.6 years) volunteers to undergo [¹¹C]MPDX PET scanning, and 11 young (22.7 ± 2.7 years) and six elderly (60.7 ± 8.5 years) volunteers to undergo [¹¹C]TMSX PET scanning. A dynamic series of decay-corrected PET scans was performed for 60 min following injection of [¹¹C]MPDX or [¹¹C]TMSX. We calculated the binding potential (BP(ND) ) of [¹¹C]MPDX and distribution volume ratio (DVR) of [¹¹C]TMSX in the striatum. The BP(ND) of [¹¹C]MPDX was significantly lower in elderly than in young subjects, both in the putamen and head of the caudate nucleus. The BP(ND) was negatively correlated with age in both the putamen and the head of the caudate nucleus. However, no difference was found between the DVR of [¹¹C]TMSX in the striata of young and elderly subjects, nor was there a correlation between age and the DVR of [¹¹C]TMSX. The effect of age on the distribution of A₁Rs in the human striatum described herein is similar to previous reports of age-related decreases in dopamine D₁ and D₂ receptors. Unlike A₁Rs, however, this study suggests that the distribution of A(2A) Rs does not change with age.

Pharmacokinetics of levodopa

This paper reviews the clinically relevant determinants of levodopa peripheral pharmacokinetics and main observed changes in the levodopa concentration-effect relationship with Parkinson's disease (PD) progression. Available clinically practical strategies to optimise levodopa pharmacokinetics and pharmacodynamics are briefly discussed. Levodopa shows particular pharmacokinetics including an extensive presystemic metabolism, overcome by the combined use of extracerebral inhibitors of the enzyme L: -amino acid decarboxylase and rapid absorption in the proximal small bowel by a saturable facilitated transport system shared with other large neutral amino acids. Drug transport from plasma to the brain is mediated by the same carriers operating in the intestinal mucosa. The main strategies to assure reproducibility of both intestinal absorption and delivery to the brain, and the clinical effect include standardization of levodopa dosing with respect to meal times and a controlled dietary protein intake. Levodopa plasma half-life is very short, resulting in marked plasma drug concentration fluctuations which are matched, as the disease progresses, to swings in the therapeutic response ("wearing-off" phenomena). "Wearing-off" phenomena can also be associated, at the more advanced disease stages, with a "negative", both parkinsonism-exacerbating and dyskinetic effect of levodopa at low, subtherapeutic plasma concentrations. Dyskinesias may also be related to high-levodopa, excessive plasma concentrations. Recognition of the different levodopa toxic response patterns can be difficult on a clinical basis alone and simultaneous monitoring of the levodopa concentration-effect relationship may prove useful to disclose the underlying mechanism and in planning the correct management. Clinically practical strategies to optimise levodopa pharmacokinetics, and possibly its therapeutic response, include liquid drug solutions, controlled release formulations and the use of inhibitors of levodopa metabolism. Unfortunately, these attempts have proved so far only partly successful, due to the complex alterations in cerebral levodopa kinetics which accompany the progressive degeneration of the nigrostriatal dopaminergic system in PD patients.

A randomized pilot trial of estrogen replacement therapy in post-menopausal women with Parkinson's disease

OBJECTIVE

To assess short-term safety and tolerability of estrogen replacement therapy in post-menopausal women with Parkinson's disease (PD).

METHODS

In a multi-center randomized, double-blind, placebo-controlled pilot trial, post-menopausal women with PD and motor fluctuations received either 0.625 mg/day of conjugated equine estrogens or matching placebo for 8 weeks. The primary outcome was the ability of participants to complete the trial. Other outcome measures included adverse events and changes from baseline to Week 8 in Unified PD Rating Scale scores, "on" time, dyskinesia ratings, and neuropsychological test results.

RESULTS

Twenty-three women (age 62.9(6.3) years, total Unified PD Rating 25.0(13.4), 8.8(6.0) years since symptom onset) were enrolled. There were no serious adverse events. One subject withdrew due to worsening of tremor and dystonia. The most commonly reported adverse events were vaginal spotting, breast enlargement and breast tenderness. The estrogen group showed improved total and motor Unified PD Rating scores although these did not reach statistical significance (mean changes from baseline, estrogen vs. placebo: Total -5.0 vs. 2.8, treatment effect = -7.8, p = 0.10; Motor -3.0 vs. 2.4, treatment effect = -5.4, p = 0.16).

CONCLUSIONS

Estrogen replacement therapy was safe and well-tolerated over 8 weeks in post-menopausal women with advanced PD. This pilot data suggests that estrogen replacement may be associated with improvement in motor symptoms. While larger studies of longer duration are necessary to determine the effects of estrogen in PD, the complex risk/benefit profile and continued controversy surrounding estrogen are obstacles to clinical trials.

Pharmacokinetics of levodopa/carbidopa delivered from gastric-retentive extended-release formulations in patients with Parkinson's disease

The investigators conducted a single-dose pharmacokinetic (PK) study of levodopa/carbidopa delivered from novel gastric-retentive extended-release (ER) tablets versus a comparator ER tablet (M-ER) in patients with Parkinson's disease. Two levodopa/carbidopa (200 mg/50 mg) gastric-retentive ER formulations (4 hours and 6 hours) and M-ER were administered orally with food. Blood samples were collected for up to 24 hours post dose to determine levodopa and carbidopa concentrations. Tolerability was assessed by monitoring adverse events and measuring vital signs. PK modeling was conducted to estimate the release characteristics for future gastric-retentive ER formulations to achieve a less fluctuating plasma concentration profiles. Compared with M-ER, both gastric-retentive ER formulations exhibited a longer time to reach a lower maximal plasma concentration for levodopa and carbidopa. The 4-hour formulation demonstrated a similar area under the concentration-time curve compared with M-ER, whereas the 6-hour formulation demonstrated a lower area under the concentration-time curve. All formulations were well tolerated. Modeling suggests that a gastric-retentive ER formulation with a longer release duration administered twice daily may achieve a less fluctuating levodopa concentration profile than M-ER administered 3 times daily. This study demonstrates that gastric-retentive ER dosage forms may reduce dose frequency while minimizing the plasma peak-to-trough fluctuation and consequently reduce motor fluctuation in patients with Parkinson's disease.

Rule-based categorization deficits in focal basal ganglia lesion and Parkinson's disease patients

Patients with basal ganglia (BG) pathology are consistently found to be impaired on rule-based category learning tasks in which learning is thought to depend upon the use of an explicit, hypothesis-guided strategy. The factors that influence this impairment remain unclear. Moreover, it remains unknown if the impairments observed in patients with degenerative disorders such as Parkinson's disease (PD) are also observed in those with focal BG lesions. In the present study, we tested patients with either focal BG lesions or PD on two categorization tasks that varied in terms of their demands on selective attention and working memory. Individuals with focal BG lesions were impaired on the task in which working memory demand was high and performed similarly to healthy controls on the task in which selective-attention demand was high. In contrast, individuals with PD were impaired on both tasks, and accuracy rates did not differ between on and off medication states for a subset of patients who were also tested after abstaining from dopaminergic medication. Quantitative, model-based analyses attributed the performance deficit for both groups in the task with high working memory demand to the utilization of suboptimal strategies, whereas the PD-specific impairment on the task with high selective-attention demand was driven by the inconsistent use of an optimal strategy. These data suggest that the demands on selective attention and working memory affect the presence of impairment in patients with focal BG lesions and the nature of the impairment in patients with PD.

Large differences in levodopa dose requirement in Parkinson's disease: men use higher doses than women

BACKGROUND AND PURPOSE

The characteristics of levodopa dosing are not well described in the literature. The aims were to investigate the use of levodopa in a nationwide Swedish survey and to study the characteristics of low-dose and high-dose patients with Parkinson's disease (PD) in a university hospital.

METHODS

Patients with >or= 1 and >or= 2 purchases of levodopa during 2007 were selected from the prescribed drug register. Daily levodopa doses were estimated. Records of 504 patients with PD who visited the neurology clinic at Uppsala University Hospital during 2006-2007 were examined to select a low-dose group (< or = 400 mg levodopa daily, n = 21) and a high-dose group (>or= 1200 mg daily, n = 26) with at least 5 years of PD duration.

RESULTS

In total, 33 534 levodopa users with > or = 1 levodopa purchase were found. Daily levodopa dose range was large; median daily dose was 465 mg for men and 395 mg for women (P < 0.0001). Almost half (46%) of the patients used < 400 mg levodopa daily. Significantly, more men were treated with doses >or= 1200 mg daily. Dose and age correlated negatively (P < 0.0001). Patients with high dose at 5 years PD duration continuously increased their dosage the following years, whereas low-dose patients did not. The occurrence of dyskinesias was about the same in both groups despite the large difference in levodopa dose.

CONCLUSIONS

We conclude that the levodopa requirement in PD ranges considerably, and that men use higher levodopa dose than women. Levodopa requirement is constant during the progression of the disease in low-dose patients but increases in high-dose patients.

Update on the use of pramipexole in the treatment of Parkinson's disease

Pramipexole is a non-ergot dopamine agonist shown to be efficacious in the treatment of Parkinson's disease (PD). This review addresses the literature concerning pramipexole's efficacy in treating motor and non-motor symptoms in PD, its impact on the development of dyskinesias and response fluctuations, the issue of neuroprotection, and the risk for developing adverse events such as increased somnolence, attacks of sudden onset of sleep, cardiac valvulopathy and impulse control disturbances.

Neurotrophic and neuroprotective actions of estrogen: basic mechanisms and clinical implications

Estrogen is an important hormone signal that regulates multiple tissues and functions in the body. This review focuses on the neurotrophic and neuroprotective actions of estrogen in the brain, with particular emphasis on estrogen actions in the hippocampus, cerebral cortex and striatum. Sex differences in the risk, onset and severity of neurodegenerative disease such as Alzheimer's disease, Parkinson's disease and stroke are well known, and the potential role of estrogen as a neuroprotective factor is discussed in this context. The review assimilates a complex literature that spans research in humans, non-human primates and rodent animal models and attempts to contrast and compare the findings across species where possible. Current controversies regarding the Women's Health Initiative (WHI) study, its ramifications, concerns and the new studies needed to address these concerns are also addressed. Signaling mechanisms underlying estrogen-induced neuroprotection and synaptic plasticity are reviewed, including the important concepts of genomic versus nongenomic mechanisms, types of estrogen receptor involved and their subcellular targeting, and implicated downstream signaling pathways and mediators. Finally, a multicellular mode of estrogen action in the regulation of neuronal survival and neurotrophism is discussed, as are potential future directions for the field.

Gender disparities in Parkinson's disease

Parkinson's disease is a chronic neurodegenerative disorder of unknown etiology. There are sparse data on gender differences in this disorder, but it is clear that there are gender discrepancies in incidence, symptoms, medication effects and treatments. There also appear to be lifecycle fluctuations in the disease course of female Parkinson's disease patients. The effect of estrogen in this disorder is multifold and its role in the development and treatment of PD will be discussed.

Pharmacokinetic optimisation in the treatment of Parkinson's disease : an update

Pharmacotherapy for Parkinson's disease is focused on dopaminergic drugs, mainly the dopamine precursor levodopa and dopamine receptor agonists. The elimination half-life (t(1/2)) of levodopa from plasma (in combination with a decarboxylase inhibitor) of about 1.5 hours becomes more influential as the disease progresses. The long-duration of response to levodopa, which is evident in early Parkinson's disease, diminishes and after a few years of treatment motor performance is closely correlated to the fluctuating plasma concentrations of levodopa. Absorption of levodopa in the proximal small intestine depends on gastric emptying, which is erratic and may be slowed in Parkinson's disease. The effects of levodopa on motor function are dependent on gastric emptying in patients in the advanced stages of disease. The current treatment concept is continuous dopaminergic stimulation (CDS). Sustained-release formulations of levodopa may provide more stable plasma concentrations. Oral liquid formulations shorten the time to reach peak concentration and onset of effect but do not affect plasma levodopa variability. The t(1/2) of levodopa can be prolonged by adding a catechol-O-methyltransferase inhibitor (entacapone or tolcapone), which may reduce fluctuations in plasma concentrations, although both peak and trough concentrations are increased with frequent administration. Intravenous and enteral (duodenal/jejunal) infusions of levodopa yield stable plasma levodopa concentrations and motor performance. Enteral infusion is feasible on a long-term basis in patients with severe fluctuations. Among the dopamine receptor agonists the ergot derivatives bromocriptine, cabergoline, dihydroergocryptine and pergolide, and the non-ergot derivatives piribedil, pramipexole and ropinirole, have longer t(1/2) compared with levodopa. Thus, they stimulate dopamine receptors in a less pulsatile manner, yet pharmacokinetic studies of repeated doses of dopamine receptor agonists are few. Optimisation of these drugs is often performed with standardised titration schedules. Apomorphine and lisuride have short t(1/2) and are suitable for subcutaneous infusion, with results similar to those of levodopa infusion. Transdermal administration of dopamine receptor agonists such as rotigotine might be an alternative in the future. In general, initial dopamine receptor agonist monotherapy is associated with poorer motor performance and lower incidence of motor complications compared with levodopa. Buccal administration of the monoamine oxidase-B inhibitor selegiline (deprenyl) provides better absorption and less formation of metabolites compared with standard tablets. To conclude, several new drugs, formulations and routes of administration have been introduced in the treatment of Parkinson's disease during the last decade, mainly with CDS as the aim. CDS can be approached by optimising the use of dopaminergic drugs based on pharmacokinetic data.