Carbidopa in Parkinson disease and in nausea and vomiting of levodopa

Metabolite profiling of foslevodopa/foscarbidopa in plasma of healthy human participants by LC-HRMS indicates no major differences compared to administration of levodopa/carbidopa intestinal gel

Analysis was conducted to compare levodopa/carbidopa pharmacokinetics and drug-related material in plasma of healthy participants after receiving a continuous infusion of Levodopa/Carbidopa Intestinal Gel (LCIG) to a continuous subcutaneous infusion of foslevodopa/foscarbidopa. Study samples were from a randomized, open-label, 2-period crossover study in 20 healthy participants. Participants received either 24-h foslevodopa/foscarbidopa SC infusion to the abdomen or LCIG delivered for 24 h to the jejunum through a nasogastric tube with jejunal extension. Serial blood samples were collected for PK. Comparability of the LD PK parameters between the two treatment regimens was determined. Selected plasma samples were pooled per treatment group and per time point for metabolite profiling. LC-MSn was performed using high-resolution mass spectrometry to identify drug-related material across the dosing regimens and time points. The LD PK parameter central values and 90% confidence intervals following the foslevodopa/foscarbidopa subcutaneous infusion were between 0.8 and 1.25 relative to the LCIG infusion. With LCIG administration, LD, CD, 3-OMD, DHPA, DOPAC, and vanillacetic acid were identified in plasma at early and late time points (0.75 and 24 h); the metabolic profile after administration of foslevodopa/foscarbidopa demonstrated the same drug-related compounds with the exception of the administered foslevodopa. 3-OMD and vanillacetic acid levels increased over time in both treatment regimens. Relative quantification of LC-MS peak areas showed no major differences in the metabolite profiles. These results indicate that neither the addition of monophosphate prodrug moieties nor SC administration affects the circulating metabolite profile of foslevodopa/foscarbidopa compared to LCIG.

An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease

Sleep disorders are among the most common nonmotor symptoms in Parkinson's disease and are associated with reduced cognition and health-related quality of life. Disturbed sleep can often present in the prodromal or early stages of this neurodegenerative disease, rendering it crucial to manage and treat these symptoms. Levodopa and dopaminergic agonists are frequently prescribed to treat motor symptoms in Parkinson's disease, and there is increasing interest in how these pharmacological agents affect sleep and their effect on concomitant sleep disturbances and disorders. In this review, we discuss the role of dopamine in regulating the sleep-wake state and the impact of neurodegeneration on sleep. We provide an overview of the effects of levodopa and dopaminergic agonists on sleep architecture, insomnia, excessive daytime sleepiness, sleep-disordered breathing, rapid eye movement sleep behavior disorder, and restless legs syndrome in Parkinson's disease. Levodopa and dopaminergic drugs may have different effects, beneficial or adverse, depending on dosing, method of administration, and differential effects on the different dopamine receptors. Future research in this area should focus on elucidating the specific mechanisms by which these drugs affect sleep in order to better understand the pathophysiology of sleep disorders in Parkinson's disease and aid in developing suitable therapies and treatment regimens.

CITATION

Scanga A, Lafontaine A-L, Kaminska M. An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson's disease. J Clin Sleep Med. 2023;19(6):1133-1144.

Dual-Drug Delivery by Anisotropic and Uniform Hybrid Nanostructures: A Comparative Study of the Function and Substrate-Drug Interaction Properties

By utilizing nanoparticles to upload and interact with several pharmaceuticals in varying methods, the primary obstacles associated with loading two or more medications or cargos with different characteristics may be addressed. Therefore, it is feasible to evaluate the benefits provided by co-delivery systems utilizing nanoparticles by investigating the properties and functions of the commonly used structures, such as multi- or simultaneous-stage controlled release, synergic effect, enhanced targetability, and internalization. However, due to the unique surface or core features of each hybrid design, the eventual drug-carrier interactions, release, and penetration processes may vary. Our review article focused on the drug's loading, binding interactions, release, physiochemical, and surface functionalization features, as well as the varying internalization and cytotoxicity of each structure that may aid in the selection of an appropriate design. This was achieved by comparing the actions of uniform-surfaced hybrid particles (such as core-shell particles) to those of anisotropic, asymmetrical hybrid particles (such as Janus, multicompartment, or patchy particles). Information is provided on the use of homogeneous or heterogeneous particles with specified characteristics for the simultaneous delivery of various cargos, possibly enhancing the efficacy of treatment techniques for illnesses such as cancer.

Redefining the strategy for the use of COMT inhibitors in Parkinson's disease: the role of opicapone

INTRODUCTION

Levodopa remains the gold-standard Parkinson's disease (PD) treatment, but the inevitable development of motor complications has led to intense activity in pursuit of its optimal delivery.

AREAS COVERED

Peripheral inhibition of dopa-decarboxylase has long been considered an essential component of levodopa treatment at every stage of illness. In contrast, only relatively recently have catechol-O-methyltransferase (COMT) inhibitors been utilized to block the other major pathway of degradation and optimize levodopa delivery to the brain. First and second-generation COMT inhibitors were deficient because of toxicity, sub-optimal pharmacokinetics or a short duration of effect. As such, they have only been employed once 'wearing-off' has developed. However, the third-generation COMT inhibitor, opicapone has overcome these difficulties and exhibits long-lasting enzyme inhibition without the toxicity observed with previous generations of COMT inhibitors. In clinical trials and real-world PD studies opicapone improves the levodopa plasma profile and results in a significant improvement in ON time in 'fluctuating' disease, but it has not yet been included in the algorithm for early treatment.

EXPERT OPINION

This review argues for a shift in the positioning of COMT inhibition with opicapone in the PD algorithm and lays out a pathway for proving its effectiveness in early disease.

Importance of Nanoparticles for the Delivery of Antiparkinsonian Drugs

Parkinson's disease (PD) affects around ten million people worldwide and is considered the second most prevalent neurodegenerative disease after Alzheimer's disease. In addition, there is a higher risk incidence in the elderly population. The main PD hallmarks include the loss of dopaminergic neurons and the development of Lewy bodies. Unfortunately, motor symptoms only start to appear when around 50-70% of dopaminergic neurons have already been lost. This particularly poses a huge challenge for early diagnosis and therapeutic effectiveness. Actually, pharmaceutical therapy is able to relief motor symptoms, but as the disease progresses motor complications and severe side-effects start to appear. In this review, we explore the research conducted so far in order to repurpose drugs for PD with the use of nanodelivery systems, alternative administration routes, and nanotheranostics. Overall, studies have demonstrated great potential for these nanosystems to target the brain, improve drug pharmacokinetic profile, and decrease side-effects.

Subcutaneous Administration of Carbidopa Enhances Oral Levodopa Pharmacokinetics: A Series of Studies Conducted in Pigs, Mice, and Healthy Volunteers

OBJECTIVES

Although commercially available levodopa (LD) formulations include carbidopa (CD) or benserazide for gastrointestinal L-aromatic amino acid decarboxylase inhibition, little is known how manipulating CD delivery affects the pharmacokinetics of LD. Our research systematically evaluated the peripheral and central pharmacokinetics of LD during continuous subcutaneous CD delivery.

METHODS

We conducted pharmacokinetic experiments in pigs, mice, and humans to characterize effects of continuous subcutaneous CD delivery co-administered with LD as compared with oral LD/CD administration on LD pharmacokinetics. The porcine and human studies compared peripheral LD pharmacokinetic parameters (area under the curves [AUCs], peak plasma concentrations [Cmax], and plasma elimination half-life [t1/2]) and the mouse studies compared brain LD and dopamine concentrations.

RESULTS

In the pig, supplementary subcutaneous CD delivery significantly increased the LD t1/2 and AUC versus LD/CD alone and versus additional oral CD administration. In mice, administration of supplementary subcutaneous CD substantially increased mean plasma concentrations of both LD and CD versus oral LD/CD alone at all time points. These increases were mirrored by increased brain dopamine levels for at least the 7 hours of study. In healthy human subjects, continuous subcutaneous CD administration, 3.33 mg/h x24h, increased the plasma LD t1/2, Cmax, and AUC by 17.4%, 40.5%, and 22.3%, respectively (P < 0.003).

CONCLUSIONS

This series of studies demonstrates that small continuous dosing of subcutaneous CD has an unexpected effect on LD pharmacokinetics greater than the extent of decarboxylase inhibition achieved by additional oral CD administration.

From medications to surgery: advances in the treatment of motor complications in Parkinson's disease

Motor complications are responsible for the large burden of disability and poor quality of life in Parkinson’s disease (PD). The pulsatile nature of stimulation with oral dopaminergic therapies due to relatively short pharmacokinetic profiles and dysfunctional gastrointestinal absorption have been attributed to the development of PD motor complications. In this review, we will provide an overview of the pharmacologic and surgical therapies currently available and under investigation for the treatment of motor fluctuations and dyskinesia.

Levodopa in Parkinson's Disease: Current Status and Future Developments

BACKGROUND

Ever since the pioneering reports in the 60s, L-3,4-Dioxyphenylalanine (levodopa) has represented the gold standard for the treatment of Parkinson's Disease (PD). However, long-term levodopa (LD) treatment is frequently associated with fluctuations in motor response with serious impact on patient quality of life. The pharmacokinetic and pharmacodynamic properties of LD are pivotal to such motor fluctuations: discontinuous drug delivery, short half-life, poor bioavailability, and narrow therapeutic window are all crucial for such fluctuations. During the last 60 years, several attempts have been made to improve LD treatment and avoid long-term complications.

METHODS

Research and trials to improve the LD pharmacokinetic since 1960s are reviewed, summarizing the progressive improvements of LD treatment.

RESULTS

Inhibitors of peripheral amino acid decarboxylase (AADC) have been introduced to achieve proper LD concentration in the central nervous system reducing systemic adverse events. Inhibitors of catechol-O-methyltransferase (COMT) increased LD half-life and bioavailability. Efforts are still being made to achieve a continuous dopaminergic stimulation, with the combination of oral LD with an AADC inhibitor and a COMT inhibitor, or the intra-duodenal water-based LD/ carbidopa gel. Further approaches to enhance LD efficacy are focused on new non-oral administration routes, including nasal, intra-duodenal, intrapulmonary (CVT-301) and subcutaneous (ND0612), as well as on novel ER formulations, including IPX066, which recently concluded phase III trial.

CONCLUSION

New LD formulations, oral compounds as well as routes have been tested in the last years, with two main targets: achieve continuous dopaminergic stimulation and find an instant deliver route for LD.

Classics in chemical neuroscience: levodopa

Levodopa was the first and most successful breakthrough in the treatment of Parkinson's disease (PD). It is estimated that PD affects approximately 1 million people in the United States alone. Although PD was discovered in 1817, prior to levodopa's discovery there was not an effective treatment for managing its symptoms. In 1961, Hornykiewicz pioneered the use of levodopa to enhance dopamine levels in the striatum, significantly improving symptoms in many patients. With the addition of carbidopa in 1974, the frequency of gastrointestinal adverse drug reactions (ADRs) was significantly reduced, leading to the modern treatment of PD. Although levodopa treatment is more than 50 years old, it remains the "gold standard" for PD treatment. This Review describes in detail the synthesis, metabolism, pharmacology, ADRs, and importance of levodopa therapy to neuroscience in the past and present.

Anti-Parkinson's disease drugs and pharmacogenetic considerations

INTRODUCTION

The development of pharmacogenetic-based clinical practice guidelines for the use of anti-Parkinson's disease drugs requires, as a pre-requisite, the identification and validation of genetic biomarkers. These biomarkers are then used as surrogate endpoints. This review analyzes potential genetic biomarkers which can be used to improve anti-Parkinson's disease therapy.

AREAS COVERED

The authors present an overview of current knowledge of pharmacogenetic implications of anti-Parkinson's disease drugs, including genes coding for the corresponding drug-metabolizing enzymes and drug targets. The gene/drug pairings with the strongest potential for pharmacogenetic recommendations include: CYP2C19/benztropine, COMT/levodopa and entacapone, CYP2B6/selegiline, UGT1A/entacapone, DRD2/ropinirole, pramipexole and cabergoline, and DRD3/ropinirole and pramipexole. Evidence supporting the effect of substrates, inhibitor or inducers for drug specific metabolizing enzymes in anti-Parkinson's disease drug response includes CYP1A2 in the response to ropinirole and rasagiline, and CYP3A4 in the response to bromocriptine, lisuride, pergolide and cabergoline. The authors present and discuss the current information on gene variations according to the 1000 genomes catalog and other databases with regards to anti-Parkinson's disease drugs. They also review and discuss the clinical implications of these variations.

EXPERT OPINION

The goal of pharmacogenomic testing for anti-Parkinson's disease drugs should be conservative and aimed at selecting determined drugs for determined patients. However, much additional research is still needed to obtain reliable pre-prescription tests.

Motor and nonmotor complications in Parkinson's disease: an argument for continuous drug delivery?

The complications of long-term levodopa therapy for Parkinson’s disease (PD) include motor fluctuations, dyskinesias, and also nonmotor fluctuations—at least equally common, but less well appreciated—in autonomic, cognitive/psychiatric, and sensory symptoms. In seeking the pathophysiologic mechanisms, the leading hypothesis is that in the parkinsonian brain, intermittent, nonphysiological stimulation of striatal dopamine receptors destabilizes an already unstable system. Accordingly, a major goal of PD treatment in recent years has been the attainment of continuous dopaminergic stimulation (CDS)—or, less theoretically (and more clinically verifiable), continuous drug delivery (CDD). Improvements in the steadiness of the plasma profiles of various dopaminergic therapies may be a signal of progress. However, improvements in plasma profile do not necessarily translate into CDS, or even into CDD to the brain. Still, it is reassuring that clinical studies of approaches to CDD have generally been positive. Head-to-head comparative trials have often failed to uncover evidence favoring such approaches over an intermittent therapy. Nevertheless, the findings among recipients of subcutaneous apomorphine infusion or intrajejunal levodopa/carbidopa intestinal gel suggest that nonmotor PD symptoms or complications may improve in tandem with motor improvement. In vivo receptor binding studies may help to determine the degree of CDS that a dopaminergic therapy can confer. This may be a necessary first step toward establishing whether CDS is, in fact, an important determinant of clinical efficacy. Certainly, the complexities of optimal PD management, and the rationale for an underlying strategy such as CDS or CDD, have not yet been thoroughly elucidated.

Cyclic vomiting associated with excessive dopamine in Riley-day syndrome

GOALS

To analyze the neurochemical profile during the recurrent attacks of nausea and vomiting in patients with Riley-day syndrome.

BACKGROUND

One of the most disabling features of patients with Riley-day syndrome are recurrent attacks of severe nausea/retching/vomiting accompanied by hypertension, tachycardia, and skin flushing, usually triggered by emotional or other stresses.

STUDY

We monitored blood pressure and heart rate and measured plasma catecholamines during typical dysautonomic crises triggered by emotionally charged situations. For comparison, measurements were repeated at follow-up after the symptoms had resolved and the patients were feeling calm and well.

RESULTS

During a typical attack, patients were hypertensive and tachycardic. In all patients, circulating levels of norepinephrine (P < 0.002) and dopamine (P < 0.007) increased significantly.

CONCLUSIONS

Activation of dopamine receptors in the chemoreceptor trigger zone may explain the cyclic nausea/retching/vomiting of patients with Riley-day syndrome.

Familial dysautonomia (Riley-Day syndrome): when baroreceptor feedback fails

Familial dysautonomia (FD) is a rare hereditary disorder caused by mutations within the gene that encodes for I-κ-B kinase complex associated protein (IKAP). A deficiency of IKAP affects the development of primary sensory neurons including those carrying baroreflex afferent volleys, a feature that explains their characteristic sensory loss and labile blood pressure. This review describes the history, the genotype of FD and the unusual cardiovascular autonomic phenotype of these patients. We outline the main consequences of a failure to receive information from arterial baroreceptors, including the characteristic "autonomic storms" and severe end-organ target damage.

Are high doses of carbidopa a concern? A randomized, clinical trial in Parkinson's disease

Recommended doses of carbidopa are 75-200 mg/day. Higher doses could inhibit brain aromatic amino-acid decarboxylase and reduce clinical effects. We compared 4-week outpatient treatments with carbidopa (75 and 450 mg/day) administered with L-dopa on the subjects' normal schedule. After each treatment phase, subjects had two 2-hour L-dopa infusions. The first infusion examined the effects of carbidopa doses administered the preceding 4 weeks, and the second infusion determined the acute effects of the two dosages of carbidopa. The antiparkinsonian effects and L-dopa and carbidopa plasma concentrations were monitored during the infusions. Twelve subjects completed the study. Carbidopa concentrations were eight times higher after the high-carbidopa phase. Area under the curve (AUC) for clinical ratings did not differ for the four L-dopa infusions, although AUC for plasma L-dopa was modestly increased with 450 mg of carbidopa. Nine subjects reported that the high-carbidopa outpatient phase was associated with greater response to L-dopa. Doses of 450 mg/day of carbidopa did not reduce the responses to L-dopa infusion, extending the safe range of carbidopa to 450 mg/day.

Double-blind trial of levodopa/carbidopa/entacapone versus levodopa/carbidopa in early Parkinson's disease

We performed a 39-week, randomized, double-blind, multicenter study to compare the efficacy, safety, and tolerability of levodopa/carbidopa/entacapone (LCE, Stalevo) with levodopa/carbidopa (LC, Sinemet IR) in patients with early Parkinson's disease (PD). Four hundred twenty-three patients with early PD warranting levodopa were randomly assigned to treatment with LCE 100/25/200 or LC 100/25 three-times daily. The adjusted mean difference in total Unified Parkinson's disease Rating Scale (UPDRS) Parts II and III between groups using the analysis of covariance model (prespecified primary outcome measure) was 1.7 (standard error = 0.84) points favoring LCE (P = 0.045). Significantly greater improvement with LCE compared with LC was also observed in UPDRS Part II activities of daily living (ADL) scores (P = 0.025), Schwab and England ADL scores (blinded rater, P = 0.003; subject, P = 0.006) and subject-reported Clinical Global Impression (CGI) scores (P = 0.047). There was no significant difference in UPDRS Part III or investigator-rated CGI scores. Wearing-off was observed in 29 (13.9%) subjects in the LCE group and 43 (20.0%) in the LC group (P = 0.099). Dyskinesia was observed in 11 (5.3%) subjects in the LCE group and 16 (7.4%) in the LC group (P = 0.367). Nausea and diarrhea were reported more frequently in the LCE group. LCE provided greater symptomatic benefit than LC and did not increase motor complications.

Does levodopa accelerate Parkinson's disease?

Therapeutic options for the treatment of Parkinson's disease (PD) have expanded tremendously over the last 5 years, although levodopa remains the gold standard of therapy. A major therapeutic controversy has been the question of levodopa's potential to cause toxic effects on nigrostriatal cells, thus potentiating the progression of the disease. The answer to that question will guide physicians in the timing of levodopa initiation and its dosage. The issue of levodopa toxicity was initially raised because of its potential to cause long term adverse effects (dyskinesias and motor fluctuations), which are not observed in untreated patients. Levodopa-induced toxicity can be related to its potential to produce free radicals, which are known to be toxic to cells, in the process of its conversion to dopamine. In vitro data reveals some evidence of the toxic effect of levodopa although recent studies suggest that levodopa toxicity is dependent on its concentration and can be ameliorated in the presence of glial cells. In vivo data from healthy animals and humans does not convincingly demonstrate levodopa toxicity. There is no evidence of levodopa-induced neurotoxicity in patients with PD. Despite the absence of toxic effect in patients with PD, levodopa can cause long term complications like motor fluctuations and dyskinesias and should be used judiciously in the minimal clinically effective dose. In this article we review evidence for and against levodopa neurotoxicity and the implications of the 'levo-dopa controversy' on clinical practice.

Carbidopa dosage modifies L-dopa induced side effects and blood levels of L-dopa and other amino acids in advanced parkinsonism

Thirty-four patients with advanced Parkinson's disease showing intolerance to therapeutic doses of L-DOPA were treated with L-DOPA plus carbidopa at two different proportions. Ten patients preferred medication containing 10% carbidopa while 24 preferred 25% carbidopa. The increase of carbidopa reduced gastrointestinal disturbances and psychiatric side effects related to L-DOPA, but improvement of disability when measured according to objective tests was modest. Higher doses of carbidopa reduced peripheral DOPA metabolism and increased blood levels of tryptophan, 3-OM-DOPA and DOPA in relation to the administered dose.

Metabolism of carbidopa to alpha-methyldopamine and alpha-methylnorepinephrine in rats

Recent observations on the central and peripheral actions of carbidopa (CD) combined with our own results with the compound led us to examine its metabolism and effects on brain catecholamines in rats. CD was found to undergo a two-stage N-deamination process in vivo giving rise to alpha-methyldopa (AMD) and alpha-methyldopamine respectively. Further, beta-hydroxylation yielded alpha-methylnorepinephrine. These metabolic products were demonstrated in rat brain with reductions in norepinephrine and 3-methoxy-4-hydroxyphenylglycol, and little effect on dopamine. These results are consistent with the alpha-2 agonist effects of alpha-methylnorepinephrine. The relative formation of alpha-methyldopamine from CD was about 26% of an equivalent dose of AMD. It is concluded that some of the central effects of CD may be mediated by its metabolism to AMD, which readily crosses the blood-brain barrier. Possible implications of the findings are discussed.

Levodopa/benserazide ('Madopar') combination therapy in elderly patients with parkinsonism

A clinical evaluation was carried out in 20 elderly patients with parkinsonism to assess the effectiveness and acceptability of treatment with a combination preparation of levodopa and benserazide over a period of 9 months. Mean daily maintenance dosage was 612.5 mg levodopa and 140 mg benserazide. The effects of treatment on clinical features and activities of daily living were monitored at monthly intervals. Significant improvement occurred in the first month and optimal improvement was usually reached by the end of 3-months' treatment. Akinesia and rigidity were abolished or improved in the majority of patients but the effect on tremor was less satisfactory. The preparation was well tolerated and side-effects were not troublesome.

A double-blind comparison of levodopa, Madopa, and Sinemet in Parkinson disease

A sixteen-week study examined the effect of Madopa and Sinemet on patients with Parkinson disease disease suffering nausea or vomiting as side-effects of levodopa therapy and compared the efficacy of the three preparations in controlling the symptoms of Parkinson disease. Following a control period on levodopa, 20 patients underwent four consecutive four-week regimens as follows: (1) double-blind, in which a randomized half received levodopa and half received Madopa; (2) single-blind, in which all received Madopa; (3) double-blind, in which a re-randomized half received Madopa and half Sinemet; and (4) single-blind, in which all received Sinemet. Levodopa administration via Sinemet and Madopa was held to a fixed 20% of prior levodopa dosage. Almost all patients showed great reduction in nausea and vomiting with both Madopa and Sinemet. Seventy percent of the patients showed improvement in disability compared to their levodopa baseline levels. Group means showed no difference between the improvement seen on Madopa and that seen on Sinemet. However, examination of individual responses showed that the majority of patients fared distinctly better on either Sinemet or Madopa.

Clinical pharmacokinetics of levodopa in parkinson's disease

Although levodopa has provided a major advance in the treatment of parkinsonism, its maximum benefits have not yet been realised, in part because of its complicated pharmacokinetics. This review summarises that available pharmacokinetic data involving levodopa, especially as it relates to therapeutic response of parkinsonian patients. A large number of factors, including protein intake, gastric emptying time, pyridoxine ingestion, and dopa decarboxylase activity, affect plasma levels of levodopa attained following oral administration of this drug. Other variables influence the rate of brain uptake of levodopa from the blood. Even so, plasma levodopa concentration correlates significantly with dosage size in a large parkinsonian population and also coincides with therapeutic response in many, but not all, patients. Therefore, in certain instances, valuable information may be derived by correlating clinical response with plasma levodopa concentration. Cerebrospinal fluid levels of homovanillic acid, a major metabolite of dopamine, may have some value in predicting clinical response to levodopa. This relationship, however, has not been firmly established. Concentration of homovanillic acid or levodopa in body fluids may also be closely related to certain adverse side-effects, including abnormal involuntary movements, gastric discomfort and psychiatric disturbances. Evidence indicates that a clearer understanding of levodopa pharmacokinetics may improve the clinical management of parkinsonism.