Pathological gambling and dopamine agonists: A phenotype?

Current Therapies in Clinical Trials of Parkinson's Disease: A 2021 Update

Parkinson's disease (PD) is a progressive neurodegenerative disorder that currently has no cure, but treatments are available to improve PD symptoms and maintain quality of life. In 2020, about 10 million people worldwide were living with PD. In 1970, the United States Food and Drug Administration approved the drug levodopa as a dopamine replacement to manage PD motor symptoms; levodopa-carbidopa combination became commercialized in 1975. After over 50 years of use, levodopa is still the gold standard for PD treatment. Unfortunately, levodopa therapy-induced dyskinesia and OFF symptoms remain unresolved. Therefore, we urgently need to analyze each current clinical trial's status and therapeutic strategy to discover new therapeutic approaches for PD treatment. We surveyed 293 registered clinical trials on ClinicalTrials.gov from 2008 to 16 June 2021. After excluded levodopa/carbidopa derivative add-on therapies, we identified 47 trials as PD treatment drugs or therapies. Among them, 19 trials are in phase I (41%), 25 trials are in phase II (53%), and 3 trials are in phase III (6%). The three phase-III trials use embryonic dopamine cell implant, 5-HT_1A receptor agonist (sarizotan), and adenosine A_2A receptor antagonist (caffeine). The therapeutic strategy of each trial shows 29, 5, 1, 5, 5, and 2 trials use small molecules, monoclonal antibodies, plasma therapy, cell therapy, gene therapy, and herbal extract, respectively. Additionally, we discuss the most potent drug or therapy among these trials. By systematically updating the current trial status and analyzing the therapeutic strategies, we hope this review can provide new ideas and insights for PD therapy development.

Comparable efficacy and tolerability between twice daily and three times daily betahistine for Ménière's disease

CONCLUSION

Betahistine at oral doses of 16 mg tid and 24 mg bid provides similar efficacy and tolerability in the treatment of vertigo in patients with Ménière's disease.

OBJECTIVE

To compare the efficacy and tolerability of betahistine 16 mg tid and 24 mg bid in the treatment of vertigo in patients with Ménière's disease.

PATIENTS AND METHODS

This was a randomized, open-label study of 120 consecutive patients with well-established Ménière's disease treated with betahistine 16 mg tid or 24 mg bid for 24 weeks. Treatment efficacy, assessed by clinical outcome level in terms of severity, frequency and duration of vertigo spells, was evaluated at baseline and at weeks 4, 12 and 24. Between-group comparisons of outcome data (Wilcoxon, Mann-Whitney U test) and adverse events (chi-squared test) were made.

RESULTS

Betahistine 16 mg tid or 24 mg bid showed a significant improvement in clinical outcome level from baseline to week 24 (p < 0.01). There was no significant difference between dosage groups regarding improvement in vertigo at any time point during the study. There was no significant difference between groups in the incidence of adverse events, which was low (maximum: headache, 16 mg tid, 16.7% of patients at week 4; 6.7% at week 24). The number of patients reporting adverse events diminished with time.

Pharmacogenetic basis for therapeutic optimization in Alzheimer's disease

Alzheimer's disease is a major health problem in developed countries. Approximately 10-15% of direct costs in dementia are attributed to pharmacological treatment, and only 10-20% of the patients are moderate responders to conventional antidementia drugs, with questionable cost effectiveness. The phenotypic expression of Alzheimer's disease is characterized by amyloid deposition in brain tissue and vessels (amyloid angiopathy), intracellular neurofibrillary tangle formation, synaptic and dendritic loss, and premature neuronal death. Primary pathogenic events underlying this neurodegenerative process include genetic factors involving more than 200 different genes distributed across the human genome, accompanied by progressive cerebrovascular dysfunction, and diverse environmental factors. Mutations in genes directly associated with the amyloid cascade (APP, PSEN1, PSEN2) are present in less than 5% of the Alzheimer's disease population; however, the presence of the epsilon4 allele of the apolipoprotein E gene (APOE) represents a major risk factor for more than 40% of patients with dementia. Genotype-phenotype correlation studies and functional genomics studies have revealed the association of specific mutations in primary loci and/or APOE-related polymorphic variants with the phenotypic expression of biological traits. It is estimated that genetics accounts for between 20% and 95% of the variability in drug disposition and pharmacodynamics. Recent studies indicate that the therapeutic response in Alzheimer's disease is genotype specific, depending on genes associated with Alzheimer's disease pathogenesis and/or genes responsible for drug metabolism (e.g. cytochrome P450 [CYP] genes). In monogenic studies, APOEepsilon4/epsilon4 genotype carriers are the worst responders to conventional treatments. Some cholinesterase inhibitors currently being use in the treatment of Alzheimer's disease are metabolized via CYP-related enzymes. These drugs can interact with many other drugs that are substrates, inhibitors or inducers of the CYP system, this interaction eliciting liver toxicity and other adverse drug reactions. CYP2D6 enzyme isoforms are involved in the metabolism of more than 20% of drugs used in CNS disorders. The distribution of the CYP2D6 genotypes in the European population of the Iberian peninsula differentiates four major categories of CYP2D6-related metabolizer types: (i) extensive metabolizers (EM) [51.61%]; (ii) intermediate metabolizers (IM) [32.26%]; (iii) poor metabolizers (PM) [9.03%]; and (iv) ultra-rapid metabolizers (UM) [7.10%]. PMs and UMs tend to show higher transaminase activity than EMs and IMs. EMs and IMs are the best responders, and PMs and UMs are the worst responders to pharmacologic treatments in Alzheimer's disease. At this early stage of the development of pharmacogenomic/pharmacogenetic procedures in Alzheimer's disease therapeutics, it seems very plausible that the pharmacogenetic response in Alzheimer's disease depends on the interaction of genes involved in drug metabolism and genes associated with Alzheimer's disease pathogenesis.