Does istradefylline really have a dystonic mechanism?

Studies on the Crystal Forms of Istradefylline: Structure, Solubility, and Dissolution Profile

Istradefylline as a selective adenosine A2A-receptor antagonist is clinically used to treat Parkinson’s disease and improve dyskinesia in its early stages. However, its crystal form, as an important factor in the efficacy of the drug, is rarely studied. Herein, three kinds of crystal forms of istradefylline prepared from ethanol (form I), methanol (form II), and acetonitrile (form III) are reported by use of a crystal engineering strategy. These three crystal forms were characterized and made into tablets for dissolution testing. Both the solubility and the dissolution rates were also determined. The dissolution rate of form I and form III is significantly higher than form II at pH 1.2 (87.1%, 58.2%, and 87.7% for form I, form II, and form III, respectively), pH 4.5 (88.1%, 58.9%, and 87.1% for form I, form II, and form III, respectively) and pH 6.8 (87.5%, 58.2%, and 86.0% for form I, form II, and form III, respectively) at 60 min. Considering the prepared solution and the proper dissolution profile, form I is anticipated to possess promising absorption for bioavailability.

Efficacy and safety of istradefylline in patients with Parkinson's disease presenting with postural abnormalities: Results from a multicenter, prospective, and open-label exploratory study in Japan

Postural abnormalities in Parkinson's disease (PD) can devastatingly impair the quality of life, especially in patients with advanced disease, and are generally refractory to dopaminergic agents. The objective of this exploratory study was to investigate the efficacy and safety of istradefylline for the treatment of postural abnormalities in PD. In this open-label, 24-week, single-arm prospective trial, PD patients with postural abnormalities experiencing the wearing-off phenomenon on levodopa-containing therapies were enrolled and received a starting dose of 20 mg/day istradefylline orally for 4 weeks, which was then increased to 40 mg/day. The primary endpoint was the change from baseline to week 24 in the 14-item Unified Dystonia Rating Scale (UDRS) total score. Pivotal secondary endpoints were changes in the sub-items of UDRS, Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III, and adverse drug reactions (ADRs). Overall, 24/31 enrolled patients completed the study; mean (standard deviation) age and duration of motor complications were 73.3 (7.7) years and 3.2 (4.4) years, respectively. Mean (95% confidence interval [CI]) change in the UDRS total score was 4.84 (1.97, 7.71; P = 0.002), with significant improvements in the neck, right distal arm and hand, and trunk severity scores. Mean (95% CI) change in the MDS-UPDRS part III score was 7.84 (4.34, 11.34; P < 0.001). The most common ADRs were malaise, dyskinesia exacerbation, and visual hallucinations in 2 (6.5%) patients each. This exploratory study demonstrated that istradefylline could be efficacious for postural abnormalities and was generally well tolerated in patients with PD experiencing the wearing-off phenomenon with levodopa-containing therapies.

Istradefylline - a first generation adenosine A2A antagonist for the treatment of Parkinson's disease

Introduction It is now accepted that Parkinson's disease (PD) is not simply due to dopaminergic dysfunction, and there is interest in developing non-dopaminergic approaches to disease management. Adenosine A_2A receptor antagonists represent a new way forward in the symptomatic treatment of PD.Areas covered In this narrative review, we summarize the literature supporting the utility of adenosine A_2A antagonists in PD with a specific focus on istradefylline, the most studied and only adenosine A_2A antagonist currently in clinical use.Expert opinion: At this time, the use of istradefylline in the treatment of PD is limited to the management of motor fluctuations as supported by the results of randomized clinical trials and evaluation by Japanese and USA regulatory authorities. The relatively complicated clinical development of istradefylline was based on classically designed studies conducted in PD patients with motor fluctuations on an optimized regimen of levodopa plus adjunctive dopaminergic medications. In animal models, there is consensus that a more robust effect of istradefylline in improving motor function is produced when combined with low or threshold doses of levodopa rather than with high doses that produce maximal dopaminergic improvement. Exploration of istradefylline as a 'levodopa sparing' strategy in earlier PD would seem warranted.

How do adenosine A2A receptors regulate motor function?

Adenosine A_2A receptor antagonism is a new therapeutic strategy in the symptomatic treatment of Parkinson's disease (PD). This review addresses how adenosine A_2A receptors are involved with the control of motor function via the basal ganglia-thalamocortical circuit, and considers the anatomical localization and physiological function of the receptor, along with its ultrastructural localization in critical areas/neurons of the circuit. Based on this understanding of the functional significance of the adenosine A_2A receptor in the basal ganglia, the mode of action of A_2A receptor antagonists is explored in terms of the dynamic functioning of the basal ganglia and the activity of the internal circuits of the striatum in PD. Finally, the pathophysiological differences between the normal and PD states are examined to emphasize the importance of the adenosine A_2A receptor.

Separation and identification of an impurity from the istradefylline intermediate

Istradefylline is a selective adenosine antagonist for the A_2a receptor, and it is used to treat the Parkinson's disease and improve dyskinesia in the early stage of the Parkinson's disease. An impurity in the istradefylline intermediate A₁ (6-amino-1,3-diethyl-2,4-(1H,3H)-pyrimidinedione) was identified by high performance liquid chromatography (HPLC); it was separated by preparative HPLC and further characterized by UV, IR, MS, NMR, 2D NMR and single-crystal XRD analyses. The impurity was identified as (E)-N-ethyl-2-cyano-3-ethylamino-2-butenamide, which originated from the synthetic process of the intermediate A₁. The structure of this impurity might affect the efficiency and safety of istradefylline; therefore, the research and control of this impurity are necessary for ensuring the quality of istradefylline.

An impurity has been separated by preparative HPLC and characterized by IR, MS, NMR and XRD analyses as (E)-N-ethyl-2-cyano-3-ethylamino-2-butenamide, which is a by-product of the intermediate A₁ obtained from the istradefylline.