Istradefylline is a first-in-class adenosine A2A receptor antagonist antiparkinsonian agent and has been marketed as the brand name NOURIAST® in Japan since May 30, 2013. NOURIAST is indicated for the improvement of wearing-off phenomena in patients with Parkinson’s disease on concomitant treatment with levodopa-containing products.

Regadenoson (Lexiscan), a low affinity agonist of the A2A adenosine receptor, increases coronary blood flow (CBF) and mimics the increase in CBF caused by exercise. Myocardial uptake of the radiopharmaceutical is proportional to CBF creating the contrast required to identify stenotic coronary arteries. It is a pharmacologic stress agent indicated for radionuclide myocardial perfusion imaging (MPI) in patients unable to undergo adequate exercise stress. The most common adverse reactions to Lexiscan are dyspnea, headache, flushing, chest discomfort, dizziness, angina pectoris, chest pain, and nausea. Methylxanthines, e.g., caffeine and theophylline, may interfere with the activity of Lexiscan. Aminophylline may be used to attenuate severe and/or persistent adverse reactions to Lexiscan.

Caffeine is a methylxanthine alkaloid found in the seeds, nuts, or leaves of a number of plants native to South America and East Asia that is structurally related to adenosine and acts primarily as an adenosine receptor antagonist with psychotropic and anti-inflammatory activities. Upon ingestion, caffeine binds to adenosine receptors in the central nervous system (CNS), which inhibits adenosine binding. This inhibits the adenosine-mediated downregulation of CNS activity; thus, stimulating the activity of the medullary, vagal, vasomotor, and respiratory centers in the brain. The anti-inflammatory effects of caffeine are due the nonselective competitive inhibition of phosphodiesterases. Caffeine is used by mouth or rectally in combination with painkillers (such as aspirin and acetaminophen) and a chemical called ergotamine for treating migraineheadaches. It is also used with painkillers for simple headaches and preventing and treating headaches after epidural anesthesia. Caffeine creams are applied to the skin to reduce redness and itching in dermatitis. Healthcare providers sometimes give caffeine intravenously (by IV) for headache after epidural anesthesia, breathing problems in newborns, and to increase urine flow. In foods, caffeine is used as an ingredient in soft drinks, energy drinks, and other beverages.

Vipadenant (V2006) is a small molecule, adenosine A2A receptor antagonist that was being investigated in Parkinson's disease. Due to safety concerns development ceased in 2010 and the rights were regained from Biogen Idec in 2011 with no further investment made. In October 2014, RedoxTherapies licensed Vipadenant as it has the potential to disrupt an immunosuppressive mechanism of tumour protection, generating improved efficacy for immunotherapies of certain cancers when used in combination with other drugs.

Rolofylline is an adenosine A1-receptor antagonist. Plasma adenosine levels are elevated in patients with heart failure and adenosine A1 receptors in the kidney mediate vasoconstriction of afferent arterioles, reabsorption of sodium and water in proximal tubules, and tubuloglomerular feedback in the juxtaglomerular apparatus. Accordingly, inhibition of these receptors would be expected to increase renal blood flow and enhance diuresis. However, rolofylline showed no difference from placebo in the main efficacy end points in Phase III clinical trials for acute heart-failure patients.

Tozadenant (SYN115) is an adenosine A2A receptor antagonist initially developed for treatment of Parkinson's disease but may also have utility in other CNS disorders. A2a receptors are expressed in high concentration in the striatum of the brain and play an important role in regulating motor function. Tozadenant blocks the effect of endogenous adenosine at the A2a receptors, resulting in the potentiation of the effect of dopamine at the D2 receptor and inhibition of the effect of glutamate at the mGluR5 receptor. This enables restoration of motor function in Parkinson’s disease. Tozadenant has the potential for use as mono-therapy or adjunctive therapy in combination with L-Dopa and dopamine agonists for the treatment of the motor and non-motor symptoms associated with Parkinson’s disease. may also have neuroprotective effects, which raises the possibility that it could slow the deterioration of dopamine producing cells and modify disease progression. As was reported in international, multicentre, phase 2b, randomised, double-blind, placebo-controlled, parallel-group, dose-finding clinical trial of tozadenant in levodopa-treated patients with Parkinson's disease who had motor fluctuations tozadenant at 120 or 180 mg twice daily was generally well tolerated and was effective at reducing off-time.

UK-432097 is a selective adenosine A2a agonist which was in development with Pfizer as an inhaled treatment for asthma and chronic obstructive pulmonary disease. UK-432097 had been in phase II clinical trials by Pfizer for the treatment of chronic obstructive pulmonary disease (COPD). However, this study was terminated prematurely due to futility based on results of interim analysis.

Enprofylline is a xanthine derivative that shares theophylline's bronchodilator properties. It can be considered a relatively selective, though not potent adenosine A2B receptors antagonist. Enprofylline is used in asthma, chronic obstructive pulmonary disease, and in the management of cerebrovascular insufficiency, sickle cell disease, and diabetic neuropathy. Long-term enprofylline administration may be associated with the elevation in liver enzyme levels and unpredictable blood levels.

Preladenant (SCH-420814) is an adenosine A(2A) receptor antagonist with a high affinity and very high selectivity for adenosine A(2A) receptors, which is being developed by Merck & Co Inc (following its acquisition of Schering-Plough Corp) for the potential treatment of Parkinson's disease. Preladenant is a potent competitive antagonist of the human A2Areceptor (Ki = 1.1 nM) and has >1000-fold selectivity over all other adenosine receptors, making this compound the most selective A2A receptor antagonist reported to date. Preladenant was being researched as a potential treatment for Parkinson's disease. Positive results were reported in Phase II clinical trials in humans, but it did not prove itself to be more effective than a placebo during Phase III trials, and so was discontinued in May 2013.