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.

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.

Capadenoson (BAY 68-4986) is a nonnucleoside agonist for the A1 Adenosine Receptor (A1AR) and the A2BAR. Capadenoson has undergone two Phase IIa clinical trials, initially in patients with atrial fibrillation and subsequently in patients with stable angina. Capadenoson has also been shown to decrease cardiac remodeling in an animal model of advanced heart failure and a capadenoson derivative, neladenoson bialanate, recently entered clinical development for the treatment of chronic heart failure. The therapeutic effects of capadenoson are currently thought to be mediated through the A1AR.

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.

Tecadenoson is a novel selective A1 adenosine receptor agonist that is currently being evaluated for the conversion of paroxysmal supraventricular tachycardia (PSVT) to sinus rhythm. Adenosine is a naturally occurring compound that stimulates all adenosine receptor subtypes in the body, including the A2 adenosine receptor which lowers blood pressure. In non-clinical trials, tecadenoson selectively stimulated the A1 adenosine receptor in the Atrioventricular node (AV node) and slowed the speed of electrical conduction across the AV node, reducing the number of electrical impulses that reached the ventricle, without affecting blood pressure. Clinical studies to date with intravenous tecadenoson suggest that it may slow the speed of AV nodal conduction by selectively stimulating the A1 adenosine receptor, and may avoid blood pressure lowering by not stimulating the A2 adenosine receptor. Thus, it may be possible to use intravenous tecadenoson to convert patients from PSVT to normal sinus rhythm without lowering blood pressure or causing adverse events related to vasodilation such as flushing, palpitations or a headache.

CVT-6883 (GS 6201) is an A2B adenosine receptor antagonist originated by CV Therapeutics and developed by Gilead Sciences or the treatment of pulmonary diseases. In vitro studies have suggested that the activation of the A2B adenosine receptor may potentially have Proinflammatory and profibrotic effects that could be significant in the development of lung diseases. In adenosine deaminase (ADA) deficient mice, treatment with GS 6201 resulted in significantly less pulmonary inflammation, fibrosis, and alveolar airway enlargement compared with ADA-deficient mice treated with placebo. A range of doses of GS 6201 was well tolerated in healthy volunteers in a phase I multiple ascending dose trial.