Trial to evaluate the management of paroxysmal supraventricular tachycardia during an electrophysiology study with tecadenoson

Targeting of G-protein coupled receptors in sepsis

The Third International Consensus Definitions (Sepsis-3) define sepsis as life-threatening multi-organ dysfunction caused by a dysregulated host response to infection. Sepsis can progress to septic shock-an even more lethal condition associated with profound circulatory, cellular and metabolic abnormalities. Septic shock remains a leading cause of death in intensive care units and carries a mortality of almost 25%. Despite significant advances in our understanding of the pathobiology of sepsis, therapeutic interventions have not translated into tangible differences in the overall outcome for patients. Clinical trials of antagonists of various pro-inflammatory mediators in sepsis have been largely unsuccessful in the past. Given the diverse physiologic roles played by G-protein coupled receptors (GPCR), modulation of GPCR signaling for the treatment of sepsis has also been explored. Traditional pharmacologic approaches have mainly focused on ligands targeting the extracellular domains of GPCR. However, novel techniques aimed at modulating GPCR intracellularly through aptamers, pepducins and intrabodies have opened a fresh avenue of therapeutic possibilities. In this review, we summarize the diverse roles played by various subfamilies of GPCR in the pathogenesis of sepsis and identify potential targets for pharmacotherapy through these novel approaches.

Medicinal Chemistry and Therapeutic Potential of Agonists, Antagonists and Allosteric Modulators of A1 Adenosine Receptor: Current Status and Perspectives

Adenosine is a purine nucleoside, responsible for the regulation of a wide range of physiological and pathophysiological conditions by binding with four G-protein-coupled receptors (GPCRs), namely A1, A2A, A2B and A3 adenosine receptors (ARs). In particular, A1 AR is ubiquitously present, mediating a variety of physiological processes throughout the body, thus represents a promising drug target for the management of various pathological conditions. Agonists of A1 AR are found to be useful for the treatment of atrial arrhythmia, angina, type-2 diabetes, glaucoma, neuropathic pain, epilepsy, depression and Huntington's disease, whereas antagonists are being investigated for the treatment of diuresis, congestive heart failure, asthma, COPD, anxiety and dementia. However, treatment with full A1 AR agonists has been associated with numerous challenges like cardiovascular side effects, off-target activation as well as desensitization of A1 AR leading to tachyphylaxis. In this regard, partial agonists of A1 AR have been found to be beneficial in enhancing insulin sensitivity and subsequently reducing blood glucose level, while avoiding severe CVS side effects and tachyphylaxis. Allosteric enhancer of A1 AR is found to be potent for the treatment of neuropathic pain, culminating the side effects related to off-target tissue activation of A1 AR. This review provides an overview of the medicinal chemistry and therapeutic potential of various agonists/partial agonists, antagonists and allosteric modulators of A1 AR, with a particular emphasis on their current status and future perspectives in clinical settings.

Focusing on Adenosine Receptors as a Potential Targeted Therapy in Human Diseases

Adenosine is involved in a range of physiological and pathological effects through membrane-bound receptors linked to G proteins. There are four subtypes of adenosine receptors, described as A1AR, A2AAR, A2BAR, and A3AR, which are the center of cAMP signal pathway-based drug development. Several types of agonists, partial agonists or antagonists, and allosteric substances have been synthesized from these receptors as new therapeutic drug candidates. Research efforts surrounding A1AR and A2AAR are perhaps the most enticing because of their concentration and affinity; however, as a consequence of distressing conditions, both A2BAR and A3AR levels might accumulate. This review focuses on the biological features of each adenosine receptor as the basis of ligand production and describes clinical studies of adenosine receptor-associated pharmaceuticals in human diseases.

Myocardial Energetics and Heart Failure: a Review of Recent Therapeutic Trials

PURPOSE OF REVIEW

Several novel therapeutics being tested in patients with heart failure are based on myocardial energetics. This review will provide a summary of the recent trials in this area, including therapeutic options targeting various aspects of cellular and mitochondrial metabolism.

RECENT FINDINGS

Agents that improve the energetic balance in myocardial cells have the potential to improve clinical heart failure status. The most promising therapies currently under investigation in this arena include (1) elamipretide, a cardiolipin stabilizer; (2) repletion of iron deficiency with intravenous ferrous carboxymaltose; (3) coenzyme Q10; and (4) the partial adenosine receptor antagonists capadenoson and neladenosone. Myocardial energetics-based therapeutics are groundbreaking in that they utilize novel mechanisms of action to improve heart failure symptoms, without causing the adverse neurohormonal side effects associated with current guideline-based therapies. The drugs appear likely to be added to the heart failure therapy armamentarium as adjuncts to current regimens in the near future.

Partial Adenosine A1 Agonist in Heart Failure

Adenosine exerts a variety of physiological effects by binding to cell surface G-protein-coupled receptor subtypes, namely, A1, A2a, A2b, and A3. The central physiological role of adenosine is to preclude tissue injury and promote repair in response to stress. In the heart, adenosine acts as a cytoprotective modulator, linking cardiac function to metabolic demand predominantly via activation of adenosine A1 receptors (A1Rs), which leads to inhibition of adenylate cyclase activity, modulation of protein kinase C, and opening of ATP-sensitive potassium channels. Activation of myocardial adenosine A1Rs has been shown to modulate a variety of pathologies associated with ischemic cardiac injury, including arrhythmogenesis, coronary and ventricular dysfunction, apoptosis, mitochondrial dysfunction, and ventricular remodeling. Partial A1R agonists are agents that are likely to elicit favorable pharmacological responses in heart failure (HF) without giving rise to the undesirable cardiac and extra-cardiac effects observed with full A1R agonism. Preclinical data have shown that partial adenosine A1R agonists protect and improve cardiac function at doses that do not result in undesirable effects on heart rate, atrioventricular conduction, and blood pressure, suggesting that these compounds may constitute a valuable new therapy for chronic HF. Neladenoson bialanate (BAY1067197) is the first oral partial and highly selective A1R agonist that has entered clinical development for the treatment of HF. This review provides an overview of adenosine A1R-mediated signaling in the heart, summarizes the results from preclinical and clinical studies of partial A1R agonists in HF, and discusses the potential benefits of these drugs in the clinical setting.

The association between apelin-12 levels and paroxysmal supraventricular tachycardia

AIMS

Our aim was to investigate the apelin-12 levels in patients with atrioventricular tachyarrhythmias and compare with those in patients with lone atrial fibrillation.

METHODS

Forty four patients with supraventricular tachycardia as atrial fibrillation, 44 patients with paroxysmal supraventricular tachycardia (P-SVT) as atrioventricular tachyarrhythmias, including atrioventricular nodal reentrant tachycardia or atrioventricular reentrant tachycardia, and 30 age- and sex-matched healthy individuals were included in the study.

RESULTS

The apelin-12 levels were significantly lower in both atrial fibrillation and P-SVT groups than control group. In post-hoc analysis, there was no significant difference in apelin-12 levels between atrial fibrillation and P-SVT groups (P = 0.9). Patients in atrial fibrillation group and patients in P-SVT group had significantly lower apelin-12 levels than control group, separately (P < 0.001 and P < 0.001, respectively). The sensitivity and specificity values of the apelin-12 levels for predicting SVT, including both atrial fibrillation and atrioventricular reentrant tachycardia or atrioventricular nodal reentrant tachycardia were 64.77 and 90%, respectively (cut-off value was 0.87). The area under the receiver operator characteristic curve was 0.834 for the apelin-12 levels (P = 0.0001).

CONCLUSION

Apelin-12 levels are lower in patients with atrial fibrillation and P-SVT than control groups. Lower apelin levels in patients with atrial fibrillation and P-SVT would be expected to result in a decrease in the conduction velocity.

Adenosine--a physiological or pathophysiological agent?

This minireview briefly summarizes the evidence that adenosine, acting on four G-protein coupled receptors, can play physiological roles, but is also critically involved in pathological processes. The factors that decide which of these is the more important in a specific cell or organ are briefly summarized. The fact that drugs that target adenosine receptors in disease will also hit the physiological processes will make drug development more tricky.

Adenosine and its receptors as therapeutic targets: An overview

The main goal of the authors is to present an overview of adenosine and its receptors, which are G-protein coupled receptors. The four known adenosine receptor subtypes are discussed along with the therapeutic potential indicating that these receptors can serve as targets for various dreadful diseases.

Chronic therapy with a partial adenosine A1-receptor agonist improves left ventricular function and remodeling in dogs with advanced heart failure

BACKGROUND

Adenosine elicits cardioprotection through A1-receptor activation. Therapy with adenosine A1-receptor agonists, however, is limited by undesirable actions of full agonism, such as bradycardia. This study examined the effects of capadenoson (CAP), a partial adenosine A1-receptor agonist, on left ventricular (LV) function and remodeling in dogs with heart failure.

METHODS AND RESULTS

Twelve dogs with microembolization-induced heart failure were randomized to 12 weeks oral therapy with CAP (7.5 mg BID; n=6) or to no therapy (control; n=6). LV end-diastolic and end-systolic volumes, ejection fraction, plasma norepinephrine, and n-terminal pro-brain natriuretic peptide were measured before (pre) and 1 and 12 weeks after therapy (post). LV tissue obtained at post was used to assess volume fraction of interstitial fibrosis, sarcoplasmic reticulum calcium ATPase-2a activity, expression of mitochondria uncoupling proteins (UCP) and glucose transporters (GLUT). In controls, end-diastolic and end-systolic volumes increased and ejection fraction decreased significantly from pre to post (ejection fraction, 30±2 versus 27±1%; P<0.05). In CAP-treated dogs, end-diastolic volume was unchanged; ejection fraction increased significantly after 1 week (36±2 versus 27±2%; P<0.05) with a further increase at post (39±2%; P<0.05), whereas end-systolic volume decreased. CAP significantly decreased volume fraction of interstitial fibrosis, normalized sarcoplasmic reticulum calcium ATPase-2a activity and expression of UCP-2 and UCP-3, and GLUT-1 and GLUT-2 and significantly decreased plasma norepinephrine and n-terminal pro-brain natriuretic peptide.

CONCLUSIONS

In heart failure dogs, CAP improves LV function and prevents progressive remodeling. Improvement of LV systolic function occurs early after initiating therapy. The results support development of partial adenosine A1-receptor agonists for the treatment of chronic heart failure.

Novel effects of adenosine receptors on pericellular hyaluronan matrix: implications for human smooth muscle cell phenotype and interactions with monocytes during atherosclerosis

Hyaluronan (HA) is responsive to pro-atherosclerotic growth factors and cytokines and is thought to contribute to neointimal hyperplasia and atherosclerosis. However, the specific function of the pericellular HA matrix is likely depend on the respective stimuli. Adenosine plays an important role in the phenotypic regulation of vascular smooth muscle cells (VSMC) and is thought to inhibit inflammatory responses during atherosclerosis. The aim of this study was to examine the regulation and function of HA matrix in response to adenosine in human coronary artery SMC (HCASMC). The adenosine receptor agonist NECA (10 μM) caused a strong induction of HA synthase (HAS)1 at 6 h and a weaker induction again after 24 h. Use of selective adenosine receptor antagonists revealed that adenosine A2(B) receptors (A2(B)R) mediate the early HAS1 induction, whereas late HAS1 induction was mediated via A2(A)R and A3R. The strong response after 6 h was mediated in part via phosphoinositide-3 kinase- and mitogen-activated protein kinase pathways and was inhibited by Epac. Functionally, NECA increased cell migration, which was abolished by shRNA-mediated knock down of HAS1. In addition to HA secretion, NECA also stimulated the formation of pronounced pericellular HA matrix in HCASMC and increased the adhesion of monocytes. The adenosine-induced monocyte adhesion was sensitive to hyaluronidase. In conclusion, the current data suggest that adenosine via adenosine A2(B)R and A2(A)R/A3R induces HAS1. In turn a HA-rich matrix is formed by HCASMC which likely supports the migratory HCASMC phenotype and traps monocytes/macrophages in the interstitial matrix.

Therapeutic potential of adenosine analogues and conjugates

This review summarizes current knowledge of adenosine analogues and conjugates with promising therapeutic properties. Adenosine is a signaling molecule that triggers numerous physiological responses. It acts through the adenosine receptors (ARs), belonging to the family of G-protein-coupled receptors and widely distributed throughout the body. Moreover, adenosine is involved in key biochemical processes as a part of ATP, the universal energy currency. Thus, compounds that are analogues of adenosine and its conjugates have been extensively studied as potential therapeutics. Many inhibitors of ARs are in clinical trials as promising agents in treatment of inflammation, type 2 diabetes, arrhythmia and as vasodilators used in the myocardial perfusion imaging (MPI) stress test. Furthermore, adenosine analogues revealed high efficacy as enzyme inhibitors, tested for antitrypanosomal action and as bivalent ligands and adenosine-oligoarginine conjugates as inhibitors of protein kinases.

[New developments in the antiarrhythmic therapy of atrial fibrillation]

Atrial fibrillation, which is associated with a worsening of congestive heart failure symptoms, an increased rate of stoke, and increased mortality, is still difficult to treat. New therapies must not only increase effectiveness, but also have to have an improved safety profile, in order to avoid sodium channel block in the ventricle of older patients with atrial fibrillation, and also prevent electrical and morphological remodeling. Dronedarone is less effective compared to amiodarone, but has a better side effect profile which leads to fewer discontinuations of treatment. The atrial ion channels are specifically blocked by a number of prospective antiarrhythmic substances. The most advanced is the testing of vernakalant (RSD1235), which primarily suppresses the I(Kur) current. Ranolazine is a new antianginal substance which influences the atrial ion channels and leads to a significant reduction of atrial and more specifically ventricular tachyarrhythmias. A number of other drugs are in development. They will lead to a better understanding of which form of atrial fibrillation can be best treated with which antiarrhythmic agent.

Antiarrhythmic Drug Therapy of Supraventricular Tachycardia

Pharmacologic therapy is commonly used for the acute treatment and termination of paroxysmal supraventricular tachycardia (SVT) and continues to be an important long-term option for some patients. Drug choice depends on the correct diagnosis of the arrhythmia and an understanding of its mechanism. Pharmacologic agents commonly used in the acute and chronic treatment of SVT are reviewed along with their effect on the various types of SVT. Drugs that are well tolerated with minimal side effects are preferred over agents with perhaps more efficacy but higher risk of toxicity.

Mechanisms by which adenosine restores conduction in dormant canine pulmonary veins

BACKGROUND

Adenosine acutely reconnects pulmonary veins (PVs) after radiofrequency application, revealing "dormant conduction" and identifying PVs at risk of reconnection, but the underlying mechanisms are unknown.

METHODS AND RESULTS

Canine PV and left-atrial (LA) action potentials were recorded with standard microelectrodes and ionic currents with whole-cell patch clamp before and after adenosine perfusion. PVs were isolated with radiofrequency current application in coronary-perfused LA-PV preparations. Adenosine abbreviated action potential duration similarly in PV and LA but significantly hyperpolarized resting potential (by 3.9+/-0.5%; P<0.05) and increased dV/dt(max) (by 34+/-10%) only in PV. Increased dV/dt(max) was not due to direct effects on I(Na), which was reduced similarly by adenosine in LA and PV but correlated with resting-potential hyperpolarization (r=0.80). Adenosine induced larger inward rectifier K(+)current (I(KAdo)) in PV (eg, -2.28+/-0.04 pA/pF; -100 mV) versus LA (-1.28+/-0.16 pA/pF). Radiofrequency ablation isolated PVs by depolarizing resting potential to voltages positive to -60 mV. Adenosine restored conduction in 5 dormant PVs, which had significantly more negative resting potentials (-57+/-6 mV) versus nondormant (-46+/-5 mV, n=6; P<0.001) before adenosine. Adenosine hyperpolarized both, but more negative resting-potential values after adenosine in dormant PVs (-66+/-6 mV versus -56+/-6 mV in nondormant; P<0.001) were sufficient to restore excitability. Adenosine effects on resting potential and conduction reversed on washout. Spontaneous recovery of conduction occurring in dormant PVs after 30 to 60 minutes was predicted by the adenosine response.

CONCLUSIONS

Adenosine selectively hyperpolarizes canine PVs by increasing I(KAdo). PVs with dormant conduction show less radiofrequency-induced depolarization than nondormant veins, allowing adenosine-induced hyperpolarization to restore excitability by removing voltage-dependent I(Na) inactivation and explaining the restoration of conduction in dormant PVs.

A1 adenosine receptor antagonists, agonists, and allosteric enhancers

Intense efforts of many pharmaceutical companies and academicians in the A(1) adenosine receptor (AR) field have led to the discovery of clinical candidates that are antagonists, agonists, and allosteric enhancers. The A(1)AR antagonists currently in clinical development are KW3902, BG9928, and SLV320. All three have high affinity for the human (h) A(1)AR subtype (hA(1) K (i) < 10 nM), > 200-fold selectivity over the hA(2A) subtype, and demonstrate renal protective effects in multiple animal models of disease and pharmacologic effects in human subjects. In the A(1)AR agonist area, clinical candidates have been discovered for the following conditions: atrial arrhythmias (tecadenoson, selodenoson and PJ-875); Type II diabetes and insulin sensitizing agents (GR79236, ARA, RPR-749, and CVT-3619); and angina (BAY 68-4986). The challenges associated with the development of any A(1)AR agonist are to obtain tissue-specific effects but avoid off-target tissue side effects and A(1)AR desensitization leading to tachyphylaxis. For the IV antiarrhythmic agents that act as ventricular rate control agents, a selective response can be accomplished by careful IV dosing paradigms. The treatment of type II diabetes using A(1)AR agonists in the clinic has met with limited success due to cardiovascular side effects and a well-defined desensitization of full agonists in human trials (GR79236, ARA, and RPR 749). However, new partial A(1)AR agonists are in development, including CVT-3619 hA(1) AR K(i) = 55nM, hA(2A:hA2B:hA(3))1,000:20, CV Therapeutics), which have the potential to provide enhanced insulin sensitivity without cardiovascular side effects and tachyphylaxis. The nonnucleosidic A(1)AR agonist BAY 68-4986 (capadenoson) represents a novel approach to angina wherein both animal studies and early human studies are promising. T-62 is an A(1)AR allosteric enhancer that is currently being evaluated in clinical trials as a potential treatment for neuropathic pain. The challenges associated with developing A(1)AR antagonists, agonists, or allosteric enhancers for therapeutic intervention are now well defined in humans. Significant progress has been made in identifying A(1)AR antagonists for the treatment of edema associated with congestive heart failure (CHF), A(1)AR agonists for the treatment of atrial arrhythmias, type II diabetes and angina, and A(1)AR allosteric enhancers for the treatment of neuropathic pain.

New antiarrhythmic treatment of atrial fibrillation

Antiarrhythmic pharmaceutical development for the treatment of atrial fibrillation (AF) is moving in several directions. The efficacy of existing drugs, such as carvedilol, for rate control and, possibly, suppression of AF, is more appreciated. Efforts are being made to modify existing agents, such as amiodarone, in an attempt to ameliorate safety and adverse effect concerns. This has resulted in promising data from the deiodinated amiodarone analog, dronedarone, and further work with celivarone and ATI-2042. In an attempt to minimize ventricular proarrhythmia, atrial selective drugs, such as intravenous vernakalant, have demonstrated efficacy in terminating AF in addition to promising data in suppression recurrences when used orally. Several other atrial selective drugs are being developed by multiple manufacturers. Other novel therapeutic mechanisms, such as drugs that enhance GAP junction conduction, are being developed to achieve more effective drug therapy than is offered by existing compounds. Finally, nonantiarrhythmic drugs, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, high-mobility group coenzyme A enzyme inhibitors and omega-3 fatty acids/fish oil, appear to have a role in suppressing AF in certain patient subtypes. Future studies will clarify the role of these drugs in treating AF.

Future directions in antiarrhythmic drug therapy for atrial fibrillation

Atrial fibrillation is the most commonly sustained cardiac arrhythmia. Drugs currently approved by the US FDA for the treatment of this arrhythmia are imperfect owing to either side effects or limited efficacy. Drug development strategies have focused on two areas: the modification of existing agents – such as Class III drugs aimed at improving their safety and efficacy profile – and targeting newly postulated mechanisms of atrial fibrillation. In this article, we review new drugs currently in development and promising drug strategies for atrial fibrillation prevention and treatment.

Tecadenoson: a novel, selective A1 adenosine receptor agonist

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. By selectively targeting the A1 receptor, tecadenoson may be associated with fewer adverse effects such as flushing, dyspnea, chest discomfort, and hypotension than adenosine, which is a nonselective agonist of all 4 adenosine receptors. Based on the results of phase I and phase II clinical trials, tecadenoson appears to be an effective agent for producing rapid and sustained conversion of PSVT to sinus rhythm. Additionally, the adverse effects that are typically attributed to adenosine's nonselective stimulation of the A2A, A2B, and A3 receptors appear to occur less frequently with the use of tecadenoson. Tecadenoson also appears to be associated with a lower incidence of atrial fibrillation following conversion of PSVT compared with the rates that have been associated with adenosine in the literature. A randomized, prospective trial will need to be conducted in the future to appropriately compare the safety and efficacy of tecadenoson and adenosine.

Adenosine receptors as therapeutic targets

Adenosine receptors are major targets of caffeine, the most commonly consumed drug in the world. There is growing evidence that they could also be promising therapeutic targets in a wide range of conditions, including cerebral and cardiac ischaemic diseases, sleep disorders, immune and inflammatory disorders and cancer. After more than three decades of medicinal chemistry research, a considerable number of selective agonists and antagonists of adenosine receptors have been discovered, and some have been clinically evaluated, although none has yet received regulatory approval. However, recent advances in the understanding of the roles of the various adenosine receptor subtypes, and in the development of selective and potent ligands, as discussed in this review, have brought the goal of therapeutic application of adenosine receptor modulators considerably closer.

A Population Pharmacokinetic/Pharmacodynamic Analysis of Regadenoson, an Adenosine A2A-Receptor Agonist, in Healthy Male Volunteers

OBJECTIVES

The aims of this study were to investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of regadenoson (CVT-3146) in healthy, male volunteers.

METHODS

Thirty-six healthy, male volunteers aged 18-50 years were included in this randomised, double-blind, crossover, placebo-controlled study to evaluate single intravenous bolus doses of regadenoson that ranged from 0.1 to 30.0 micro g/kg. Subjects received one dose of regadenoson or placebo on successive days while supine, then the same dose of regadenoson or placebo on successive days while standing. As part of the safety evaluation, vital signs and adverse events were monitored and recorded throughout the course of the study in all subjects. Up to 20 plasma samples were collected for regadenoson concentration determination within the 24 hours after each supine dosage. All urine was collected during the 24-hour time period post-dose and an aliquot was used for the determination of the regadenoson concentration. Heart rate and blood pressure were recorded at many of the same timepoints that the samples for the pharmacokinetic analysis were taken. A non linear mixed-effect modelling approach, using the software NONMEM, was utilised in modelling the plasma and urine concentration-time profiles and temporal changes in heart rate after regadenoson administration in the supine position. The influences of several covariates, including bodyweight, body mass index and age, on pharmacokinetic model parameters were investigated.

RESULTS

Adverse events were more prevalent at regadenoson doses above 3 micro g/kg, and the increase in the occurrence of adverse events was dose-related. Most of the adverse events were related to vasodilation and an increase in heart rate and were generally of mild to moderate severity. Based on the severity and frequency of adverse events, the maximum tolerated doses of regadenoson were deemed to be 10 micro g/kg in the standing position and 20 micro g/kg in the supine position. The pharmacokinetics of regadenoson were successfully described by a three-compartment model with linear clearance. Following intravenous bolus dose administration, regadenoson was rapidly distributed throughout the body, followed by relatively slower elimination (terminal elimination half-life of approximately 2 hours). The clearance was estimated to be 37.8 L/h, with renal excretion accounting for approximately 58% of the total elimination. The volume of distribution of the central compartment and the volume of distribution at steady state were estimated to be 11.5L and 78.7L, respectively. Individual pharmacokinetic parameter estimates were fixed in the pharmacodynamic model, where changes in heart rate were related to plasma drug concentrations using a Michaelis-Menten model. The maximum heart rate increase (Emax) and plasma regadenoson concentration causing a 50% increase in the maximum heart rate (EC50) were estimated to be 76 beats per minute and 12.3 ng/mL, respectively. None of the tested covariates was found to be correlated with any of the pharmacokinetic model parameters.

CONCLUSIONS

The pharmacokinetics and the effects of regadenoson on heart rate were successfully described using pharmacokinetic/pharmacodynamic modelling. The lack of a correlation between the model estimates and various baseline patient demographics supports unit-based dose administration of regadenoson.