Antiplatelet therapy in acute coronary syndromes: focus on ticagrelor

Comparison of Clopidogrel, Prasugrel and Ticagrelor Response of Patients by PFA-100-Innovance Test Results

Devices such as stents and flow diverters require the use of safe and fast antiplatelet therapy. We aimed to compare the responses to clopidogrel, prasugrel, and ticagrelor by assessing the Platelet Function Analysis (PFA-100)-Innovance test results of patients undergoing endovascular stenting to determine their resistance rates. Sixty-one women and 55 men, aged 18-87 years, were included in this study. Patients were divided into three groups: clopidogrel treatment, prasugrel treatment, and ticagrelor treatment. The systemic diseases of the patients, especially hypertension and diabetes, were recorded. The test results were evaluated according to the results for the collagen/epinephrine (COL-EPI), collagen/adenosine (COL-ADP), and P2Y results. The PFA-100-Innovance results for COL-EPI and P2Y were significantly higher for patients treated with prasugrel and ticagrelor compared with patients treated with clopidogrel (COL-EPI, p = 0.001; P2Y, p = 0.001). Clopidogrel resistance was identified in 31 patients (26.7%), and prasugrel resistance was identified in 4 patients (3.4%). Ticagrelor resistance was not detected. Therefore, 30.1% of patients were classified as drug-resistant. Perioperative bleeding was not detected in any patient. Hypertension was the most common disease recorded for patients being treated for cerebral aneurysm, and diabetes was the most common disease recorded for patients who underwent peripheral artery stenting (p = 0.002). Potent antiplatelet agents, such as prasugrel and ticagrelor, have a low rate of resistance but are associated with an increased bleeding risk. Thus, the choice of a suitable drug during the treatment window remains a critical factor when determining treatment strategies.

P2Y12 receptor antagonism inhibits proliferation, migration and leads to autophagy of glioblastoma cells

Glioblastoma (GBM) is the most aggressive and lethal among the primary brain tumors, with a low survival rate and resistance to radio and chemotherapy. The P2Y₁₂ is an adenosine diphosphate (ADP) purinergic chemoreceptor, found mainly in platelets. In cancer cells, its activation has been described to induce proliferation and metastasis. Bearing in mind the need to find new treatments for GBM, this study aimed to investigate the role of the P2Y₁₂R in the proliferation and migration of GBM cells, as well as to evaluate the expression of this receptor in patients' data obtained from the TCGA data bank. Here, we used the P2Y₁₂R antagonist, ticagrelor, which belongs to the antiplatelet agent's class. The different GBM cells (cell line and patient-derived cells) were treated with ticagrelor, with the agonist, ADP, or both, and the effects on cell proliferation, colony formation, ADP hydrolysis, cell cycle and death, migration, and cell adhesion were analyzed. The results showed that ticagrelor decreased the viability and the proliferation of GBM cells. P2Y₁₂R antagonism also reduced colony formation and migration potentials, with alterations on the expression of metalloproteinases, and induced autophagy in GBM cells. Changes were observed at the cell cycle level, and only the U251 cell line showed a significant reduction in the ADP hydrolysis profile. TCGA data analysis showed a higher expression of P2Y₁₂R in gliomas samples when compared to the other tumors. These data demonstrate the importance of the P2Y₁₂ receptor in gliomas development and reinforce its potential as a pharmacological target for glioma treatment.

Integrating Mechanisms in Thrombotic Peripheral Arterial Disease

Peripheral arterial disease (PAD), a manifestation of systemic atherosclerosis, is underdiagnosed in the general population. Despite the extensive research performed to unravel its pathophysiology, inadequate knowledge exists, thus preventing the development of new treatments. This review aims to highlight the essential elements of atherosclerosis contributing to the pathophysiology of PAD. Furthermore, emphasis will be placed on the role of thrombo-inflammation, with particular focus on platelet and coagulation activation as well as cell-cell interactions. Additional insight will be then discussed to reveal the contribution of hypercoagulability to the development of vascular diseases such as PAD. Lastly, the current antithrombotic treatments will be discussed, and light will be shed on promising new targets aiming to aid the development of new treatments.

Comparison of Safety and Efficacy Between Clopidogrel and Ticagrelor in Elderly Patients With Acute Coronary Syndrome: A Systematic Review and Meta-Analysis

Background: Dual antiplatelet therapy combining aspirin with a P2Y12 adenosine diphosphate receptor inhibitor is a therapeutic mainstay for acute coronary syndrome (ACS). However, the optimal choice of P2Y12 adenosine diphosphate receptor inhibitor in elderly (aged ≥65 years) patients remains controversial. We conducted a meta-analysis to compare the efficacy and safety of ticagrelor and clopidogrel in elderly patients with ACS. Methods: We comprehensively searched in Web of Science, EMBASE, PubMed, and Cochrane databases through 29^th March, 2021 for eligible randomized controlled trials (RCTs) comparing the efficacy and safety of ticagrelor or clopidogrel plus aspirin in elderly patients with ACS. Four studies were included in the final analysis. A fixed effects model or random effects model was applied to analyze risk ratios (RRs) and hazard ratios (HRs) across studies, and I² to assess heterogeneity.

Results: A total number of 4429 elderly patients with ACS were included in this analysis, of whom 2170 (49.0%) patients received aspirin plus ticagrelor and 2259 (51.0%) received aspirin plus clopidogrel. The ticagrelor group showed a significant advantage over the clopidogrel group concerning all-cause mortality (HR 0.78, 95% CI 0.63–0.96, I² = 0%; RR 0.79, 95% CI 0.66–0.95, I² = 0%) and cardiovascular death (HR 0.71, 95% CI 0.56–0.91, I² = 0%; RR 0.76, 95% CI 0.62–0.94, I² = 5%) but owned a higher risk of PLATO major or minor bleeding (HR 1.46, 95% CI 1.13–1.89, I² = 0%; RR 1.40, 95% CI 1.11–1.76, I² = 0%). Both the groups showed no significant difference regarding major adverse cardiovascular events (MACEs) (HR 1.06, 95% CI 0.68–1.65, I² = 77%; RR 1.04, 95% CI 0.69–1.58, I² = 77%).

Conclusion: For elderly ACS patients, aspirin plus ticagrelor reduces cardiovascular death and all-cause mortality but increases the risk of bleeding. Herein, aspirin plus ticagrelor may extend lifetime for elderly ACS patients compared with aspirin plus clopidogrel. The optimal DAPT for elderly ACS patients may be a valuable direction for future research studies.

Coronary Heart Disease (CHD) in Elderly Patients: Which Drug to Choose, Ticagrelor and Clopidogrel? A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: A new generation P2Y12 receptor inhibitor (ticagrelor) is recommended in current therapeutic guidelines to treat patients with coronary heart disease (CHD). However, it is unknown if ticagrelor is more effective than clopidogrel in elderly patients. Therefore, a systematic review was done to assess the effectiveness and safety of ticagrelor and clopidogrel in older patients with CHD to determine the appropriate antiplatelet treatment plan. Methodology: We performed a systematic review of randomized controlled trials (RCTs) to compare the effectiveness and safety of ticagrelor vs. clopidogrel in elderly patients with CHD. We selected eligible RCTs based on specified study criteria following a systematic search of PubMed and Scopus databases from January 2007 to May 2021. Primary efficacy outcomes assessed were major adverse cardiovascular events (MACEs), myocardial infarction (MI), stent thrombosis (ST), and all-cause death. The secondary outcome assessed was major bleeding events. We used RevMan 5.3 software to conduct a random-effects meta-analysis and estimated the pooled incidence and risk ratios (RRs) with 95% confidence intervals (CIs) for ticagrelor and clopidogrel. Results: Data from 6 RCTs comprising 21,827 elderly patients were extracted according to the eligibility criteria. There was no significant difference in the MACE outcome (incidence: 9.23% vs. 10.57%; RR = 0.95, 95% CI = 0.70–1.28, p = 0.72), MI (incidence: 5.40% vs. 6.23%; RR = 0.94, 95% CI= 0.69–1.27, p = 0.67), ST (incidence: 2.33% vs. 3.17%; RR = 0.61, 95% CI= 0.32–1.17, p = 0.13), and all-cause death (4.29% vs. 5.33%; RR = 0.86, 95% CI = 0.65–1.12, p = 0.25) for ticagrelor vs. clopidogrel, respectively. In addition, ticagrelor was not associated with a significant increase in the rate of major bleeding (incidence: 9.98% vs. 9.33%: RR = 1.37, 95% CI = 0.97–1.94, p = 0.07) vs. clopidogrel. Conclusions: This study did not find evidence that ticagrelor is significantly more effective or safer than clopidogrel in elderly patients with CHD.

Suspected Ticagrelor-Induced Bullous Fixed Drug Eruption

We describe a case of a suspected cutaneous hypersensitivity reaction to ticagrelor. The patient displayed a localized bullous fixed drug eruption after being loaded with ticagrelor, which resolved with oral antihistamines and topical steroids after one week. Clopidogrel and rivaroxaban were successfully administered as alternative antithrombotic therapy without any apparent further hypersensitivity skin reaction.

Comparison of Light Transmission Aggregometry With Impedance Aggregometry in Patients on Potent P2Y12 Inhibitors

Since data on the agreement between light transmission aggregometry (LTA) and multiple electrode aggregometry (MEA) in patients on the more potent P2Y₁₂ inhibitors are missing so far, we investigated if the evaluation of the responsiveness to therapy by LTA can be replaced by MEA in 160 acute coronary syndrome (ACS) patients on dual antiplatelet therapy with aspirin and prasugrel or ticagrelor (n = 80 each). Cut-off values for high on-treatment residual platelet reactivity (HRPR) in response to adenosine diphosphate (ADP) or arachidonic acid (AA) were defined according to previous studies showing an association of HRPR with the occurrence of adverse ischemic outcomes. ADP- inducible platelet aggregation was 33% and 37% (P = 0.07) by LTA and 19 AU and 20 AU (P = 0.38) by MEA in prasugrel- and ticagrelor-treated patients, respectively. AA- inducible platelet aggregation was 2% and 3% by LTA and 15 AU and 16 AU by MEA, (all P ≥ 0.3) in patients on prasugrel and ticagrelor, respectively. By LTA, HRPR ADP and HRPR AA were seen in 5%/5% and in 4%/ 13% of patients receiving prasugrel- and ticagrelor, respectively. By MEA, HRPR ADP and HRPR AA were seen in 3%/ 25% and 0%/24% of prasugrel- and ticagrelor-treated patients, respectively. ADP-inducible platelet reactivity by MEA correlated significantly with LTA ADP in prasugrel-treated patients (r = 0.4, P < 0.001), but not in those receiving ticagrelor (r = 0.09, P = 0.45). AA-inducible platelet aggregation by LTA and MEA did not correlate in prasugrel- and ticagrelor-treated patients. Sensitivity/specificity of HRPR by MEA to detect HRPR by LTA were 25%/99% for MEA ADP and 100%/79% for MEA AA in prasugrel-treated patients, and 0%/100% for MEA ADP and 70%/83% for MEA AA in ticagrelor-treated patients. In conclusion, on-treatment residual ADP-inducible platelet reactivity by LTA and MEA shows a significant correlation in prasugrel- but not ticagrelor-treated patients. However, in both groups LTA and MEA revealed heterogeneous results regarding the classification of patients as responders or non-responders to P2Y₁₂ inhibition.

An updated drug profile of ticagrelor with considerations on the treatment of patients with coronary artery disease and diabetes mellitus

INTRODUCTION

Ticagrelor is an antiplatelet agent acting through direct and reversible competitive inhibition of the platelet P2Y₁₂ receptor. While the clinical merits of ticagrelor in patients who experienced an acute coronary syndrome are widely accepted, its role in stable coronary artery disease is less established. Recently, large-scale trials of ticagrelor have been published in this setting, including a trial in patients with diabetes mellitus (DM).

AREAS COVERED

This review aims to inform about recent findings on ticagrelor, by appraising the current body of evidence on its use in different clinical scenarios, particularly in DM, ranging from pharmacology to clinical outcomes and future directions.

EXPERT OPINION

The results of the THEMIS trial, conducted in DM patients with stable coronary artery disease and no prior stroke or myocardial infarction, showed that although ticagrelor in addition to aspirin reduced the risk of ischemic events, this was associated with a parallel increase in bleeding complications. However, patients with history of percutaneous coronary intervention seemed to benefit more from adjunctive ticagrelor therapy. Careful bleeding and ischemic risk stratification remains crucial to define the best antithrombotic strategy for the individual patient.

Ticagrelor Use in Indian Patients Undergoing Neuroendovascular Procedures: A Single Center Experience

PURPOSE

A safe and efficacious antiplatelet drug is needed for patients with clopidogrel resistance who undergo neuroendovascular procedures. Ticagrelor is a new reversibly binding, oral, direct-acting P2Y receptor antagonist with no known resistance. We describe our clinical experience using ticagrelor for neuroendovascular procedures in Indian patients with clopidogrel resistance at the NH Institute of Neurosciences, Narayana Health City, Bangalore.

MATERIALS AND METHODS

We retrospectively reviewed our endovascular procedure database for all patients with predefined clopidogrel resistance. Clopidogrel resistance was defined as P2Y12 inhibition <40%. Patients were administered ticagrelor along with aspirin prior to the procedure.

RESULTS

Of 127 patients, 32 (25%) were non-responders to clopidogrel (22 [69%] males, 10 [31%] females; median age, 54 years [range, 20-75]). All patients were treated with a 180-mg loading dose of ticagrelor, followed by 90 mg twice daily. Twenty patients (63%) underwent endovascular intervention for intracranial aneurysm, two (6%) for dissecting aneurysms, nine (28%) for stenotic lesions, and one (3%) for carotico-cavernous fistula. No patient experienced any adverse effects related to the use of Ticagrelor in the postoperative period.

CONCLUSION

Ticagrelor is an effective alternative to clopidogrel for use in conjunction with aspirin in patients with clopidogrel resistance. None of our patients had adverse effects from ticagrelor. Drug cost, twice-daily dosing, and risk of faster platelet aggregation activation after discontinuation should be taken into consideration prior to its use in such patients.

Effect of Chewing vs Swallowing Ticagrelor on Platelet Inhibition in Patients With ST-Segment Elevation Myocardial Infarction: A Randomized Clinical Trial

Importance

Dual anti-platelet therapy represents standard care for treating patients with ST-segment elevation myocardial infarction (STEMI). Ticagrelor is a direct-acting P2Y12 inhibitor and, unlike clopidogrel and prasugrel, does not require metabolic activation.

Objective

To evaluate whether chewing a loading dose (LD) of ticagrelor, 180 mg, vs traditional oral administration of an equal dose enhances platelet inhibition at 30 minutes and 1 hour after LD administration in patients with STEMI.

Design, Setting, and Participants

A randomized clinical trial was conducted in adults aged 30 to 87 years from May to October 2016 in a large tertiary care center. Analyses were intention-to-treat.

Interventions

Fifty patients with STEMI were randomized to either chewing an LD of ticagrelor, 180 mg, or standard oral administration of an equal dose.

Main Outcomes and Measures

P2Y12 reaction units were evaluated using VerifyNow (Accumentrics) at baseline, 30 minutes, 1 hour, and 4 hours after LD.

Results

Baseline characteristics were similar in both groups. The mean (SD) of P2Y12 reaction units in the chewing group compared with the standard group at baseline, 30 minutes, 1 hour, and 4 hours after ticagrelor LD were 224 (33) vs 219 (44) (95% CI, -16.77 to 27.73; P = .26), 168 (78) vs 230 (69) (95% CI, -103.77 to -19.75; P = .003), 106 (90) vs 181 (89) (95% CI, -125.15 to -26.29; P = .005), and 43 (41) vs 51 (61) (95% CI, -36.34 to 21.14; P = .30), respectively. Platelet reactivity in the chewing group was significantly reduced by 24% at 30 minutes after LD (95% CI, 19.75 to 103.77; P = .001). The relative inhibition of platelet aggregation in the chewing vs the standard group were 51% vs 10% (95% CI, 13.69 to 67.67; P = .005) at 1 hour and 81% vs 76% (95% CI, -12.32 to 16.79; P = .24) at 4 hours, respectively. Major adverse cardiac and cardiovascular event rate at 30 days was low (4%) and occurred in 1 patient in each group (95% CI, 0.06 to 16.93; P > .99).

Conclusions and Relevance

Chewing an LD of ticagrelor, 180 mg, in patients with STEMI is feasible and facilitates better early platelet inhibition compared with a standard oral LD. Larger studies are warranted to see if our preliminary findings translate into clinical outcomes.

Trial Registration

clinicaltrials.gov Identifier: NCT02725099.

A brief review on resistance to P2Y12 receptor antagonism in coronary artery disease

Background

Platelet inhibition is important for patients with coronary artery disease. When dual antiplatelet therapy (DAPT) is required, a P2Y₁₂-antagonist is usually recommended in addition to standard aspirin therapy. The most used P2Y₁₂-antagonists are clopidogrel, prasugrel and ticagrelor. Despite DAPT, some patients experience adverse cardiovascular events, and insufficient platelet inhibition has been suggested as a possible cause. In the present review we have performed a literature search on prevalence, mechanisms and clinical implications of resistance to P2Y₁₂ inhibitors.

Methods

The PubMed database was searched for relevant papers and 11 meta-analyses were included. P2Y₁₂ resistance is measured by stimulating platelets with ADP ex vivo and the most used assays are vasodilator stimulated phosphoprotein (VASP), Multiplate, VerifyNow (VN) and light transmission aggregometry (LTA).

Discussion/conclusion

The frequency of high platelet reactivity (HPR) during clopidogrel therapy is predicted to be 30%. Genetic polymorphisms and drug-drug interactions are discussed to explain a significant part of this inter-individual variation. HPR during prasugrel and ticagrelor treatment is estimated to be 3–15% and 0–3%, respectively. This lower frequency is explained by less complicated and more efficient generation of the active metabolite compared to clopidogrel. Meta-analyses do show a positive effect of adjusting standard clopidogrel treatment based on platelet function testing. Despite this, personalized therapy is not recommended because no large-scale RCT have shown any clinical benefit. For patients on prasugrel and ticagrelor, platelet function testing is not recommended due to low occurrence of HPR.

Comparisons between ticagrelor and clopidogrel following percutaneous coronary intervention in patients with acute coronary syndrome: a comprehensive meta-analysis

Background

The efficacy and safety of ticagrelor following percutaneous coronary intervention for patients with acute coronary syndrome remains unclear. This study sought to evaluate clinical outcomes of ticagrelor as part of dual-antiplatelet treatment for these patients.

Methods

PubMed, MEDLINE, Embase, and other Internet sources were searched for eligible citations. The primary end point was major adverse cardiovascular and cerebrovascular events, consisting of cardiovascular death, myocardial infarction, and stroke. The secondary end point was the occurrence of definite/probable stent thrombosis (ST). The risk of bleeding was chosen to be the safety end point.

Results

Eleven clinical trials – six randomized trials and five observational trials – were finally analyzed. A tendency toward reduction in the risk of major adverse cardiovascular and cerebrovascular events was observed only with respect to ticagrelor (OR 0.83, 95% CI 0.66–1.03; P=0.091), which might have resulted from the lower risk of cardiovascular death (OR 0.78, 95% CI 0.68–0.89; P<0.001). The overall incidence of ST differed significantly between the ticagrelor group and the clopidogrel group (OR 0.74, 95% CI 0.59–0.93; P=0.009), but the risk of bleeding, regardless of major or minor bleeding, increased significantly.

Conclusion

As part of dual-antiplatelet treatment following percutaneous coronary intervention, ticagrelor significantly reduced the risk of cardiovascular death and ST in acute coronary syndrome patients, but at the cost of bleeding. More powerful relevant randomized trials are still warranted to guide clinical decision-making.

Dental management of patients on anti-thrombotic agents

The number of geriatric patients seeking dental service is ever-rising because of increased life expectancy, also with problem of increased chronic medical conditions. One of them are patients on anti-thrombotic medication. Bleeding complication after minor oral surgery by anti-thrombotic agents is of concerns to dentists on dental management of these patients. Risk and benefit of the anti-thrombotic agents must be weighed before initiating dental procedures, which should be established as a treatment guideline. Purpose of the paper is to optimize the management of the dental patients on anti-thrombotic medication via standardization of treatment protocol of such a patient.

The P2Y12 Receptor Antagonist Ticagrelor Reduces Lysosomal pH and Autofluorescence in Retinal Pigmented Epithelial Cells From the ABCA4-/- Mouse Model of Retinal Degeneration

The accumulation of partially degraded lipid waste in lysosomal-related organelles may contribute to pathology in many aging diseases. The presence of these lipofuscin granules is particularly evident in the autofluorescent lysosome-associated organelles of the retinal pigmented epithelial (RPE) cells, and may be related to early stages of age-related macular degeneration. While lysosomal enzymes degrade material optimally at acidic pH levels, lysosomal pH is elevated in RPE cells from the ABCA4^-/- mouse model of Stargardt's disease, an early onset retinal degeneration. Lowering lysosomal pH through cAMP-dependent pathways decreases accumulation of autofluorescent material in RPE cells in vitro, but identification of an appropriate receptor is crucial for manipulating this pathway in vivo. As the P2Y₁₂ receptor for ADP is coupled to the inhibitory G_i protein, we asked whether blocking the P2Y₁₂ receptor with ticagrelor could restore lysosomal acidity and reduce autofluorescence in compromised RPE cells from ABCA4^-/- mice. Oral delivery of ticagrelor giving rise to clinically relevant exposure lowered lysosomal pH in these RPE cells. Ticagrelor also partially reduced autofluorescence in the RPE cells of ABCA4^-/- mice. In vitro studies in ARPE-19 cells using more specific antagonists AR-C69931 and AR-C66096 confirmed the importance of the P2Y₁₂ receptor for lowering lysosomal pH and reducing autofluorescence. These observations identify P2Y₁₂ receptor blockade as a potential target to lower lysosomal pH and clear lysosomal waste in RPE cells.

Ticagrelor - toward more efficient platelet inhibition and beyond

Novel antiplatelet drugs, including ticagrelor, are being successively introduced into the therapy of atherothrombotic conditions due to their superiority over a standard combination of clopidogrel with acetylsalicylic acid in patients with acute coronary syndromes (ACS). A P2Y12 receptor antagonist, ticagrelor, is unique among antiplatelet drugs, because ticagrelor inhibits the platelet P2Y12 receptor in a reversible manner, and because it demonstrates a wide palette of advantageous pleiotropic effects associated with the increased concentration of adenosine. The pleiotropic effects of ticagrelor comprise cardioprotection, restoration of the myocardium after an ischemic event, promotion of the release of anticoagulative factors and, eventually, anti-inflammatory effects. Beyond the advantageous effects, the increased concentration of adenosine is responsible for some of ticagrelor's adverse effects, including dyspnea and bradycardia. Large-scale clinical trials demonstrated that both standard 12-month therapy and long-term use of ticagrelor reduce the risk of cardiovascular events in patients with ACS, but at the expense of a higher risk of major bleeding. Further trials focused on the use of ticagrelor in conditions other than ACS, including ischemic stroke, peripheral artery disease and status after coronary artery bypass grafting. The results of these trials suggest comparable efficacy and safety of ticagrelor and clopidogrel in extra-coronary indications, but firm conclusions are anticipated from currently ongoing studies. Here, we summarize current evidence on the superiority of ticagrelor over other P2Y12 antagonists in ACS, discuss the mechanism underlying the drug-drug interactions and pleiotropic effects of ticagrelor, and present future perspectives of non-coronary indications for ticagrelor.

Hypersensitivity to ticagrelor and low response to clopidogrel: a case report

Ticagrelor is widely used to treat acute coronary syndrome. Hypersensitivity reaction of ticagrelor is rarely recognized. A low response to clopidogrel, which occurs in up to 23% of patients, is an independent risk factor for stent thrombosis. Management of patients with a low response to clopidogrel and ticagrelor hypersensitivity who are undergoing antithrombotic therapy remains to be a challenge. Herein, we report a patient with low response to clopidogrel and ticagrelor hypersensitivity, who was successfully managed using aspirin and warfarin.

A Comparative Study of Molecular Structure, pKa, Lipophilicity, Solubility, Absorption and Polar Surface Area of Some Antiplatelet Drugs

Theoretical chemistry methods have been used to study the molecular properties of antiplatelet agents (ticlopidine, clopidogrel, prasugrel, elinogrel, ticagrelor and cangrelor) and several thiol-containing active metabolites. The geometries and energies of most stable conformers of these drugs have been computed at the Becke3LYP/6-311++G(d,p) level of density functional theory. Computed dissociation constants show that the active metabolites of prodrugs (ticlopidine, clopidogrel and prasugrel) and drugs elinogrel and cangrelor are completely ionized at pH 7.4. Both ticagrelor and its active metabolite are present at pH = 7.4 in neutral undissociated form. The thienopyridine prodrugs ticlopidine, clopidogrel and prasugrel are lipophilic and insoluble in water. Their lipophilicity is very high (about 2.5–3.5 logP values). The polar surface area, with regard to the structurally-heterogeneous character of these antiplatelet drugs, is from very large interval of values of 3–255 Ų. Thienopyridine prodrugs, like ticlopidine, clopidogrel and prasugrel, with the lowest polar surface area (PSA) values, exhibit the largest absorption. A high value of polar surface area (PSA) of cangrelor (255 Ų) results in substantial worsening of the absorption in comparison with thienopyridine drugs.

Newer agents in antiplatelet therapy: a review

Antiplatelet therapy remains the mainstay in preventing aberrant platelet activation in pathophysiological conditions such as myocardial infarction, ischemia, and stroke. Although there has been significant advancement in antiplatelet therapeutic approaches, aspirin still remains the gold standard treatment in the clinical setting. Limitations in safety, efficacy, and tolerability have precluded many of the antiplatelet inhibitors from use in patients. Unforeseen incidences of increased bleeding risk and recurrent arterial thrombosis observed in patients have hampered the development of superior next generation antiplatelet therapies. The pharmacokinetic and pharmacodynamic profiles have also limited the effectiveness of a number of antiplatelet inhibitors currently in use due to variability in metabolism, time to onset, and reversibility. A focused effort in the development of newer antiplatelet therapies to address some of these shortcomings has resulted in a significant number of potential antiplatelet drugs which target enzymes (phosphodiesterase, cyclooxygenase), receptors (purinergic, prostaglandins, protease-activated receptors, thromboxane), and glycoproteins (αIIbβ3, GPVI, vWF, GPIb) in the platelet. The validation and search for newer antiplatelet therapeutic approaches proven to be superior to aspirin is still ongoing and should yield a better pharmacodynamic profile with fewer untoward side-effects to what is currently in use today.