Dual antiplatelet therapy (DAPT) — a combination of a P2Y₁₂ receptor inhibitor and aspirin — has revolutionized antithrombotic treatment options in an acute coronary syndrome (ACS) patients with and without invasive management.1)2) The accessibility of a variety of P2Y₁₂ inhibitors enabled physicians to switch these drugs in reflection of individual patient features including their bleeding and thrombotic risk after stent implantation. The potent P2Y₁₂ inhibitors prasugrel and ticagrelor exhibit a strong and more consistent platelet inhibition when compared to clopidogrel. These pharmacologic properties resulted in a significant reduction in ischemic events, albeit at the expense of an increased bleeding risk in ACS patients undergoing percutaneous coronary intervention (PCI).3)4)5) The challenge of preventing ischemic events with an acceptable bleeding risk of ACS patients by adapting P2Y₁₂ receptor inhibitor therapy is a field of intensive research.2)6) Switching between oral P2Y₁₂ inhibitors can either result in a stronger P2Y₁₂ receptor inhibition (e.g. clopidogrel to prasugrel or ticagrelor) or reduced P2Y₁₂ receptor inhibition (e.g. ticagrelor or prasugrel to clopidogrel). Those strategies are defined as DAPT escalation and de-escalation, respectively.7) In the pivotal phase III trials (PLATO, TRITON-TIMI 38) ticagrelor and prasugrel significantly reduced ischemic events especially in the early period after PCI when compared to clopidogrel.3)4)8) However, bleeding complications are an omnipresent issue during the entire maintenance phase of DAPT (Figure 1). In addition, switching to clopidogrel may have an economic advantage given the high treatment costs of ticagrelor and prasugrel.7) An unguided DAPT de-escalation approach is already adopted by many physicians when treating ACS patients after PCI9) but the limited data that is available is still conflicting.9)10) Moreover, the current clinical practice guidelines offer no clear recommendations on de-escalation of P2Y₁₂ inhibitors, leaving clinicians uninformed on how to manage these patients.11)12) Our review summarizes and explains the rationale as well as the current evidence on de-escalating P2Y₁₂ receptor inhibitor treatment, including both un-guided and guided treatment approaches.

Oral P2Y₁₂ receptor inhibitor treatment is a key element for secondary prevention of thrombotic events in ACS patients and especially for those patients with invasive management by means of PCI.2) For ACS patients the current clinical practice guidelines recommend a one-year treatment period with a potent P2Y₁₂ inhibitors combined with aspirin.12)13)14) Prasugrel and ticagrelor are superior to clopidogrel in preventing ischemic events³⁾⁴⁾ due to a more immediate and intense platelet inhibition. In general, escalated DAPT is accompanied by a higher risk for bleeding events and those bleeds are very prominent during the maintenance phase of treatment (Figure 1).3)4)15)16)17)18) Therefore, identification of appropriate patients for DAPT de-escalation may prove useful for an optimized and more personalized P2Y₁₂ receptor treatment after PCI. As outlined in Figure 2 there are factors that favor and there are factors against a DAPT de-escalation approach. In clinical practice, there is a variety of possibilities to downgrade the potency of antiplatelet treatment over time and this may include a dose reduction of potent P2Y₁₂ receptor blockers,19) a discontinuation of aspirin12)20) and a possible shortening of the DAPT duration. Our review focuses on a true DAPT de-escalation defined as a switch from a potent P2Y₁₂ blocker such as prasugrel or ticagrelor to clopidogrel.7) Indeed, many physicians already shorten the treatment duration with the potent drugs to the early weeks or months after the ACS event.9)21)22)23) The main reasons for de-escalation in this setting are reduced costs and concerns of bleeding during prasugrel and ticagrelor treatment, respectively. In case of ticagrelor, side effects such as dyspnea represent an additional possibility for modifying the ongoing treatment.3)24)25)26) Although there is general paucity of randomized data on de-escalating P2Y₁₂ blocker therapy (Table 1), 2 randomized controlled trials have provided first and promising results on the efficacy and safety of such a biologically plausible treatment regimen. Whereas the timing of optimal platelet inhibition after acute coronary syndrome (TOPIC)27) trial investigated an unguided DAPT strategy that included both ticagrelor and prasugrel, Testing Responsiveness to Platelet Inhibition on Chronic Antiplatelet Treatment for Acute Coronary Syndrome (TROPICAL-ACS)28)29) used platelet function testing to guide DAPT de-escalation from the potent P2Y₁₂ inhibitor prasugrel to clopidogrel.

Observational data suggests an in-hospital de-escalation rate of 5–14% and a post-hospital switching rate of 5–8%.30) For instance, Treatment With Adenosine Diphosphate (ADP) Receptor Inhibitors: Longitudinal Assessment of Treatment Patterns and Events After Acute Coronary Syndrome (TRANSLATE ACS), a large multicenter, longitudinal registry in 12,365 ACS patients captured data on post discharge switching in patients with acute myocardial infarction.30) Among patients discharged on prasugrel or ticagrelor a switch to clopidogrel was very common and strongly associated with having a government medication insurance and financial hardship of medication costs. Bleeding events and increase in creatinine clearance were also associated factors prior to the switching. By contrast, a higher education was correlated with continuation of P2Y₁₂ inhibitors suggesting costs as a main driver of switching. Switching after discharge from prasugrel or ticagrelor to clopidogrel was not associated with a significant increase in thrombotic events and GUSTO moderate/severe bleeding. Comparable results are derived from randomized data of the Comparison of Prasugrel and Ticagrelor in the Treatment of Acute Myocardial Infarction (PRAGUE-18) trial, which compared ticagrelor versus prasugrel in 1,280 ST-elevation myocardial infarction or high-risk non-ST-elevation myocardial infarction patients. After 12 months no significant differences in the composite endpoint (death, cardiovascular death, myocardial infarction, stent thrombosis, stroke and bleeding) were seen for ticagrelor and prasugrel in the intention to treat analysis (5.7% vs. 6.6%; p=0.50).31) Approximately half of the patients were switched and de-escalated to clopidogrel at the 12-month follow-up. Interestingly, most of the switches were due to economic reasons and 70% of them occurred early and during the 30-day period after the index event. In the PRAGUE-18 trial, an economically driven de-escalation to clopidogrel was associated with a reduction in thrombotic and bleeding events, whereas a non-economically switch was accompanied by a higher ischemic event rate. Overall, patients who de-escalated to clopidogrel due to economic reasons had reduced risk compared with those who continued on ticagrelor or prasugrel. However, it must be emphasized that PRAGUE-18 investigators reported those outcome measures in relation to switch of treatment, while the trial was not specifically designed to address those questions.10)

Non-randomized registry data from the Switching From Clopidogrel to New Oral Antiplatelet Agents During Percutaneous Coronary Intervention (SCOPE) registry in 1,363 patients revealed that ischemic events were substantially increased in patients undergoing a de-escalation approach after PCI for ACS.32) Such findings should raise a note of caution to an unguided de-escalation approach, although randomized data from a smaller single-center trial is promising. Indeed, the TOPIC trial evaluated the clinical benefit of an unguided DAPT de-escalation by switching from prasugrel or ticagrelor to clopidogrel one month after PCI for ACS (Figure 3). This smaller single-center study enrolled 646 patients and the primary end point — a net clinical benefit endpoint consisting of cardiovascular death, urgent revascularization, stroke and bleeding as defined by the Bleeding Academic Research Consortium (BARC) classification — occurred in 13.4% in the switched versus 26.3% in the unswitched group (hazard ratio [HR], 0.48; 95% confidence interval [CI], 0.34–0.68; p<0.01). This net benefit favoring DAPT de-escalation was driven by a reduction in overall bleeding events but it must be emphasized that ischemic events like stent thrombosis or myocardial infarctions were not reported in a detailed manner at all. Interestingly, in a platelet function testing (PFT) sub-study of the TOPIC trial (TOPIC-VASP) de-escalated DAPT was superior regardless of initial platelet reactivity, but the benefit was greater in low on-treatment platelet reactivity patients.33) Considering all the available evidence on an unguided DAPT de-escalation approach it must be emphasized that the data available is conflicting and that further studies in larger cohorts of patients are urgently needed to lend more support to such an unguided approach of de-escalating DAPT (early or late) in ACS patients after PCI.

The pro-drug clopidogrel is characterized by a significant response variability and a substantial proportion of patients exhibit a status of high on-treatment platelet reactivity (HPR). This and other circumstances triggered the development of ex-vivo PFT assays.34)35)36)37) Indeed, DAPT de-escalation from a potent P2Y₁₂ inhibitor to the less potent clopidogrel should account for the large response variability of the latter34) and the consequential issue of HPR, which exists in a relevant number of ACS patients.35)38)39) HPR patients exhibit a higher risk for ischaemic events including myocardial infarction and stent thrombosis.35)38)39) Hence, PFT could serve to safeguard a DAPT de-escalation by identifying HPR patients on clopidogrel, as those patients may be exposed to a higher risk of thrombotic events due to insufficient P2Y₁₂ inhibition and they should therefore continue with potent P2Y₁₂ inhibitors. Taking all these relevant aspects into consideration, the objective of the randomized, multi-center investigator-initiated TROPICAL-ACS trial (n=2,610 patients) was to investigate the safety and efficacy of a PFT-guided early de-escalation of antiplatelet treatment compared to standard prasugrel therapy in ACS patients undergoing PCI. The trial met its primary endpoint and demonstrated non-inferiority for a net clinical benefit endpoint in patients scheduled for PFT guided de-escalation vs. conventional prasugrel treatment.29) Importantly, the rates of ischemic events including CV death, MI or stroke were similar in the guided de-escalation study group vs. control group and a trend towards less bleeding during guided treatment was reported. Therefore, a strategy of guided DAPT de-escalation can be considered in selected ACS patients (NSTEMI and STEMI) as an alternative to 12 months treatment with ticagrelor or prasugrel. It must be acknowledged that such a guided de-escalation strategy results in clopidogrel treatment in most but not in all patients, as some patients would have to be escalated back to prasugrel. The TROPICAL-ACS trial was powered for demonstrating non-inferiority for the primary endpoint (net clinical benefit) and was not powered for ischemic events alone. Thus, large-scale trials would be helpful to corroborate the safety of such a concept with respect to ischemic risk of ACS patients after treatment de-escalation. For the time being and based on the reported results a selective use of a guided DAPT de-escalation strategy seems reasonable and this strategy may be a good alternative for DAPT in selected patients and especially for those who cannot go for 1-year potent platelet inhibition.

Elderly ACS patients have a unique risk profile for both ischemic and bleeding events. The ANTARCTIC trial (Adjust Antiplatelet Therapy in Elderly Patients Stented for an Acute Coronary Syndrome) aimed to assess the safety and efficacy of PFT in 877 ACS patients ≥75 years.40) The study compared a reduced dose of prasugrel (5 mg/d, as recommended for elderly patients) vs. PFT-guided escalation (10 mg prasugrel) or de-escalation (75 mg clopidogrel) in the intervention arm. Study results were neutral, with similar ischemic and bleeding rates in both groups (28% vs. 28%; HR, 1.003; 95% CI, 0·78–1·29; p=0·98). When interpreting ANTARCTIC results it should be noted that superiority of low-dose prasugrel over standard clopidogrel treatment in terms of clinical outcomes has not been demonstrated, independent of whether or not PFT was included.41) A subgroup analysis of TROPICAL-ACS also addressed the impact of age on clinical outcomes after guided de-escalation. In patients younger than 70 years the incidence of the primary endpoint (cardiovascular death, myocardial infarction, stroke, BARC bleeding) was significantly lower in the guided de-escalation versus the control group (5.9% vs. 8.3%; HR, 0.70; 95% CI, 0.51–0.96; p=0.03; NNT=42) mainly driven by reduced bleeding events. In patients older than 70 years the primary endpoint occurred more frequent but was indistinguishable between both groups (15.5% vs. 13.6%).42) Thus, the age-dependent results from TROPICAL-ACS confirmed ANTARCTIC study results and a possible benefit of PFT with individualized treatment may be confined to younger patients while effects are neutral in the elderly.

Specific considerations must be reflected for the large population of East Asian patients, who carry a different and very specific risk profile for both ischemic and bleeding complications when compared to the Caucasian population.43) Related to this, a different and specific genetic profile (higher prevalence for the CYP2C19*2 and *3 Loss-of-Function [LoF] alleles) is associated with a significantly higher rate of HPR in East Asian patients. Despite this difference and very surprisingly, East Asians do not show an elevated risk for thrombotic complications. In contrast, a significantly lower risk of ischemic events was described leading to a phenomenon further referred to as the ‘East Asian paradox.’ Thus, based on these specific clinical observations, a right-shifted therapeutic window of on-treatment P2Y₁₂-directed platelet reactivity with higher cut-offs for HPR may apply to East Asian patients in contrast to Caucasians and this may have an impact on drugs and drug dosing for those patients. Moreover, with respect to a lower body mass index reduced doses of prasugrel and ticagrelor may be a good choice for East Asian patients specifically.

In conclusion and based on the results of the pivotal phase III trials3)4) a 12 months DAPT that includes prasugrel or ticagrelor for ACS patients after PCI is standard of care in 2018 and beyond.12)13)14) However, a DAPT de-escalation must be considered as an attractive alternative treatment concept and may be considered in specific clinical scenarios (bleeding events, high bleeding risk, socio-economic indications) as an alternative to DAPT with potent P2Y₁₂ receptor inhibitors (Figures 1 and 2). Based upon the current evidence any DAPT de-escalation should be guided and an unguided de-escalation may carry a substantial risk for the patient. Alternative treatment regimens of single antiplatelet therapy after stopping aspirin early after PCI and with continued treatment with a potent P2Y₁₂ receptor inhibitor (ticagrelor) are under clinical investigation in the GLOBAL LEADERS (ClinicalTrials.gov, NCT01813435) and TWILIGHT (ClinicalTrials.gov, NCT02270242) trials. Those trials may have the potential to reduce bleeding risk without influencing antithrombotic efficacy. In contrast to a PFT guided adjustment of antiplatelet therapy, the TAILOR PCI (ClinicalTrials.gov, NCT01742117) and POPular Genetics trial (ClinicalTrials.gov, NCT01761786) use a genetic approach of individualized DAPT. As clopidogrel response is dependent on CYP2C19 polymorphisms,44)45)46)47) these trials investigate the usefulness of selective genotyping (CYP2C19) during P2Y₁₂ receptor inhibitor treatment. All the published and ongoing trials in concert are important as attempts to move forward and to pave the way for a contemporary concept of a more personalized P2Y₁₂ receptor inhibitor therapy that includes both escalation and de-escalation strategies for selected patients.