Despite the currently recommended dual antiplatelet treatment (DAT) with aspirin and P2Y12 inhibition in patients with coronary artery disease (CAD) there is a risk of adverse clinical outcome. Pharmacodynamic (PD) poor response to clopidogrel occurs in ~ 30% of clopidogrel-treated patients and is associated with an increased risk of recurrent thrombotic events. The aims of this thesis were to compare the PD and pharmacokinetic effects of clopidogrel 600 mg loading dose (LD)/ 75 mg standard maintenance dose (MD) with the novel P2Y12 inhibitor prasugrel 60 mg LD/10 mg MD, in 110 patients with CAD. The mechanisms behind clopidogrel poor response were investigated by assessing the pharmacodynamics after adding clopidogrel active metabolite (AM) and genotyping for variation in CYP-genes involved in thienopyridine metabolism. In another study, we compared the on-clopidogrel platelet reactivity of patients with stent thrombosis (ST) (n=48) or myocardial infarction (MI) (n=30) while on DAT and their matched controls (n=50 + 28). Prasugrel achieved a faster and greater P2Y12-mediated platelet inhibition than clopidogrel measured with light transmission aggregometry, VASP and VerifyNow® P2Y12. Prasugrel’s greater platelet inhibition was associated with higher exposure of AM. The addition of clopidogrel AM led to maximal platelet inhibition in all subjects, suggesting that prasugrel’s greater antiplatelet effect was related to more efficient AM generation compared to that of clopidogrel. Lower levels of AM as well as less platelet inhibition were seen in clopidogrel-treated patients with reduced-metabolizer genotype CYP2C19 compared to those with normal genotype. Patients with ST while on DAT showed higher on-clopidogrel platelet reactivity compared to matched stented controls. Patients with spontaneous MI after stenting did not. In conclusion, these results showed a high rate PD poor response to a high bolus dose of clopidogrel because of a partly genetically caused lower generation of AM which could be overcome by prasugrel treatment. In patients after coronary stenting, clopidogrel poor response was related to ST but not to spontaneous MI, illustrating difficulties in optimizing treatment with clopidogrel based on platelet function or genetic testing in individual patients.

Cardiovascular disease is the leading cause of death worldwide and ischemic heart disease is the most common manifestation. Despite improved outcomes during the last decades, patients with acute coronary syndromes (ACS) are still at substantial risk of recurrent ischemic events and mortality. The aims of this thesis were to investigate the effect of the novel antiplatelet agent ticagrelor versus clopidogrel in patients with non-ST-elevation ACS (NSTE-ACS), overall and in relation to initial revascularization, and to explore this effect in relation to cardiac biomarkers. The impact of timing of revascularization in non-ST-elevation myocardial infarction (NSTEMI) was also studied, by assessing risk of mortality and recurrent myocardial infarction in relation to delay of percutaneous coronary intervention (PCI) in a nation-wide cohort. Finally, a novel clinical prediction model based on angiographic findings, biomarkers, and clinical characteristics was developed to estimate risk of ischemic events after performed revascularization. Ticagrelor treatment compared with clopidogrel was associated with a reduction in the composite endpoint of cardiovascular death/myocardial infarction/stroke and mortality alone, without any increase in overall major bleeding, but increased non-CABG-related major bleeding. The effect of ticagrelor over clopidogrel was consistent independent of initial revascularization. Elevated high-sensitivity cardiac troponin-T predicted benefit of ticagrelor over clopidogrel, while no difference between treatments was detected at normal levels. In patients with NSTEMI, PCI treatment within two days after hospital admission was associated with lower risk of all-cause death and recurrent myocardial infarction compared with delayed PCI. The new clinical prediction model included the following variables: prior vascular disease, extent of coronary artery disease, level of N-terminal pro-B-type natriuretic peptide and estimated glomerular filtration rate; and showed good discriminatory ability for the risk prediction of cardiovascular death/myocardial infarction/stroke and cardiovascular death alone. In conclusion, these results show that ticagrelor reduces the risk of recurrent ischemic events and mortality in patients with NSTE-ACS when compared with clopidogrel, and this effect seems independent of performed revascularization. The results also indicate that biomarkers could be used to select patients who would benefit most from more intense platelet inhibition. Furthermore, early PCI in NSTEMI seems to be associated with improved outcome. Finally, the novel clinical prediction model based only on four variables showed good discriminatory ability, which makes it a potentially effective and simple tool for tailored treatment based on individual risk of recurrent events.