Evolving Approaches to Antithrombotics in Stroke Prevention and Treatment

Vijayakumar Javalkar, MD, MCh; Okkes Kuybu, MD; Abdallah Amireh, MD; Roger E. Kelley, MD

South Med J. 2020;113(11):585-592.

Conclusions

The optimization of antithrombotic therapy for acute stroke treatment and secondary prevention remains in the process of refinement; however, options have improved dramatically with the release of the NOACs and the results of RCTs to assess potential benefits versus potential risks for our patients in an individualized fashion. It is particularly valuable to have options for our patients when the initial choice of therapy does not demonstrate benefit or is not well tolerated. Recent studies, for example, have supported the benefit and relative safety of short-term DAPT has for minor stroke and TIA but not for triple therapy. Alternative choices such as cilostazol and possibly ticagrelor for refractory patients also may help in the decision-making process. Table 4 summarizes pertinent information from recent antithrombotic therapies in stroke and TIA trials.

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Table 1. Aspirin therapy for primary prevention of stroke ^1,2
	Level of evidence
Not considered beneficial for the prevention of first stroke in low-risk individuals	Class III; Level of Evidence A
The use of aspirin for cardiovascular or cerebrovascular prophylaxis is reasonable for people at sufficiently high ischemic risk. The 10-y risk identified is >10% for the benefits to outweigh the risks associated with treatment.	Class IIa; Level of Evidence A
Aspirin at 81 mg/d or 100 mg every other day may be of potential value for primary stroke prevention in women with diabetes mellitus and whose risk is sufficiently high, factoring in risks versus the benefits of treatment.	Class IIa; Level of Evidence B
Aspirin is not useful in primary stroke prevention in diabetic patients in the absence of other high-risk comorbid factors.	Class III; Level of Evidence A
As a result of a lack of relevant clinical trials, antiplatelet regimens other than aspirin, as well as cilostazol, are not recommended for the prevention of a first stroke.	Class III; Level of Evidence C

Table 2. Comparison of aspirin, aspirin plus dipyridamole, and clopidogrel
RCT/meta-analysis	Antiplatelet studied	Primary endpoint	Results
CAPRIE³	Clopidogrel 75 mg vs aspirin 325 mg/d	Ischemic stroke, MI, or vascular death.	Annual endpoint risk was 5.32% with clopidogrel vs 5.83% with aspirin (P = 0.043). The RR reduction was 8.7% in favor of clopidogrel In the ischemic stroke subgroup, the RR reduction was 7.3% (not significant) There were no major differences in terms of safety with similar rates of hemorrhage
Meta-analysis²	Aspirin vs aspirin plus dipyridamole	Recurrent stroke	Extended-release dipyridamole showed a statistically significant difference in favour of the combination for stroke alone with RR 0.76 and for the composite outcome with RR 0.82
PRoFESS⁴	Clopidogrel vs ASA-ERDP	Recurrent stroke	Recurrent stroke of any type, clopidogrel (8.8%) vs ASA-ERDP (9%), (HR 1.01, 95% CI 0.92–1.11) More hemorrhagic events in the ASA-ERDP group (HR 1.15, 95% CI 1–1.32)

ASA-ERDP, Aspirin plus Extended Release Dipyridamole; CAPRIE, Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events; CI, confidence interval; HR, hazard ratio; MI, myocardial infarction; PRoFESS, Prevention Regimen for Effectively Avoiding Second Strokes; RCT, randomized controlled trial; RR, relative risk.

Table 3. Antithrombotic agents, mechanism of action, and dosing
	Mechanism of action	Suggested dosing
Antiplatelets
Aspirin	Inhibits platelet cyclooxygenase and the synthesis of prostaglandin and thromboxane A2; inhibits platelet aggregation	Initial acute stroke dose 160–325 mg Long-term dose 81–325 mg
Clopidogrel	Inhibitor of ADP-induced pathway for platelet aggregation Activemetabolite irreversibly binds to the P2Y12 class of ADP receptors on platelets	300–600 mg loading dose when indicated, followed by 75 mg/d
Dipyridamole	Inhibition of adenosine uptake into platelets, erythrocytes, and endothelial cells, thereby inhibiting platelet reactivity Phosphodiesterase inhibition increasing cAMP in platelets Inhibition of thromboxane A2 formation	Available in 200mg combined with 25 mg aspirin to be given twice daily
Ticagrelor	Drug and its major metabolite reversibly interact with the platelet P2Y12 ADP receptor to prevent signal transduction and platelet activation	Loading dose of 180mg when indicated followed by 90 mg twice daily
Cilostazol	Inhibits phosphodiesterase III, causing cAMP to increase, which in turn inhibits platelet aggregation Causes homogeneous vasodilation	100 mg twice daily Has been effective in stroke prevention when combined with aspirin or clopidogrel
NOAC
Apixaban	Blocks selectively and reversibly the active site of factor Xa without requiring a cofactor for activity; no direct effect on platelet aggregation but indirectly inhibits platelet aggregation induced by thrombin (blood coagulation cascade is dependent on the activation of factor X to factor Xa via the intrinsic and extrinsic pathways)	5 mg twice daily Dose reduced to 2.5 mg/d if 2 of the 3 dose-reducing criteria are met^a
Rivaroxaban	Blocks selectively the active site of factor Xa without requiring a cofactor for activity	20 mg/d for atrial fibrillation Showed efficacy at 2.5mg twice daily plus aspirin in presence of concomitant stable CAD or PAD
Edoxaban	Blocks selectively and reversibly the active site of factor Xa without requiring a cofactor for activity	CrCl >50 mL/min: 60 mg/d CrCl 15–50 mL/min: 30 mg/d
Dabigatran	Prevents thrombus development through direct, competitive inhibition of thrombin (thrombin enables fibrinogen conversion to fibrin during the coagulation cascade)	CrCl >30 mL/min: 150 mg twice daily CrCl 15–30 mL/min: 75 mg twice daily

ADP, adenosine diphosphate; CAD, coronary artery disease; cAMP, cyclic adenosine monophosphate; CrCl, creatinine clearance; NOAC, non-vitamin K oral anticoagulants; PAD, peripheral artery disease
^aApixaban dose is reduced to 2.5 mg twice daily when 2 of the following criteria are met: age ≥80 y, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL.

Table 4. Antithrombotic regimens used in major trials and meta-analyses
Trial/meta-analysis	Antithrombotic regimen
Symptomatic intracranial stenosis (SAMMPRIS)⁴⁹	Aspirin 325 mg/d and clopidogrel 75 mg for 90 d, management of the primary risk factors with control of systolic blood pressure <140 mm Hg (<130 mm Hg, if diabetic) and low-density lipoprotein-cholesterol <1.81 mmol/L, management of secondary risk factors (diabetes mellitus, non–high-density lipoprotein-cholesterol, smoking, weight, exercise) with the help of lifestyle-modification programs
Minor stroke/high-risk TIA (pooled analysis of CHANCE and POINT)⁴⁷	The benefit of DAPT (aspirin plus clopidogrel) appeared to be confined to the first 21 d after minor ischemic stroke or high-risk TIA
Aortic Arch Disease with complex features (ARCH and the subgroup analysis of NAVIGATE ESUS)^62–65	Warfarin (INR 2–3) was not superior to aspirin (75–150 mg) plus clopidogrel 75 mg Rivaroxaban 15 mg/d was not superior to aspirin 100 mg/d
Extracranial Cervical Artery or Vertebral Artery Dissection (CADISS)⁵⁴	No difference in stroke recurrence among aspirin-only, clopidogrel-only, dipyridamole-only, or in dual therapy or anticoagulation
Symptomatic Ipsilateral Intracranial/Extracranial Stenosis (SOCRATES)⁵²	Ticagrelor at an initial dose of 180 mg, followed by 90 mg b.i.d. for 90 d was superior to aspirin 300 mg, followed by 100 mg/d
High-risk noncardioembolic stroke⁴⁴ (meet at least 1 of the following 3 criteria: at least 50% stenosis of a major intracranial artery, at least 50% stenosis of an extracranial artery, and ≥2 risk factors derived from the Essen Stroke Risk Score and Fukuoka Stroke Risk Score)	Cilostazol 100 mg b.i.d. plus aspirin (81 or 100 mg/d) or clopidogrel (50 or 75 mg/d) was superior to monotherapy aspirin or clopidogrel
Stable CAD and PVD (COMPASS)⁵³	Rivaroxaban 2.5 mg b.i.d. + aspirin 100 mg daily was superior than aspirin 100 mg daily only or rivaroxaban 5 mg twice daily only
Atrial fibrillation in ACS or after PCI (AUGUSTUS)¹²	Apixaban 5 mg b.i.d. plus Plavix 75 mg
Nonvalvular atrial fibrillation⁷	NOACs
PFO²²	In patients <60 years old, PFO closure + medical antithrombotic (primarily antiplatelet) beneficial reduction in recurrent ischemic stroke when compared with long-term antithrombotic therapy (antiplatelet or anticoagulant) alone

ARCH, Aortic Arch Related Cerebral Hazard; ACS, acute coronary syndrome; AUGUSTUS, Aspirin Placebo in Patients with Atrial Fibrillation and Acute Coronary Syndrome or Percutaneous Coronary Intervention; CAD, coronary artery disease; CHANCE, Clopidogrel With Aspirin in Acute Minor Stroke or Transient Ischemic Attack; COMPASS, Stroke Outcomes In The Cardiovascular Outcomes For People Using Anticoagulation Strategies Dual Antiplatelet Therapy; INR, international normalized ratio; NAVIGATE-ESUS, The New Approach Rivaroxaban Inhibition of Factor Xa in a Global Trial vs. ASA to Prevent Embolism in Embolic Stroke of Undetermined Source; NOAC, non-vitamin K oral anticoagulants; PCI, percutaneous coronary intervention; PFO, patent foramen ovale; POINT, The Platelet-Oriented Inhibition in New TIA and Minor Ischemic Stroke; SAMMPRIS, Aggressive medical treatment with or without stenting in high-risk patients with intracranial artery stenosis; SOCRATES, The Acute Stroke or Transient Ischemic Attack Treated with Aspirin or Ticagrelor and Patient Outcomes; TIA, transient ischemic attack.

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