Safety and efficacy of intensive vs. guideline antiplatelet therapy in high‐risk patients with recent ischemic stroke or transient ischemic attack: rationale and design of the Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke (TARDIS) trial (ISRCTN47823388)

Rationale The risk of recurrence following a stroke or transient ischemic attack is high, especially immediately after the event. Hypothesis Because two antiplatelet agents are superior to one in patients with non‐cardioembolic events, more intensive treatment might be even more effective. Sample size estimates The sample size of 4100 patients will allow a shift to less recurrence, and less severe recurrence, to be detected (odds ratio 0·68) with 90% power at 5% significance. Methods and design Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke (ISRCTN47823388) is comparing the safety and efficacy of intensive (combined aspirin, clopidogrel, and dipyridamole) vs. guideline antiplatelet therapy, both given for one‐month. This international collaborative parallel‐group prospective randomized open‐label blinded‐end‐point phase III trial plans to recruit 4100 patients with acute ischemic stroke or transient ischemic attack. Randomization and data collection are performed over a secure Internet site with real‐time data validation and concealment of allocation. Outcomes, serious adverse events, and neuroimaging are adjudicated centrally with blinding to treatment allocation. Study outcome The primary outcome is stroke recurrence and its severity (‘ordinal recurrence’ based on modified Rankin Scale) at 90 days, with masked assessment centrally by telephone. Secondary outcomes include vascular events, functional measures (disability, mood, cognition, quality of life), and safety (bleeding, death, serious adverse events). Discussion The trial has recruited more than 50% of its target sample size (latest number: 2399) and is running in 104 sites in 4 countries. One‐third of patients presented with a transient ischemic attack.


Introduction and rationale
Following stroke or transient ischemic attack (TIA), the risk of recurrence is very high over the first few hours and days, reaching 10·3% by three-months (1,2). Risk then declines and totals about 40% by five-years. Importantly, recurrent strokes are usually more severe than first events and so are more likely to lead to dependency, cognitive impairment and dementia, depression, poor quality of life, and need for long-term institutional care (3,4).
Antiplatelet therapy for acute ischemic stroke is based on aspirin alone as a result of the IST-1 and CAST mega-trials (17,18), although the effect size for improving functional outcome was small (absolute risk reduction ∼1·1%), mostly explained by aspirin reducing early recurrence. Until recently, the acute treatment of TIA had not been investigated. Early and short-term use of two agents appears to be superior to monotherapy, as suggested by observational studies (EXPRESS, SOS (1,2)), small trials (FASTER, EARLY) (24,25), and a post hoc subgroup analysis of the PRoFESS mega-trial (26). These findings were strengthened by the large CHANCE trial that showed that the combination of aspirin + clopidogrel was superior to aspirin alone in reducing stroke recurrence (23). Indeed, it appears in meta-analyses that any pair of antiplatelets is superior to any single agent (27,28). A potential advantage of multi-antiplatelet therapy is that it will help cover treatment resistance seen with monotherapy for either aspirin or clopidogrel (29)(30)(31).
The situation in acute stroke and TIA differs from chronic stroke (long-term secondary prophylaxis) where dual therapy with aspirin + dipyridamole reduced events by 23% in comparison with aspirin or dipyridamole alone without increasing the risk of bleeding (ESPS-2, ESPRIT) (19,21). However, dual therapy based on aspirin + clopidogrel was not superior to monotherapy with either agent alone (CHARISMA, MATCH) (32,33). In MATCH, dual therapy caused more bleeding than clopidogrel alone but without a significant reduction in recurrence (33,34).
If dual therapy is more effective at preventing recurrence than monotherapy for acute prophylaxis, then intensive therapy with triple antiplatelets (combined aspirin + clopidogrel + dipyridamole) may be better still, provided the risk of recurrence is high and bleeding does not become excessive. We have performed a series of 'proof-of-mechanism' and 'proof-of-concept' laboratory studies and clinical trials investigating this approach (35)(36)(37)(38)(39). In vitro studies starting in 2000 found that triple therapy was most effective in inhibiting platelet aggregation, platelet-leucocyte conjugation, and leucocyte activation (35)(36)(37). In multiway crossover phase I and II trials, short-term administrations of mono (aspirin, clopidogrel, or dipyridamole), dual (combinations of aspirin and clopidogrel, aspirin and dipyridamole, or clopidogrel and dipyridamole), and triple (combined aspirin, clopidogrel, and dipyridamole) antiplatelet therapy were compared; the combination of aspirin and clopidogrel, with or without dipyridamole, was most potent in inhibiting platelet function ex vivo in both normal volunteers and participants with previous stroke/ TIA (38,39). (Of note, the platelet function tests used in these studies are relatively insensitive to the intracellular effects of dipyridamole.) In the only parallel group trial of intensive/triple therapy in participants with stroke, we found that combined aspirin, clopidogrel, and dipyridamole (vs. aspirin alone, chosen because it was the UK standard of care at the time) was feasible to administer in a pilot trial for up to 24 months (40). However, the trial was stopped early on publication of ESPRIT (21) confirming the superiority of combined aspirin and dipyridamole over aspirin alone. There was a non-significant trend to increased bleeding with triple antiplatelet therapy vs. aspirin alone. Although unintended, the participants were at low risk of recurrence (young/recruited months after the event/many lacunar strokes) (40), a problem also seen in MATCH and CHARISMA (32,33). The study concluded that future trials of combined aspirin, clopidogrel, and dipyridamole needed to target participants at high risk of recurrence and for a short treatment duration to minimize bleeding, so that benefit is likely to outweigh hazard. Clinical use of triple antiplatelet therapy has also been reported in a case series (41).
The TARDIS trial was designed to build on these laboratory and clinical studies and aims to test the overall safety and efficacy of intensive antiplatelet therapy with three agents in comparison with guideline treatment.

Primary research question
Is intensive antiplatelet therapy (combined aspirin, clopidogrel, and dipyridamole) safe and effective in reducing recurrence and its severity at three-months, as compared with guideline antiplatelet therapy (clopidogrel, or combined aspirin and dipyridamole), when given acutely after stroke or TIA for one-month?

Design
TARDIS is an international collaborative multicenter parallelgroup prospective randomized open-label blinded-end-point phase III controlled trial.

Patient population
Inclusion criteria:  (43)), stroke severity [National Institutes of Health Stroke Scale, (NIHSS) (44)], BP, full blood count, and electrocardiogram (ECG) are determined after consent/assent and before randomization. Neuroimaging -computerized tomography (CT) or magnetic resonance (MR) scanning -is performed for patients with ischemic stroke to exclude intracranial haemorrhage and non-stroke diagnoses. If thrombolysis is performed, CT/MR must be undertaken afterward and prior to randomization to exclude haemorrhagic transformation. Patients presenting with a TIA do not have to have a CT/MR as this reflects routine practice at many stroke centers. Patients with cerebral events that occur during treatment must also be re-scanned to identify potential secondary bleeding. Local site reporting of scans is recorded; all scans are also uploaded over the Internet for independent adjudication using a validated structured classification system [as used in IST-3 and Efficacy of Nitric Oxide in Stroke trial (ENOS)] (45-48) and masked to treatment.
At baseline and day 7 ± 1, optional research blood samples may be taken for substudies involving biomarkers and genetics; some samples are centrifuged to collect plasma and serum, and then frozen.

Randomization
All randomization, data collection, and serious adverse event (SAE) and CT adjudication are performed over a secure password-protected and data-encrypted Internet website: www-.tardistrial.org. Patients are randomized in real time with: Stratification on: • In 5% of patients Stratification and minimization allow for improved matching at baseline, stratification allows variable categories to be treated as trials in their own right, minimization increases statistical power (50), and simple randomization reduces predictability.

Investigational medicinal products
Trial interventions are given open label for one-month (28 or 30 days depending on treatment pack size, to cover the period of maximum risk of recurrence but minimize bleeding) and comprise ( Fig. 1 (54)] Sites choose in advance which guideline treatment regimen they wish to use, a choice that is made separately for ischemic stroke (IS) and TIA: • Aspirin + dipyridamole, or clopidogrel (1:1) • Aspirin + dipyridamole • Clopidogrel The principal investigator (PI) may change the choice of comparator at any stage during the trial with 48-h notice, that is, a change cannot influence treatment for a patient who is in the process of being enrolled.
Antiplatelet agents may be administered after the index stroke/ TIA event and before randomization as follows:

The TARDIS Trial Investigators
• Aspirin may be given after the index event and prior to randomization in any potential trial participant.
• Clopidogrel is only allowed if the patient may receive it as part of the trial according to the PI's choice of comparator, that is, the patient can only be randomized to intensive antiplatelets vs. clopidogrel alone.
• Dipyridamole (in combination with aspirin) is only allowed if the patient may receive it as part of the trial according to the PI's choice of comparator, that is, the patient can only be randomized to intensive antiplatelets vs. combined aspirin and dipyridamole.
• If the patient is given a 'confounding' antiplatelet after their event and before randomization, the patient may still be included but randomization will then only involve the appropriate comparison to prevent confounding of treatment.
Patients who have received combined clopidogrel and aspirin, clopidogrel and dipyridamole, cilostazol (whether singly or in combination), or triflusal (whether singly or in combination) are excluded from the trial.
Study drugs may be stopped around procedures that become necessary after enrollment; trial drugs should be re-started as soon as possible after the procedure once clinically appropriate. Participants can be withdrawn from therapy either at their own request, for safety reasons, or if unacceptable adverse events develop. After the 28-30-day treatment period, participants are expected to return to guideline antiplatelet therapy as recommended by local, national, and international guidelines. Patients are also offered standard 'best care' prophylaxis, including lifestyle advice, BP and lipid-lowering drugs, and carotid endarterectomy (as necessary).

Primary outcome
The primary outcome is the frequency and severity of recurrent strokes and TIA in participants who have a recurrent event, with assessment at day 90. Severity is measured using a six-level ordered categorical scale that incorporates the mRS: • Fatal stroke/severe non-fatal stroke (mRS 4 or 5)/moderate stroke (mRS 2 or 3)/mild stroke (mRS 0 or 1)/TIA/no stroke-TIA ¶ Ascertainment of recurrent events, and mRS, is determined centrally by telephone by a trained assessor who is masked to outcome at day 90 ± 7. To ensure recurrent events are identified, corroborating information is sought from the general practitioner and recruiting hospital site.
The effect of the intervention on the primary outcome will be performed within the following subgroups: (l) Type of comparator: AD, C, either ¶ (m) Systolic BP: ≤140, 141-160, >160 mmHg ¶ (n) Time, event to randomization >24, 12·1-24, ≤12 h ¶ (o) Use of low dose heparin: no, yes ¶ (p) Treated with alteplase prior to randomization (stroke only): yes, no (q) Gastroprotection: yes, no ¶ (r) Carotid stenosis (ipsilateral ≥50%): no, yes ¶ (s) Old lesion on baseline neuroimaging: no, yes ¶ Secondary, bleeding, and safety outcomes Investigators assess secondary outcomes at days 7 ± 1 and 35 ± 3, and on discharge from hospital (if admitted). The National Coordinating Centre assesses secondary outcomes at day 90 ± 7 by a telephone call between the patient (or carer) and an assessor blinded to treatment. Reported outcomes (stroke, MI) and SAEs are adjudicated by a member of the independent adjudicator panel who is blinded to treatment.
Day 7 ¶ (a) Headache that required treatment or led to discontinuation (b) Recurrent stroke or TIA (c) Impairment (NIHSS, including death) (d) Neurological deterioration (increase in NIHSS by four points or more) (e) Composite vascular event (f) Venous thromboembolism (g) Haemoglobin Δ will not be collected if carer answers questions without recourse to participant.

Sample size
TARDIS was designed with a start-up phase (funded by British Heart Foundation, and assessing safety, feasibility, and tolerability) and a main phase (funded by Health Technology Assessment, and assessing safety and efficacy).

Statistical analyses
Analyses will be performed by intention-to-treat using binary logistic regression for binary outcomes, ordinal logistic regression for ordered categorical variables (including the primary outcome), multiple regression for continuous variables, and Cox proportional hazards regression for time-to-event data. Analyses will be adjusted for stratification and minimization factors. Detailed analysis plans are given in the Statistical Analysis Plan.

Study organization and oversight
TARDIS is an independent academic trial performed by an international collaborative group. The Trial Steering Committee provides oversight and strategic input, and comprises independent members, grant applicants, and patient, sponsor, and funder representatives; it meets twice yearly. An International Advisory Committee meets annually and provides advice on national issues including recruitment and follow-up. The Trial Management Committee runs the trial on a day-to-day basis and is based at the TARDIS Trial Coordinating Centre in Nottingham. A National Coordinating Centre and national coordinator are based in each participating country. Outcomes, SAEs, and brain imaging are adjudicated by trained assessors masked to treatment assignment.
The independent Data Monitoring Committee reviews unblinded data twice yearly in respect of safety and efficacy, and review recruitment, baseline data, balance in baseline factors between the treatment groups, completeness of data, compliance to treatment, co-administered treatments, outcome by subgroups, SAEs (both adjudicated and unadjudicated), and protocol violations. They also take findings in the context of other published evidence.
Research governance TARDIS is conducted in accordance with the ethics and principles enshrined in the Declaration of Helsinki and good clinical practice, and is run in accordance with the UK Medicines for Human Use Regulations and Health Research Governance Framework. The management of personal data adheres to the UK Data Protection Act (1998

Summary and conclusions
TARDIS is addressing a key issue in the management of patients with acute stroke and TIA, namely the safety and efficacy of short-term intensive (combined aspirin, clopidogrel, and dipyridamole) vs. guideline antiplatelet therapy. The primary outcome is the frequency and severity of stroke recurrence; TARDIS is the first trial to use this novel end-point. The sample size of 4100 patients means that a modest but worthwhile clinical effect can be detected with high statistical power (90%); to date, 2399 patients have been recruited from 104 sites in 4 countries, with one-third presenting with a TIA. A positive trial would mean that triple antiplatelet therapy could be introduced rapidly into clinical practice as the drugs are already licensed, readily available, and inexpensive. We invite centers from around the world to join this important collaborative international venture.