Evidence Table 29Aspirin +/− antiplatelet therapy vs no prophylaxis

Bibliographic referenceStudy TypeEvidence levelNo. of patientsPatients characteristicsInterventionComparisonLength of follow upOutcome measuresEffect sizeComments
Antiplatelet Trialists’ Collaboration, 199421

55 trials from 53 papers 1,12,22,69,98,99,109,111,135,153,172, 188,211,232,255,258,261,263,297,298, 300,310,376,406,407,436,437,464,498, 511,519,528,533,550,551,587,590,609, 612,648,665,666,669,682,700,703,710716

28 of these studies were included in the guideline review 1,12,69,70,111,153, 157,172,234,261,407,433,436,464,498, 511,528,533,550,587,590,609,612,682, 700,711,715,716

4 studies with heparin as background prophylaxis reported below in next table.

9 studies in high risk medical patients excluded from our analysis
Systematic review1+Type of surgery:
Surgical and high risk medical patients:

General surgery patients: 24 trials

Traumatic orthopaedic surgery patients: 11 trials

Elective orthopaedic surgery patients: 16 trials
Antiplatelet therapy:

Drugs included in review:
Aspirin & dipyridamole
unmarketed drugs
No interventionMajority 1, 2 or 3 week studiesDVT Confirmed by: fibrinogen uptake test or venographyInt: 604/2551
Control: 711/2286
p value: <0.0001
Trials did not always define what was considered a major bleed

Reported pulmonary emboli but did not state how if they were confirmed.

Not reported:
QoL, survival, LoS, PTS, funding
Proximal DVT
Confirmed by: fibrinogen uptake test or venography
Int: 65/641
Control: 92/556
p value: 0.0008
Major bleedInt: 22/3264
Control: 11/2781
p value: 0.44
Study detailsPatientsInterventionsOutcome measuresEffect sizeComments
Antiplatelet Trialists Collaboration, 199421

Country of study: UK

Study design: Systematic review with 58 trials in surgical patients and 11 trials in high risk medical patients

List who was masked to interventions: Unclear from systematic review

Evidence level: 1+

Duration of follow-up: Treatment varied between 1–78 weeks with 7/9 studies treating for 1–4wks
Patient group:
High Risk Medical patients
 Population included within individual studies unclear


Study Inclusion criteria:
Unconfounded RCTs

Study Exclusion criteria:
Poor allocation concealment (e.g. odd or even dates, record numbers) if treatment comparisons were considered confounded.

All patients
N: 520

Group 1 - Antiplatelets
No. randomised: 275
No. of dropouts: Unknown

Group 2 - Control
No. randomised: 283
No. of dropouts: Unknown
Group 1
Various antiplatelets – see table below
Duration: 1–78 weeks

Group 2
Control Duration: 1–78 weeks

Additional non- comparative prophylaxis:
Information not given
All cause mortalityGroup1: 22/256
Group 2: 23/261
P value: NS
No information provided
Pulmonary embolism diagnosed using any method.
Literature search did not include all medical databases.
Lack of information about population or heterogeneity
Outcomes not reported:
LoS, QoL, PTS, Pulmonary hypertension, Fatal bleeding, minor bleeding, HIT

Additional outcomes reported:
No additional outcomes reported.

Data presented for medical patients only.
* P-value calculated by NCC team using 2-tailed Fisher’s exact.
Fatal pulmonary embolism (confirmed by: any method)Group1: 2/256
Group 2: 4/261
P value: 0.686*
Pulmonary embolism, asymptomatic or symptomatic (confirmed by: any method)Group1: 1/182
Group 2: 2/187
P value: NS
DVT, asymptomatic or symptomatic (confirmed by: see table below)Group1: 39/256
Group 2: 56/264
P value: 0.089*
Thigh DVT(confirmed by: see table below)Group1: 1/32
Group 2: 7/34
P value: 0.055*
Major bleeding (definition: severe enough to require transfusion)Group1: 0/99
Group 2: 1/102
P value: NS

From: Appendix D, Evidence tables

Cover of Venous Thromboembolism
Venous Thromboembolism: Reducing the Risk of Venous Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism) in Patients Admitted to Hospital.
NICE Clinical Guidelines, No. 92.
National Clinical Guideline Centre – Acute and Chronic Conditions (UK).
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