10.4081/btvb.2022.10
Optimal duration of anticoagulation in patients with a first venous thromboembolism (VTE) is still uncertain. Extended anticoagulant treatment beyond the first 3 to 6 months is recommended in patients with unprovoked VTE for their high risk of recurrence, provided the risk of bleeding during anticoagulation is not high. Recent meta-analyses indicated that only one-third of these patients have a recurrence 10 years after anticoagulation is stopped, whereas the risk of major bleeding is consistent and persistent during anticoagulation. We designed the prospective, multicenter Apidulcis study to test whether serial D-dimer measurements, using commercial assays with predefined sex-specific cutoffs (350 ng/mL and 500 ng/mL for men and women, respectively, for assays expressing results as fibrinogen equivalent units), may be useful to stratify patients for the risk of recurrence. Those presenting positive D-dimer results, considered at higher risk, will receive low dose Apixaban, 2.5 mg tablets BID for 18 months, whereas those with persistently negative D-dimer results, considered at lower risk, will remain without anticoagulant treatment. Outpatients with a first VTE (unprovoked or associated with weak risk factors), aged 18 to 74 years, who have already received anticoagulation for at least 12 months are eligible for the study.
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Bleeding, Thrombosis and Vascular Biology
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Rationale and design of a study on D-dimer use to stratify patients after a first unprovoked venous thromboembolism for their risk of recurrence: extended low-dose Apixaban given only to patients with positive D-dimer results: The Apidulcis study
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Bleed Thromb Vascul Biol
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Tosetto A, Testa S, Martinelli I, et al. External validation of the DASH prediction rule: a retrospective cohort study. J Thromb Haemost 2017;15:1963-70.
Rationale and design of a study on D-dimer use to stratify patients after a first unprovoked venous thromboembolism for their risk of recurrence: extended low-dose Apixaban given only to patients with positive D-dimer results: The Apidulcis study
https://www.btvb.org/btvb/article/download/10/11
1
                                                                                                            STUDY PROTOCOL

Rationale and design of a study on D-dimer use to stratify patients after a first
unprovoked venous thromboembolism for their risk of recurrence:
extended low-dose Apixaban given only to patients with positive D-dimer results.
The Apidulcis study
Gualtiero Palareti,1 Paolo Prandoni,1 Cristina Legnani,1 Emilia Antonucci,1 Serena Zorzi,1 Alberto Tosetto,2
Lorenza Bertù,3 Sophie Testa,4 Vittorio Pengo,5 Walter Ageno,6 Ida Martinelli,7 Benilde Cosmi,8 Eugenio Bucherini,9
Daniela Poli10
1
 Arianna Anticoagulazione Foundation, Bologna, Italy; 2Department of Hematology, Center for Hemorrhagic and Thrombotic Diseases,
AULSS8 Berica, Vicenza, Italy; 3Research Center on Thromboembolic Diseases and Antithrombotic Therapies, University of Insubria,
Varese, Italy; 4Department of Laboratory Medicine, Haemostasis and Thrombosis Center, AO Istituti Ospitalieri, Cremona, Italy;
5
  Thrombosis Research Laboratory, Department of Cardiac-Thoracic-Vascular Sciences and Public Health, University of Padua, Italy;
6
  Department of Medicine and Surgery, University of Insubria, Varese, Italy; 7A. Bianchi Bonomi Hemophilia and Thrombosis Center,
Fondazione IRCCS Ca’ Granda - Ospedale Maggiore Policlinico, Milano, Italy; 8Simple Departmental Structure - Angiology and
Coagulation Diseases, IRCCS Bologna University Hospital, Università di Bologna Italy; 9Simple Departmental Structure - Vascular
                                                                      Medicine and Angiology, Ospedale Civile Faenza, Faenza (RA),
                                                                      Italy; 10Thrombosis Center, Careggi Hospital, Florence, Italy




                                                                                                     ly
                                                                                             on
  Correspondence: Gualtiero Palareti, “Arianna Anticoagulazione”
  Foundation, Via Paolo Fabbri 1/3, 40138 Bologna, Italy.
  Tel.: +39.3282279868 - Fax: +39.051.343604.
                                                                           ABSTRACT
                                                                                Optimal duration of anticoagulation in patients with a first



                                                                                        e
  E-mail: gualtiero.palareti@unibo.it
                                                                           venous thromboembolism (VTE) is still uncertain. Extended an-
                                                                                us
  Key words: Venous thromboembolism, Anticoagulation, Extended             ticoagulant treatment beyond the first 3 to 6 months is recom-
  anticoagulation, D-dimer, Apixaban.                                      mended in patients with unprovoked VTE for their high risk of
                                                                           recurrence, provided the risk of bleeding during anticoagulation
                                                                           al
  Contributions: GP and PP designed the study; GP wrote the first          is not high. Recent meta-analyses indicated that only one-third
  draft of the article; all the authors contributed to the design of the
                                                                           of these patients have a recurrence 10 years after anticoagulation
                                                                 ci

  study, and to the final version of the article; SZ particularly con-
  tributed to achieve authorization to the study; AT and LB particu-
                                                                           is stopped, whereas the risk of major bleeding is consistent and
                                                               er



  larly contributed to the statistical plan of the study.                  persistent during anticoagulation. We designed the prospective,
                                                                           multicenter Apidulcis study to test whether serial D-dimer meas-
                                                              m




  Conflict of interest: The authors declare no potential conflict of in-   urements, using commercial assays with predefined sex-specific
  terest.                                                                  cutoffs (350 ng/mL and 500 ng/mL for men and women, respec-
                                                   om




                                                                           tively, for assays expressing results as fibrinogen equivalent
  Funding: None                                                            units), may be useful to stratify patients for the risk of recur-
                                                                           rence. Those presenting positive D-dimer results, considered at
                                             -c




  Ethical statement: The study has been recorded at https://www.clin-
  icaltrials.gov (NCT03678506, registration date 19/09/2018) and at
                                                                           higher risk, will receive low dose Apixaban, 2.5 mg tablets BID
                                                                           for 18 months, whereas those with persistently negative D-dimer
                                    on




  EudraCT (2017-002340-32). The study protocol (V1.1 date
  16/01/2018), was designed in compliance with the current version         results, considered at lower risk, will remain without anticoag-
  of the Declaration of Helsinki and the GCP, and was authorized by        ulant treatment. Outpatients with a first VTE (unprovoked or as-
                              N




  AIFA (“Agenzia Italiana del Farmaco” ref. number                         sociated with weak risk factors), aged 18 to 74 years, who have
  AIFA/SC/P/16556, date 15/02/2018); it was approved by the inde-          already received anticoagulation for at least 12 months are eli-
  pendent Ethics Committee of the Azienda Ospedaliera Careggi,             gible for the study.
  Florence, Italy (reference number: CE 12152_spe, dated
  17/04/2018) as lead ethics committee and will be approved by
  ethics committees at all participating sites before starting the en-
  rolment. The study will be conducted in accordance with the Dec-
  laration of Helsinki. Written informed consent will be collected
                                                                           INTRODUCTION
  before starting.                                                             Venous thromboembolism (VTE), encompassing deep
  Received for publication: 22 December 2021.                              vein thrombosis (DVT) of lower limbs and/or pulmonary
  Accepted for publication: 9 February 2022.                               embolism (PE), tends to recur. Anticoagulation is the
                                                                           mainstay treatment for acute and long-term VTE events,
  This work is licensed under a Creative Commons Attribution Non-
  Commercial 4.0 License (CC BY-NC 4.0).
                                                                           as well as for secondary prevention. It has been shown,
                                                                           however, that whatever the duration of anticoagulant
  ©
   Copyright: the Author(s), 2022                                          treatment, its benefit fades after anticoagulation is stopped
  Licensee PAGEPress, Italy
                                                                           and the risk of recurrence increases again.1-4 The duration
  Bleeding, Thrombosis and Vascular Biology 2022; 1:10
  doi:10.4081/btvb.2022.10                                                 of anticoagulant therapy can be regulated by the estimated
                                                                           risk of recurrence. This is low when the event is provoked

                                              Bleeding, Thrombosis and Vascular Biology 2022; 1:10
                                         Rationale and design of a study on D-dimer use                                      39



by a reversible risk factor, such as surgery, thus deserving           We designed the prospective, multicenter Apidulcis
short treatment,5 or very high when VTE is associated              study to test whether D-dimer assay, performed during
with a permanent factor such as cancer in which case an-           and after standard anticoagulation, can be used to stratify
ticoagulant therapy is usually continued indefinitely.6            the risk of recurrence in patients with a first unprovoked
When the initial thrombotic event occurs without any ap-           proximal DVT or PE. Patients with a positive D-dimer re-
parent provoking factor (“unprovoked” or “idiopathic”              sult, considered at higher risk, will receive Apixaban 2.5
VTE), or when it is associated with weak risk factors              mg twice a day for 18 months, whereas those with per-
(such as minor surgery or short bed resting, etc.), the risk       sistently negative D-dimer results, considered at lower
of recurrence can be intermediate and the indication for           risk, will remain without any specific treatment. All pa-
an indefinite anticoagulation is uncertain, especially if the      tients will be followed-up for 18 months. The final aim of
risk of major bleeding - inevitably associated with anti-          the study is to see whether, in patients with a first VTE
coagulation – is considered. A recent meta-analysis                that was unprovoked or associated with weak risk factors
showed that the rate of recurrence after an unprovoked             (WRFs), it is possible to achieve a rate of recurrence com-
event is about 10% in the first year after interruption of         parable to that expected in a population of patients with
anticoagulation and decreases in following years, reaching         provoked VTE, using D-dimer assay to give low dose
a cumulative incidence of 36% at 10 years.7 On the other           Apixaban for extended treatment to patients with positive
hand, the risk of major bleeding is persistent during ex-          D-dimer and avoid extension of anticoagulation in those




                                                                                    ly
tended anticoagulation and was found to be 1.74% pt-y in           with negative D-dimer and at lower recurrence risk.




                                                                             on
patients treated with vitamin K antagonists (VKAs) and
1.12% pt-y in those receiving direct oral anticoagulants
(DOACs).8 It would be useful to stratify individual risk           METHOD AND ANALYSIS



                                                                        e
of recurrence to avoid extension of anticoagulant treat-           Primary and secondary objectives
ment in patients at lower risk. It was shown that patients
                                                                 us    The primary efficacy objective is the composite of
with unprovoked VTE have a higher risk of recurrence if
they have elevated D-dimer levels after stopping therapy.9-        confirmed recurrent proximal DVT and/or PE episodes,
                                                           al
11
   However, whether negative D-dimer levels can be used            and of VTE-related mortality. The primary safety end-
                                                                   point is the incidence of major bleeding (MB) complica-
                                              ci

to stop anticoagulation after the usual period of treatment
is still uncertain and conflicting results have been re-           tions occurring during the follow-up period in all included
                                            er



ported. Kearon et al.12 showed that in patients with nega-         patients.16 The secondary endpoint for efficacy is the com-
                                                                   posite of hospitalization and deaths due to cardiovascular
                                           m




tive D-dimer results, using a qualitative D-dimer assay,
the rate of recurrent VTE was 6.7% (CI, 4.8%-9.0%), ex-            events. Secondary safety endpoint is the cumulative inci-
                                  om




ceeding the limit (5% per patient-year) suggested by the           dence of MB, clinically relevant non major bleeding
International Society for Thrombosis and Hemostasis to             (CRNMB) complications,17 and overall mortality. Signs
decide which patients with unprovoked VTE can stop an-             and/symptoms of post-thrombotic syndrome will also be
                             -c




ticoagulation after a VTE.13 In contrast, the Dulcis man-          recorded using the Villalta score.18 All suspected outcome
agement study,14 where D-dimer levels were repeatedly              events and deaths will be evaluated by a central adjudi-
                      on




assessed using quantitative assays, showed that recurrent          cation committee whose members will be unaware of pa-
VTE developed in the 3.0% pt-y (CI, 2.0-4.4%) of pa-               tient name, D-dimer testing results, type of management
                 N




tients with D-dimer results persistently lower than pre-es-        or enrolling center.
tablished cutoffs who stopped anticoagulation. In patients
who resumed anticoagulation at the first positive D-dimer          Patients, study design
result (above the predefined cutoffs values) the rate of re-           The Apidulcis is an investigator-initiated, multicenter,
currence was 0.7% pt-y (CI, 0.2-1.7; P=0.0006). How-               prospective cohort, no-profit study conducted in many
ever, after resuming anticoagulation with VKAs (the only           (>40) Italian study sites. Patients of both genders are eli-
anticoagulant drug available at that time), the rate of            gible for the study, aged >18 and up to 74 years at screen-
major bleeds was quite high, standing at 2.3% pt-y (CI,            ing, with first episode of lower extremity proximal DVT
1.3-3.9) in these patients. In the following years, DOACs          and /or PE, idiopathic or associated with weak or removed
became available for use in our country to treat VTE. In           risk factors and who have completed a course of antico-
particular, the administration of low dose apixaban (2.5           agulant treatment (regardless of the drug used) of at least
mg × 2 daily) for secondary prophylaxis after a period of          12 months. The inclusion and exclusion criteria are listed
standard anticoagulation in patients with a first unpro-           in Table 1. Prior to enrollment, the investigators obtain in-
voked VTE was shown to be effective in reducing the rate           formed consent from patients and recommend continuing
of recurrence compared to placebo and associated with a            ongoing anticoagulant therapy until first D-dimer test is
low risk of bleeding events.15                                     performed. As shown in Figure 1, the first D-dimer assay

                                     Bleeding, Thrombosis and Vascular Biology 2022; 1:10
40                                                                  G. Palareti et al.




Table 1. Criteria for inclusion/exclusion in the study.
Inclusion criteria                                                  Prespecified criteria for exclusion
- Age >18 y and not >74 y                                           -   Age <18 y or >74 y
- First episode of proximal DVT of lower limbs and/or PE that       -   Duration of anticoagulation after the event < 12 months
  was:                                                              -   VTE post major surgery, trauma, plasters, or immobilization (within 3 months)
  idiopathic or associated with one or more of following            -   VTE post bed resting (>4 d)
  factors: minor, arthroscopic, or laparoscopic general surgery,    -   High bleeding risk
  pregnancy or puerperium, contraceptive or replacement             -   Limited life expectation (<1 y)
  hormonal therapy, long trip (>6 h), minor trauma (not             -   Increased systolic pulmonary arterial pressure (values >35 mm Hg [or > 40 mm
  requiring hospitalization, plaster casting, or immobilization),       Hg if BMI >30] estimated with echocardiography)
  hospitalization in medical hospital, reduced mobility (not        -   Geographical inaccessibility
  complete immobilization)                                          -   Venous thrombosis in different sites
- Ability to provide informed consent                               -   >1 documented VTE episode (proximal DVT and/or PE)
                                                                    -   Active cancer or hematologic disease
                                                                    -   Known serious thrombophilic alterations
                                                                    -   Antiphospholipid antibody syndrome (Sydney criteria)
                                                                    -   PE with shock or life-threatening prolonged hypotension
                                                                    -   Different indications for anticoagulation
                                                                    -   Severe cardiorespiratory insufficiency (NYHA 3 or 4)
                                                                    -   Pregnancy or puerperium (first 6 weeks after birth) at the time of screening




                                                                                                                ly
                                                                        examination




                                                                                                        on
                                                                    -   Severe renal (creatinine level > 2 mg/dL [177 mmol/L]) or liver failure (eg, acute
                                                                        hepatitis, chronic active hepatitis, or cirrhosis; or an alanine aminotransferase
                                                                        level that was 3 times the upper limit of the normal range or higher)
                                                                    -   Inability or refusal to give consent




                                                                                                  e
                                                                                          us
DVT: deep vein thrombosis; PE: pulmonary embolism; VTE: venous thromboembolism; BMI: body mass index; NYHA: New York Heart Association.
                                                                                  al
                                                                ci
                                                              er
                                                             m
                                                   om
                                            -c
                                   on
                              N




Figure 1. Flow chart of the study.


                                             Bleeding, Thrombosis and Vascular Biology 2022; 1:10
                                                Rationale and design of a study on D-dimer use                                       41



is carried out, using commercial assays, during anticoag-                 stored securely and kept confidential. Study sites are su-
ulant treatment; if the result is negative (below predefined              pervised by a dedicated remote monitor throughout the
cutoff levels) the patient is invited to stop treatment and               entire study. Before starting patient enrolment, investiga-
receives three dates for further D-dimer testing (15, 30                  tors receive visual electronic training sessions with the
and 60 days after anticoagulation discontinuation). At first              study monitor to clarify study design, protocol require-
positive D-dimer assay patients are invited to continue or                ments and correct eCRF use. The study monitor will make
resume anticoagulation treatment using Apixaban 2.5 mg                    sure study procedures are stuck to and check complete-
tablets (kindly provided by Alliance BMS-Pfizer) for the                  ness and correctness entries into the eCRF
subsequent 18 months. Patients with persistently negative                     Patients are instructed to contact the clinical center im-
D-dimer assay are asked to stay off anticoagulation. All                  mediately if symptoms develop suggestive of VTE or in
patients are followed for 18 months. The study aims to                    case of bleeding. In case of suspected recurrent DVT, com-
enroll a total of 1150 patients.                                          pression ultrasonography (CUS) is compared with the last
    In Table 2 are listed the commercial D-dimer assays                   available previous CUS. A recurrent DVT is diagnosed if a
allowed in the study and the respective cutoff levels for                 previously fully compressible segment (contralateral or ip-
negative/positive results. The cutoffs for men are lower                  silateral) is no longer compressible or if an increase of at
than those for women, to compensate for the higher risk                   least 4 mm in the diameter of the residual thrombus during
of recurrences in men. In contrast, no different cutoff lev-              compression is detected.20 In case of suspected PE, recur-




                                                                                           ly
els are adopted in relation to patient age, even though it                rence will be diagnosed based on objective algorithms,21,22




                                                                                    on
is well known that D-dimer levels physiologically in-                     including clinical probability, helical CT (or ventilation-
crease with age. In the previous Dulcis study the cutoffs                 perfusion lung scanning), CUS, and D-dimer testing as ap-
adopted were higher in patients aged 70 years or more;14                  propriate. Suspected outcome events and deaths are



                                                                               e
however, the clinical results of the study were not satis-                evaluated by a central adjudication committee (appendix
fying in that patient population. According to the ACCP
                                                                        usA) whose members are unaware of the patient’s name, the
                                                                          enrolling center, the results of D-dimer performed at inclu-
guidelines,19 elderly patients (especially if >75 years) are
at high bleeding risk during anticoagulant therapy, and                   sion, and whether the patient was receiving or not Apixaban
                                                                   al

therefore extended treatment beyond the first 3-6 month                   therapy at the moment of the event.
                                                                              Patients are censored in case of primary outcomes, se-
                                                    ci

from acute event should not be recommended. For the
above reasons, patients aged 75 years, or more are ex-                    rious adverse events, occurrence of a pathology requiring
                                                  er



cluded from this study.                                                   full anticoagulant treatment, onset of cancer or other serious
                                                                          pathology, withdrawal of informed consent, or a decision
                                                 m




Data management                                                           by the attending physician. Temporary discontinuation is
                                       om




                                                                          permitted in case of surgery, invasive procedure, or when-
    Demographic data (collected anonymously), informa-                    ever prophylactic treatment with LMWH is recommended
tion about index VTE event, baseline general clinical con-                by the attending physician. Pharmacovigilance for the pa-
                                 -c




ditions, possible complications, new events or diseases,                  tients receiving apixaban will be carried out by Dr. Elisa-
and adverse events (AEs) are all recorded by investigators                betta Bigagli, from the “Dipartimento di Neuroscienze,
                         on




in the electronic case-report-form (eCRF) and collected                   Psicologia, Area del Farmaco e Salute del Bambino, NEU-
in the central database. All patient information will be                  ROFARBA”, University of Florence, Italy (farmacovigi-
                   N




                                                                          lanza-noprofit@neurofarba.unifi.it).

Table 2. Predefined D-dimer cut-off levels (ng/ml) for                    Statistical considerations and sample size
negative/positive results in men or women (aged 18-74 years).
                                                                              The aim of this management study is to show that, in
                                                   Men     Women
                                                                          patients with a first unprovoked VTE, combining the use
Methods that espress results in FEU                350       500          of a prediction rule based on D-dimer assay with low-dose
- VIDAS D-dimer,
                                                                          Apixaban in subjects at higher risk of recurrence can de-
- Innovance D-dimer,
- Stago Liatest D-dimer,                                                  termine a recurrence risk similar to that in patients with
- HemosIL D-dimer HS 500)                                                 provoked VTE. Our calculations are based on the follow-
Methods that espress results in D-dimer units      175       250          ing assumptions: i) Based on the results of the Dulcis
- HemosIL D-dimer HS,                                                     study,14 approximately 52% of all eligible patients are ex-
- Sclavo Auto D-dimer                                                     pected to discontinue anticoagulation after permanently
D-dimer should be measured at the following time points.                  negative D-dimer assay, with an annual rate of recurrent
T0 = during anticoagulation                                               VTE events around 3% (95% 2.0 to 4.4%); ii) In the re-
T1 = 15±2 days after anticoagulation is stopped
T2 = 30±4 days after anticoagulation is stopped                           maining 48% of patients who will be encouraged to use
T3 = 60±5 days after anticoagulation is stopped                           low-dose apixaban, the expected rate of recurrent VTE

                                           Bleeding, Thrombosis and Vascular Biology 2022; 1:10
42                                                      G. Palareti et al.




based on the results of the Amplify Extension study is               (Bologna, Italy). The study is supported by Alliance
around 1.7% after the first year of treatment;15 iii) Based          BMS-Pfizer, which also will provide the drug Apixaban
on the metanalysis by Iorio et al.5 the annual recurrence            2.5 mg × BID. The study is registered at https://www.clin-
risk in patients with provoked VTE is 3.7% (CI, 0.9-15.5).           icaltrials.gov (NCT03678506, registration date
Based on these assumptions, we expect the recurrence rate            19/09/2018) and at EudraCT (2017-002340-32). The
at 12 months to be: 0.52*0.03+0.48*0.017=2.4%. With                  study protocol (V1.1 date 16/01/2018), was designed in
an expected annual recurrence rate of 2.4% in the study              compliance with the current version of the Declaration of
population, we calculate the sample size to demonstrate,             Helsinki and the GCP, and was authorized by AIFA
with an 80% power, that the upper limit of 95% CI is                 (“Agenzia Italiana del Farmaco” ref. number
below 3.5% according to Shen.23 The required sample size             AIFA/SC/P/16556, date 15/02/2018); it was approved by
is about 1150 patients to be recruited for the purpose of            the independent Ethics Committee of the Azienda Os-
the Apidulcis study.                                                 pedaliera Careggi, Florence, Italy (reference number: CE
                                                                     12152_spe, dated 17/04/2018) as lead ethics committee
Safety endpoint and interim analysis                                 and will be approved by ethics committees at all partici-
                                                                     pating sites before enrolment starts. The study will be con-
    Based on a 2.2% annual event rate, a total sample size
                                                                     ducted in accordance with the Declaration of Helsinki.
of around 1150 patients and 18 months of follow-up, we
                                                                     Written informed consent will be collected before starting.




                                                                                             ly
expect around 38 recurrences and 2 major bleedings in
                                                                     Protocol amendments will be communicated to study sites
our study. Since low-dose Apixaban may be considered




                                                                                      on
                                                                     by the sponsor. The steering committee (appendix A) has
the gold-standard treatment, we plan an interim analysis
                                                                     responsibility for the design, carrying out and analysis of
where 20 primary endpoints are registered. A Data Mon-
                                                                     the study as well as decisions on publication of results and
itoring and Safety Board (DMSB) will perform the in-


                                                                                 e
                                                                     has full access to the data set. All safety and efficacy end-
terim analysis and apportion the primary endpoints to the                    us
                                                                     points will be evaluated by an independent Data Monitor-
two groups of patients. The study will be interrupted if
                                                                     ing Safety Board (DMSB, appendix A) blind to the
the relative risk of primary endpoints (HR) in the obser-
                                                                     treatment of patients, eCRF, e-trial system, data capture
                                                                   al
vational non-treatment group is >3 HR, with a P value
                                                                     and monitoring. A DMSB (appendix A), blind to patient
<0.0001, compared to the group receiving Apixaban.
                                                                     D-dimer results and treatment, will supervise the study
                                                      ci


                                                                     and will perform interim analysis. The trial supporter (Al-
Statistical plan
                                                    er



                                                                     liance BMS-Pfizer) has no role in collection, analysis and
    All included subjects will be examined for efficacy              interpretation of data, or submission of results. Study find-
                                                   m




and safety. Collected data for continuous variables will be          ings will be disseminated to Alliance BMS-Pfizer, to the
                                          om




described as mean with standard deviation and 95% con-               participating centers, at research conferences, and in peer-
fidence interval if normally distributed, or as median with          reviewed journals.
range interquartile and 95% CI in case of deviation from
                                     -c




a normal distribution. Nominal variables will be described
as absolute and relative frequency tables. Statistical analy-        DISCUSSION
                             on




sis of the baseline variables [analysis of variance
                                                                         The optimal duration of anticoagulant treatment to
(ANOVA) complemented with the Tukey and Dunnet
                                                                     avoid recurrence after a first VTE is still an open issue.
                         N




tests, or Kruskal–Wallis test, as appropriate, and chi-
                                                                     While some authors do not agree with the idea of distin-
square test for nominal variables] is planned for those
                                                                     guishing VTE events between unprovoked and provoked
variables that at the descriptive analysis throw up potential
                                                                     to decide the duration of anticoagulation,24,25 international
differences in terms of clinical relevance. Kaplan–Meier
                                                                     guidelines still recommend indefinite anticoagulant treat-
survival curves will be plotted to estimate the cumulative
                                                                     ment (extended beyond the first 3-6 months) only in sub-
incidence of symptomatic recurrent VTE; hazard ratios
                                                                     jects with an unprovoked first VTE event, provided the
(HR) and their 95% confidence intervals (CI) will be cal-
                                                                     risk of bleeding is not high. A recent systematic review
culated for subgroup analysis. The Villalta score,18 will be
                                                                     and meta-analysis reported a cumulative incidence of re-
analyzed as a continuous variable and as a nominal vari-
                                                                     currence in patients with a first unprovoked VTE of
able, using the cut-off >5 points to identify the post-
                                                                     16.0% (13.3% to 18.8%) at 2 years, 25.2% (21.3% to
thrombotic syndrome and the cut-off >14 to classify the
                                                                     29.3%) at 5 years, and 36.1% (27.8% to 45.0%) at 10
syndrome as severe.
                                                                     years after stopping anticoagulation.7 This means that
                                                                     about two-third of all patients with unprovoked events are
Ethics and dissemination
                                                                     expected to remain free from recurrence over 10 years.
  The Apidulcis is an investigator-initiated study pro-              On the other hand, a recent meta-analysis has calculated
moted by the “Arianna Anticoagulazione” Foundation                   an incidence of MB events during extended anticoagula-

                                     Bleeding, Thrombosis and Vascular Biology 2022; 1:10
                                          Rationale and design of a study on D-dimer use                                           43



tion of 1.74 (1.34 to 2.20 events) per 100 patient-years            study,12 patients aged 75 years or more will be excluded
with VKAs and 1.12 events (0.72 to 1.62) with DOACs,                from the present study. This exclusion is justified by the
with a 5-year cumulative incidence of 6.3% (3.6% to                 high risk of bleeding during anticoagulation for these pa-
10.0%) with VKAs (no data are available for treatment               tients,19 as well as the fact that the predictive value of D-
with DOACs beyond one year).8 Furthermore, while the                dimer testing is expected to be lower in elderly patients
rate of recurrence decreases over time, bleeding is stable          since D-dimer levels increase with age.26
during anticoagulant treatment. Additionally, the case-fa-              An interim analysis of the study results is pre-defined
tality rate of MB is much higher compared to that of re-            when 20 primary outcomes (both for efficacy and safety)
current events (more than double according to data in the           occur during the study. We have opted for the interim
above-mentioned meta-analysis studies: MB: 8.3% and                 analysis because we want to be sure that new patients will
9.7% during VKA or DOAC treatments, respectively, ver-              not be enrolled in case the incidence of outcomes would
sus 4% of recurrences).                                             result unacceptably higher in patients with negative D-
    The above-mentioned meta-analyses indicate that only            dimer assay, who remain without anticoagulation, com-
one-third of subjects with a first unprovoked VTE event             pared to those who will receive low dose Apixaban. In
will have a recurrence in 10 years and that the risk of MB          principle, all patients included in the study can technically
and of associated complications is not-negligible during            be considered at high risk of recurrence and therefore
anticoagulation. It seems justified, therefore, to look for         would deserve extended anticoagulation.




                                                                                       ly
management strategies aimed at stratifying subjects at risk             The study has some limitations. First, it is an investi-




                                                                               on
of recurrence after a first unprovoked event. To this end,          gator-initiated study, with limited financial resources. For
and in line with what was done in the Dulcis study,14 serial        this reason, periodic on-site monitoring will not be possi-
D-dimer assay in the Apidulcis study will be used to strat-         ble. However, a dedicated remote monitor will assure ad-



                                                                         e
ify higher or lower risks of recurrence in patients with            equate training of all participant investigators for the study
positive or negative D-dimer results. The former will re-
                                                                  usprocedures before enrolling the first patient. Moreover,
                                                                    the dedicated monitor will regularly check site compli-
ceive extended anticoagulation, whereas the latter will go
without anticoagulation or other specific treatment. A cru-         ance to protocol and complete and correct entry into
                                                            al

cial difference versus Dulcis is that in the present study          eCRF. Second, though sites are asked to enroll all consec-
                                                                    utive patients eligible to the study, we cannot be sure this
                                               ci

low-dose Apixaban (2.5 mg BID) will be used for ex-
tended anticoagulant treatment, in line with what was               will happen since some sites are often overwhelmed by
                                             er



done in the Amplify Extension study,15 instead of VKAs              routine work, especially in this pandemic period.
                                            m




(at usual INR 2.0-3.0 range) as used in the Dulcis. We ex-
pect in this way to have less MB and a similar protection
                                   om




against recurrence in treated patients as that of the Dulcis        CONCLUSIONS
study. Another important difference versus the Dulcis and               The aim of the prospective, multicenter Apidulcis
Amplify Extension studies is that in the present study pa-          study is to find out whether it is possible to stratify, for
                             -c




tients are eligible only after completion of at least 12            risk of recurrence, patients who have had a single VTE
months of standard anticoagulant treatment, compared to
                      on




                                                                    event (proximal DVT of the lower limb and/or PE) un-
at least three months in Dulcis and 6-12 months in Am-              provoked or associated with WRF, and who have already
plify-Extension. We recognize that this is not an inclusion         received at least one year of standard anticoagulant treat-
                 N




criterion decided by the Steering Committee of the                  ment after the event. Stratification is done by performing
Apidulcis but rather the sole criterion Alliance BMS-               serial D-dimer assay using local routinely used, quantita-
Pfizer required for providing the drug for the study. We            tive methods and adopting pre-specified cutoff levels dif-
believe that the main scope for this long anticoagulant             ferent for men and women. Patients with persistently
treatment course before inclusion is to assure that the in-         negative D-dimer results (considered at low risk) will go
cluded patients will really deserve an extended treatment.          without anticoagulant therapy, whereas patients at first
In fact, it will be a factor in favor of inclusion of patients      positive result will receive Apixaban 2.5 mg BID. All pa-
at high risk of recurrence, since the treating physicians           tients will be followed-up for 18 months.
tend to give lengthier anticoagulation to subjects consid-
ered at high risk. While we have accepted this criterion,
we believe it may be a factor for delayed inclusion of pa-          REFERENCES
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