Factors influencing doctors’ selection of dabigatran innon-valvular atrial fibrillationCindy Huang PharmD1, Michele Siu PharmD1, Lily Vu PharmD1, Soo Wong PharmD1 and Jaekyu ShinPharmD MS BCPS2

1Pharmacy Students, 2Assistant Professor of Clinical Pharmacy, Department of Clinical Pharmacy, School of Pharmacy, University of California SanFrancisco, San Francisco, CA, USA

Keywords

dabigatran, oral anticoagulants, physicianbehaviour, prescribing decision, prescription,warfarin

doi:10.1111/j.1365-2753.2012.01886.x

Correspondence

Dr. Jaekyu ShinDepartment of Clinical Pharmacy, School ofPharmacyUniversity of California San Francisco521 Parnassus AvenueC-152, Box 0622San Francisco, CA 94143-0622USAE-mail: shinj@pharmacy.ucsf.edu O

Accepted for publication: 19 June 2012

doi:10.1111/j.1365-2753.2012.01886.x

AbstractRationale, aims and objectives This study was designed to examine the factors thatinfluence doctors’ decision in initiating or switching from warfarin to dabigratran.Method A survey questionnaire was sent to 181 doctors who were most likely to prescribedabigatran (e.g. cardiologists and general internists) at the University of California, SanFrancisco Medical Center between November 2011 and February 2012. Survey participantswere asked to complete an electronic or a paper version of the questionnaire, whichconsisted of 17 multiple-choice questions. Fisher’s exact test and Cochran–Mantel–Haenszel test were used to compare survey responses between cardiologists and generalinternists.Results A total of 65 survey responses were received (35.9% response rate). There were 13cardiologists and 51 general internists who participated in the study. Cost (25%), renalfunction (21%) and CHADS2 score (18%) were the three factors doctors considered mostoften to determine a patient’s eligibility for dabigatran in warfarin-naïve patients. On theother hand, histories of unstable international normalized ratio (37%) and missed appoint-ments (17%) along with cost (19%) were most often considered in patients on warfarin.Cardiologists had prescribed dabigatran more often and had a significantly higher level ofcomfort with prescribing the drug than general internists (P = 0.003; 77% vs. 27%).Conclusions Cost was the most important factor influencing doctors’ decision to prescribedabigatran. Safety and effectiveness of dabigatran as well as patient preference wereadditional factors influencing their decision. General internists were less comfortable withprescribing dabigatran than cardiologists.

IntroductionFor over 50 years, warfarin has been the standard of carefor long-term anticoagulation therapy. Dabigatran etexilate(Pradaxa®) is the first new oral anticoagulant approved by theUS Food and Drug Administration (FDA) since warfarin for theprevention of strokes and systemic embolism for patients withnon-valvular atrial fibrillation. Dabigatran is a reversible, directthrombin inhibitor, a novel drug in its class.

Warfarin, a vitamin K antagonist, is effective for stroke preven-tion in patients with atrial fibrillation. However, there are alsomany barriers to its use. Warfarin has a narrow therapeuticwindow, which requires frequent monitoring; has wide inter-individual dose requirements affected by genetic variance; and hasmany drug–drug and drug–food interactions [1].

Dabigatran represents an effective and convenient alternative towarfarin. Dabigatran etexilate is an oral prodrug that is rapidly

converted by serum esterase to the active form, reaching peakconcentrations in about 2 hours. Eighty per cent of a given dose isexcreted by the kidneys with a half-life of 12–17 hours. Dabigat-ran provides stable anticoagulation at a fixed dose without theneed for laboratory monitoring so regular blood draws is notrequired [2,3]. Dabigatran 150 mg twice daily was shown to besuperior to warfarin in reducing rates of stroke and systemicembolism while yielding similar rates of major haemorrhage inthe randomized evaluation of long-term anticoagulation therapytrial [2].

However, dabigatran also has its drawbacks. It requires twicedaily administration, lacks a reliable reversal agent, does not havea clinically useful and specific laboratory monitoring tool, is moreexpensive than warfarin, and is associated with an increased risk ofgastrointestinal side effects including bleeding [4]. Additionally,post-market reports of serious bleeding events have prompted areview of dabigatran by the FDA [5].

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Journal of Evaluation in Clinical Practice ISSN 1365-2753

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Despite the promising data behind dabigatran, its initial clinicaluptake has been slower than expected [6]. Some experts suggestthat possible reasons for the low uptake of dabigatran are cost,need for twice daily dosing, inability to easily measure the degreeof anticoagulation, and the lack of an immediate antidote preop-eratively or post-trauma [6]. In addition, levels of comfort withprescribing dabigatran may differ among doctors and this differ-ence may have contributed to the low uptake of the drug. Thus, wesought to identify the factors that influence doctors’ decision toprescribe dabigatran in clinical practice and compared levels ofcomfort with prescribing dabigatran between cardiologists andgeneral internists, two main prescriber categories of the drug byusing a survey. Our data may help elucidate the reasons for the lowuptake of dabigatran from doctors’ perspective.

Methods

Subjects

A total of 181 doctors affiliated with Department of Internal Medi-cine, Cardiology, or Hospital Medicine at the University of Cali-fornia, San Francisco (UCSF) Medical Center were invited toparticipate in this survey study because they were major users ofanticoagulants in our institution. Each doctor’s contact informa-tion was obtained from the UCSF directory. The survey was sent tothe participants through e-mail four times or mail one timebetween November 2011 and February 2012. Survey participantscompleted an electronic questionnaire through http://www.surveymonkey.com or a paper version of the questionnaire; thestudy was anonymous. Our study was approved by the UCSFCommittee for Human Research (CHR).

Survey questionnaire

A survey was developed to identify factors that influence doctors’decision to prescribe dabigatran in warfarin-naïve patients andpatients on warfarin. The survey questionnaire consists of 17multiple-choice questions requiring single or multiple answers(Appendix). The questions were designed to elicit informationregarding doctor demographics, knowledge and experience withdabigatran, and factors that influence decisions to prescribedabigatran in warfarin-naïve patients and patients on warfarin. Onesurvey question was included to assess participants’ knowledge ofdabigatran. This question was a true-or-false question asking par-ticipants whether dabigatran is more effective in preventing non-haemorrhagic stroke compared with patients on warfarin therapywith international normalized ratio (INR) in the therapeutic rangegreater than 72.6% of the time.

Statistical analysis

Descriptive statistics was used to determine frequency distribu-tions, percentage distributions, means and standard deviations, andinclusive ranges as evidenced by the data.

Because of the small sample size, variables with multiple levelswere recoded to two levels. These recoded variables included theparticipant’s title (faculty vs. non-faculty), percentage of eligiblepatients the participant has discussed dabigatran with the totalnumber of patients the participant has prescribed dabigatran (0–10

vs. >10) and the participant’s level of comfort with prescribingdabigatran (somewhat to very comfortable vs. the other catego-ries). In addition, the rank variables were collapsed such that therecoded variables indicated whether the participant had rankedthem or not (i.e. if ranked, 1; else 0).

Because cardiologists and general internists may have a differ-ence in factors influencing their decisions to prescribe dabigatran,survey responses were compared by discipline (i.e. cardiology vs.general internists). Fisher’s exact test was performed to comparesurvey responses by discipline. Because years of doctor licensureand faculty status may influence level of comfort with prescribingdabigatran, these two factors were compared for level of comfortwithin each discipline by using the Cochran–Mantel–Haenszeltest. SAS (version 9.1, Cary, NC, USA) was used and a P value<0.05 was considered statistically significant.

Results

Characteristics of the participants

A total of 65 responses (35.9% response rate) were received.Table 1 describes baseline characteristics of participants. Majorityof participants (78%) were general internists and 85% of partici-pants saw 0–20 patients with atrial fibrillation per month. About a

Table 1 Baseline characteristics of the participants (n = 65)

Characteristic n (%)

Age (years)20–29 11 (16.9)30–39 29 (44.6)40–49 17 (26.2)50–59 5 (7.7)�60 3 (4.6)

Male 27 (42)Title

Faculty 47 (72.3)Resident 17 (26.2)Fellow 1 (1.5)

Area of practiceCardiology 13 (20.0)Internal medicine 51 (78.5)Other 1 (1.5)

Years as a licensed physician�5 28 (43.1)>5 but �10 9 (13.8)>10 but �20 18 (27.7)>20 2 (3.1)

No. of patients seen per month on anticoagulant for atrial fibrillation0–20 55 (84.6)21–40 8 (12.3)41–60 2 (3.1)

Percent of eligible patients with whom dabigatran was discussed0 211–25 2826–50 451–75 576–100 7

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© 2012 Blackwell Publishing Ltd2

half (43%) of participants were licensed as doctors for less than orequal to 5 years. Top three sources from which the participantsobtained information on dabigatran were medical journals (51%),in-services in the form of peer-to-peer lectures and presentations(43%), and medical conferences (38%). Majority of participants(74%) discussed dabigatran with eligible patients less than 25% ofthe time. About 40% of participants were somewhat uncomfort-able with prescribing dabigatran in dabigatran-eligible patients(Fig. 1). For the one true-or-false survey question, 55% of partici-pants answered this question correctly, 43% of participantsanswered incorrectly and 2% did not answer the question.

Factors influencing the choice of dabigatran

Patient’s ability to afford dabigatran was among the top threefactors to determine eligibility for dabigatran treatment in bothwarfarin-naïve patients and patients on warfarin (Table 2). Renalfunction and cardiac failure, hypertension, age � 75, diabetesmellitus, stroke (CHADS2) score were ranked among the top threefactors to determine eligibility for dabigatran treatment inwarfarin-naïve patients while histories of unstable INR and missedappointments were among the top three factors for the dabigatraneligibility in patients on warfarin.

The three most common reasons for prescribing dabigatran inwarfarin-naïve patients were reduced clinic visits (66%), less drug/food interactions (41%) and patient request (33%) (Table 3). Theparticipants ranked cost (64%), limited experience (63%) and lackof antidote (50%) as the three common reasons not to prescribedabigatran in warfarin-naïve patients.

The three most common reasons for prescribing dabigatran inpatients on warfarin were reduced clinic visits (52%), unstableINR in the absence of non-compliance (37%) and less drug/foodinteractions (27%) (Table 4). The participants ranked stable INRon warfarin (61%), cost (47%) and limited experience (47%) as thethree common reasons not to prescribe dabigatran in patients onwarfarin.

Prescriber analyses

Prescribers having prescribed dabigatran in more than 10 patientsfelt more comfortable with prescribing the drug than those havenot (P < 0.0001; 100% vs. 30%). Cardiologists were morecomfortable with prescribing dabigatran than general internists(P = 0.003; 77% vs. 27%). Within each discipline (e.g. cardiologyand general internal medicine), the level of comfort with prescrib-ing dabigtran was not associated with length of licensure or facultystatus. However, cardiologists were more likely to have prescribeddabigatran for more than 10 patients than general internists(P < 0.001; 46% vs. 4%).

Cardiologists were more likely to use CHADS2 score thangeneral internists to determine eligibility for dabigatran in

Figure 1 Level of comfort with prescribing dabigatran in dabigatran-eligible patients.

Table 2 Most important factors to determine eligibility for dabigatranin warfarin-naïve patients and patients on warfarin

Factor Percent

Warfarin-naïve patientsPatient ability to afford for dabigatran 25Renal function 21CHADS2 score 18Bleeding risk 15History of non-compliance with medications 14History of gastrointestinal diseases 7

Patients on warfarinHistory of unstable INR 37Patient ability to afford dabigatran 19History of missed appointments 17Renal function 12Bleeding risk 9History of gastrointestinal diseases 3CHADS2 score 3

CHADS2, cardiac failure, hypertension, age � 75, diabetes mellitus,stroke; INR, international normalized ratio.

Table 3 Reasons for prescribing or not prescribing dabigatran indabigatran-eligible warfarin-naïve patients

Factor Percent

Reasons for prescribingReduced clinic visits 66Less drug/food interactions 41Patient requests 33On the formulary of the patient’s insurance plan 17Superior to warfarin in efficacy 9Low risk of intracranial bleeding 9

Reasons for not prescribingCost 64Limited experience with dabigatran 63Lack of a well-documented reversal agent 50Limited clinical studies 19Concern about GI discomfort/bleeding risk 9Other oral anticoagulants in pipeline 9Lack of readily available laboratory test to monitor

degree of anticoagulation8

Twice daily dosing 6

GI, gastrointestinal.

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warfarin-naïve patients (P = 0.03; 77% vs. 41%). In addition, theywere more likely to rank superior efficacy of dabigatran thangeneral internists as a reason for prescribing dabigatran (inwarfarin-naïve patients: P = 0.005; 31% vs. 2%; in patients onwarfarin: P = 0.007; 23% vs. 0%). Moreover, they were morelikely to discuss dabigatran with dabigatran-eligible patients morethan 50% of time compared with general internists (P = 0.001;54% vs. 10%). Compared with cardiologists, general internistswere less likely to prescribe dabigatran in warfarin-naïve patientsbecause of limited experience (P = 0.02; 31% vs. 69%).

DiscussionTo our knowledge, this is the first study to examine the factorsinfluencing the selection of dabigatran and warfarin. We had threemain findings in this study. First, cost was among the most impor-tant factors doctors take into consideration when prescribingdabigatran in both warfarin-naïve patients and patients on warfa-rin. Second, except for cost, factors considered most often bydoctors to determine eligibility for dabigatran depended on theprevious exposure to warfarin. For warfarin-naïve patients, renalfunction and CHADS2 score were ranked among the top threefactors determining the eligibility for dabigatran. On the otherhand, histories of unstable INR and missed appointments wereamong the top three factors considered for patients on warfarin.Third, cardiologists have more experience in prescribing dabigat-ran and have a higher level of comfort with prescribing the drugthan general internists.

In previous studies, medication cost was of secondary impor-tance to medication effectiveness and safety as a factor influencingprescribing medications in primary and secondary care doctors[7–10]. In contrast, dabigatran cost was a primary factor influenc-ing doctors’ decision to prescribe dabigatran in our study. In addi-tion, dabigatran cost was a main reason for not prescribing it indabigatran-eligible patients. The retail cost of dabigatran currently

ranges from $200 to $300 for a 30-day supply in the United States.Even though studies have suggested that dabigatran may be cost-effective compared with warfarin when all costs associated withthe use of both drugs were considered, the high acquisition costmay have contributed to slow adoption of dabigatran in clinicalpractice [11–13]. In one qualitative study enrolling 15 doctorspractising in teaching hospitals, cost was a major factor influenc-ing doctors’ decisions on prescribing a drug [14]. As doctorsenrolled in our study practice in a teaching hospital, medicationcost may be a factor influencing prescribing dabigatran by doctorsworking in a teaching hospital.

Renal function and CHADS2 score along with cost were con-sidered most often for warfarin-naïve patients. These data suggestthat safety and indication of dabigatran are two of the most impor-tant factors influencing doctors’ selection of the drug becausedabigatran clearance relies on kidney function and patients withCHADS2 score of 0 may not need an anticoagulant [3,15]. Incontrast, histories of unstable INR and missed appointments wereconsidered most often for patients on warfarin. Because patientson warfarin are likely to have CHADS2 score greater than 0,determination of the indication may not be necessary [15]. Instead,effective anticoagulation and patient convenience may becomemore important particularly for patients who have difficulty inmaintaining good anticoagulation due to unstable INR and missedappointments because dabigatran has a predictable relationshipbetween pharmacokinetics and pharmacodynamics and does notrequire regular laboratory monitoring [3]. Overall, our datasuggest that medication safety and effectiveness are two importantfactors influencing doctors’ decision to prescribe dabigatran,which is consistent with the results of previous studies [7,9,10].

It is interesting that patient request was identified as one of themost important reasons for prescribing dabigatran in our study.Patient request has been ranked as one of the top reasons for doctorsto prescribe a new medication [16]. Dabigatran is a new drug and isheavily promoted through consumer-directed advertisements in theUnited States. Our data may reflect the doctors’ effort to preservethe doctor–patient relationship [17]. In addition, reduction in clinicvisits/blood draws and less diet restriction were two other fre-quently ranked reasons for prescribing dabigatran in our study.Consideration and incorporation of patients’ inputs and needs intothe prescribing decision may provide doctors an opportunity tobuild up long-term relationship with their patients and result inincreased patient compliance and improved outcomes [14].

In our study, doctors who have prescribed dabigatran more than10 times had a significantly higher level of comfort with prescrib-ing the drug than those have not. Because dabigatran is a drugspecific for a cardiologic disease (i.e. atrial fibrillation), cardiolo-gists may have prescribed dabigatran more often and thus seem tohave a higher level of comfort with prescribing the drug thangeneral internists. These data suggest that personal experiencemay make doctors more comfortable with prescribing a new drug.In fact, doctors’ personal experience has been identified as aninfluential factor to prescribe a drug [7,18]. In our study, the levelof comfort with prescribing dabigatran was not associated with thelength of doctor licensure or faculty status. In addition, generalinternists were more likely to rank limited experience than cardi-ologists as a reason for not prescribing dabigatran. These datasuggest that personal experience may be a factor to determine thelevel of comfort with prescribing a new drug. In addition, general

Table 4 Reasons for prescribing or not prescribing dabigatran indabigatran-eligible patients who are on warfarin

Factor Percent

Reasons for prescribingReduced clinic visits 52Unstable INR in the absence of non-compliance 37Less drug/food interactions 27Patient requests 22On the formulary of the patient’s insurance plan 10Low risk of intracranial bleeding 8Superior to warfarin in efficacy 5

Reasons for not prescribingPatient is well controlled on warfarin 61Cost 47Limited experience with dabigatran 47Lack of a well-documented reversal agent 35Limited clinical studies 21Lack of readily available laboratory test to monitor

degree of anticoagulation8

Concern about GI discomfort/bleeding risk 5Twice daily dosing 2

GI, gastrointestinal; INR, international normalized ratio.

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internists may be targeted for education to improve their level ofcomfort with dabigatran.

This study has limitations. The survey was based on a smallsample size. Our response rate (35.9%) was relatively low.However, response rate of survey studies using mainly Internet istypically about 20% and our study yielded response rate not dif-ferent from that with similar study designs [19]. Our data werecollected before the 9th edition of antithrombotic therapy andprevention of thrombosis guideline by the American College ofChest Physicians had been published [15]. This new guidelinerecommends dabigatran over dose-adjusted warfarin therapy inpatients with atrial fibrillation who require oral anticoagulation.Whether this new grade 2B recommendation would have affectedthe results of our study remains speculative. Additionally, ourstudy did not include other new oral anticoagulants such as rivar-oxaban and apixaban because these new drugs were not availableat the time the study was approved by UCSF CHR. Given manycharacteristics shared among the new oral anticoagulants includ-ing dabigatran, however, our data may provide insight on thefactors influencing doctors’ decisions to prescribe these anticoagu-lants [20]. Finally, our study focused on doctors at a teachinghospital affiliated with a university and thus, our data may not beapplicable to doctors practising in other settings.

In conclusion, cost was the most important factor influencingdoctors’ decisions to prescribe dabigatran. Doctors also tookinto consideration safety and effectiveness of dabigatran as wellas patient preferences when prescribing dabigatran. Generalinternists were less comfortable with prescribing dabigatran thancardiologists.

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Appendix: Questionnaire1. What is your age?

� 20–29� 30–39� 40–49� 50–59� �60

2. What is your gender?� Male� Female� Other

3. What is your title in the UCSF Medical Center?� Faculty� Resident� Fellow� Other: _____

4. What is your specialty? Please check one.� Cardiology� Internal medicine� Other: _____

5. How long have you been a licensed physician?� Less than or equal to 5 years� More than 5 years but less than or equal to 10 years� More than 10 years but less than or equal to 20 years� More than 20 years

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6. Where have you learned about dabigatran (Pradaxa®)?Check all that apply.� I have never heard of dabigatran (Pradaxa®).� Medical journals� In-service (peer to peer lectures and presentations)� Pharmaceutical company representative� Medical conference (s)� Manufacturer’s website� Other: _____

7. How many patients per month do you currently see in yourpractice who are on anticoagulation for atrial fibrillation?� 0–20� 21–40� 41–60� 61–80� >80

8. Please rank the three most important factors that you considerwhen determining whether a patient who has not been onwarfarin is a good candidate for dabigatran (Pradaxa®).1 = more important, 3 = least important___ Renal function___ Liver function___ Bleeding risk___ History of gastrointestinal diseases___ History of non-compliance with medications___ Patient’s ability to afford for dabigatran (Pradaxa®)___ CHADS2 score

9. For patients who are considered eligible candidates and whomyou have initiated dabigatran, what are the top three reasonsfor initiating it? (Check three only)� Less drug/food interactions� Reduce clinic visits/blood draws� Patient requests� Superior to warfarin in preventing stroke� On the formulary of the patients’ insurance plans� Lower risk of intracranial bleed according to RELY trial� Other: _____

10. For patients who are considered eligible candidates but whomyou have not initiated dabigatran, what are the top threereasons for not initiating it? (Check three only)� Limited clinical studies� Limited experience with this drug� Lack of well-documented antidote to reverse its effect� Cost� Twice daily dosing� Cannot monitor degree of anticoagulation� Other oral anticoagulants are in the pipeline [i.e. rivaroxa-

ban (Xarelto®), apixaban (Eliquis®)]� From my experience, many patients had to stop taking

dabigatran due to side effects (e.g. gastrointestinaldiscomfort/bleeding etc)

� Other: _____11. Please rank the three most important factors that you consider

when determining whether a patient who has been on warfarinis a good candidate for dabigatran (Pradaxa®).1 = more important, 3 = least important___ Renal function___ Liver function___ Bleeding risk

___ History of gastrointestinal diseases___ History of missed appointments___ Patient’s ability to afford for dabigatran (Pradaxa®)___ CHADS2 score___ History of unstable INR

12. For patients who are considered eligible candidates and whomyou have switched dabigatran from warfarin, what are the topthree reasons for switching it? (Check three only)� Less drug/food interactions� Reduce clinic visit/blood draw� Patient requests� Superior to warfarin in preventing stroke� On the formulary of the patients’ insurance plan� Lower risk of intracranial bleed according to RELY trial� Unstable INR in the absence of non-adherence� Other: _____

13. For patients who are considered eligible candidates but whomyou have not switched dabigatran from warfarin, what are thetop three reasons for not switching it? (Check three only)� Patient is well controlled on warfarin� Limited clinical studies� Limited experience with this drug� Lack of well documented antidote to reverse its effect� Cost� Twice daily dosing� Cannot monitor degree of anticoagulation� Other oral anticoagulants are in the pipeline [i.e. rivaroxa-

ban (Xarelto®), apixaban (Eliquis®)]� From my experience, many patients had to stop taking

dabigatran due to side effects (e.g. gastrointestinaldiscomfort/bleeding etc)

� Other: _____14. What percentage of eligible patients do you discuss dabigatran

(Pradaxa®) with?� 0%� 25%� 50%� 75%� 100%

15. How many total patients have you initiated with dabigatran(Praxada) or switched from warfarin to dabigatran (Praxada)?� 0–10 patients� 11–20 patients� 21–30 patients� >30 patients

16. How comfortable do you feel initiating/switching dabigatranin eligible patients?� Very comfortable� Somewhat comfortable� Neutral� Somewhat uncomfortable� Very uncomfortable

17. Is the following statement true or false? Please check one.Dabigatran is more effective in preventing non-hemorrhagicstroke compared to patients on warfarin therapy with INR inthe therapeutic range greater than 72.6% of the time.� True� False

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