Summary
In this large, prospective, nationwide cohort study conducted in general practice, 39% of the patients received at least one inappropriate DOAC prescription. The main type of inappropriate prescription was inappropriate dosing (33.7% of patients), most frequently under-dosing (31.3%). In a multinomial multivariable analysis, the factors independently associated with DOAC under-dosing (versus appropriate dosing) were older age, prescription of dabigatran or apixaban, and a higher CHA2DS2-VASc score. Factors independently associated with over-dosing were kidney failure, a HAS-BLED score ≥3, and older age.
Strengths and limitations
The study’s multicentre design and the large sample size may mean that the results can be generalised reliably. Moreover, only one other study has focused exclusively on primary care, despite the fact that GPs are closely involved in the management of patients with chronic conditions who take oral anticoagulants.6 Given that the investigator was the patient’s family physician in 95% of cases (data not shown), the study data were easy to access by using a questionnaire. However, the data were declarative and were not checked objectively, therefore representing a potential source of measurement bias. It is also possible that GPs who agreed to participate in the study were more motivated by issues such as continuing medical education, patient education, and/or anticoagulants than the average GP.
The GPs’ records may not have included all the factors that influence decisions about DOAC dosing, including patient preferences and values, and plans for imminent cardioversions. The HAS-BLED and CHA2DS2-VASc scores were assessed a posteriori. Therefore, it was not possible to tell whether prescribers knew of these scores and took them into account when prescribing DOACs. Other confounders were also included, such as a personal history of haemorrhage requiring hospitalisation (Supplementary Table S1).
Although the concomitant prescription of DOAC and aspirin is not recommended, rivaroxaban and low-dose aspirin can be given concurrently in acute coronary syndrome and AF. However, the dose of aspirin prescribed was not recorded in the study database. Finally, the absence of longitudinal data on inappropriate prescriptions constitutes a limitation for the present analysis, but this was not the main objective of the CACAO cohort study.3
Comparison with existing literature
In line with the present study’s findings, inappropriate dosing of DOAC, especially under-dosing, is usually the most prevalent issue, ranging from 7.7%6 to 32%8 in previous studies.6–12 However, the incidence of under-dosing observed in the current study (31.3%) was higher than in the literature. For example, the corresponding values were 7.2%, 9.4%, and 18% in the Canadian Primary Care cohort,6 the ORBIT-AF II Registry,11 and the FANTASIIA Registry,8 respectively. This difference might be explained by the characteristics of the study populations. In the current study, patients were older (mean age 76; standard deviation 71–75 in other studies) and more likely to have comorbidities and/or frailty factors, such as kidney failure and higher CHA2DS2-VASc scores.6,8,11
The most prescribed drug was rivaroxaban in the current study, as well as in the Canadian cohort6 and the ORBIT-AF II Registry11 (50%, 57%, and 54%, respectively), whereas dabigatran was the most prescribed drug in the FANTASIIA study (50%).8
The literature on factors associated with inappropriate dosing is contradictory.6–12 Older age9–11 and a higher CHA2DS2-VASc score10,11 were also factors associated with under-dosing in other studies. The fact that a higher CHA2DS2-VASc score (that is, higher risk of ischaemic stroke) was associated with under-dosing might reflect a degree of frailty among patients and the fear of over-dosing among prescribers. Similarly, the FANTASIIA study found that dabigatran was associated with under-dosing,8 and the ORBIT-AF II study found the same association for apixaban.11 In contrast with the literature on comorbidity, heart failure was not found to be a significant factor in the current study.6
Few studies have found that kidney failure is associated with over-dosing.9,11 This finding conflicts with previous reports,6,8,10 and might be due to the higher incidence of kidney failure in the current study’s population. However, this observation suggests that physicians might not adjust the dose level according to kidney function (possibly because of a lack of awareness or a lack of laboratory data); or perhaps they adapt the dose using the Modification of Diet in Renal Disease equation or another equation that gives better renal scores than the Cockcroft–Gault equation; or they might not have an up-to-date record of the patient’s body weight.
Other similar factors associated with over-dosing in the literature include a higher bleeding score and older age.9,11 However, bleeding scores (ORBIT and/or HAS-BLED) may also reflect comorbidities and/or frailty, such as older age and kidney failure, suggesting that GPs do not follow the guidelines on DOAC prescriptions.
The only other primary care study, which was carried out in Canada, reported a lower incidence of inappropriate DOAC prescriptions.6 Although this difference may be explained, at least in part, by the characteristics of the respective study populations (with more kidney failure and higher CHA2DS2-VASc scores in the current study), dabigatran was also less frequently prescribed in the Canadian study (34% of patients) than in the present study (43%). Moreover, around 20% of the participating physicians in the Canadian cohort were in academic practice, which may explain the lowest inappropriate prescription rate, that is, because these 20% would be less likely to make inappropriate prescriptions.
Most of the patients in the current study were first prescribed an oral anticoagulant by a cardiologist (77%); this might result in therapeutic inertia, with GPs reluctant to modify another physician’s prescription.
Implications for practice
It is well established that higher-than-recommended dose levels of DOACs are associated with elevated all-cause mortality, and under-dosing is associated with more frequent hospitalisation for cardiovascular problems.11 However, some studies of off-label prescriptions have reported that stroke severity and clinical outcomes are no worse in patients with under-dosed DOACs than in patients on the recommended dose.10,20
In the present cohort of patients managed in primary care, most DOAC prescriptions were for the recommended doses. However, the appropriateness of DOAC prescribing can be improved for a third of patients, especially in older individuals, those with kidney failure, a higher risk of ischaemic stroke, and/or higher risk for bleeding. Cardiologists and GPs have a key role in increasing the proportion of appropriate DOAC prescriptions via informational, educational, and/or management strategies.