The full spectrum of SLC22 OCT1 mutations illuminates the bridge between drug transporter biophysics and pharmacogenomics.

Mutations in transporters can impact an individual's response to drugs and cause many diseases. Few variants in transporters have been evaluated for their functional impact. Here, we combine saturation mutagenesis and multi-phenotypic screening to dissect the impact of 11,213 missense single-amino-acid deletions, and synonymous variants across the 554 residues of OCT1, a key liver xenobiotic transporter. By quantifying in parallel expression and substrate uptake, we find that most variants exert their primary effect on protein abundance, a phenotype not commonly measured alongside function. Using our mutagenesis results combined with structure prediction and molecular dynamic simulations, we develop accurate structure-function models of the entire transport cycle, providing biophysical characterization of all known and possible human OCT1 polymorphisms. This work provides a complete functional map of OCT1 variants along with a framework for integrating functional genomics, biophysical modeling, and human genetics to predict variant effects on disease and drug efficacy.

Influence of Bile Acids on Clindamycin Hydrochloride Skin Permeability: In Vitro and In Silico Preliminary Study.

BACKGROUND AND OBJECTIVE: Topical clindamycin formulations are widely used in clinical practice, but poor bioavailability and restricted skin penetration considerably limit their therapeutic efficacy. Penetration enhancement represents a promising and rational strategy to overcome the drawbacks of conventional topical pharmaceutical formulations. We aim to assess the influence of cholic acid (CA) and deoxycholic acid (DCA) on the permeability of clindamycin hydrochloride by performing the in vitro skin parallel artificial membrane permeability assay (skin-PAMPA) at two relevant pH values (5.5 and 6.5) and the interactions of tested substances with skin ATP-binding cassette (ABC) transporters in silico. METHODS: After the incubation period, the clindamycin hydrochloride concentrations in both compartments were determined spectrophotometrically, and the apparent permeability coefficients (Papp) were calculated. Vienna LiverTox web service was used to predict the interactions of clindamycin and bile acids with potential drug transporters located in human skin. RESULTS: Both CA and DCA at the highest studied concentration of 100 µM in the tested solutions increased the skin-PAMPA membrane permeability of clindamycin hydrochloride. This effect was more pronounced for CA and at a higher studied pH value of 6.5, which is characteristic of most dermatological indications treated with topical clindamycin preparations. Clindamycin transport may also be mediated by ABC transporters located in skin and facilitated in the presence of bile acids. CONCLUSIONS: The results of this study provide a solid foundation for further research directed at the improvement of topical formulations using bile acids as penetration-enhancing excipients, as well as the therapeutic efficacy of clindamycin hydrochloride.

Coevolution-Driven Method for Efficiently Simulating Conformational Changes in Proteins Reveals Molecular Details of Ligand Effects in the ß2AR Receptor.

With the advent of AI-powered structure prediction, the scientific community is inching closer to solving protein folding. An unresolved enigma, however, is to accurately, reliably, and deterministically predict alternative conformational states that are crucial for the function of, e.g., transporters, receptors, or ion channels where conformational cycling is innately coupled to protein function. Accurately discovering and exploring all conformational states of membrane proteins has been challenging due to the need to retain atomistic detail while enhancing the sampling along interesting degrees of freedom. The challenges include but are not limited to finding which degrees of freedom are relevant, how to accelerate the sampling along them, and then quantifying the populations of each micro- and macrostate. In this work, we present a methodology that finds relevant degrees of freedom by combining evolution and physics through machine learning and apply it to the conformational sampling of the ß2 adrenergic receptor. In addition to predicting new conformations that are beyond the training set, we have computed free energy surfaces associated with the protein's conformational landscape. We then show that the methodology is able to quantitatively predict the effect of an array of ligands on the ß2 adrenergic receptor activation through the discovery of new metastable states not present in the training set. Lastly, we also stake out the structural determinants of activation and inactivation pathway signaling through different ligands and compare them to functional experiments to validate our methodology and potentially gain further insights into the activation mechanism of the ß2 adrenergic receptor.

Determinants of sugar-induced influx in the mammalian fructose transporter GLUT5.

In mammals, glucose transporters (GLUT) control organism-wide blood-glucose homeostasis. In human, this is accomplished by 14 different GLUT isoforms, that transport glucose and other monosaccharides with varying substrate preferences and kinetics. Nevertheless, there is little difference between the sugar-coordinating residues in the GLUT proteins and even the malarial Plasmodium falciparum transporter PfHT1, which is uniquely able to transport a wide range of different sugars. PfHT1 was captured in an intermediate 'occluded' state, revealing how the extracellular gating helix TM7b has moved to break and occlude the sugar-binding site. Sequence difference and kinetics indicated that the TM7b gating helix dynamics and interactions likely evolved to enable substrate promiscuity in PfHT1, rather than the sugar-binding site itself. It was unclear, however, if the TM7b structural transitions observed in PfHT1 would be similar in the other GLUT proteins. Here, using enhanced sampling molecular dynamics simulations, we show that the fructose transporter GLUT5 spontaneously transitions through an occluded state that closely resembles PfHT1. The coordination of D-fructose lowers the energetic barriers between the outward- and inward-facing states, and the observed binding mode for D-fructose is consistent with biochemical analysis. Rather than a substrate-binding site that achieves strict specificity by having a high affinity for the substrate, we conclude GLUT proteins have allosterically coupled sugar binding with an extracellular gate that forms the high-affinity transition-state instead. This substrate-coupling pathway presumably enables the catalysis of fast sugar flux at physiological relevant blood-glucose concentrations.

Reconstructing the transport cycle in the sugar porter superfamily using coevolution-powered machine learning.

Sugar porters (SPs) represent the largest group of secondary-active transporters. Some members, such as the glucose transporters (GLUTs), are well known for their role in maintaining blood glucose homeostasis in mammals, with their expression upregulated in many types of cancers. Because only a few sugar porter structures have been determined, mechanistic models have been constructed by piecing together structural states of distantly related proteins. Current GLUT transport models are predominantly descriptive and oversimplified. Here, we have combined coevolution analysis and comparative modeling, to predict structures of the entire sugar porter superfamily in each state of the transport cycle. We have analyzed the state-specific contacts inferred from coevolving residue pairs and shown how this information can be used to rapidly generate free-energy landscapes consistent with experimental estimates, as illustrated here for the mammalian fructose transporter GLUT5. By comparing many different sugar porter models and scrutinizing their sequence, we have been able to define the molecular determinants of the transport cycle, which are conserved throughout the sugar porter superfamily. We have also been able to highlight differences leading to the emergence of proton-coupling, validating, and extending the previously proposed latch mechanism. Our computational approach is transferable to any transporter, and to other protein families in general.

The full spectrum of OCT1 (SLC22A1) mutations bridges transporter biophysics to drug pharmacogenomics.

Membrane transporters play a fundamental role in the tissue distribution of endogenous compounds and xenobiotics and are major determinants of efficacy and side effects profiles. Polymorphisms within these drug transporters result in inter-individual variation in drug response, with some patients not responding to the recommended dosage of drug whereas others experience catastrophic side effects. For example, variants within the major hepatic Human organic cation transporter OCT1 (SLC22A1) can change endogenous organic cations and many prescription drug levels. To understand how variants mechanistically impact drug uptake, we systematically study how all known and possible single missense and single amino acid deletion variants impact expression and substrate uptake of OCT1. We find that human variants primarily disrupt function via folding rather than substrate uptake. Our study revealed that the major determinants of folding reside in the first 300 amino acids, including the first 6 transmembrane domains and the extracellular domain (ECD) with a stabilizing and highly conserved stabilizing helical motif making key interactions between the ECD and transmembrane domains. Using the functional data combined with computational approaches, we determine and validate a structure-function model of OCT1s conformational ensemble without experimental structures. Using this model and molecular dynamic simulations of key mutants, we determine biophysical mechanisms for how specific human variants alter transport phenotypes. We identify differences in frequencies of reduced function alleles across populations with East Asians vs European populations having the lowest and highest frequency of reduced function variants, respectively. Mining human population databases reveals that reduced function alleles of OCT1 identified in this study associate significantly with high LDL cholesterol levels. Our general approach broadly applied could transform the landscape of precision medicine by producing a mechanistic basis for understanding the effects of human mutations on disease and drug response.

Adherence to protocols for the use of reversal agents in patients treated with direct oral anticoagulants.

OBJECTIVES: This study aimed to evaluate the adherence to protocols for the use of reversal agents in direct oral anticoagulant (DOAC) users in Dutch hospitals. METHODS: A retrospective cohort study was conducted in seven hospitals in the Netherlands. Treatment protocols for bleeding and (urgent) procedures in patients on DOAC were collected from each hospital. All patient data on the use of reversal agents were retrospectively collected from September 2021 to April 2022 and compared to the protocols. The degree of per-protocol adherence (compliance score) was categorized into four levels as follows: poor (<45%), moderate (45-79%), high (80-89%), and full (> 90%) adherence rates. RESULTS: A total of 290 patients were included in our study. In patients with bleeding under DOAC, the protocol adherence for prothrombin complex concentrate (PCC) was "moderate" (61%). In the remaining cases (39%), non-adherence was mainly caused by underdosing (68%), overdosing (12%), and a lack of indication (14%). Furthermore, idarucizumab was administered for bleeding with "full" adherence (96%). For andexanet alfa, adherence to the hospital bleeding protocol was "moderate" (67%), with a lack of indication being the only reason for non-adherence. In case of reversal for an urgent procedure, the protocol adherence for PCC was "low" (45%), with underdosing, a lack of indication, and missing lab data being the main reasons for non-adherence. Missing lab data on dabigatran plasma concentration before reversal was the main reason for "low" adherence (26%) in idarucizumab. The adherence for andexanet alfa was also "low" (0%). CONCLUSION: In case of reversal for bleeding under DOAC, overall adherence to the protocol was "moderate"; however, in patients needing an urgent procedure, it was "low." The major reasons for non-adherence were underdosing, off-label use, and a lack of specific lab testing. The results of this study can assist in improving the implementation of hospital protocols.

Protocols for perioperative management of direct oral anticoagulants in hospitals: opportunities for improvement.

OBJECTIVES: To investigate and describe the protocolized perioperative management in patient using Direct oral anticoagulants (DOACs) in Dutch hospitals. METHODS: Between August and December 2020, a nationwide survey in 70 hospitals in the Netherlands was conducted. We asked hospital pharmacists to submit their protocols for perioperative management of DOAC (apixaban, dabigatran, edoxaban and rivaroxaban) users. The protocols were assessed for a number of parameters divided into categories: interruption and restart timetables DOACs for elective procedures, criteria for the start of an urgent procedure without antidotes, criteria for the use of antidotes and advised antidotes for urgent procedures. RESULTS: A total of 49 hospitals (70%) sent a protocol for perioperative management of DOACs. Two pairs of protocols were identical because hospitals cooperated closely, leaving 47 individual protocols for analysis. Thirty-five of these protocols contained a policy for both elective and urgent procedure; five protocols contained only a policy for elective and seven only for urgent procedures. In protocols for elective procedure, we found great variation in interruption and restart timetables intended for patients with renal impairment (Estimated Glomerular Filtration Ratio < 80 ml/min). In case of urgent procedures, there is variation in choice of antidote, criteria for administration of an antidote and antidote dosing. CONCLUSION: This study provides an overview of the current state of the perioperative protocols in the Netherlands in patients treated with direct oral anticoagulants. Protocols are often not complete and show important and unwanted variation. We have found that national guidelines do not provide unambiguous advice on all points (urgent procedures) and are therefore often elaborated at a local level. The results of this research can help in improving and harmonizing the perioperative protocols on a national level.

Protocolized management of bleeding in hospitals in The Netherlands in patients treated with direct oral anticoagulants.

OBJECTIVE: To investigate and describe the protocolized treatment of DOAC-related bleeds in all Dutch hospitals. METHODS: From August to December 2020 a nationwide survey among all 70 hospitals in the Netherlands was conducted on their protocols for management of bleeding in patients treated with direct oral anticoagulants (DOACs, i.e. apixaban, edoxaban, rivaroxaban and dabigatran). The protocols were assessed the following characteristics: bleeding definitions (mild, moderate and severe bleed), diagnostic parameters (hemoglobin [Hb], loss of blood, surgical procedure needed, etc), first and second choice of treatment, effectiveness criteria and the level of evidence/references upon which protocols were based. RESULTS: All 70 hospitals responded (100%). We received 69 protocols in total, 6 of which were identical because hospitals worked together. In 35 (50%) of the protocols a definition of minor, moderate or severe bleeds was described. Diagnostic parameters for bleeds were present in 2%, 41% and 47% of protocols for a mild, moderate and severe bleed. While the first choice treatment for severe bleeding under dabigatran was idarucizumab in 96% of protocols, considerably more therapeutic options (mostly different prothrombin complex concentrate (PCC) doses) are described for Xa inhibitors. When considering criteria for effectiveness more than 90% of protocols did not have a clear description. CONCLUSION: This study provides an overview of the current state of protocols for management of DOAC-related bleeding in The Netherlands. Protocols vary in the content of information provided and often do not include information, especially for diagnostic criteria and criteria for establishing the effectiveness of the intervention. The results of this study can assist in improving and harmonizing the protocols.

Principal Component Analysis (PCA) of Molecular Descriptors for Improving Permeation through the Blood-Brain Barrier of Quercetin Analogues.

Despite its beneficial pharmacological effects in the brain, partly by modulating inositol phosphate multikinase (IPMK) activity, the therapeutic use of quercetin is limited due to its poor solubility, low oral bioavailability, and low permeability through the blood-brain barrier (BBB). We aimed to identify quercetin analogues with improved BBB permeability and preserved binding affinities towards IPMK and to identify the molecular characteristics required for them to permeate the BBB. Binding affinities of quercetin analogues towards IPMK were determined by molecular docking. Principal component analysis (PCA) was applied to identify the molecular descriptors contributing to efficient permeation through the BBB. Among 34 quercetin analogues, 19 compounds were found to form more stable complexes with IPMK, and the vast majority were found to be more lipophilic than quercetin. Using two distinct in silico techniques, insufficient BBB permeation was determined for all quercetin analogues. However, using the PCA method, the descriptors related to intrinsic solubility and lipophilicity (logP) were identified as mainly responsible for clustering four quercetin analogues (trihydroxyflavones) with the highest BBB permeability. The application of PCA revealed that quercetin analogues could be classified with respect to their structural characteristics, which may be utilized in further analogue syntheses and lead optimization of BBB-penetrating IPMK modulators as neuroprotective agents.

Extracorporeal hemoadsorption with the CytoSorb device as a potential therapeutic option in severe intoxications: Review of the rationale and current clinical experiences.

WHAT IS KNOWN AND OBJECTIVE: Many severe intoxications occur with substances with no specific antidote, which is why methods of extracorporeal elimination represent a particularly useful and even critical component in their management. The purpose of this review is to summarize the accumulating evidence and clinical results from the application of CytoSorb hemoadsorption therapy in patients with severe intoxications. COMMENT: The technology represents a promising technique with an increasing number of publications in a variety of severe intoxication scenarios suggesting that early intervention might provide rapid substance removal with subsequent overall clinical improvement. WHAT IS NEW AND CONCLUSION: Given the tremendous challenges in performing prospective, randomized trials in this field, the strong safety profile of the device and the high acuity of these life-threatening situations, CytoSorb should be considered as a therapeutic option in severe intoxications, particularly when direct antidotes are not available. However, further clinical data are desirable to provide precise recommendations.

On Existence and Admissibility of Singular Solutions for Systems of Conservation Laws.

A weak notion of solution for systems of conservation laws in one dimension is put forward. In the framework introduced here, it can be shown that the Cauchy problem for any n × n system of conservation laws has a solution. The solution concept is an extension of the notion of singular δ -shocks which have been used to provide solutions for Riemann problems in various systems, for example in cases where strict hyperbolicity or the genuine-nonlinearity condition are not satisfied, or in cases where initial conditions have large variation. We also introduce admissibility conditions which eliminate a wide range of unreasonable solutions. Finally, we provide an example from the shallow water system which justifies introduction of δ -distributions as a part of solutions to systems of conservation laws.

Thromboembolic Events While Taking Direct Oral Anticoagulants: An Analysis of Post-market WHO Database Reports from 2012 to 2020.

BACKGROUND AND OBJECTIVE: Several cases of venous thromboembolism in patients treated with direct oral anticoagulants (DOACs) have been reported in the literature, but a quantative analysis of postmarketing reports is lacking. The objective of this study was to determine the post-marketing odds ratio (OR) and reporting odds ratio (ROR) of venous thromboembolism in patients receiving DOACs compared among each other and to vitamin K antagonists (VKAs). METHODS: The OR and ROR were used to determine the ratio of reports for deep vein thrombosis and pulmonary embolism between 1 January, 2012 and 15 November, 2020 using the World Health Organization VigiLyze database. This was performed using all venous thromboembolism events in which a DOAC or a VKA was the suspected medication. The OR and ROR including 95% confidence intervals were calculated for each DOAC drug in comparison to all VKAs as a group. RESULTS: The OR of deep vein thrombosis was highest for rivaroxaban compared with dabigatran and apixaban [2.63 (2.41-2.89); 1.84 (1.72-1.97)]. The OR of deep vein thrombosis was lowest for edoxaban compared with dabigatran, apixaban and rivaroxaban [0.44 (0.32-0.61); 0.31 (0.22-0.42); 0.17 (0.12-0.23)]. The OR of pulmonary embolism was also highest for rivaroxaban compared with dabigatran and apixaban [2.59 (2.37-2.83); 1.79 (1.68-1.92)]. The OR of pulmonary embolism was also lowest for edoxaban compared with dabigatran, apixaban and rivaroxaban [0.77 (0.60-0.97); 0.59 (0.41-0.67); 0.30 (0.23-0.37)]. Comparing RORs of various DOACs with VKAs, rivaroxaban had the highest RORs for deep vein thrombosis/pulmonary embolism, in comparison to apixaban, dabigatran and edoxaban. CONCLUSIONS: Our findings may indicate a higher association between rivaroxaban therapy and venous thromboembolism as compared with apixaban, dabigatran and edoxaban. These findings are uncertain owing to the reliability of a post-marketing registration system that is negatively influenced by a high level of under-reporting. However, based on pharmacodynamics, we cannot exclude the possibility that there is a real effect that may be driven by non-adherence.

Impact of minor bleeds on confidence in anticoagulation therapy, adherence to treatment and quality of life in patients using a non-vitamin K antagonist oral anticoagulant for atrial fibrillation.

OBJECTIVE: In a previous study on the reasons for discontinuation of novel oral anticoagulation therapy (NOAC) in patients with atrial fibrillation, we showed that minor bleeding was the second most important reason for NOAC discontinuation. This finding suggest that the impact of minor bleeds on the patient's perspective on NOACs cannot be ignored, especially those minor bleeds for which the patient searched medical care. We therefore performed a study in which we explored the impact of minor bleed (clinically relevant non-major bleeds) on patient confidence in therapy, adherence to treatment and quality of life in AF patients using NOAC's. METHODS: Details on NOAC therapy, level of confidence, adherence and quality of life were assessed using a semi-structured telephone interview. Questions related to annoyance, concern and trust were scored on a scale of 1-10, with score 10 representing the highest level of impact or trust. For the adherence to treatment before and after a minor bleed the Medication Adherence Rating Scale (MARS-5) questionnaire was used. The total MARS-5 score ranges from 5 to 25; score 5 is indicative of poor adherence and 25 suggest perfect adherence. Furthermore, the impact (restrictions) of a bleed on physical activities and daily life was assessed using a VAS score ranging from 1 to 10; score 10 representing the highest level of restriction. RESULTS: A total of 142 patients were included. During NOAC treatment, minor bleeds were reported by 87 patients (61%) of whom 16 (11%) suffered from a CRNMB. All patients that suffered from a CRNMB contacted their treating physician and 13 received treatment. The most frequently reported CRNMBs were epistaxis (n = 6), a bleed after injury (n = 3), rectal bleed (n = 2) and an eye bleed (n = 2). With regard to the impact of a CRNMB, the median level of annoyance was 8 (min-max 2-10)) and the level of concern 4 (min-max 1-10). The MARS-5 score for adherence to treatment was only marginally influenced. Also the level of trust remained high after the CRNMB. Out of 12 patients, only 2 patients reported a reduction of 1 and 8 points, respectively. Ten patients scored no change and one patient scored a 1 point increase in the level of trust. The mean reduction in trust was 0.7 (95%CI -0.8 to 2.2). With regard to the reported restrictions on physical activities, 8 out of 12 patients reported no (score 1) or only marginal impact (score 2), 2 patients reported a moderate impact (score 5 and 6) and 2 patients reported a high impact score 7 (mean score 2.9 (95%CI 1.3-4.5). For the daily life impact question, 5 out of 9 patients reported no or only marginal impact, 3 patients reported a moderate impact (scores 4 and 5) and 1 patient reported maximal impact (score 10) (mean score 3.2 (95%CI 0.9-5.5)). CONCLUSION: In our study the level of trust, annoyance and concern were not significantly impacted by the CRNMB, nor the adherence to treatment and impact on daily life and physical activities. However, on an individual basis, there were patients that reported a high impact. We hope that future data on impact of this type of minor bleeds will help us identify and guide suboptimaly adherent NOAC patients in shared decision manner.

Costs of minor bleeds in atrial fibrillation patients using a non-vitamin K antagonist oral anticoagulant.

BACKGROUND: A very common side effect of non-vitamin K antagonist oral anticoagulant (NOAC) is (minor) bleeding. Data about impact and costs of minor bleeds in NOAC therapy is still limited or not present in current literature. In this patient orientated study, we aim to provide an estimate of the costs of minor bleeds in patients with atrial fibrillation (AF) treated with a NOAC. METHODS: A retrospective observational cohort study was conducted. Patients with AF and on NOAC therapy were included. Data was obtained by questionnaires and information from electronic patient records. Reference prices were used to calculate the costs per patient. Furthermore, cost of minor bleeds per patient is compared with literature-based costs of minor and major bleeding. RESULTS: 139 patients were included. A total of 94 minor bleed were reported by 71 patients. The sum of minor bleeding costs from societal perspective were €9,851.49, or on average €70,87 (95% CI €54,37- €85,68) per patient with AF. The biggest cost drivers were rectal and vaginal bleeds, epistaxis was most commonly reported. CONCLUSION: Total costs of minor bleeds from a societal perspective, in AF patients using NOACs, are non-trivial and exceed the costs presented in existing literature.

On the image inpainting problem from the viewpoint of a nonlocal Cahn-Hilliard type equation.

Motivated by the fact that the fractional Laplacean generates a wider choice of the interpolation curves than the Laplacean or bi-Laplacean, we propose a new non-local partial differential equation inspired by the Cahn-Hilliard model for recovering damaged parts of an image. We also note that our model is linear and that the computational costs are lower than those for the standard Cahn-Hilliard equation, while the inpainting results remain of high quality. We develop a numerical scheme for solving the resulting equations and provide an example of inpainting showing the potential of our method.

Minor bleeding in patients with atrial fibrillation using a non-vitamin-K antagonist oral anticoagulant.

AIMS: We sought to investigate the magnitude of minor bleeding and identify risk factors for minor bleeds during non-vitamin-K antagonist oral anticoagulant (NOAC) therapy. METHODS: This was an observational cohort study of patients with atrial fibrillation (AF) referred to a regional NOAC outpatient clinic between February 2013 and October 2017. The study population consisted of 875 consecutive patients with AF who visited the NOAC outpatient unit to initiate treatment with apixaban (N = 303), dabigatran (N = 267) or rivaroxaban (N = 305) for long-term ischemic stroke prophylaxis. Minor bleed was defined as every overt bleeding that does not fulfil the criteria of major or non-major clinically relevant bleeding according to the International Society on Thrombosis and Haemostasis. RESULTS: Overall rate of minor bleeds was 19.2 per 100 patient years of follow-up. Bleeding rates for apixaban, dabigatran and rivaroxaban were 26, 8.3 and 23 per 100 patient-years of follow-up. Next to the type of NOAC, the main risk indicators for minor bleedings during NOAC therapy were a HAS-BLED score of 3 or higher and novel anticoagulant use (no history of vitamin K antagonist use). LIMITATION: This was a retrospective observational study evaluating NOAC treatment in a non-randomized setting. CONCLUSION: Our data showed that minor bleeds are common in novel NOAC users, especially when using apixaban and rivaroxaban. In the latter two NOACs, hematoma (bruises) and nose bleeds were more frequently observed and accounted for the difference with dabigatran. Besides type of NOAC, a higher HAS-BLED score and novel anticoagulant drug use were associated with an increased risk of minor bleeding.

Reasons for discontinuation of novel oral anticoagulant therapy in patients with atrial fibrillation.

Aims: We sought to investigate the reasons for, and rates of, novel oral anticoagulant (DOAC) therapy discontinuation.Methods: This was an observational cohort study of patients with atrial fibrillation (AF) referred to a regional DOAC outpatient clinic between February 2013 and October 2017. The study population consisted of 875 consecutive patients with AF who visited the DOAC outpatient unit to initiate treatment with apixaban (N = 303), dabigatran (N = 267) or rivaroxaban (N = 305) for long-term ischemic stroke prophylaxis. All the patients came from the Leeuwarden Medical Center cardiology outpatient clinic, which offers a well structured and nurse-run DOAC unit in cooperation with the hospital's thrombosis service. This clinic operates according to the Dutch nationwide guidelines on integration of anticoagulation services.Results: Overall rate of discontinuation was 11.9 per 100 patient-years of follow-up. Discontinuation rates for apixaban, dabigatran and rivaroxaban were 8.1, 16.6 and 11.5 per 100 patient-years of follow-up.Apixaban had the lowest rate of discontinuation during the 36 month follow-up period. Dabigatran and rivaroxaban had high discontinuation rates during the 3-6 month period following DOAC therapy initiation. The main reasons for discontinuation of DOAC therapy were adverse side effects, patient-initiated discontinuation and any bleed.Limitation: This was a retrospective and non-randomized study, and our results should be interpreted in light of these observations.Conclusion: DOAC discontinuation rates varied significantly and appeared related to drug-specific side effects, patient-initiated discontinuation and bleeding. We observed longer-term administration of apixaban, suggesting that this drug is better tolerated than dabigatran or rivaroxaban.