Anticoagulant-Related Nephropathy as a Cause of Early Graft Dysfunction.

Anticoagulant-related nephropathy is an increasingly recognized entity, characterized by the presence of hematuria in the context of a supratherapeutic international normalized ratio with the development of secondary acute kidney injury, which may require renal replacement therapy and may progress to chronic kidney disease. We present the case of a 63-year-old patient who started anticoagulant therapy with acenocoumarol 2 months after her kidney transplant and presented with graft dysfunction concomitant to a supratherapeutic international normalized ratio.

The effect of administering preprocedural VITamin K on the international normalized ratio in patients anticoagulated with ACEnocoumarol (VITKACE-study): a prospective cohort study.

BACKGROUND: The effect of the vitamin K antagonist acenocoumarol on coagulation needs to be reversed when patients undergo an invasive procedure with considerable bleeding risk. A strategy to achieve this is by administering oral vitamin K before a procedure while continuing acenocoumarol. OBJECTIVES: To assess the effect on periprocedural international normalized ratio (INR) values and safety using oral vitamin K as anticoagulant reversal method. METHODS: In this prospective cohort study, consecutive patients using acenocoumarol undergoing elective procedures between 2019 and 2022 were included. According to standard of care in our hospital, patients took 10 mg oral vitamin K 36 to 48 hours before the procedure while continuing their normal use of acenocoumarol. Effectiveness to lower INR to <1.8 preprocedural was assessed. Bleeding and thrombotic complications within 30 days after the procedure were assessed. Periprocedural course of INR was monitored by collecting additional blood samples. RESULTS: Seventy-four patients were included for analysis. On the day of the procedure, an adequate INR of <1.8 was achieved in 99% of patients. One clinically relevant nonmajor bleeding complication and no thrombotic complications were observed during the first 30 days after the procedure. INR gradually restored to therapeutic level during the days after the procedure. CONCLUSION: Using oral vitamin K while patients continue acenocoumarol intake is an effective way to adequately lower INR before an invasive procedure. Low amount of bleeding complications and absence of thromboembolic complications suggest that this is a safe strategy. The INR values returned gradually to therapeutic range after the procedure, probably contributing to the observed low bleeding rate.

Rivaroxaban plus aspirin versus acenocoumarol to manage recurrent venous thromboembolic events despite systemic anticoagulation with rivaroxaban.

INTRODUCTION: The evaluation and management of patients who sustain recurrent thromboembolic events while taking therapeutic anticoagulation have not been well characterized; moreover, there has been no systematic review or randomized trial focused on treating patients with recurrent deep vein thrombosis (DVT) and pulmonary embolism (PE) during anticoagulant treatment. Therefore, we developed a pilot trial to compare rivaroxaban plus aspirin versus acenocoumarol in patients with recurrent venous thromboembolism despite ongoing anticoagulation with rivaroxaban. MATERIALS AND METHODS: The study was a multicenter, randomized clinical trial. We randomly assigned patients with objectively documented recurrent venous thromboembolism to receive rivaroxaban (20 mg once a day) plus aspirin (300 mg once a day) or an adjusted dose of acenocoumarol. The study was designed to evaluate the incidence of recurrent thromboembolic events (recurrent ipsilateral or contralateral DVT, PE, ischemic stroke, and myocardial infarction) and hemorrhagic events. RESULTS: A total of 58 patients were randomized: 28 were allocated to the rivaroxaban plus aspirin group and 30 to the acenocoumarol group. After 90 days of follow-up, three recurrent thromboembolic events (primary outcome) occurred in the acenocoumarol group - two DVTs and one ischemic stroke - and zero events in the rivaroxaban plus aspirin group (risk ratio [RR] 0.15; 95 % confidence interval [CI] 0.008-2.83; P = 0.20). Minor bleeding occurred in five patients in the acenocoumarol group and zero in the rivaroxaban plus aspirin group (RR 0.09; 95 % CI 0.005-1.68; p = 0.10). There was one non-fatal gastrointestinal major bleed in the rivaroxaban plus aspirin group. CONCLUSIONS: In this pilot study, there were no significant differences in any outcome assessed; however, recurrent thromboembolic events and minor bleeding events occurred numerically less frequently in the rivaroxaban plus aspirin group. These data suggest the need to carry out more extensive randomized studies with sufficient statistical power to clarify these results.

Azathioprine and Acenocoumarol Drug Interaction in Patients with Crohn's Disease: A Case Report.

BACKGROUND: Acenocoumarol is an anticoagulant with numerous drug reactions. We report here, an unusual interaction between acenocoumarol and azathioprine. CASE PRESENTATION: A 35-year-old woman, treated with acenocoumarol for thrombosis of the superior mesenteric vein, was prescribed azathioprine for Crohn's disease. Three days later, INR values decreased from 2.36 to 1.48. The dose of acenocoumarol had to almost be doubled to reach an INR value of 2.56. The interaction between azathioprine and acenocoumarol was then suspected. Few similar cases of interactions between azathioprine and another coumarin derivative, warfarin, have been reported. To our knowledge, this is the second case of such interaction reported with acenocoumarol in literature. CONCLUSION: Thus, despite the rarity of this interaction reporting, we draw attention to the importance of close monitoring of INR values in patients treated with acenocoumarol associated with azathioprine.

Over-anticoagulation by vitamin K antagonists and gender differences.

BACKGROUND: Several studies have shown that in patients treated with vitamin K antagonists (VKAs) time spent in therapeutic range (TTR) is lower in females than in males. This retrospective study has evaluated a possible association among over-anticoagulation and gender, type and indications to VKAs, TTR and bleeding. Moreover, the decrease of the INR level, after VKAs withdrawal, was considered. METHODS: From December 2020 to January 2004, 1230 patients with venous thromboembolism or atrial fibrillation were enrolled. Age, gender, type of VKAs, clinical indications, INR values and bleeding events were recorded. TTR was calculated considering the entire period of treatment. RESULTS: A total of 1616 and 1759 over-anticoagulation episodes were found in males and females, respectively. The median INR value was 4.5 (4.0-19.04). Thirty-two percent of the patients did not have an overdose throughout the observation period. The median number of over-anticoagulation per year was significantly higher in females (0.39-year) than in males (0.28-year). After 24 h of VKAs withdrawal, INRs were similar in both genders. Logistic regression analysis showed that the episodes of over-anticoagulation per year were associated with females, atrial fibrillation, warfarin therapy, follow-up length longer than 4 years, and TTR <73%, but were not associated to bleeding episodes. CONCLUSION: The higher number of over-anticoagulation can explain the lower TTR in females. An excess of anticoagulation is not associated with bleeding events. The recovery of INR performs better when acenocoumarol is used, therefore, in patients who present several episodes of over-anticoagulation, acenocumarolo could replace warfarin.

Characteristics and management of patients with stroke and major hemorrhagic episodes with atrial fibrillation under vitamin K antagonist therapy. EVENTHO study.

INTRODUCTION AND OBJECTIVE: In Spain, vitamin K antagonists (VKA) remain the standard treatment for the prevention of thromboembolic and hemorrhagic complications in patients with atrial fibrillation (AF), despite the high risks of suffering adverse effects. The objective of this study was to characterize the profile of VKA-treated patients suffering from stroke/systemic embolism (SE) or major hemorrhagic episodes, their evolution and the actions taken after those episodes. MATERIALS AND METHODS: EVENTHO was an observational multicenter study conducted in 22 Anticoagulation Spanish Units. The study included patients ≥18 years with AF who suffered major hemorrhagic episodes (67.8%) or stroke/SE (32.1%) during 2016 whileon VKA treatment [acenocoumarol (98.2%) or warfarin (1.8%)]. Time in therapeutic range (TTR) was calculated according to the Rosendaal method based on the international normalized ratio (INR) values of the previous 6 months. RESULTS: The study included 585 patients (median age [range] 82.3 [43.6-96.2] years; 51.1% men; mean [95% confidence interval, CI] CHA2DS2-VASc: 4.3 [4.2-4.4] and HAS-BLED: 2.2 [2.1-2.3]). Poor anticoagulation and VKA maintenance were higher in patients with major hemorrhagic episode (p<0.0001). The most common situations after hospital discharge were: functional dependence, neurological sequelae and death. CONCLUSIONS: In the sample studied, half of the AF patients who suffered stroke/SE or major hemorrhagic episode had inadequate TTR and, despite this, after hospital discharge, they restarted treatment with VKA. These results highlight the need to evaluate safer and effective therapeutic alternatives in AF patients with poor TTR control after suffering a stroke/SE or major hemorrhagic episode.

Riesgo de sangrado en pacientes anticoagulados con antagonistas de la vitamina K que reciben antibióticos / Risk of bleeding in anticoagulated patients with vitamin K antagonists who receive antibiotics

Lograr un adecuado nivel de anticoagulación con antagonistas orales de la vitamina K suele ser un desafío frecuente en la práctica clínica, dado que su estrecho rango terapéutico suele verse afectado por diversas interacciones farmacológicas,alimentos y condiciones clínicas. A partir de un caso de un paciente anticoagulado que presenta una hemorragia gastro-intestinal posterior a realizar un tratamiento antibiótico, la autora de este artículo revisó la evidencia sobre el riesgo desangrado secundario a la interacción entre este tipo de anticoagulantes y antibióticos orales. Su conclusión tras realizar una búsqueda bibliográfica y seleccionar la mejor evidencia disponible, es que existe un aumento del riesgo relativo desangrado en pacientes anticoagulados que reciben antibióticos, por lo que deberían evitarse aquellos antibióticos con conocido potencial de interacción. Si ello no fuera posible, se recomienda monitorizar el estado de anticoagulación con dosaje de la razón internacional normatizada (RIN) posterior a la introducción del antibiótico. (AU)

Achieving an adequate level of anticoagulation with oral vitamin K antagonists is often a frequent challenge in clinical practice, given that their narrow therapeutic range is often affected by various drug interactions, food, and clinical conditions. Based on a case of an anticoagulated patient who presented gastrointestinal bleeding after antibiotic treatment, the authorof this article reviewed the evidence on the risk of secondary bleeding due to the interaction between this type of anticoagulants and oral antibiotics. Their conclusion, after performing a literature search and selecting the best available evidence, is that there is an increased relative risk of bleeding in anticoagulated patients receiving antibiotics, so antibiotics with known potential for interaction should be avoided. If it weren't possible, it is recommended to monitor the anticoagulation status with International Normalized Ratio (INR) dosing after the introduction of the antibiotic. (AU)

Vitamin K antagonist anticoagulant usage is associated with increased incidence and progression of osteoarthritis.

OBJECTIVES: Vitamin K is hypothesised to play a role in osteoarthritis (OA) pathogenesis through effects on vitamin K-dependent bone and cartilage proteins, and therefore may represent a modifiable risk factor. A genetic variant in a vitamin K-dependent protein that is an essential inhibitor for cartilage calcification, matrix Gla protein (MGP), was associated with an increased risk for OA. Vitamin K antagonist anticoagulants (VKAs), such as warfarin and acenocoumarol, act as anticoagulants through inhibition of vitamin K-dependent blood coagulation proteins. VKAs likely also affect the functioning of other vitamin K-dependent proteins such as MGP. METHODS: We investigated the effect of acenocoumarol usage on progression and incidence of radiographic OA in 3494 participants of the Rotterdam Study cohort. We also examined the effect of MGP and VKORC1 single nucleotide variants on this association. RESULTS: Acenocoumarol usage was associated with an increased risk of OA incidence and progression (OR=2.50, 95% CI=1.94-3.20), both for knee (OR=2.34, 95% CI=1.67-3.22) and hip OA (OR=2.74, 95% CI=1.82-4.11). Among acenocoumarol users, carriers of the high VKORC1(BB) expression haplotype together with the MGP OA risk allele (rs1800801-T) had an increased risk of OA incidence and progression (OR=4.18, 95% CI=2.69-6.50), while this relationship was not present in non-users of that group (OR=1.01, 95% CI=0.78-1.33). CONCLUSIONS: These findings support the importance of vitamin K and vitamin K-dependent proteins, as MGP, in the pathogenesis of OA. Additionally, these results may have direct implications for the clinical prevention of OA, supporting the consideration of direct oral anticoagulants in favour of VKAs.

Spontaneous massive pectoral hematoma induced by vitamin K antagonist therapy: a case report.

Vitamin K antagonists (VKA) based oral anticoagulation, is widely used for the prevention and treatment of thromboembolic disease. The major complication of this therapy is bleeding, and sometimes it can occur in unsuspected areas. Spontaneous pectoral hematoma is one of the rare complications due to over anticoagulation by VKA therapy, with only a few cases reported in the literature. Concomitant use of this therapy with commonly used antibiotic, especially in the elderly with multiple comorbidities, can increase the risk of bleeding. Herein, we report a case of a 72-year-old woman under VKA for the treatment of atrial fibrillation, who presented with a spontaneous massive pectoral hematoma, while using antibiotic to treat a respiratory tract infection, who was successfully managed.

Selecting the right anticoagulant for stroke prevention in atrial fibrillation.

OBJECTIVE: The embolization of thrombi formed within the atria can occur in any form of atrial fibrillation (AF), i.e., paroxysmal, persistent, or permanent. Although ischemic stroke is the most frequent embolic event associated with AF, embolization to other sites in the pulmonary and systemic circulations may occasionally occur. To avert the risk of embolization, long-term oral anticoagulation therapy is recommended for all AF patients if the CHA2DS2-VASC score is at least 1 for men and at least 2 for women. Since anticoagulant therapy is associated with an increased risk of bleeding, the choice of oral anticoagulant agent should be made by careful consideration of the benefit-to-risk ratio. The use of a newer class of direct oral anticoagulants (DOACs) as an alternative to the anti-vitamin K (AVK) anticoagulants (warfarin, acenocumarol, etc.) can help mitigate the need for periodic monitoring of International Normalized Ratio (INR) and adverse bleeding events that are commonly associated with the use of AVK anticoagulants. Though the use of DOACs (dabigatran, rivaroxaban, edoxaban, apixaban, etc.) is gaining ground due to their relative safety profile and the low overall cost, quite a few clinicians remain skeptical about their use. PATIENTS AND METHODS: Our objective was to evaluate the risk of thromboembolism, stroke, neuropsychiatric illness, depression, and dementia, in patients with non-valvular atrial fibrillation who have been treated with either acenocumarol or apixaban, as well as to see the inflammatory status (ESR) and levels of fibrinogen. Our team at Municipal Emergency University Hospital, Timisoara, Romania, conducted a retrospective study using the medical records of AF patients who were treated with either apixaban or acenocumarol between 2016-2019. We divided the patients into two groups and compared the groups for the aforementioned outcomes. RESULTS: AF patients who were prescribed apixaban had a lower rate of stroke and psychiatric illness compared to those on acenocumarol. No significant correlation was found in terms of risk of developing depression or dementia between the groups. CONCLUSIONS: Non-valvular AF patients on apixaban had lower rates of thromboembolic events than the patients on acenocumarol. This article will serve as a reminder of the positive health and financial outcomes of apixaban use, especially to those healthcare systems that are still oblivious to the decrease in economic burden and gain in quality-adjusted life years (QALY) by the long-term use of NOACS/ DOACS instead of the AVK anticoagulants.

Introducing the "Bleeding Team": Urgent Reconstruction of an Open Fracture in a Patient Receiving Acenocoumarol: A Case Report.

CASE: An elderly, polytrauma patient receiving vitamin K antagonist (VKA) for atrial fibrillation required immediate surgery for open distal tibial fracture. As the initial reversal with vitamin K and fresh frozen plasma by the trauma team was ineffective, the "Bleeding Team" was convened and administrated the appropriate four-factor prothrombin complex regimen, reversing the VKA in a timely manner. Surgery was performed under peripheral nerve blockade subsequently. The postoperative course of the patient was uneventful. CONCLUSION: The individualized approach and the multidisciplinary experts' team guidance is of outmost importance in patients who are treated with anticoagulants and present for nonelective surgery.

RHEDAR study: Determination of the risk of gastrointestinal hemorrhage in treatment with dabigatran, acenocoumarol and rivaroxaban.

BACKGROUND AND AIM: Atrial fibrillation is a major cause of death and disability due to stroke. Vitamin K antagonist drugs are effective for prevention, but they have a narrow therapeutic range and multiple pharmacological interactions. In recent years, new therapeutic alternatives have been searched to minimize complications. The main objective is to evaluate the risk of gastrointestinal bleeding in anticoagulated patients and compare the classic treatment with new anticoagulants. METHODS: We conducted a retrospective cohort study to determine the risk of gastrointestinal bleeding in patients treated with acenocoumarol/dabigatran/rivaroxaban, between 2012 and 2016. We compared the classic with the new anticoagulant group, and a multivariate logistic regression analysis was used to determinate the risk factors of gastrointestinal bleeding. RESULTS: A total of 1213 patients were selected, 52.7% male patients, a mean age of 72.6 years old (± 14.563). 73.6% had atrial fibrilation. 14.5% of patients used acetylsalicylic acid, and 4% clopidogrel. 67.2% had a high-risk CHADS-2 Score, and 36.9% a high-risk HAS-BLED Score. We determined a 5.6% (68) of gastrointestinal bleeding, without differences according to anticoagulant used. The multivariate model showed a greater risk for digestive hemorrhage in patients with a previous hemorrhagic event (odds ratio [OR] = 2.422 95% confidence interval [CI]: 1.101-5.327) and the concomitant therapy with clopidogrel (OR = 2.373 95% CI: 0.996-5.652). CONCLUSIONS: No differences were found in the risk of gastrointestinal bleeding between the different anticoagulants. A previous gastrointestinal bleeding were considered independent risk factor. The HAS-BLED score should be taken into account to make clinical decisions about to prescribe anticoagulant treatment.

Unintentional ingestion of a high dose of acenocoumarol in a young child.

Acute intoxication with a vitamin K antagonist may cause serious coagulopathy. We report the accidental ingestion of a high dose of acenocoumarol in a young child. Two intravenous administrations of 5 mg of vitamin K, in combination with fast and repeated administration of activated charcoal and sodium sulfate, were sufficient to prevent coagulopathy and related symptoms, despite a confirmed elevated blood acenocoumarol concentration (260 µg/L).

Clinical outcomes of nonvitamin K oral anticoagulants and acenocoumarol for stroke prevention in contemporary practice: A population-based propensity-weighted cohort study.

AIMS: Acenocoumarol is a vitamin-K antagonist (VKA) primarily used in certain countries (e.g. India, Netherlands, Spain). The half-life of acenocoumarol is similar to that of non-VKA oral anticoagulants (NOAC), unlike warfarin, and this could affect comparative effectiveness and safety (CES). However, data on CES for NOAC come almost exclusively from studies using warfarin as the comparator. We aimed to assess outcomes of NOAC and acenocoumarol in people with non-valvular atrial fibrillation (NVAF) in real-world clinical practice. METHODS: This is a population-based retrospective cohort study. All new users of oral anticoagulants from November 2011 to December 2015 with NVAF were included (n = 41,560). Data were obtained by linking several health electronic records of the Valencia region, Spain. Incidence rates were estimated. We used the inverse probability of treatment weighted Cox analysis to control for indication bias when assessing the risk of effectiveness and safety outcomes for each NOAC compared with acenocoumarol. Several sensitivity analyses were performed. RESULTS: We did not find differences in the risk of mortality, ischaemic stroke or any gastrointestinal bleeding. However, we did find a decreased risk of intracranial haemorrhage for dabigatran (HR: 0.34, 95% CI 0.20-0.56) and rivaroxaban (HR: 0.55, 95% CI 0.35-0.85) as compared to acenocoumarol. In subanalyses, apixaban showed a higher risk of ischaemic stroke in high-risk persons (≥75 years and CHA2DS2-VASC score ≥ 2). CONCLUSIONS: No differences in clinical outcomes were found between NOAC and acenocoumarol overall, although dabigatran and rivaroxaban showed a lower risk of intracranial haemorrhage. Findings on the potential inferiority of specific NOAC in high-risk subgroups should be studied further.

Incidence and cost of bleeding events requiring hospitalization in patients with atrial fibrillation treated with acenocoumarol in Greece.

BACKGROUND: To estimate the incidence of hemorrhagic events in patients with atrial fibrillation (AF) treated with acenocoumarol, and the management cost of those requiring hospitalization in Greece. METHODS: A nationwide telephone survey was conducted between December 2017 and January 2018, to identify cardiologists who treat AF patients with acenocoumarol. A total of 300 cardiologists were selected and reported the number of AF acenocoumarol-treated patients during the past 12 months and the number of those who experienced a hemorrhagic event. The hospital charges to sickness fund and the cost of resource utilization of AF patients hospitalized between January 2013 and June 2017 at a tertiary hospital in Athens due to acenocoumarol-related bleedings were retrieved. RESULTS: Out of 48,255 AF patients, 12,633 (26.2%) were treated with acenocoumarol. In all, 5.1% of patients experienced a hemorrhagic event with the incidence of bleeding requiring hospitalization being 1.7%. The most common bleeding site was the gastrointestinal system (51.5%). The mean (95% CI) management cost per bleeding event requiring hospitalization was €1,202 (€1,058-€1,420). The higher cost was that of intracranial bleeding €3,887 (€2,700-€5,046). The expected annual economic burden for the management of bleedings related to acenocoumarol and requiring hospitalization was estimated at €1,463,955. CONCLUSIONS: The incidence of bleeding events in AF acenocoumarol-treated patients in Greece as well as the estimated annual economic burden for the management of bleeding events requiring hospitalization, emphasize the need to comply with the current guidelines and to optimize therapeutic strategies for the management of AF side effects with oral anticoagulants, particularly in patients with high bleeding risk.

More precise dosing of acenocoumarol for better control in patients aged above 80 years, a randomised controlled pilot study.

INTRODUCTION: Many elderly patients are confined to treatment with vitamin K antagonists (VKA) instead of direct oral anticoagulants (DOACs). However, quality of VKA treatment declines with age. This might be caused by the lower dose requirements with increasing age, which result in relatively large day-by-day VKA dose differences. Therefore, more precise dosing with smaller dose increments might improve quality of VKA treatment in the elderly. METHODS: We randomised 80 elderly patients (≥80 years, using 0.5-2 mg acenocoumarol daily) to either conventional dosing with 1.0 mg acenocoumarol increments, or more precise dosing with 0.5 mg increments, to assess effect sizes and feasibility of a larger trial. We compared changes in the time in therapeutic range (TTR), INR variability and anticoagulation-related quality of life (measured with the PACT-Q) between treatment groups. RESULTS: Overall, baseline TTR was 61.3 ± 19.2. After six study months, TTR had improved to 69.5 ± 19.7 in the precise dosing group versus 67.7 ± 21.2 in the conventional dosing group (absolute difference 3.4 (95% CI -6.7 to 13.6)). The between-groups difference in INR variability was not assessed because of baseline differences. PACT-Q convenience declined slightly with more precise dosing, compared with conventional dosing: 2.1/100 (95% CI 0.5-3.7). Satisfaction decreased equally in both groups with -6.4 ± 8.6/100. Four dosing errors occurred: three with precise and one with conventional dosing. CONCLUSION: Although more precise dosing of acenocoumarol leads to a slightly higher TTR, this effect is too small to convey a relevant clinical benefit and could be abolished by the increased risk of medication errors.

[Learning with COVID-19: what about anticoagulation?]

Infection caused by SARS-CoV-2 (COVID-19) is associated with an increased risk of thromboembolic disease. So-me authors recommend anticoagulation at therapeutic doses for, at least, the most severely ill patients; this practice is not free of risks, which is why only thromboembolic prophylaxis is recommended by other consensuses. In the case of previously anticoagulated patients, changing the oral anticoagulant for a low molecular weight heparin (LMWH) is generally recommended. We present the cases of two patients admitted due to COVID-19, without serious clinical data, in whom anticoagulation (acenocoumarol and rivaroxaban, respectively) was replaced by LMWH at therapeutic doses, both presenting abdominal bleeding. This type of bleeding is an infrequent complication in anticoagulated patients, but the concurrence of two cases in a short period of time in the context of the COVID-19 pandemic leads us to consider that there is not yet any clear evidence on therapeutic anticoagulation in SARS-CoV-2 infection.

Drug-drug interactions with metronidazole and itraconazole in patients using acenocoumarol.

PURPOSE: Various population-based cohort studies have shown that antimicrobial agents increase the risk of overanticoagulation in patients using coumarins. In this study, we assessed this association in hospitalized patients. METHODS: We included all patients hospitalized in the Spaarne Gasthuis (Haarlem/Hoofddorp, the Netherlands), who started using an antimicrobial agent during acenocoumarol treatment or vice versa between 1 January 2015 and 1 July 2019. Patients were followed from start of concomitant therapy until 48 h after termination of the concomitant therapy or discharge, whichever came first. We analyzed the association between the antimicrobial agents and the risk of overanticoagulation, defined as an interpolated INR above 6, using Cox regression analysis. We corrected for multiple testing with the Bonferroni correction. Patients who started using acenocoumarol and amoxicillin/clavulanic acid were used as reference group. RESULTS: In the study population, sixteen antimicrobial agents were started frequently concomitantly with acenocoumarol treatment. We included 2157 interaction episodes in 1172 patients. Patients who started using the combination of co-trimoxazole (HR 3.76; 95% CI 1.47-9.62; p = 0.006), metronidazole (HR 2.55; 95% CI 1.37-4.76; p = 0.003), or itraconazole (HR 4.11; 95% CI 1.79-9.45; p = 0.001) concomitantly with acenocoumarol treatment had an increased risk of overanticoagulation compared with patients using acenocoumarol and amoxicillin/clavulanic acid concomitantly. The associations for metronidazole (p = 0.045) and itraconazole (p = 0.015) remained statistically significant after correction for multiple testing. CONCLUSION: Co-trimoxazole, metronidazole, and itraconazole increase the risk of overanticoagulation in patients using acenocoumarol. These combinations should be avoided if possible or otherwise acenocoumarol doses should be reduced and INR measured more frequently.