Coumarin anticoagulants and co-trimoxazole: avoid the combination rather than manage the interaction

Prevalence of polypharmacy and risk of potential drug-drug interactions among hospitalized patients with emphasis on the pharmacokinetics

BACKGROUND

Both polypharmacy and potential drug-drug interactions (pDDIs), especially those at the pharmacokinetic level, are common in hospitalized patients and are associated with adverse effects and failure of therapy.

OBJECTIVE

The aim of the present study is to investigate retrospectively the prevalence of polypharmacy and the risk of potential pharmacokinetic drug-drug interaction among hospitalized patients.

METHODS

The medical documentation of hospitalized patients in the unit of internal diseases at the hospital "St Marina" in Varna, Bulgaria for a period of six months (January-July 2016) was retrospectively reviewed. Lexicomp® Drug Interaction software was used for the detection of pDDI. Descriptive statistic and logistic regression were used for data analysis.

RESULTS

In this study, 294 patients out of 510 (57%) were selected with polypharmacy. The number of detected potential pharmacokinetic DDIs (pPKDDIs) was only 216 (or 12,4%), but almost 40% of patients with polypharmacy were exposed to at least one pPKDDIs. The most common pPKDDIs occur at the biotransformation level - 78 (36,1%), and the most common enzyme form that is involved in these interactions is cytochrome 3A4 (44 or 20,4%). The number of prescribed medications (>7) was found to increase the possibility of having pDDIs (OR 25.535, 95% CI 12.529 to 52.042; p = <0.001) and pPKDDIs (OR 5.165, 95% CI 3.430 to 7.779; p = <0.001) as well.

CONCLUSION AND RELEVANCE

Caution should be taken in patients taking more than seven drugs and careful assessment of the pPKDDIs should be made. When such interactions are detected, they need to be properly evaluated and managed.

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.

Warfarin monitoring in nursing homes assessed by case histories. Do recommendations and electronic alerts affect judgements?

PURPOSE

Older adults treated with warfarin are prone to complications, and high-quality monitoring is essential. The aim of this case history based study was to assess the quality of warfarin monitoring in a routine situation, and in a situation with an antibiotic-warfarin interaction, before and after receiving an electronic alert.

MATERIALS AND METHODS

In April 2014, a national web-based survey with two case histories was distributed among Norwegian nursing home physicians and general practitioners working part-time in nursing homes. Case A represented a patient on stable warfarin treatment, but with a substantial INR increase within the therapeutic interval. Case B represented a more challenging patient with trimethoprim sulfamethoxazole (TMS) treatment due to pyelonephritis. In both cases, the physicians were asked to state the next warfarin dose and the INR recall interval. In case B, the physicians could change their suggestions after receiving an electronic alert on the TMS-warfarin interaction.

RESULTS

Three hundred and ninety eight physicians in 292 nursing homes responded. Suggested INR recall intervals and warfarin doses varied substantially in both cases. In case A, 61% gave acceptable answers according to published recommendations, while only 9% did so for case B. Regarding the TMS-warfarin interaction in case history B, the electronic alert increased the percentage of respondents correctly suggesting a dose reduction from 29% to 53%. Having an INR instrument in the nursing home was associated with shortened INR recall times.

CONCLUSIONS

Practical advice on handling of warfarin treatment and drug interactions is needed. Electronic alerts as presented in electronic medical records seem insufficient to change practice. Availability of INR instruments may be important regarding recall time.

Old and new oral anticoagulants: Food, herbal medicines and drug interactions

The most commonly prescribed oral anticoagulants worldwide are the vitamin K antagonists (VKAs) such as warfarin. Factors affecting the pharmacokinetics of VKAs are important because deviations from their narrow therapeutic window can result in bleedings due to over-anticoagulation or thrombosis because of under-anticoagulation. In addition to pharmacodynamic interactions (e.g., augmented bleeding risk for concomitant use of NSAIDs), interactions with drugs, foods, herbs, and over-the-counter medications may affect the risk/benefit ratio of VKAs. Direct oral anticoagulants (DOACs) including Factor Xa inhibitors (rivaroxaban, apixaban and edoxaban) and thrombin inhibitor (dabigatran) are poised to replace warfarin. Phase-3 studies and real-world evaluations have established that the safety profile of DOACs is superior to those of VKAs. However, some pharmacokinetic and pharmacodynamic interactions are expected. Herein we present a critical review of VKAs and DOACs with focus on their potential for interactions with drugs, foods, herbs and over-the-counter medications.

Quality indicators for pharmaceutical care: a comprehensive set with national scores for Dutch community pharmacies

Background The quality of pharmaceutical care in community pharmacies in the Netherlands has been assessed annually since 2008. The initial set has been further developed with pharmacists and patient organizations, the healthcare inspectorate, the government and health insurance companies. The set over 2012 was the first set of quality indicators for community pharmacies which was validated and supported by all major stakeholders. The aims of this study were to describe the validated set of quality indicators for community pharmacies and to report their scores over 2012. In subanalyses the score development over 5 years was described for those indicators, that have been surveyed before and remained unchanged. Methods Community pharmacists in the Netherlands were invited in 2013 to provide information for the set of 2012. Quality indicators were mapped by categories relevant for pharmaceutical care and defined for structures, processes and dispensing outcomes. Scores for categorically-measured quality indicators were presented as the percentage of pharmacies reporting the presence of a quality aspect. For numerical quality indicators, the mean of all reported scores was expressed. In subanalyses for those indicators that had been questioned previously, scores were collected from earlier measurements for pharmacies providing their scores in 2012. Multilevel analysis was used to assess the consistency of scores within one pharmacy over time by the intra-class correlation coefficient (ICC). Results For the set in 2012, 1739 Dutch community pharmacies (88 % of the total) provided information for 66 quality indicators in 10 categories. Indicator scores on the presence of quality structures showed relatively high quality levels. Scores for processes and dispensing outcomes were lower. Subanalyses showed that overall indicators scores improved within pharmacies, but this development differed between pharmacies. Conclusions A set of validated quality indicators provided insight into the quality of pharmaceutical care in the Netherlands. The quality of pharmaceutical care improved over time. As of 2012 quality structures were present in at least 80 % of the community pharmacies. Variation in scores on care processes and outcomes between individual pharmacies and over time can initiate future research to better understand and facilitate quality improvement in community pharmacies.

Trends in antithrombotic drug use and adherence to non-vitamin K oral anticoagulants in the Netherlands

BACKGROUND

Non-vitamin K oral anticoagulants (NOACs) became available in the Netherlands in 2008, providing another antithrombotic treatment besides vitamin K antagonists (VKAs) and antiplatelet agents (APAs).

OBJECTIVE

To describe the patterns of antithrombotic drug use between 2008 and 2013 by examination of dispensing data form community pharmacies in the Netherlands; to determine the concomitant use of NOACs with VKAs and APAs and switching between the drug classes; and to compare adherence to NOACs with adherence to APAs.

SETTING

An observational retrospective study was conducted using routinely collected dispensing data from Dutch community pharmacies.

METHODS

For each calendar year, the numbers of NOAC, VKA, and APA users were calculated. Adherence was determined for NOACs and APAs by the percentage of days covered by medication (PDC). Information on the prescribed daily dose of VKAs was unavailable.

MAIN OUTCOME MEASURES

Comparison of age, sex, and co-medications of users of the three drug classes; concomitant use of different antithrombotic drug classes and switching between these in each year; and mean PDC and percentages of all users with a PDC above 80 %.

RESULTS

NOAC use increased during the study period to 29,687 users in 2013. In that year there were 484,024 VKA users and 1313,032 APA users. Compared with users of VKAs, NOAC users were slightly younger and more frequently used antiarrhythmic drugs and beta blockers as co-medications. Substantial numbers of patients were dispensed potentially harmful combinations in 2013: 820 subjects were dispensed NOACs together with VKAs, and 684 subjects were dispensed NOACs, VKAs, and APAs concomitantly. Mean adherence to NOACs was 84.2 % compared with 87.3 % to APA. One in four NOAC users had a PDC lower than 80 % compared with one in five APA users.

CONCLUSION

Our findings show increasing use of NOACs by outpatients. The number of patients taking potentially harmful combinations of antithrombotic drugs was substantial. Adherence to NOACs in daily practice may be suboptimal to prevent thrombotic events.

Evaluation of quality indicators for Dutch community pharmacies using a comprehensive assessment framework

BACKGROUND

In 2008, the Dutch Health Care Transparency Programme (Zichtbare Zorg) was set up to develop and apply quality indicators (QIs) for health care. These QIs serve a range of purposes and can be categorized into those for internal use--for meeting quality standards and to continuously measure improvement (formative)--and external use--to enable patients and health insurance companies to distinguish between health care providers (summative). In order to assess the validity of QIs, a comprehensive Indicator Assessment Framework (IAF) was developed. This framework specifies the following criteria for validation: content validity, absence of selection bias, absence of measurement bias, and statistical reliability. Because of the intended summative use, the IAF was used for structural assessment of the QIs set for Dutch community pharmacists.

OBJECTIVE

To assess the validity of the current set of 52 QIs for community pharmacies using the IAF.

METHODS

An expert panel applied the IAF criteria to the set of QIs collected in 1,807 Dutch community pharmacies on their performance in 2011. The QIs were judged as meeting, partly meeting, or not meeting the requirements regarding these criteria. The judgments were evaluated for QI type (structure, process, or outcome) and for predefined domains.

RESULTS

Thirteen QIs (25%) were judged as meeting the requirements for all criteria. Among them were 12 structure indicators and 1 process indicator. For process indicators, the criterion for measurement bias poorly met the requirements, and content validity was unsatisfactory for outcome indicators. The 13 overall valid QIs covered 6 out of 10 predefined domains: continuity of care, clinical risk management, compounding, dispensing of medication, management, and quality management.

CONCLUSIONS

When subjecting the QI set for community pharmacies to the requirements of the IAF, only a quarter of the QIs met all requirements. To increase the number of valid process and outcome indicators, meaningful aspects for the outcome of pharmaceutical care have to be defined, and uniform measurement of relevant processes has to be implemented.

Interaction of vitamin K antagonists and trimethoprim-sulfamethoxazole: ignore at your patient's risk

The aim of the study was to summarize available literature regarding the interaction between vitamin K antagonists (VKAs) and trimethoprim-sulfamethoxazole (co-trimoxazole, TMP-SMX), and to provide recommendations for managing patient risk from this interaction. Data sources were English-language publications in the medical literature and Internet databases. Relevant publications that directly or indirectly addressed the VKA-TMP-SMX interaction were selected and reviewed. The mechanism of the VKA-TMP-SMX interaction, frequency of concurrent use, effect on international normalized ratio (INR), increased risk of bleeding, and strategies for risk reduction are summarized. The concurrent use of VKA and TMP/SMX rapidly and consistently raises INR and is associated with a two- to five-fold increase in bleeding. Concurrent use of VKA and TMP-SMX should be avoided when possible. When VKA and TMP-SMX are co-prescribed, VKA dose reduction is usually required. Patient education as well as early and frequent INR monitoring is recommended to reduce risk from this interaction.

Impact of GATA4 variants on stable warfarin doses in patients with prosthetic heart valves

Interindividual variability in stable warfarin doses is largely attributed to VKORC1 and CYP2C9 variants. On the basis of a recent finding of the role of GATA4 in control of CYP2C9 expression, we tested a possible effect of GATA4 genotypes on variability in warfarin response using 201 Korean patients with prosthetic cardiac valves. Two single-nucleotide polymorphisms (SNPs), rs2645400 (G>T) and rs4841588 (G>T), were significantly associated with stable warfarin doses in patients carrying CYP2C9 wild-type homozygotes; homozygote carriers of these two SNPs required higher doses than those with other genotypes (5.94±1.73 versus 5.34±1.88 mg, P=0.026; 5.94±1.66 versus 5.37±1.92, P=0.036, respectively). Multivariate analysis showed that two GATA4 combinations, rs867858 (G>T)/rs10090884 (A>C) and rs2645400 (G>T)/rs4841588 (G>T), increased contribution to the overall warfarin dose variability from 36.4 to 40.9%. This study revealed that GATA4 can be predictive of stable warfarin dose and extended warfarin pharmacogenetics further to the regulation of CYP2C9 expression.

Potential statin-drug interactions: prevalence and clinical significance

Background

Statins are cholesterol-lowering drugs widely used for cardiovascular prevention. Although safe when used alone, in combination with other drugs the likelihood of adverse drug reactions increases significantly. The exposure of the Bulgarian population to coprescriptions leading to potential statin-drug interactions is currently unknown.

Objective

The aim of this study was to investigate the incidence of coprescriptions involving statins and to compare the exposure of outpatients and inpatients to potential statin-drug interactions.

Setting

A cardiology clinic of the teaching University hospital in Varna, Bulgaria.

Method

This observational retrospective study examined the medical records of hospitalized patients prescribed a statin in combination with potentially interacting drugs. Patients who entered the hospital with a statin coprescription (considered outpatients) were compared with those coprescribed a statin at discharge from hospital (considered inpatients). Potentially interacting drugs included inhibitors and inducers of cytochrome P450 (CYP) enzymes and drugs of narrow safety margin (coumarin anticoagulants, digitalis).

Main outcome measure

The proportion of patients exposed to statin coprescriptions with potentially interacting drugs at hospital admission and discharge. Secondary outcome measures: laboratory evidence supporting possible statin-drug interactions.

Results

Out of 1641 hospitalized patients examined, 572 were prescribed a statin, either at hospital admission or discharge. Simvastatin was most commonly prescribed and simvastatin-drug coprescription predominated, especially at discharge. The exposure to all potential statin-drug interactions was similar at hospital admission (26.1%) and discharge (24.4%), as was the exposure to statin combinations with CYP inhibitors, 6.4% and 4%, correspondingly. Overall, more coprescriptions were generated, than were eliminated by hospital physicians. Amiodarone was the CYP inhibitor most frequently coprescribed. Of all interacting drugs acenocoumarol was the most commonly found, the proportions of statin-acenocoumarol coprescriptions being roughly the same at hospital entry (11.5%) and discharge (12.4%). In 7 patients out of 69 exposed to the combination, INR was found to be higher than 3, indicating a risk of over-anticoagulation.

Conclusions

Potential statin-drug interactions are common. Although they do not differ between outpatient and inpatient settings, new hazardous coprescriptions are more frequently generated in hospital. Caution is required when acenocoumarol is coprescribed with statins, especially simvastatin.

Bleeding complications and liver injuries during phenprocoumon treatment: a multicentre prospective observational study in internal medicine departments

BACKGROUND

Even after the recent approval of newer oral anticoagulants for clinical use, the vitamin K antagonist phenprocoumon remains an important treatment option for many patients. In order to quantify the hitherto "accepted" risks of phenprocoumon treatment, we analyzed adverse drug reactions (ADRs) that led to hospitalization on the internal medicine wards of four German pharmacovigilance centers.

METHODS

We prospectively analyzed ADRs leading to hospitalization on the internal medicine wards of the hospitals belonging to the German Network of Regional Pharmacovigilance Centers (Rostock, Greifswald, Jena, and the Sophien- und Hufeland-Klinikum in Weimar) in the years 2000 to 2008.

RESULTS

The 851 patients hospitalized for a phenprocoumon-associated ADR accounted for 12.4% of the 6887 ADR-related hospitalizations in the period of the study. 723 (85%) were admitted for a hemorrhage, usually in the gastrointestinal tract (482 patients); 8 patients died as a consequence of hemorrhage associated with phenprocoumon exposure. Using drug utilization data for the catchment areas of the participating hospitals, we calculate a rate of 5 to 7 hemorrhages leading to hospitalization in an internal medicine ward per 1000 patient-years under phenprocoumon treatment. One-third of the patients who had a hemorrhage were taking other interacting drugs, mainly inhibitors of platelet aggregation and non-steroidal anti-inflammatory drugs. Among the patients who were taking phenprocoumon because of a history of thromboembolic events or for atrial fibrillation, 60% to 70% of those who had hemorrhages had an international normalized ratio (INR) that was above the upper limit of the therapeutic range. Phenprocoumon-associated impairment of liver function arose in 23 patients (2.7%).

CONCLUSION

In this study, about one-eighth of all ADR-related admissions to hospital internal medicine wards were associated with phenprocoumon. There is a need for a comparative risk-benefit assessment of phenprocoumon and the newer oral anticoagulants under real-life conditions.

Evaluation of the effect of genetic variations in GATA-4 on the phenprocoumon and acenocoumarol maintenance dose

Aim: To investigate whether the phenprocoumon and acenocoumarol maintenance doses are influenced by genetic variations in GATA-4, a transcription factor of CYP2C9. Patients & methods: The influence of seven GATA-4 SNPs on the coumarin maintenance dose was investigated by performing an analysis of variance trend analysis, stratified for CYP2C9 genotypes. Results of the best-explaining SNP were validated in the Rotterdam Study cohort. Results: The largest dose differences were found for rs3735814 in patients using acenocoumarol and having the common allele for CYP2C9. The mean dosages decreased from 2.92 mg/day for the patients having the GATA-4 common alleles to 2.65 mg/day for the patients carrying one GATA-4 variant allele and to 2.37 mg/day for patients carrying two GATA-4 variant alleles (p = 0.004). Results could not be replicated in the validation cohort. For phenprocoumon, no significant effects were observed. Conclusion: Genetic variation in GATA-4 does not seem relevant for clinical implementation.

Original submitted 31 August 2012; Revision submitted 12 October 2012

Genotype-guided dosing of coumarin derivatives: the European pharmacogenetics of anticoagulant therapy (EU-PACT) trial design

The narrow therapeutic range and wide interpatient variability in dose requirement make anticoagulation response to coumarin derivatives unpredictable. As a result, patients require frequent monitoring to avert adverse effects and maintain therapeutic efficacy. Polymorphisms in VKORC1 and CYP2C9 jointly account for about 40% of the interindividual variability in dose requirements. To date, several pharmacogenetic-guided dosing algorithms for coumarin derivatives, predominately for warfarin, have been developed. However, the potential benefit of these dosing algorithms in terms of their safety and clinical utility has not been adequately investigated in randomized settings. The European Pharmacogenetics of Anticoagulant Therapy (EU-PACT) trial will assess, in a single-blinded and randomized controlled trial with a follow-up period of 3 months, the safety and clinical utility of genotype-guided dosing in daily practice for the three main coumarin derivatives used in Europe. The primary outcome measure is the percentage time in the therapeutic range for international normalized ratio. This report describes the design and protocol for the trial.