Dicloxacillin-Warfarin Drug-Drug Interaction - A Register-Based Study and In Vitro Investigations in 3D Spheroid Primary Human Hepatocytes

AIM

Dicloxacillin is used to treat staphylococcal infections and we have previously shown that dicloxacillin is an inducer of cytochrome P450 enzymes (CYPs). Here, we employed a translational approach to investigate the effect of a treatment with dicloxacillin on warfarin efficacy in Danish registries. Furthermore, we assessed dicloxacillin as an inducer of CYPs in vitro.

METHODS

We conducted a register-based study and analyzed international normalized ratio (INR) levels in chronic warfarin users before and after short- and long-term use of dicloxacillin (n=1023) and flucloxacillin (n=123). Induction of CYPs were investigated in a novel liver model of 3D spheroid primary human hepatocytes (PHHs) at the level of mRNA, and protein and enzyme activity.

RESULTS

Short- and long-term dicloxacillin treatments decreased INR levels by -0.65 (95% CI: -0.57 to -0.74) and -0.76 (95% CI: -0.50 to -1.02), respectively. More than 90% of individuals experienced subtherapeutic INR levels (below 2) after long-term dicloxacillin treatment. Flucloxacillin decreased INR levels by -0.37 (95% CI: -0.14 to -0.60). In 3D spheroid PHHs, the maximal induction of CYP3A4 mRNA, protein and enzyme activity by dicloxacillin were 4.9-, 2.9- and 2.4-fold, respectively. Dicloxacillin also induced CYP2C9 mRNA by 1.7-fold.

CONCLUSION

Dicloxacillin induces CYP enzymes and reduces the clinical efficacy of warfarin in patients. This effect is substantially exacerbated during long-term treatment with dicloxacillin. The in vitro results corroborated this drug-drug interaction and correlated to the clinical findings. Caution is warranted for warfarin patients that initiate dicloxacillin or flucloxacillin, especially for a long-term treatment of endocarditis.

Modeling patients' time, travel, and monitoring costs in anticoagulation management: societal savings achievable with the shift from warfarin to direct oral anticoagulants

BACKGROUND

Anticoagulation therapy is used for atrial fibrillation (AF) patients for reducing the risk of cardioembolic complications such as stroke. The previously recommended anticoagulant, warfarin, has a narrow therapeutic window, and it requires regular laboratory monitoring, unlike direct oral anticoagulants (DOAC). From a societal perspective, it is important to measure time and travel costs associated with warfarin monitoring to better compare the total therapy costs of these two alternative forms of anticoagulation management. In this study we design a georeferenced cost model to investigate societal savings achievable with the shift from warfarin to DOACs in the study region of North Karelia in Eastern Finland.

METHODS

Individual-level patient data of 6519 AF patients was obtained from the regional patient database. Patients' geocoded home addresses and other GIS data were used to perform a network analysis for the optimal routes for warfarin monitoring visits. These measures of revealed accessibility were then used in the cost model to measure monetary time and travel costs in addition to direct healthcare costs of anticoagulation management.

RESULTS

The share of time and travel costs in warfarin monitoring is 26.6% of the total therapy costs in our study region. With current drug retail prices in Finland, the societal expense of anticoagulation management is only 2.6% higher with DOACs than in the baseline with warfarin. However, when 25% lower distributor's prices are used, the total societal cost decreases by 13.6% with DOACs.

CONCLUSIONS

Our results indicate that patients' time and travel costs critically increase the societal cost of warfarin therapy; and despite the higher price of DOACs, they are already cost-efficient alternatives to warfarin in anticoagulation management. In the future, the cost of AF complications should be included in the cost comparison between warfarin and DOACs. Our modeling approach applies to different geographical regions and to different healthcare processes requiring patient monitoring.

Preemptive Dose Adjustment Effect on the Quality of Anticoagulation Management in Warfarin Patients With Drug Interactions: A Retrospective Cohort Study

One strategy to manage patients on warfarin starting an interacting drug is to increase the frequency of monitoring. Another strategy is to adjust warfarin dose around the time patient is started on an interacting medication, which is known as “preemptive warfarin dose adjustment.” The main objective of this study is to compare preemptive to nonpreemptive strategy and their impact on the quality of anticoagulation management. This is a retrospective cohort study performed at the pharmacist-managed anticoagulation clinic in a tertiary hospital in the State of Qatar. Over a 4-year period, 340 patients were evaluated, and 58 warfarin–drug interaction encounters were identified. Mean age of the patients was (57.7 ± 13.7), and 50% of them were females. Preemptive dose adjustment was used in 17 (29.3%) cases. Incidence of out-of-target international normalized ratio (INR) was statistically lower in the preemptive arm compared to the control group (41.2% [7/17] vs 69.2% [27/39], P = .048). Incidence of extreme out-of-target INR was numerically lower in the preemptive arm compared to the control but did not reach statistical significance (11.8% [2/17] vs 29.3% [12/41], P = .139). Change in frequency of INR monitoring was not different between the 2 groups. However, overall frequency of INR monitoring after onset/discontinuation of interacting medication increased compared to baseline (7 [9] vs 21 [16] days, P < .001). Preemptive strategy was shown in our study to decrease incidence of the out-of-target INR visits, although patients remained in need for close monitoring.

Systematic review of societal costs associated with stroke, bleeding and monitoring in atrial fibrillation

Aim: Economic consequences associated with the rise in nonvitamin K antagonist oral anticoagulant use on a societal level remain unclear. Materials & methods: Evidence from the past decade on the societal economic burden associated with stroke, bleeding and international normalized ratio monitoring in atrial fibrillation was collected and summarized through a systematic literature review. Results: There were 14 studies identified that reported indirect costs, which were highest among patients with hemorrhagic stroke and intracranial hemorrhage. The contribution of indirect costs to the total was marginal during acute treatment but substantially increased (30-50%) 2 years after stroke and bleeding events. Conclusion: Limited data were available on societal costs in atrial fibrillation and further research is warranted.

Cost of Healthcare Associated With Deep Vein Thrombosis in Patients Treated With Warfarin in Turkey: 2010-2013 Database Analysis of a Tertiary Care Center

OBJECTIVES

To evaluate the cost of healthcare with respect to the quality of anticoagulation in patients with deep vein thrombosis (DVT) treated with warfarin in daily practice via the database analysis of a tertiary care center in the period 2010 to 2013.

METHODS

Of 258 307 records in total, 42 582 unique patients with DVT and 32 012 patients with international normalized ratio (INR) measurements were included. Overall, 6720 unique patients with DVT diagnosis and one or more INR measurements were identified, and the records of 4377 out of 6720 unique patients were validated and included in the analysis data set. The cost analysis was based on direct medical costs from the payer's perspective. Cost items were related to healthcare resource utilization (inpatient and outpatient services) during the study period, which provided a basis for calculation of per-patient, outpatient, inpatient, and total direct medical costs.

RESULTS

Mean outpatient, inpatient, and total hospital admission costs were $578, $2195, and $2785, respectively, for patients with time in the therapeutic range of 70% or more, whereas the same costs were $571, $2163, and $3192, respectively, for patients with time in the therapeutic range of less than 70%.

CONCLUSIONS

Our findings for a retrospective cohort of patients with DVT undergoing warfarin therapy reveal that patients spent 70% or more, as opposed to less than 70%, of follow-up time within the therapeutic INR range and that outpatient care, as opposed to inpatient care, was associated with lower healthcare costs. Given the significant contribution that hospital stay makes to the cost burden of DVT, our findings also highlight the association between poor warfarin anticoagulant control and increased hospitalization costs.

Conservative Management of Overanticoagulation in Patients With Low-Moderate Risk for Bleeding Complications

Despite long-standing experience with warfarin, anticoagulation clinic services are often confronted with the challenging clinical situation of patients with overanticoagulation. This requires repeat international normalized ratio (INR) monitoring and in some cases administration of vitamin K to minimize the risk of bleeding. A study was performed to determine the safety and efficacy of outpatient management in order to provide guidance on the management of patients with prolonged INRs. Patients on stable warfarin therapy for more than 1 month attending a dedicated academic hospital anticoagulation clinic who had an INR ≥5 were identified over a 1-year period. Follow-up INR results and outcomes were recorded for 30 days. One hundred and ninety-five episodes of overanticoagulation in 148 patients were identified. Patients were classified as low risk (n = 85, 57.4%) and moderate risk of bleeding (n = 63, 42.6%). The mean index INR was 7.22 (1.88). Management with low-dose oral vitamin K (n = 32, 16.4%) did not significantly result in a more rapid correction of the INR when compared to conservative management (n = 163, 83.6%; P = .103). Follow-up INR testing was performed at a mean of 11.1 (8.9) days from the index measurement. A mean of 1.6 (0.9) follow-up INR tests were performed per episode. During the 30-day follow-up, there was 1 (0.5%) episode of major bleeding and 1 (0.5%) death. The management of asymptomatic outpatients with overanticoagulation is associated with a low risk of major bleeding within 30 days. Conservative management of overanticoagulation is as effective as utilizing low-dose oral vitamin K.

The cost of warfarin treatment for stroke prevention in patients with non-valvular atrial fibrillation in Russia from a collective perspective

AIMS

Vitamin K antagonists (VKAs) are used for stroke prevention in patients with non-valvular atrial fibrillation (NVAF), but necessitate regular monitoring of prothrombin time via international normalized ratio (INR) testing. This study explores the economic burden of VKA therapy for Russian patients with NVAF.

METHOD

Cardiologists provided clinical characteristics and healthcare resource use data relating to the patient's first year of treatment. Data were used to quantify direct medical costs (INR testing, consultations, drug costs). The same patients completed a questionnaire providing data on direct non-medical costs (travel/expenses for attendance at VKA appointments) and indirect costs (opportunity cost and reduced work productivity). Mean costs per patient per year are described (US dollars).

RESULTS

Cardiologists (n = 50) provided data on 400 patients (mean age = 63, 47% female), and 351 patients (88%) completed the patient questionnaire. Patients had a mean of nine INR tests. Estimated direct medical costs totaled $151.06, and 18.5% of direct medical costs were attributable to drug costs. Estimated annual direct non-medical costs were $22.89 per patient, and indirect costs were $275.59 per patient.

LIMITATIONS

Included patients had been treated for 12-24 months, so are not fully representative of the broader treatment population.

CONCLUSION

Although VKA drugs costs are relatively low, regular INR testing and consultations drive the economic burden for Russian NVAF patients treated with VKA.