Malabsorption-associated warfarin resistance

One Rare Warfarin Resistance Case and Possible Mechanism Exploration

One 59-year-old female patient with deep venous thrombosis (DVT) and pulmonary embolism (PE) was treated with 6 mg warfarin once daily as an anticoagulant. Before taking warfarin, her international normalized ratio (INR) was 0.98. Two days after warfarin treatment, her INR did not change from baseline. Due to the high severity of the PE, the patient needed to reach her target range (INR goal = 2.5, range = 2~3) rapidly, so the dose of warfarin was increased from 6 mg daily to 27 mg daily. However, the patient's INR did not improve with the dose escalation, still maintaining an INR of 0.97-0.98. We drew a blood sample half an hour before administering 27 mg warfarin and detected single nucleotide polymorphism for the following genes, which were identified to be relevant with warfarin resistance: CYP2C9 rs1799853, rs1057910, VKORC1 rs9923231, rs61742245, rs7200749, rs55894764, CYP4F2 rs2108622, and GGCX rs2592551. The trough plasma concentration of warfarin was 196.2 ng/mL after 2 days of warfarin administration with 27 mg QD, which was much lower than the therapeutic drug concentration ranges of warfarin (500-3,000 ng/mL). The genotype results demonstrate that the CYP4F2gene has rs2108622 mutation which can explain some aspect of warfarin resistance. Further investigations are necessary to fully characterize other pharmacogenomics or pharmacodynamics determinants of warfarin dose-response in Chinese.

The Natural History, Treatments, and Outcomes of Portal Vein Thrombosis in Patients With Inflammatory Bowel Disease

BACKGROUND

Portal vein thrombosis (PVT) is a poorly described complication of inflammatory bowel disease (IBD). We sought to better characterize presentations, compare treatments, and assess outcomes in IBD-related PVT.

METHODS

We conducted a retrospective investigation of IBD-related PVT at our institution. Multivariable Cox proportional hazards modeling was used to estimate adjusted hazard ratios across treatments.

RESULTS

Sixty-three patients with IBD-related PVT (26 with Crohn disease, 37 with ulcerative colitis) were followed for a median 21 months (interquartile ratio [IQR] = 9-52). Major risk factors included intra-abdominal surgery (60%), IBD flare (33%), and intra-abdominal infection (13%). Primary hematologic thrombophilias were rare and did not impact management. Presentations were generally nonspecific, and diagnosis was incidental. Ninety-two percent of patients (58/63) received anticoagulation (AC), including 23 who received direct oral anticoagulants (DOACs), 22 who received warfarin, and 13 who received enoxaparin. All anticoagulated patients started AC within 3 days of diagnosis. Complete radiographic resolution (CRR) of PVT occurred in 71% of patients. We found that DOACs were associated with higher CRR rates (22/23; 96%) relative to warfarin (12/22; 55%): the hazard ratio of DOACs to warfarin was 4.04 (1.83-8.93; P = 0.0006)). Patients receiving DOACs required shorter courses of AC (median 3.9 months; IQR = 2.7-6.1) than those receiving warfarin (median 8.5 months; IQR = 3.9-NA; P = 0.0190). Incidence of gut ischemia (n = 3), symptomatic portal hypertension (n = 3), major bleeding (n = 4), and death (n = 2) were rare, and no patients receiving DOACs experienced these adverse outcomes.

CONCLUSIONS

We show that early and aggressive use of AC can lead to excellent outcomes in IBD-associated PVT and that DOACs are associated with particularly favorable outcomes in this setting.

Warfarin Dose Adjustment After Biliopancreatic Diversion/Duodenal Switch Bariatric Surgery

BACKGROUND

The absorption of drugs and fat-soluble vitamins is impaired after bariatric surgery on which intestinal length and function are altered. In this context, the anticoagulant effect of warfarin is difficult to predict in the postoperative period.

OBJECTIVE

This study aimed at describing the average weekly warfarin dose required to maintain a therapeutic international normalized ratio (INR) before and up to 1 year after sleeve gastrectomy with biliopancreatic diversion and duodenal switch (BPD/DS). Secondary end points included the number of patients requiring a minimal 20% reduction in their weekly dose of warfarin following the BPD/DS.

METHODS

This descriptive and retrospective longitudinal population study included 20 patients using warfarin who underwent BPD/DS. An INR was considered nontherapeutic if it was below or above 15% of the targeted therapeutic range for any given patient.

RESULTS

One month after the surgery, the median weekly dose of warfarin was 55% lower than the preoperative dose ( P < 0.0001). In the 9 patients with full follow-up data, the warfarin dose at 1 year was still 39% lower than the preoperative dose ( P < 0.05). At that time, all patients presented a minimal dose reduction of 20%.

CONCLUSIONS

BPD/DS robustly reduced the requirement of warfarin, which resulted in lower doses after surgery. This persisted over the first year after the surgery, likely because of enhanced sensitivity. The mechanisms for this effect remain multifactorial, and the exact extent of change in dose cannot be predicted.

Comparison of Warfarin Dosages and International Normalized Ratios Before and After Roux-en-Y Gastric Bypass Surgery

STUDY OBJECTIVE

As data are limited for dosing warfarin in patients who have undergone bariatric surgery, our objective was to gather data on warfarin pharmacotherapy to aid in the prescribing practices and dosage adjustment of warfarin after Roux-en-Y gastric bypass (RYGB) surgery.

DESIGN

Retrospective medical record review.

SETTING

Anticoagulation clinic.

PATIENTS

Twelve patients who underwent RYGB surgery between 2009 and 2011.

MEASUREMENTS AND MAIN RESULTS

Data were collected on patient demographics, therapeutic indications for warfarin, weekly warfarin doses, and international normalized ratio (INR) values before and after RYGB surgery. To examine whether the relationship between the warfarin dose and therapeutic effect (i.e., INR) of warfarin changed from before to after surgery, we generated a ratio between each INR measurement and the weekly warfarin dose that immediately preceded it (warfarin dose/INR ratio). Mean weekly warfarin dose after RYGB surgery decreased significantly relative to presurgery dose (estimated marginal mean ± SE presurgery dose 37.08 ± 3.31 mg vs postsurgery dose 28.08 ± 3.27 mg; [F(205.63) = 13.23, p<0.001]), whereas INRs increased significantly after surgery from presurgery levels (estimated marginal mean ± SE presurgery INR 2.36 ± 0.15 vs postsurgery INR 2.94 ± 0.14; [F(213.76) = 6.55, p<0.05]). The ratio of warfarin dose/INR from presurgery (estimated marginal mean ± SE 17.64 ± 1.67) to postsurgery (estimated marginal mean ± SE 10.94 ± 1.64) was also significantly reduced [F(206.47) = 20.61, p<0.001], suggesting that a lower warfarin dose was required to produce the desired INR after surgery compared with before surgery.

CONCLUSION

Warfarin dosages tended to decrease after RYGB surgery, in agreement with previously published literature. These findings suggest the need for increased INR monitoring and patient education for patients taking warfarin after RYGB surgery.

Supratherapeutic International Normalized Ratio Due to Reduced Vitamin K Intake Secondary to Prolonged Vomiting in a Patient on Warfarin

OBJECTIVE:

To report a case of prolonged vomiting during warfarin therapy, leading to an elevated international normalized ratio (INR).

CASE SUMMARY:

A 32-year-old female with a history of cyclic vomiting syndrome since early childhood and bilateral pulmonary emboli diagnosed 4 months prior to this acute event presented to the clinic for routine monitoring of warfarin therapy. The warfarin dose had been maintained at 35 mg/wk for 3½ months (INR 2-3.5), but it was increased to 37.5 mg/wk because the INR had trended down to the low goal range over the preceding month. At presentation, the patient reported a 15-day history of vomiting with minimal oral intake that required intravenous fluids to prevent dehydration. The INR was 4.7; warfarin was withheld, and oral vitamin K 5 mg as well as subcutaneous vitamin K 10 mg was administered the following day. The INR then decreased to 1.3. Therapy was transitioned to subcutaneous enoxaparin 1 mg/kg every 12 hours for the duration of the patient's anticoagulation therapy.

DISCUSSION:

Multiple reports have demonstrated malabsorption of warfarin and decreased INR response in the presence of underlying gastrointestinal disease. Despite a prolonged episode of cyclic vomiting syndrome, our patient had an elevated INR. In normal circumstances, warfarin is rapidly absorbed from the gastrointestinal tract and reaches maximum serum concentrations in approximately 90 minutes. Studies have shown that although the presence of food does not affect overall absorption of the medication, it can decrease the rate of absorption. Our patient was vomiting 20-30 minutes after oral dose administration. Because the patient was not consuming food, absorption of warfarin was potentially prompt, thus contributing to the elevated INR. The variability of vitamin K in the diet also can have significant impact on the response to warfarin. Our patient's INR had been stable while she consumed 3 servings each week of foods rich in vitamin K. This consumption was abruptly discontinued with the onset of the cyclic vomiting syndrome. We believe that decreased intake and retention of oral vitamin K–containing foods from the diet due to the prolonged vomiting coupled with the rapid onset of absorption resulted in a notably increased INR and subsequent bruising in our patient.

CONCLUSIONS:

In the presence of prolonged vomiting, warfarin therapy requires more frequent monitoring than usual to detect fluctuations in INR that may increase the risk of adverse events.

Exacerbation of Hereditary Warfarin Resistance by Azathioprine

A 39-year-old Afro-Caribbean man with Crohn disease with recurrent deep vein thromboses and pulmonary emboli was commenced on lifelong warfarin treatment. The patient required high-dose warfarin (>140 mg/wk), which increased further during azathioprine treatment. Cessation of azathioprine resulted in an increase in the international normalized ratio (INR). Mutation analysis identified a Val66Met substitution in vitamin K epoxide reductase complex subunit 1 (VKORC1), consistent with severe warfarin resistance. This report is the first presentation where the patient had a defined hereditary resistance to warfarin, which was aggravated by concomitant azathioprine. It is important for clinicians to be aware of the interaction between warfarin and azathioprine, to monitor clinical response closely, and to manage the doses of both drugs accordingly.