Induction of tolerance to warfarin after anaphylaxis with a desensitization protocol.

Warfarin hypersensitivity is exceedingly rare. A 59-year-old male with acute renal infarction and a history of allergy to warfarin underwent evaluation, confirming presence of warfarin hypersensitivity. Induction of tolerance to warfarin was successfully completed using an oral desensitization protocol, which has not previously been reported.

Low-dose warfarin functions as an immunomodulator to prevent cyclophosphamide-induced NOD diabetes.

Warfarin has been used as an anticoagulant for a long time. Recently, the pleiotropic effect of warfarin has been investigated. As low-dose warfarin has been reported to have anti-inflammatory effect through suppression of IL-6 secretion and inhibit the immune-associated signal between Tyro3 and its ligand, Gas6, the effect of low-dose warfarin on autoimmune diabetes in NOD mice was examined. To investigate the anti-inflammatory effect of warfarin, IL-6 secretion by splenocytes was examined in the presence of various concentrations of warfarin. Low concentration of warfarin inhibited IL-6 secretion. mRNA expression of Rse, one of the Tyro3 receptor family members, and Gas6 were analyzed in NOD mice. It was detected in islets, splenocytes and bone-marrow derived dendritic cells. 0.25 mg/l or 0.50 mg/l of warfarin was orally administered to NOD mice as a cyclophosphamide-induced diabetes model. Oral administration of warfarin at much lower doses than those clinically used as an anticoagulant significantly reduced the degree of insulitis and diabetes incidence in this model. We previously demonstrated that anti-FasL Ab-treatment led to complete prevention of autoimmune diabetes in NOD mice. As Fas/FasL signaling is reported to be essential for cyclophosphamide-induced diabetes model, we extracted RNA from lymphocytes of the inguinal lymph nodes of anti-FasL Ab-treated NOD mice and performed real-time PCR to determine expression of Rse gene. Interestingly, the expression of Rse gene related to the blockade of Fas/FasL signaling was reduced to less than half the level of untreated mice. In conclusion, low-dose warfarin is a potential immunomodulator which can prevent autoimmune diabetes.

Unusual hypersensitivity to warfarin in a critically ill patient.

A patient was admitted to the intensive care unit because of respiratory failure, and warfarin therapy was started at 2 mg/day for the treatment of pulmonary embolism, together with other medications. Despite the low dosage of warfarin, international normalized ratio (INR) was markedly elevated from 1.15 to 11.28 for only 4 days, and bleeding symptoms concurrently developed. Vitamin K2 was infused along with discontinuation of warfarin. One day later, the INR was found to have decreased, and bleeding was also improved. An objective causality assessment indicated a probable relationship between clotting abnormality and warfarin administration, although the degree of elevation of the INR was unusual in the light of the daily warfarin dose and duration of its exposure. Based on the clinical status of the patient, it was suspected that several conditions contributed to the abnormal hypersensitivity to warfarin. Contributory factors probably included pharmacokinetic interactions with co-administrated drugs, vitamin K deficiency caused by decreased dietary intake, reduced gut bacterial production, impaired intestinal absorption and hepatic synthetic capacity, and increased consumption of clotting factors. In view of our experience in the present case, it should be stressed that close monitoring of coagulation capacity is necessary in critically ill patients in order to avoid fatal haemorrhage after initiating warfarin therapy regardless of the dosage.

Immunotoxicity of epicutaneously applied anticoagulant rodenticide warfarin: evaluation by contact hypersensitivity to DNCB in rats.

The immunotoxicity of epicutaneously administered anticoagulant rodenticide warfarin (WF) was examined in this work by using experimental contact hypersensitivity (CHS) reaction to hapten dinitrochlorobenzene (DNCB). WF (0.05 and 0.5 mg/kg) administration 24 h before the induction of CHS does not change expression of CHS evaluated by ear swelling assay. Regional draining lymph node response during sensitization phase was characterized by decreased cellularity but increased spontaneous and IL-2 stimulated proliferation of draining lymph node cells (DLC). No changes in IL-2 production and in numbers of CD25(+) cells were noted and even decreased proliferative index (ratio of IL-2 stimulated to unstimulated DLC proliferation) was detected. Increase in granulocyte activity (MTT reduction and adhesion to plastic) was noted following application of WF solely with further increase following subsequent application of DNCB, when granulocyte activation (NBT reduction) was noted also. Access of WF into general circulation might be responsible for observed changes, what was supported by ex vivo changes in DLC and granulocyte functions assessed before initiation of sensitization and by in vitro effect of exogenous WF as well. Differential effects of WF on lymphocytes and granulocytes noted in this study highlight the need for simultaneous testing of both cell type activity what might constitute a more integrated approach in immunotoxicity studies.

The effect of drugs used in anticoagulation therapy on T lymphocyte activation in vitro. II. Warfarin inhibits T lymphocyte activation.

The effect of warfarin on T lymphocyte activation in vitro was investigated. Warfarin was found to cause a dose-dependent inhibition of both antigen- and PHA-stimulated proliferation. The drug had to be present during the early steps in T lymphocyte activation to cause inhibition. Warfarin seemed to have no effect on antigen processing or presentation. Warfarin inhibited Interleukin 2 (IL-2) production, but had only minimal effects on expression of IL-2 receptors or IL-2 dependent proliferation. The inhibition in most in vitro models was found only at warfarin concentrations exceeding the therapeutic serum level.

Anti-warfarin antibody preparation and its characterization for radioimmunoassay.

Anti-warfarin antiserum was prepared in rabbits by immunization with a synthesized warfarin antigen, 4'-azo-warfarin human serum albumin, which possesses two enantiomorphic haptenic sites of warfarin on the molecule. The antiserum recognized both R- and S-warfarin to the same degree, 50% cross reactivities of racemic warfarin, respectively. One of the warfarin metabolites, racemic warfarin alcohol, showed 1% cross reactivity, and R- or S-warfarin alcohol have half the reactivity of the racemic alcohol. Rabbit plasma warfarin levels were determined by radioimmunoassay using this antiserum and racemic [14C]warfarin and by fluorometric assay after isolation by thin layer chromatography. After a single administration of warfarin (2 mg kg-1 orally or 500 microgram kg-1 i.v.), the plasma levels determined by both assay methods showed a good correlation (r = 0.97, P less than 0.001, Y = 1.04-0.09). The results show that the radioimmunoassay can determine total plasma warfarin without interference of plasma metabolite. The applicability and limitation of the radioimmunoassay for pharmacokinetic study are discussed.

Warfarin enantiomer disposition: determination by stereoselective radioimmunoassay.

Immunoassay techniques offer promise for the selective analysis of enantiomeric substances without prior separation. In a demonstrationof this selective analysis, radioimmunoassays were developed for R- and S-warfarin. The 4'-carboxyethyl analog of R,S-warfarin was resolved and the enantiomeric acids were coupled to bovine serum albumin. Immunization of rabbits with the conjugates led to formation of antisera which selectively bound the predicted enantiomer. Cross-reactions with various metabolites of warfarin were low (0.1--4%) except for 4'-hydroxywarfarin, as were cross-reactions with the opposite enantiomer (0.3--3%). Assays were developed and used to determine enantiomer half-lives in rats dosed with racemic warfarin. Results were consistent with those found previously by administration of individual enantiomers, thus indicating the utility of the radioimmunoassay method.