Incidence and risk factors for life-threatening bleeding after allogeneic stem cell transplant.

Bleeding is a frequent complication after allogeneic haematopoietic stem cell transplantation (HSCT) and may affect survival. The purpose of this study was to determine the incidence and risk factors for life-threatening bleeding after HSCT by retrospective evaluation of 491 allogeneic HSCT recipients. With a median follow-up of 33 months, 126 out of 491 allogeneic HSCT recipients experienced a haemorrhagic event (25·7%) and 46 patients developed a life-threatening bleeding episode (9·4%). Pulmonary and gastrointestinal bleeding were the most common sites for life-threatening bleeding, followed by central nervous system. In multivariate analyses, the presence of severe thrombocytopenia after day +28 and the development of grade III-IV acute graft-versus-host disease (GVHD) or thrombotic microangiopathy (TMA) retained their association with life-threatening bleeding events. The overall survival at 3 years among patients without bleeding was 67·1% for only 17·1% for patients with life-threatening bleeding (P < 0·001). In conclusion, life-threatening bleeding is a common complication after allogeneic HSCT. Prolonged severe thrombocytopenia, acute grade III-IV GVHD and TMA were associated with its development.

Association of the thrombomodulin gene c.1418C>T polymorphism with thrombomodulin levels and with venous thrombosis risk.

OBJECTIVE: To investigate the association of the THBD c.1418C>T polymorphism, which encodes for the replacement of Ala455 by Val in thrombomodulin (TM), with venous thromboembolism (VTE), plasma soluble TM, and activated protein C levels. In addition, human umbilical vein endothelial cells (HUVEC) isolated from 100 umbilical cords were used to analyze the relation between this polymorphism and THBD mRNA and TM protein expression. APPROACH AND RESULTS: The THBD c.1418C>T polymorphism was genotyped in 1173 patients with VTE and 1262 control subjects. Levels of soluble TM and activated protein C were measured in 414 patients with VTE (not on oral anticoagulants) and 451 controls. HUVECs were genotyped for the polymorphism and analyzed for THBD mRNA and TM protein expression and for the ability to enhance protein C activation by thrombin. The 1418T allele frequency was lower in patients than in controls (P<0.001), and its presence was associated with a reduced VTE risk, reduced soluble TM levels, and increased circulating activated protein C levels (P<0.001). In cultured HUVEC, the 1418T allele did not influence THBD expression but was associated with increased TM in cell lysates, increased rate of protein C activation, and reduced soluble TM levels in conditioned medium. CONCLUSIONS: The THBD 1418T allele is associated with lower soluble TM, both in plasma and in HUVEC-conditioned medium, and with an increase in functional membrane-bound TM in HUVEC, which could explain the increased activated protein C levels and the reduced VTE risk observed in individuals carrying this allele.

Analysis of incidence, risk factors and clinical outcome of thromboembolic and bleeding events in 431 allogeneic hematopoietic stem cell transplantation recipients.

Allogeneic hematopoietic stem cell transplantation recipients have an increasing risk of both hemorrhagic and thrombotic complications. However, the competing risks of two of these life-threatening complications in these complex patients have still not been well defined. We retrospectively analyzed data from 431 allogeneic transplantation recipients to identify the incidence, risk factors and mortality due to thrombosis and bleeding. Significant clinical bleeding was more frequent than symptomatic thrombosis. The cumulative incidence of a bleeding episode was 30.2% at 14 years. The cumulative incidence of a venous or arterial thrombosis at 14 years was 11.8% and 4.1%, respectively. The analysis of competing factors for venous thrombosis revealed extensive chronic graft-versus-host disease to be the only independent prognostic risk factor. By contrast, six factors were associated with an increased risk of bleeding; advanced disease, ablative conditioning regimen, umbilical cord blood transplantation, anticoagulation, acute III-IV graft-versus-host disease, and transplant-associated microangiopathy. The development of thrombosis did not significantly affect overall survival (P=0.856). However, significant clinical bleeding was associated with inferior survival (P<0.001). In allogeneic hematopoietic stem cell transplantation, significant clinical bleeding is more common than thrombotic complications and affects survival.

Safety and efficacy of splenectomy in over 65-yrs-old patients with immune thrombocytopenia.

AIM: Few studies specifically focus on elderly splenectomized immune thrombocytopenia (ITP) patients. Older patients with ITP and excellent health are often excluded from surgery splenectomy. We aimed to compare the safety and efficacy of splenectomy in elderly and non-elderly ITP patients and to examine the effect of age on therapeutic response. MATERIAL AND METHODS: We carried out a retrospective analysis of a series of 218 patients who had undergone splenectomy for ITP. We compared the data from the elderly group (≥65 yrs, 57 patients) with the young group (<65 yrs, 162 patients). RESULTS: Surgical technique (laparoscopy or open laparotomy splenectomy) was comparable between the two age groups. The adjusted risk of major bleeding following splenectomy for elderly patients was three times that for young patients (OR 3.05, 95% CI: 1.44-6.52). The median duration of postoperative hospital stay was longer for elderly than for young patients (8 d vs. 4 d, P < 0.001). However, we identified a subgroup of elderly ITP patients, those aged between 65 and 70 yrs who had undergone laparoscopic splenectomy, with a low risk of postoperative complications. Of the 218 patients, 89% achieved a favorable response to splenectomy. A favorable response was significantly less common in elderly than in young people (79% vs. 92%, P = 0.005). However, we observed an acceptable long-term control of ITP in the elderly group, in which the probability of maintaining response for 14 yrs after splenectomy was 56%. CONCLUSIONS: Patients aged ≥65 yrs experienced negative effects on safety and efficacy outcomes of splenectomy for ITP, but further studies are needed to identify predictors of postsplenectomy outcomes in this group.

Risk of placenta-mediated pregnancy complications or pregnancy-related VTE in VTE-asymptomatic families of probands with VTE and heterozygosity for factor V Leiden or G20210 prothrombin mutation.

BACKGROUND: Few studies have evaluated the risk of pregnancy-related adverse events in asymptomatic relatives of probands for VTE and factor V Leiden or the G20210A variant. The antepartum management of this population ranges from antepartum anticoagulation therapy to clinical surveillance. OBJECTIVE: To evaluate the risk of placenta-mediated pregnancy complications and pregnancy-related VTE in VTE-asymptomatic families of probands with VTE and who are heterozygous carriers of either factor V Leiden or PT-G20210A mutation. METHODS: One hundred and fifty-eight relatives, who had 415 pregnancies, were retrospectively evaluated. Odds ratios and 95% confidence intervals were calculated to compare pregnancy outcomes between women with and without thrombophilia. RESULTS: In the factor V Leiden group, 22 placenta-mediated pregnancy events of 152 pregnancies (14.4%) were reported, compared with 25 adverse events of 172 pregnancies in the G20210A prothrombin group (14.5%) and 13 adverse events of 91 pregnancies in the non-carrier group (14.2%). Carriers of factor V Leiden or G20210A prothrombin were not associated with a higher risk of pregnancy-adverse outcomes compared with non-carriers: OR 1.02 (95% CI, 0.40-2.25) and 1.25 (95% CI, 0.48-3.24), respectively. Four episodes of pregnancy-associated VTE of 415 pregnancies (0.96%) were recorded. Two episodes of VTE in the G20210A group, one in the factor V Leiden group, and one episode in the non-carrier group were noted. CONCLUSIONS: In VTE-asymptomatic relatives of probands with VTE, the presence of factor V Leiden or the G20210A prothrombin mutation in heterozygosis should not lead to a decision to instigate antepartum prophylaxis.

Mesenchymal stem cells are functionally abnormal in patients with immune thrombocytopenic purpura.

BACKGROUND AIMS: Immune thrombocytopenic purpura (ITP) is a bleeding disorder characterized by an accelerated destruction of platelets as a result of the presence of autoreactive antibodies. Patients with ITP also display activated platelet-autoreactive T cells. Mesenchymal stem cells (MSC) inhibit both T- and B-cell activation and may have functional impairments in autoimmune disorders. METHODS: We analyzed the potential role of MSC in the pathogenesis of ITP. RESULTS: MSC from ITP showed an impaired proliferative capacity and a lower capability of inhibiting activated T-cell proliferation compared with healthy donors. While MSC from controls showed a decreased expression of p27 after stimulation with platelet-derived growth factor, this effect was not observed in MSC from patients. Furthermore, MSC from healthy donors down-regulated p16 upon exposure to platelet-released supernatant, while this effect was not observed for ITP. Interestingly, caspase 9 expression was higher in MSC from ITP. CONCLUSIONS: These abnormalities suggest a role of MSC malfunction in the physiopathology of the disease and may have therapeutic implications.

AB0 blood group and risk of venous or arterial thrombosis in carriers of factor V Leiden or prothrombin G20210A polymorphisms.

BACKGROUND: Routine analyses for thrombophilia include determination of the presence of factor V Leiden and prothrombin 20210A polymorphisms. However, the usefulness of these determinations is controversial and the clinical benefit remains questioned because of the moderate risk of associated thrombosis in carriers. In the search for clusters of thrombotic risk factors to estimate individual risk better, we studied the effect of AB0 blood group, a highly prevalent factor with mild prothrombotic features, on the risk and severity of venous and arterial thromboses in carriers of these polymorphisms. DESIGN AND METHODS: We genotyped the AB0 blood group in 981 carriers of factor V Leiden or prothrombin 20210A polymorphisms. In order to avoid the over-representation of a particular genotype and to suppress confounding factors, we included only non-related heterozygous carriers without additional genetic risk factors. We studied 609 patients with venous thromboembolism (287 with factor V Leiden, and 322 with prothrombin 20210A), 174 patients with myocardial infarction (78 with factor V Leiden, and 96 with prothrombin 20210A), and 198 controls (96 with factor V Leiden, and 102 with prothrombin 20210A). RESULTS: Non-OO blood group did not increase the risk of myocardial infarction in carriers of factor V Leiden or prothrombin 20210A. However, non-OO blood group contributed significantly to the expression of venous thrombosis associated with both factor V Leiden (OR: 1.76; 95%CI: 1.06-2.91) and prothrombin 20210A (OR: 2.17; 95%CI: 1.33-3.53). Exclusion of A(2)A(2) and A(2)O from the non-00 blood group (because factor VIII-von Willebrand factor levels are similar in these and the 00 blood group) increased the thrombotic risk. Finally, non-OO blood group was associated with an earlier onset in symptomatic carriers of these polymorphisms. CONCLUSIONS: Our study suggests that non-OO blood group increases the risk and severity of venous thrombosis in carriers of prothrombotic polymorphisms. Thus, AB0 phenotyping or genotyping analyses may be valuable components in assessing future thrombophilic risk profiles and might have implications for the policy of thrombosis prophylaxis and treatment.

Latent and polymeric antithrombin: clearance and potential thrombotic risk.

Antithrombin, the most potent anticoagulant in vivo, displays a significant conformational flexibility. The native five-stranded anticoagulant form transforms under different conditions or mutations to inactive six-stranded conformations: latent or polymer. However, the function, potential deleterious effects, and clearance of these forms are not completely known. The dimerization of latent antithrombin with a native molecule has been suggested to have thrombotic potential. We have assessed the potential thrombogenicity of high amounts of latent and polymeric antithrombin by experiments performed in mice and human plasma. Moreover, we have analyzed the clearance of (125)I-labeled native, latent, polymer, and thrombin-complexed antithrombins in rat, as well as the clearance of latent antithrombin from plasma of patients treated with commercial concentrates. Our results show that high plasma levels of latent or polymeric antithrombin do not interfere with the anticoagulant function of native antithrombin. Moreover, we confirm that all monomeric forms of antithrombin have similar turnover. Finally, we show that polymers have the longest half-life of all conformers, being in circulation for prolonged periods of time. In conclusion, our data support that latent and polymeric antithrombin would not likely have a thrombotic effect, thus dispelling doubts about the potential harmful effect of latent antithrombin present in commercial concentrates for therapeutic use. Moreover, the suggested antiangiogenic role of latent antithrombin, together with its stability in plasma and its negligible thrombogenicity raises the possibility of its use as a new antiangiogenic drug.

Risk of recurrent venous thrombosis in patients with G20210A mutation in the prothrombin gene or factor V Leiden mutation.

The impact of the G20210A prothrombin mutation, factor V Leiden and 677T mutation of methylene tetrahydrofalate reductase (MTHFR) in recurrent deep venous thrombosis (DVT) is not so clear. We have prospectively monitored 259 patients following a first episode of DVT in order to determine which factors influence the development of a recurrent event. Several clinical and biological factors together with the genetic polymorphisms of factor V Leiden, G20210A prothrombin and 677T MTHFR were assessed. During a median follow-up of 786 patient-years, 27 patients (14%) developed one objective episode of recurrent venous thrombosis. The carriers of a double defect, homozygous or double heterozygous for factor V Leiden and G20210A, had an increased risk after a first episode of DVT, while patients who were isolated heterozygous for factor V Leiden or G20210 had a risk of recurrent DVT similar to patients who had neither mutation (annual incidence of 12.1, 3.1, 2.9 and 2.8%). The 677T MTHFR mutation alone or combined with hyperhomocysteinemia was not associated with an increased risk of recurrent events. The development of proximal DVT (P=0.01) and the presence of a double defect (P=0.01) were the only two risk factors independently associated with a high recurrence ratio in the multivariate analysis. Thus, the annual incidence of DVT recurrence in patients without any of these two risk factors was only 0.6% (95% confidence interval, 0.2-0.9). We have identified a group of patients with DVT but at very low risk of re-thrombosis in whom an extended secondary thromboprophylaxis should be carefully considered.

Detailed immunophenotypic characterization of different major and minor subsets of peripheral blood cells in patients with paroxysmal nocturnal hemoglobinuria.

BACKGROUND: Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by a deficient expression of glycosylphosphatidylinositol-anchored proteins (GPI-APs), due to somatic mutations of the phosphatidylinositolglycan complementation Class A (PIG-A) gene. STUDY DESIGN AND METHODS: In this study, the expression of a high number of GPI-APs on different subsets of peripheral blood (PB) cells from 14 PNH patients and their potential association with underlying genetic abnormalities has been analyzed. RESULTS: This study confirms the existence of variable patterns of expression of different GPI-APs on both major and minor PB-cell subsets from PNH patients. The size of the PNH clone within PB neutrophils and monocytes was systematically higher than that of other cell populations. Genetic changes were detected in the PIG-A gene in 5 of 13 cases analyzed. Interestingly, the reactivity for many GPI-APs was significantly higher on different subsets of normal PB cells from PNH patients than those observed on healthy volunteers. CONCLUSION: The best combination of markers for the diagnostic screening of PNH would include evaluation of CD14 on monocytes and of CD16 on neutrophils, although further analysis of CD55 and CD59 expression may contain additional clinically useful information. Clear association between the genetic changes detected in the PIG-A gene in 5 of 13 cases analyzed, and the phenotypic profile of PNH cells has not been found. Additionally, an abnormally higher expression of several GPI-APs among normal residual cells from PNH patients in comparison to healthy donors was observed, suggesting that factors other than the PIG-A mutation could determine the phenotypic profile of PB cells in PNH.

Homocysteine and outcome in young patients with acute coronary syndromes.

BACKGROUND: Despite the well-known pro-thrombotic and pro-inflammatory plasma homocysteine effects, it remains uncertain whether these effects can be associated with an adverse cardiac outcome in young patients admitted with acute coronary syndromes. METHODS: Homocysteine levels were determined within 24 h after admission in 244 consecutive patients aged less than 56 years who presented with an acute coronary syndrome. We evaluated the relationship between homocysteine and both short-term (death, myocardial [re]infarction), and long-term prognosis (death, recurrent acute coronary syndrome and/or ischemic stroke), after 3.4+/-1.7 years of follow-up. RESULTS: Homocysteine levels were similar in patients both with and without in-hospital event: 8.65 (5.36-10.48) vs. 8.98 (7.38-11.13) micromol/l, p=NS. However, patients who presented with the combined event during follow-up had higher homocysteine levels than those free of the event: 10.54 (7.90-11.76) micromol/l vs. 8.52 (7.11-10.23) micromol/l, p=0.001. Patients who either died (13.78 vs. 8.87 micromol/l, p=0.012) or had a myocardial infarction (10.75 vs. 8.76 micromol/l, p=0.006) or unstable angina (10.46 vs. 8.76, p=0.006) during follow-up had higher homocysteine levels. According to the Cox regression analysis: age [hazard ratio 1.05, CI 95%, 0.99-1.10], left ventricular ejection fraction < or =40% [hazard ratio 1.93, CI 95%, 0.98-3.79], and homocysteine tertile 3 [hazard ratio 2.05, CI 95%, 1.13-3.71] were the significant determinants of the combined adverse event during follow-up. Although 41 (18%) of patients presented the TT genotype of the methylen-tetrahydrofolate-reductase thermolabile variant mutation, its occurrence had a neutral effect on morbid-mortality. CONCLUSIONS: High homocysteine levels at admission strongly predict late cardiac events in young patients with acute coronary syndromes.

Antithrombin Cambridge II (A384S): an underestimated genetic risk factor for venous thrombosis.

The antithrombin A384S mutation has a relatively high frequency in the British population but has not been identified in other populations. This variant has been associated with cases of thrombotic disease, but its clinical relevance in venous thrombosis remained unclear. We have conducted a secondary analysis of the prevalence of the mutation in a large case-control study, including 1018 consecutive Spanish patients with venous thromboembolism. In addition, we evaluated its functional consequences in 20 carriers (4 homozygous). This mutation, even in the homozygous state, did not affect anti-Xa activity or antigen levels, and it only slightly impaired anti-IIa activity. Thus, routine clinical methods cannot detect this anomaly, and, accordingly, this alteration could have been underestimated. We identified this mutation in 0.2% of Spanish controls. Among patients, this variant represented the first cause of antithrombin anomalies. Indeed, 1.7% patients carried the A384S mutation, but 0.6% had any other antithrombin deficiency. The mutated allele was associated with an increased risk of venous thrombosis with an adjusted OR of 9.75 (95% CI, 2.2-42.5). This is the first study supporting that antithrombin A384S mutation is a prevalent genetic risk factor for venous thrombosis and is the most frequent cause of antithrombin deficiency in white populations.

The c.-1639G > A polymorphism of the VKORC1 gene is a major determinant of the response to acenocoumarol in anticoagulated patients.

Much of the variability in the sensitivity to warfarin in anticoagulated patients is associated with the c.-1639G > A polymorphism of the vitamin K-epoxide reductase (VKORC1) gene. However, its association with the acenocoumarol dose in patients under anticoagulant therapy has not been studied. The c.-1639G > A genotype of VKORC1 was determined in 113 patients on stable anticoagulation requiring low (n = 42), medium (n = 42) or high (n = 21) acenocoumarol doses. To evaluate the association between acenocoumarol requirements and the c.-1639G > A variant, multivariate logistic regression models were fitted, adjusting for age, gender, and the c.430C > T and c.1075A > C variants of cytochrome P450 2C9 (CYP2C9). A total of 90.5% of the patients in the low acenocoumarol dose group carried the A allele of VKORC1:c.-1639G > A. The A allele independently increased the odds of requiring a low acenocoumarol dose [odds ratio (OR) 9.4; 95% confidence interval (CI) 1.9-46.4; P = 0.006], especially when the homozygous form was present (OR 44.2; 95% CI 5.5-354.6; P < 0.001). The A allele was less frequent in the high dose group showing an inverse association with the requirement for high doses (OR 0.04; 95% CI 0.01-0.22; P < 0.001). The A allele of the c.-1639G > A polymorphism of VKORC1 is therefore associated with a low-dose requirement for acenocoumarol in patients receiving anticoagulant therapy.

A nonsense polymorphism in the protein Z-dependent protease inhibitor increases the risk for venous thrombosis.

The protein Z-dependent protease inhibitor (ZPI) is a hemostatic serpin with anticoagulant activity. As for antithrombin, deficiency of ZPI could have relevant thrombotic consequences. We have studied 6 genetic modifications affecting the ZPI gene, identifying 5 haplotypes. Haplotype H5 is featured by a stop codon at position 67. The relevance of these genetic modifications and haplotypes in venous thrombosis was evaluated in a case-control study including 1018 patients and 1018 age- and sex-matched controls. Surprisingly, the H5 haplotype was found in 0.9% of controls, supporting that the Arg67Stop change is a low frequency nonsense polymorphism. The prevalence of this haplotype increased significantly in patients (3.0%), one of whom was in a homozygous state. Multivariate analysis confirms that carriers have a 3.3-fold risk of developing venous thrombosis (P = .002; 95% CI: 1.5-7.1). Moreover, we observed a significant association of this polymorphism with familial history of thrombosis (P < .001). Our study supports that the ZPI Arg67Stop nonsense polymorphism might be an independent genetic risk factor for venous thrombosis. This polymorphism has slightly lower prevalence but similar thrombotic risk than the FV Leiden or prothrombin 20210A. Although further studies are required, all available data support that the ZPI is a candidate to play a significant role in thrombosis and should be evaluated in thrombophilic studies.

[The "Seville" Consensus Document on Alternatives to Allogenic Blood Transfusion. Sociedades españolas de Anestesiología (SEDAR), Medicina Intensiva (SEMICYUC), Hematología y Hemoterapia (AEHH), Transfusión sanguínea (SETS) Trombosis y Hemostasia (SETH)]. / Documento «Sevilla¼ de Consenso sobre Alternativas a la Transfusión de Sangre Alogénica.

The Consensus Document on Alternatives to Allogenic Blood Transfusion (AABT) has been drawn up by a panel of experts from 5 scientific societies. The Spanish Societies of Anesthesiology (SEDAR), Critical Care Medicine and Coronary Units (SEMICYUC), Hematology and Hemotherapy (AEHH), Blood Transfusion (SETS) and Thrombosis and Hemostasis (SETH) have sponsored and participated in this Consensus Document. Alternatives to blood transfusion have been divided into pharmacological and non-pharmacological, with 4 modules and 12 topics. The main objective variable was the reduction of allogenic blood transfusions and/or the number of transfused patients. The extent to which this objective was achieved by each AABT was evaluated using the Delphi method, which classifies the grade of recommendation from A (supported by controlled studies) to E (non-controlled studies and expert opinion). The experts concluded that most of the indications for AABT were based on middle or low grades of recommendation, "C", "D", or "E", thus indicating the need for further controlled studies.

Differential effects of 2C9*3 and 2C9*2 variants of cytochrome P-450 CYP2C9 on sensitivity to acenocoumarol.

The 2C9*3 and 2C9*2 polymorphisms of cytochrome P-450 CYP2C9 are associated with hypersensitivity to warfarin and bleeding. The effect of these polymorphisms on sensitivity to acenocoumarol is unknown. Three groups of patients, with low, medium, or high acenocoumarol-dose requirements, were studied. Age influenced the acenocoumarol sensitivity. Bearing the 2C9*3 allele was associated with the need for a lower acenocoumarol dose (odds ratio [OR], 6.02; 95% confidence interval [CI], 1.50-24.18); 80% of carriers of the 2C9*3 allele required a low dose. The 2C9*2 allele was associated with a lower acenocoumarol-dose requirement (OR, 2.70; 95% CI, 1.11-6.58) because of a reduced risk of the need for a high acenocoumarol dose (4.8% of the patients in the high-dose group carried the 2C9*2 allele versus 34.1% and 30.2%, respectively, in the medium-dose and low-dose groups). Therefore, carriers of 2C9*3 may need a low initial loading dose of acenocoumarol. Because acenocoumarol sensitivity with the 2C9*2 variant does not seem to be clinically relevant, the drug could be an alternative to warfarin in 2C9*2 carriers.

Prothrombin A19911G and G20210A polymorphisms' role in thrombosis.

The prothrombin G20210A polymorphism, which correlates with the plasmatic prothombin levels, is the second genetic risk factor for deep venous thrombosis (DVT), although its prothrombotic role is mild. Recently, the prothrombin A19911G polymorphism, also associated with slight variations of the prothrombin level, has been suggested to modulate the thrombotic risk of the G20210A polymorphism in a preliminary study including few patients and controls. Our study evaluated the effect of the A19911G polymorphism in the arterial and venous thrombotic risk of the prothrombin 20210G/A genotype, analysing 204 consecutive DVT patients and 204 matched controls. Moreover, we analysed 213 carriers of the 20210G/A genotype (152 with DVT, 26 with arterial thrombosis and 35 healthy subjects) and 10 homozygous 20210 A/A carriers. We developed a simple method to simultaneously determine the genotype of both polymorphisms. In accordance with our case/control study, the A19911G polymorphism did not play a significant role in the development of DVT. Analysis of 120 20210 A alleles demonstrated a complete linkage disequilibrium with the 19911 A allele. These polymorphisms (alone or combined) did not modify the risk of arterial thrombosis. However, the 19911A/G genotype slightly increased the risk of developing DVT in carriers of the 20210G/A genotype (OR 3.34 vs 5.86), supporting that the prothrombin 19911 polymorphism could modulate the risk of the G20210A polymorphism in developing DVT.

Pharmacokinetic study of the digoxin-acenocoumarol interaction in rabbits.

A study was carried out to evaluate the potential pharmacokinetic interaction between digoxin and acenocoumarol. The binding of digoxin to rabbit cardiac tissue homogenates was assessed in vitro, using the equilibrium dialysis technique. An increase in the first-order constant (p<0.05) and a reduction in the partition coefficient in the equilibrium situation (p<0.001) of digoxin were observed when the cardiac homogenates were previously treated with acenocoumarol. In the in vivo study, the kinetics of digoxin administered in single and multiple dosage regimens were compared in control rabbits and in rabbits treated simultaneously with acenocoumarol. Kinetic analysis of the results was performed using Non-linear Mixed Effects Modeling (NONMEM). In the presence of acenocoumarol, the population distribution volume (Vd) of digoxin was increased by 40-60%, no differences being found as regards the elimination clearance. Also, joint administration of both drugs led to a reduction in digoxin concentrations in the heart (p<0.01) at the end of the dosage regimen. Both sets of results point to the hypothesis of a hitherto unreported possible pharmacokinetic interaction between the two drugs affecting the distribution process. This interaction could lead to lower plasma digoxin levels, in view of the increased Vd, and a possible reduction in the therapeutic effect, owing to the decrease in affinity and in concentration in heart tissue.