Patrick Kesteven

Association of polymorphisms in the cytochrome P450 CYP2C9 with warfarin dose requirement and risk of bleeding complications

BACKGROUND The cytochrome P450 CYP2C9 is responsible for the metabolism of S-warfarin. Two known allelic variants CYP2C9*2 and CYP2C9*3 differ from the wild type CYP2C9*1 by a single aminoacid substitution in each case. The allelic variants are associated with impaired hydroxylation of S-warfarin in in-vitro expression systems. We have studied the effect of CYP2C9 polymorphism on the in-vivo warfarin dose requirement. METHODS Patients with a daily warfarin dose requirement of 1.5 mg or less (low-dose group, n=36), randomly selected patients with a wide range of dose requirements from an anticoagulant clinic in north-east England (clinic control group, n=52), and 100 healthy controls from the community in the same region were studied. Genotyping for the CYP2C9*2 and CYP2C9*3 alleles was done by PCR analysis. Case notes were reviewed to assess the difficulties encountered during the induction of warfarin therapy and bleeding complications in the low-dose and clinic control groups. FINDINGS The odds ratio for individuals with a low warfarin dose requirement having one or more CYP2C9 variant alleles compared with the normal population was 6.21 (95% CI 2.48-15.6). Patients in the low-dose group were more likely to have difficulties at the time of induction of warfarin therapy (5.97 [2.26-15.82]) and have increased risk of major bleeding complications (rate ratio 3.68 [1.43-9.50]) when compared with randomly selected clinic controls. INTERPRETATION We have shown that there is a strong association between CYP2C9 variant alleles and low warfarin dose requirement. CYP2C9 genotyping may identify a subgroup of patients who have difficulty at induction of warfarin therapy and are potentially at a higher risk of bleeding complications.

A Randomized Trial of Genotype-Guided Dosing of Warfarin

BACKGROUND The level of anticoagulation in response to a fixed-dose regimen of warfarin is difficult to predict during the initiation of therapy. We prospectively compared the effect of genotype-guided dosing with that of standard dosing on anticoagulation control in patients starting warfarin therapy. METHODS We conducted a multicenter, randomized, controlled trial involving patients with atrial fibrillation or venous thromboembolism. Genotyping for CYP2C9*2, CYP2C9*3, and VKORC1 (-1639G→A) was performed with the use of a point-of-care test. For patients assigned to the genotype-guided group, warfarin doses were prescribed according to pharmacogenetic-based algorithms for the first 5 days. Patients in the control (standard dosing) group received a 3-day loading-dose regimen. After the initiation period, the treatment of all patients was managed according to routine clinical practice. The primary outcome measure was the percentage of time in the therapeutic range of 2.0 to 3.0 for the international normalized ratio (INR) during the first 12 weeks after warfarin initiation. RESULTS A total of 455 patients were recruited, with 227 randomly assigned to the genotype-guided group and 228 assigned to the control group. The mean percentage of time in the therapeutic range was 67.4% in the genotype-guided group as compared with 60.3% in the control group (adjusted difference, 7.0 percentage points; 95% confidence interval, 3.3 to 10.6; P<0.001). There were significantly fewer incidences of excessive anticoagulation (INR ≥4.0) in the genotype-guided group. The median time to reach a therapeutic INR was 21 days in the genotype-guided group as compared with 29 days in the control group (P<0.001). CONCLUSIONS Pharmacogenetic-based dosing was associated with a higher percentage of time in the therapeutic INR range than was standard dosing during the initiation of warfarin therapy. (Funded by the European Commission Seventh Framework Programme and others; ClinicalTrials.gov number, NCT01119300.).

The value of education and self-monitoring in the management of warfarin therapy in older patients with unstable control of anticoagulation

Of 125 patients aged 65 years or over, with atrial fibrillation taking warfarin for at least 12 months, with a standard deviation (SD) of prothrombin time, expressed as the International Normalized Ratio (INR) >0·5 over the previous 6 months, 40 were randomized to continue with usual clinic care and 85 to receive education about warfarin. Of these, 44 were randomized to self‐monitor their INR and 41 returned to clinic. Compared with the previous 6 months there was a significant increase in percentage time within the therapeutic range for the 6 months following education [61·1 vs. 70·4; mean difference 8·8; 95% confidence interval (CI): −0·2–17·8; P = 0·054] and following education and self‐monitoring (57 vs. 71·1; mean difference 14·1; 95% CI: 6·7–21·5; P < 0·001), compared with those patients following usual clinic care (60·0 vs. 63·2; mean difference 3·2; 95% CI: −7·3–13·7). Using the same comparative periods, the INR SD fell by 0·24 (P < 0·0001) in the group allocated to education and self‐monitoring, 0·26 (P < 0·0001) in the group receiving education alone and 0·16 (P = 0·003) in the control group. Inter‐group differences were not statistically significant (intervention groups 0·26 ± 0·30 vs. control 0·16 ± 0·3, P = 0·10). Quality‐of‐life measurements and health beliefs about warfarin were unchanged (apart from emotional role limitation) with education or education and self‐monitoring. Patient education regarding anticoagulation therapy could be a cost‐effective initiative and is worthy of further study.

Relation of Lipid Peroxides to Macrovascular Disease in Type 2 Diabetes

Lipid peroxides are thought to be formed by free radicals and may play an important role in the development of atheromatous vascular disease. We have investigated the relationship between lipids, lipoproteins, coagulation factors, and lipid peroxides (measured as thiobarbituric acid reacting species (TBARS)) in Type 2 diabetic patients with macrovascular disease. Eighteen diabetic and 20 non‐diabetic subjects with clinical evidence of ischaemic heart disease and/or peripheral vascular disease were investigated, together with 28 healthy subjects without evidence of vascular disease. TBARS concentrations in non‐diabetic (mean 5.0 (95% CI 4.5–5.7) μmol I−1) and diabetic groups (5.6 (5.1–6.0) μmol I−1) with macrovascular disease were not significantly different although values were higher in both groups of patients with vascular disease by comparison with control subjects (2.7 (2.4–3.1) (μmol I−1, p < 0.001). Significant univariate correlations between TBARS concentrations and measures of blood glucose control (fructosamine, blood glucose and HbA,) were found for all 66 subjects (r = 0.35–0.42, p < 0.01–p < 0.001), although no independent association between these parameters and TBARS was demonstrated in multiple regression analysis. In addition, TBARS levels were significantly correlated in univariate analysis with the apolipoprotein (apo) Al:apoB ratio (r = −0.56, p< 0.001), total cholesterol:high density lipoprotein cholesterol ratio (r = 0.52, p < 0.001), apoB (r = 0.51, p < 0.001), low density lipoprotein cholesterol (r = 0.40, p < 0.001), serum total triglyceride (r = 0.46, p < 0.001), apoAl (r = −0.35, p < 0.01) and serum total cholesterol (r = 0.39, p < 0.001). Multiple regression analysis of continuous variables showed that apoB (p < 0.001), age (p < 0.001), and apoAl (p = 0.008) were independently associated with serum TBARS although these associations disappeared if macrovascular disease was added to the regression equation as a categorical variable. Our data support previous studies which demonstrate increased serum concentrations of TBARS in subjects with macrovascular disease but suggest that levels are similarly elevated in diabetic and non‐diabetic subjects.

Dietary vitamin K influences intra-individual variability in anticoagulant response to warfarin

The relationship between dietary intake of vitamin K, fat, plasma vitamin K concentrations and anticoagulation response to warfarin within individuals, as well as the contribution of dietary vitamin K to differences in warfarin dose requirements between individuals were investigated in 53 patients on warfarin therapy who had stably controlled anticoagulation. Each patient completed a dietary record of all foods consumed on a daily basis for 4 weeks. Each week a blood sample was taken for measurement of the international normalized ratio (INR), plasma vitamin K, triglycerides and warfarin enantiomer concentrations. The patients’ genotype for CYP2C9 was also determined. Regression analysis of the data showed that, for each increase of 100 μg in the daily dietary intake of vitamin K averaged over 4 d, the INR was reduced by 0·2. There was no correlation between warfarin daily dose and average daily dietary vitamin K intake when calculated over 28 d. The regression model for warfarin dose showed that, while dietary vitamin K had no effect, CYP2C9 genotype (P = 2%) and age (P < 1%) significantly contributed to inter‐patient variability in warfarin dose requirements. A consistent intake of vitamin K could reduce intrapatient variability in anticoagulation response and thus improve the safety of warfarin therapy.

Venous Thromboembolism in Patients with Primary Bone or Soft-Tissue Sarcomas

BACKGROUND Venous thromboembolism has been independently associated with both malignant disease and orthopaedic surgery. Patients with bone or soft-tissue tumors who undergo orthopaedic surgery may therefore be at high risk for thromboembolic events. The purpose of the present retrospective study was to determine the rate of clinically detected deep venous thrombosis and pulmonary embolism in patients with trunk or extremity bone or soft-tissue sarcomas. METHODS The medical records of patients with a confirmed diagnosis of primary bone or soft-tissue sarcoma who had presented to our unit between 1998 and 2003 were reviewed with use of a standardized chart abstraction tool. The data that were retrieved included patient-related data (demographic characteristics, diagnoses, and surgical interventions), the use of adjuvant chemotherapy or radiation therapy, additional risk factors for thromboembolism, the use of thromboembolic prophylaxis, and confirmed thromboembolic events. RESULTS Of the 252 patients who were identified, ninety-four had a diagnosis of primary bone sarcoma and 158 had a diagnosis of primary soft-tissue sarcoma. Approximately 70% of the cohort received thromboprophylaxis, with 57% receiving low-molecular-weight heparin. Thirty-seven patients were clinically suspected of having a deep venous thrombosis. Nine patients had a deep venous thrombosis that was confirmed radiographically, and in one case the diagnosis was made at another center, resulting in a rate of clinically evident deep venous thrombosis of 4%. Nine patients had a clinically suspected pulmonary embolism. One patient had confirmation of the pulmonary embolism with use of a ventilation-perfusion scan, one patient died of pulmonary embolism, and one patient had diagnosis of the pulmonary embolism at another center, resulting in an overall rate of pulmonary embolism of 1.2% and a rate of fatal pulmonary embolism of 0.4%. All patients with thromboembolic events had a tumor involving the hip or thigh, with the majority of the events occurring prior to definitive surgery. CONCLUSIONS The risk of a clinically apparent thromboembolic event in patients with bone or soft-tissue sarcomas is comparable with that in other orthopaedic patients. However, tumors in the hip or thigh may be associated with a particularly high risk of thromboembolism. A prospective study is needed to investigate factors that are predictive of thromboembolism and the role of chemical thromboprophylaxis.

A systematic review of outcome measures reported for the therapeutic effectiveness of oral anticoagulation.

Aims: To evaluate the evidence of therapeutic international normalised ratio (INR) control reporting and to provide recommendations for future reporting, particularly for research and audit purposes. Methods: A systematic review of literature published over a five year period describing therapeutic INR control. Papers were identified from the Medline electronic database, and those that met the quality criteria were reviewed independently by an academic general practitioner and a consultant haematologist. Results: Fifteen papers were identified that met the quality criteria for review. The sample size of studies ranged from 53 to 2545 (mean, 483.9) patients. Follow up ranged from three months to 13 years. Twelve studies reported results from secondary care only, one from primary care only, and two from both primary and secondary care. Seven of the 15 papers reported percentage time in range, five of 15 papers reported mean INR, six of 15 papers reported the proportion of tests in range, and five of 15 papers reported mean warfarin dose. Additional methods of presenting INR results were: dose changes each month, distribution of INR results, deviation of INR value from mean, percentage dose changes, time between visits, and median INR value. Six papers reported only one outcome measure, six reported two outcomes, two papers reported three outcomes, and one paper reported five outcomes. Conclusions: It is recommended that at least two outcome measures should be reported and measures should be selected so that both the INR determinations and dosing advice are monitored.

ABO-incompatible heart transplantation in infants: The Freeman Hospital experience

Background. Incompatibility of the major blood groups A, B, and O has been an absolute contraindication for heart transplantation. However, because of immunologic immaturity, infants may have relative protection from hyperacute rejection and thus could undergo transplantation with ABO-mismatched organs. Methods. Since January 2000, the authors have adopted a policy of considering infants for ABO-incompatible heart transplantation. Serum isohemagglutinin titers were measured before, during, and after transplantation. Two infants (3 and 2 months old) and a 21-month-old child underwent ABO-incompatible heart transplantation. During cardiopulmonary bypass, plasma exchange was performed. No other antibody-removal procedures were performed. A routine immunosuppressive regimen was used, and rejection was monitored by endomyocardial biopsies. An additional two patients (31 and 18 months old) were worked up but were unsuitable for ABO-incompatible transplantation because of high isohemagglutinin titers. They were successfully bridged to transplantation and received heart transplants from ABO-compatible donors. Results. All three infants with ABO-incompatible heart transplants are fit and well, 40 months, 30 months, and 12 months postoperatively. All three had serum antibodies to antigens of the donor’s blood group before transplantation. No hyperacute rejection occurred. No morbidity attributable to the ABO incompatibility has been observed. Conclusions. ABO-mismatched heart transplantation may be undertaken safely and without any short-term adverse consequences in infants and young children in whom isohemagglutinin production is not yet established.

Autotransfusion After Coronary Artery Bypass Surgery: Is There Any Benefit?

Postoperative salvage autotransfuslon of shed mediastinal blood, using the cardiotomy reservoir, is an inexpensive technique whose efficacy and safety are evaluated in this study. We randomized 75 consecutive patients into two groups. The autotransfusion group (n = 42) received autotransfusion after the completion of the coronary artery bypass grafting (CABG) until the dralnage was ≤ 50 mL per hour for 2 consecutive hours. The control group (n = 33) was treated with standard chest drainage. Both groups received homologous blood transfusion when the hematocrit fell below 30%. Packed red cells were required post‐operatively in 84.8% of the control group and 80.9% of the autotransfusion group (p = NS). Postoperative colloid fluid replacement (excluding autotransfusion fluid) did not differ significantly between the groups. The prothrombin time was significantly higher in the autotransfusion group 24 hours postoperatively (p = 0.03). The fibrin degradation products were elevated only In the serum of the autotransfusion patients (p < 0.002). More febrile patients were seen in the autotransfusion group although not significantly more than the controls. The autotransfusion group received more red cells than the control group, but it lost more red cells in the medlastlnal drains. In conclusion, the autotransfusion of shed mediastinal blood has not proved beneficial in reducing the Postoperative requirements in homologous blood in patients undergoing coronary artery bypass grafting (CABG). (J Card Surg 1994;9:314–321)

QT prolongation in patients with Type 2 diabetes and microalbuminuria.

Abstract. The link between microalbuminuria and premature death in Type 2 diabetes is not fully explained by conventional cardiovascular risk factors. We aimed to determine if QT prolongation and/or dispersion are linked to microalbuminuria in patients with Type 2 diabetes and to investigate their associations with other risk factors. We have studied asymptomatic patients with Type 2 diabetes with no clinical evidence of coronary disease (43 with microalbuminuria matched with 43 normoalbuminuric patients). Rate-corrected maximum QT interval (QTc max) was greater in the microalbuminuric group [mean (SD): 450 (23) vs 440 (20) ms1/2, p = 0.046] as was the proportion of patients with QTc max > 440 ms (67 % vs 38 %, p = 0.01). Rate-corrected QT dispersion (QTcd) was similar in the two groups [57 (21) vs 53 (23) ms1/2, p = 0.41]. Linear regression analysis showed that QTc max and/or QTcd were not strongly linked to albumin excretion rate but more strongly to factors associated with microalbuminuria such as blood pressure and factor XIIa. Our findings support the hypothesis that QT prolongation and microalbuminuria have common determinants in Type 2 diabetes. QT prolongation may contribute to the increased mortality observed in microalbuminuric subjects with Type 2 diabetes.