Steven H. Yale

A Pharmacogenetic versus a Clinical Algorithm for Warfarin Dosing

BACKGROUND The clinical utility of genotype-guided (pharmacogenetically based) dosing of warfarin has been tested only in small clinical trials or observational studies, with equivocal results. METHODS We randomly assigned 1015 patients to receive doses of warfarin during the first 5 days of therapy that were determined according to a dosing algorithm that included both clinical variables and genotype data or to one that included clinical variables only. All patients and clinicians were unaware of the dose of warfarin during the first 4 weeks of therapy. The primary outcome was the percentage of time that the international normalized ratio (INR) was in the therapeutic range from day 4 or 5 through day 28 of therapy. RESULTS At 4 weeks, the mean percentage of time in the therapeutic range was 45.2% in the genotype-guided group and 45.4% in the clinically guided group (adjusted mean difference, [genotype-guided group minus clinically guided group], -0.2; 95% confidence interval, -3.4 to 3.1; P=0.91). There also was no significant between-group difference among patients with a predicted dose difference between the two algorithms of 1 mg per day or more. There was, however, a significant interaction between dosing strategy and race (P=0.003). Among black patients, the mean percentage of time in the therapeutic range was less in the genotype-guided group than in the clinically guided group. The rates of the combined outcome of any INR of 4 or more, major bleeding, or thromboembolism did not differ significantly according to dosing strategy. CONCLUSIONS Genotype-guided dosing of warfarin did not improve anticoagulation control during the first 4 weeks of therapy. (Funded by the National Heart, Lung, and Blood Institute and others; COAG ClinicalTrials.gov number, NCT00839657.).

CYP4F2 genetic variant alters required warfarin dose.

Warfarin is an effective, commonly prescribed anticoagulant used to treat and prevent thrombotic events. Because of historically high rates of drug-associated adverse events, warfarin remains underprescribed. Further, interindividual variability in therapeutic dose mandates frequent monitoring until target anticoagulation is achieved. Genetic polymorphisms involved in warfarin metabolism and sensitivity have been implicated in variability of dose. Here, we describe a novel variant that influences warfarin requirements. To identify additional genetic variants that contribute to warfarin requirements, screening of DNA variants in additional genes that code for drug-metabolizing enzymes and drug transport proteins was undertaken using the Affymetrix drug-metabolizing enzymes and transporters panel. A DNA variant (rs2108622; V433M) in cytochrome P450 4F2 (CYP4F2) was associated with warfarin dose in 3 independent white cohorts of patients stabilized on warfarin representing diverse geographic regions in the United States and accounted for a difference in warfarin dose of approximately 1 mg/day between CC and TT subjects. Genetic variation of CYP4F2 was associated with a clinically relevant effect on warfarin requirement.

Evaluation of genetic factors for warfarin dose prediction.

Objectives: Warfarin is a commonly prescribed anticoagulant drug used to prevent thromboses that may arise as a consequence of orthopedic and vascular surgery or underlying cardiovascular disease. Warfarin is associated with a notoriously narrow therapeutic window where small variations in dosing may result in hemorrhagic or thrombotic complications. To ultimately improve dosing of warfarin, we evaluated models for stable maintenance dose that incorporated both clinical and genetic factors. Method: A model was constructed by evaluating the contribution to dosing variability of the following clinical factors: age, gender, body surface area, and presence or absence of prosthetic heart valves or diabetes. The model was then sequentially expanded by incorporating polymorphisms of cytochrome P450 (CYP) 2C9; vitamin K 2,3 epoxide reductase complex, subunit 1 (VKORC1); gamma carboxylase; factor VII; and apolipoprotein (Apo) E genes. Results: Of genetic factors evaluated in the model, CYP2C9 and VKORC1 each contributed substantially to dose variability, and together with clinical factors explained 56% of the individual variability in stable warfarin dose. In contrast, gamma carboxylase, factor VII and Apo E polymorphisms contributed little to dose variability. Conclusion: The importance of CYP2C9 and VKORC1 to patient-specific dose of warfarin has been confirmed, while polymorphisms of gamma carboxylase, factor VII and Apo E genes did not substantially contribute to predictive models for stable warfarin dose.

A randomized controlled trial of genotype-based Coumadin initiation

Purpose: A randomized controlled trial was conducted in patients initiating warfarin to determine whether algorithms that incorporate genotypes affecting warfarin metabolism and function, and Vitamin K metabolism improve prediction of therapeutic warfarin dose and anticoagulation management.Methods: A total of 230 patients were randomized to either a clinical arm where dosing algorithms considered only clinical information or an interventional arm where dosing algorithms used clinical and genotypic variables (CYP2C9, CYP4F2, and VKORC1). Subjects in the interventional arm were genotyped within 5 hours, and the initial dose was informed by genotype. Primary endpoints were absolute prediction error relative to therapeutic dose, and time in therapeutic target range during the first 14 days. Secondary endpoints included time to stable dose in therapeutic range, time to first international normalization ratio >4, and warfarin-related adverse events.Results: The model including genetics more accurately identified therapeutic dose twice as often as the clinical model (65.3% vs. 34.7%) (P < 0.0001). Patients in the interventional arm did not achieve greater time in therapeutic range. Study arms were similar regarding time to international normalization ratio >4 and adverse events.Conclusion: Genotype-informed dosing clearly improved prediction of therapeutic dose beyond that available with clinical parameters. Genetic information did not affect time in therapeutic target range during the first 14 days of therapy. Current management practices with the vagaries in dose adjustment after warfarin initiation exert a strong influence on traditional clinical outcomes.

Reliability and Feasibility of Methods to Quantitatively Assess Peripheral Edema

Objective: To evaluate methods to assess peripheral edema for reliability, feasibility and correlation with the classic clinical assessment of pitting edema. Design: Cross-sectional observational study. Setting: Large primary care clinic in Marshfield, Wisconsin, USA. Participants: Convenience sample of 20 patients with type 2 diabetes and a range of edema severity, including patients without edema. Methods: Eight methods of edema assessment were evaluated: (1) clinical assessment of pit depth and recovery at three locations, (2) patient questionnaire, (3) ankle circumference, (4) figure-of-eight (ankle circumference using eight ankle/foot landmarks), (5) edema tester (plastic card with holes of varying size pressed to the ankle with a blood pressure cuff), (6) modified edema tester (edema tester with bumps), (7) indirect leg volume (by series of ankle/leg circumferences), and (8) foot/ankle volumetry by water displacement. Patients were evaluated independently by three nurse examiners. Results: Water displacement and ankle circumference had high inter-examiner agreement (intraclass correlation coefficient 0.93, 0.96 right; 0.97, 0.97 left). Agreement was inconsistent for figure-of-eight (0.64, 0.86), moderate for indirect leg volume (0.53, 0.66), and low for clinical assessments at all locations. Agreement was low for the edema testers but varied by the pressure administered. Correlation with the classic, subjective clinical assessment was good for the nurse-performed assessments and patient questionnaire. Ankle circumference and patient questionnaires each took 1 minute to complete. Other tools took >5 minutes to complete. Conclusions: Water displacement and ankle circumference showed excellent reliability; however, water displacement is a time-consuming measure and may pose implementation challenges in the clinical and clinical trial environments. Patient-reported level and frequency of edema, based on an unvalidated questionnaire, was generally well correlated with the physician assessment of edema severity and may prove to be another reliable and accurate method of assessing edema. Additional study is needed to evaluate the validity and responsiveness of these methods.

Virchow’s Contribution to the Understanding of Thrombosis and Cellular Biology

Few physician-scientists have contributed as much to the fundamental understanding of the pathophysiology of cellular biology as Rudolf Virchow. His contribution to the cellular biomedicine paradigm along with the germ theory of Pasteur and Koch formed the basis for many of the medical advances of the twentieth century.1 He was one of the first physicians to examine disease at the cellular level, arguing that the origin of disease was caused by cellular pathology. One area that he studied extensively, and in which he has left lasting contributions to modern medicine, was in the area of thrombosis, specifically venothromboembolism (VTE). For much of the later half of the twentieth century, the so-called Virchow’s Triad has formed the basis for understanding the pathogenesis of VTE and is still widely used to assess VTE risk.2 In order to assess and appreciate the applicability of Virchow’s Triad to current medical practices, it is important first to examine how the principals of Virchow’s original theory of thrombosis continue to be applicable to modern day theory.

Changes in Gut and Plasma Microbiome following Exercise Challenge in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a disease characterized by intense and debilitating fatigue not due to physical activity that has persisted for at least 6 months, post-exertional malaise, unrefreshing sleep, and accompanied by a number of secondary symptoms, including sore throat, memory and concentration impairment, headache, and muscle/joint pain. In patients with post-exertional malaise, significant worsening of symptoms occurs following physical exertion and exercise challenge serves as a useful method for identifying biomarkers for exertion intolerance. Evidence suggests that intestinal dysbiosis and systemic responses to gut microorganisms may play a role in the symptomology of ME/CFS. As such, we hypothesized that post-exertion worsening of ME/CFS symptoms could be due to increased bacterial translocation from the intestine into the systemic circulation. To test this hypothesis, we collected symptom reports and blood and stool samples from ten clinically characterized ME/CFS patients and ten matched healthy controls before and 15 minutes, 48 hours, and 72 hours after a maximal exercise challenge. Microbiomes of blood and stool samples were examined. Stool sample microbiomes differed between ME/CFS patients and healthy controls in the abundance of several major bacterial phyla. Following maximal exercise challenge, there was an increase in relative abundance of 6 of the 9 major bacterial phyla/genera in ME/CFS patients from baseline to 72 hours post-exercise compared to only 2 of the 9 phyla/genera in controls (p = 0.005). There was also a significant difference in clearance of specific bacterial phyla from blood following exercise with high levels of bacterial sequences maintained at 72 hours post-exercise in ME/CFS patients versus clearance in the controls. These results provide evidence for a systemic effect of an altered gut microbiome in ME/CFS patients compared to controls. Upon exercise challenge, there were significant changes in the abundance of major bacterial phyla in the gut in ME/CFS patients not observed in healthy controls. In addition, compared to controls clearance of bacteria from the blood was delayed in ME/CFS patients following exercise. These findings suggest a role for an altered gut microbiome and increased bacterial translocation following exercise in ME/CFS patients that may account for the profound post-exertional malaise experienced by ME/CFS patients.

Applying Case Definition Criteria to Irritable Bowel Syndrome

Objective: The quality of documentation of signs and symptoms and validation of the diagnosis of irritable bowel syndrome (IBS) according to case definition criteria of Manning, Rome I and Rome II in an office setting has not been previously described. We sought to identify and validate cases of IBS based on the Manning, Rome I and Rome II diagnostic criteria in a rural practice setting. Setting: Marshfield Epidemiologic Study Area (MESA) Central consisting of 14 ZIP codes in central Wisconsin, USA. Methods: A retrospective cohort study involved 890 patients with the diagnostic codes 564.1 for irritable bowel syndrome and 306.4 spastic colon-psychogenic who had presented to the practice from 1993–2003. Duration, frequency, concordance and intensity of symptoms based on case definitions of IBS were abstracted from the medical records. Results: During the study period, 890 incident cases of IBS were identified. Only 404 met one or more of the three diagnostic criteria, 340 (84%) met only the Manning criteria, 35 (10%) met only Manning and Rome I criteria, 4 (1%) met both Manning and Rome II criteria, and 25 (6%) met Manning and Rome I and Rome II criteria. Age adjusted incidence rates per 100,000 person-years for validated IBS cases during the observational period were 87 to 170 by Manning (lower confidence interval [CI]: 57–127, upper CI: 116–213), 8 to 34 (lower CI: 0–14, upper CI: 16–53) for Rome I and 3 to 16 (lower CI: 0–3, upper CI: 8–28) for Rome II. Comparison of Rome I and Rome II showed moderate concordance (kappa statistic = 0.51; 95% CI: 0.39–0.64). Conclusions: Only a small percentage of IBS cases with assigned diagnostic codes met case definition criteria for IBS. There were low concordance rates among the three diagnostic criteria applied.

Jean-Martin Charcot: The Father of Neurology

To take away from neurology all the discoveries made by Charcot would be to render it unrecognizable. Joseph Babinski Jean-Martin Charcot (figure 1) was born in Paris, France in 1825 at a time when the field of Neurology had not been formally recognized as a distinct specialty. He was a gifted painter who used his artistic abilities and strong visual memory to make associations about patterns of disease in the field of medicine and anatomy. His father, financially limited, decided that the son who performed best amongst the four in school would go on to receive a higher education, a competition that Jean-Martin won, thus providing him the opportunity to enter medical school. Mastery of the French, English, German, and Italian languages enabled him to read the medical literature in these languages, which accounted for his well-rounded knowledge of a variety of subjects including gerontology, diseases of the joints and lungs, and the anatomy, physiology, and pathology of the nervous system.

Josef Brudzinski and Vladimir Mikhailovich Kernig: Signs for Diagnosing Meningitis

Inflammation of the meninges, or meningitis, is a serious neurological insult that involves the membranes (dura, pia and arachnoid matter) covering the brain and spinal cord. Meningitis may be caused by any of a host of infectious and non-infectious agents including bacteria, viruses, fungi, parasites, drugs, autoimmune disorders, or malignancy which considerably influences morbidity and mortality.1 Currently, the case-fatality rate for adults with bacterial meningitis is approximately 25% with temporary or permanent neurologic sequelae occurring in 21% to 28% of survivors.2,3 These rates are slightly lower for children older than 1 month, but remain significant, and early diagnosis is critical in improving outcomes.4,5 Symptoms of acute meningitis include high fevers, chills, joint pain, decreased mental status, headache (“worst headache of my life”), stiff neck, photophobia, and rash. Early indicators such as rash or joint pain may present abruptly depending on the etiologic agent. One study reported that initial symptoms appear on average 24 hours prior to hospital admission.6 A major predictor of outcome in patients diagnosed with bacterial meningitis is the time that has elapsed from the onset of symptoms to the initiation of antibiotic treatment.2,7,8 Empiric treatment with selected antibiotics is based on age of the patient and associated co-morbidities. Critical and timely diagnosis may be facilitated by Kernig’s and Brudzinski’s signs. These two eponyms are commonly associated with meningitis.