Prothrombin Time-international Normalized Ratio Research Articles

ドセタキセルとワルファリンの薬物相互作用によるプロトロンビン時間の変動に関する検討

Warfarin is medicine whose dosage is determined by measuring the prothrombin time international normalized ratio (PTINR) as an index of anticoagulant activity because of its interactions with other medicines and the large inter-individual variability in its anticoagulant effect.We report a case in which unexpected PT-INR elevation was observed after chemotherapy that included docetaxel.The patient had been administered warfarin after aorta valve substitution due to valvular heart disease and then developed ovarian cancer.An interaction between warfarin and docetaxel was suspected because PT-INR was elevated within a few days of each chemotherapy session.In addition,we examined other patients who had been on both warfarin therapy and chemotherapy including docetaxel from August 2004 to December 2009.In these patients,the warfarin sensitivity index (WSI) was elevated significantly from its baseline value of 0.48.to 0.89 after chemotherapy.It is still uncertain whether there is a definite interaction between warfarin and docetaxel and no detailed mechanism for one has yet been reported.Nevertheless,it is necessary to assume the possibility of PT-INR elevation and to monitor PT-INR frequently in managing patients on both warfarin and chemotherapy.

Evaluation of patient perceptions and outcomes related to anticoagulation point-of-care testing in ambulatory care clinics.

Until recently, Prothrombin Time/International Normalized Ratio (PT/INR) measurements have typically been used to monitor patients on warfarin through institutional laboratories via venous puncture. The Point-of-Care Testing (POCT) device has revolutionized the patient care process by allowing for laboratory testing outside of the central laboratory. To analyze humanistic and clinical outcomes in patients currently treated with warfarin and monitored through a pharmacist-managed anticoagulation clinic using point-of-care testing (POCT) device versus venipuncture within ambulatory care clinics at our institution. All patients currently treated with warfarin therapy who were managed by clinical pharmacists for anticoagulation monitoring at the Medical University of South Carolina (MUSC) Family Medicine Center and University Diagnostic Center, were enrolled. Patients were asked to complete a satisfaction survey regarding their anticoagulation monitoring. In addition, data related to emergency department (ED) visits, hospitalizations and percent of time in the INR therapeutic range for 6 months pre- and post-implementation of POCT device was collected. This information was obtained through an electronic patient information database, Oacis. A total of 145 patients were included in the data collection from the two clinics. The majority (41%) of these patients were taking warfarin for atrial fibrillation. Satisfaction surveys were completed by 86 (59 %) of patients. The surveys revealed that POCT device was preferred over venipuncture in 95% of patients. Reasons for the preference included more face-to-face interaction, less wait time, less pain, less blood needed, and quicker results. Of the 145 patients who were included in the objective data analysis, no significant differences were found in the number of hospitalizations, ED visits, or percent of time in the INR therapeutic range pre- and post-implementation of POCT device. The results of this study demonstrate improvement in patient satisfaction with POCT compared to venipuncture, with limited value in clinical outcomes.

Clinical value of multiple organ dysfunction syndrome score in evaluating prognosis for patients with liver failure

Objective To study clinical value of multiple organ dysfunction syndrome (MODS) score to evaluate prognosis for patients with liver failure. Methods A total of 189 patients with liver failure were recruited into the study, 125 deaths and 64 survivals. Their vital sign, platelets count (PLT), prothrombin time (PT) and international normalized ratio of PT (INRPT), fraction of inhaled oxygen (FiO2), arterial oxygen partial pressure (PaO2), serum levels of total bilirubin (TB), albumin (ALB), creatinine (Cr), pressure-adjusted heart rate (PAHR), glasgow coma score (GCS), degree of aacitic fluid (DAF) and stage of hepatic encephalopathy (SHE) were evaluated within 24 hours after admission. Each of the patients scored according to the criteria of MODS score, Child-Turcotte-Pugh (CTP) score and model for end-stage liver disease (MELD) score. Difference in MODS score between death and survival groups was compared and accuracy of prognosis of MODS score, CTP score and MELD score were evaluated by the area under receiver operating characteristic (ROC) curve. Survival time of patients in the two groups classified by their MODS scores was compared with Kaplan-Meier (K-M) survival curve. Results There was significant difference in PT, INRPT, PaO2, Cr, GCS, SHE between death and survival groups, but there was no difference in TB, ALB, PLT, FiO2, PHAR and DAF between them. Mean score of MODS in death group (9±2) was significantly higher than that in survival group (7±1) (t=9.076, P<0.01). The area under ROC curve (AUC) of MODS score (0.814) was close to that of MELD score (0.827), but higher than that of CTP score (0.714). There was significant difference in survival time between the varied groups classified by MODS score (χ2=72.451, P<0.01). Conclusions Clinical value of MODS score is equivalent to that of MELD score in evaluating prognosis for patients with liver failure, even better than that of CTP score, which can be used to evaluate short-term prognosis for patients with liver failure. Key words: Liver failure; Evaluation studies; Prognosis

Effect of gefitinib on warfarin antithrombotic activity

Despite the literature indicating adverse interactions between warfarin and cytotoxic agents, whether such an interaction occurs when warfarin and gefitinib are used concomitantly is unknown. We analyzed the prevalence of the concomitant use of warfarin and gefitinib, and the incidence of prothrombin time-international normalized ratio (PT-INR) alterations or adverse interactions in concomitant users of warfarin and gefitinib. We conducted a retrospective study of patients with non-small cell lung cancer treated at the Kitasato University Hospital who received concomitant warfarin and gefitinib between September 2002 and January 2007. Medical information, including the indication for warfarin use, warfarin dosing and dosing changes, and exposure to gefitinib were collected from computerized databases and medical records. Twelve (4.1%) of 296 patients treated with gefitinib received warfarin. PT-INR elevation occurred in 6 patients (50.0%). Two (16.7%) of the 12 patients had liver metastases. Liver dysfunction was associated with PT-INR elevation (P = 0.0100). As there is a possibility of PT-INR abnormalities occurring during the concomitant use of gefitinib and warfarin, clinicians should be aware of this interaction. Because of the potentially severe consequences of this interaction, close monitoring of PT-INR and warfarin dose adjustment are recommended for patients receiving warfarin and gefitinib, especially during the first 2 weeks in the beginning of warfarin therapy.

Influence of Laropiprant, a Selective Prostaglandin D2 Receptor 1 Antagonist, on the Pharmacokinetics and Pharmacodynamics of Warfarin

Laropiprant (LRPT), a prostaglandin D2 receptor 1 antagonist shown to reduce niacin-induced flushing symptoms, is being developed in combination with niacin for the treatment of dyslipidemia. This study assessed the pharmacokinetics/pharmacodynamics of single-dose warfarin in the presence/absence of multiple-dose LRPT. Thirteen subjects received 2 treatments in random order separated by > or =10-day washout: (1) multiple-dose LRPT 40 mg/d for 12 days (days -5 to 7) with coadministered single-dose warfarin 30 mg (day 6) and (2) single-dose warfarin 30 mg (day 1). R+- and S(-)-warfarin and international normalized ratio (INR) were assayed predose and up to 168 hours postdose. Comparability was declared if the 90% confidence intervals (CIs) for the geometric mean ratio (GMR; warfarin + LRPT/warfarin alone) of area under the plasma concentration curve from zero to infinity (AUC0-infinity) for R+- and S(-)-warfarin were contained within (0.80, 1.25). The estimated GMRs of AUC0-infinity (90% CIs) were 1.02 (0.96, 1.09) and 1.04 (0.98, 1.09) for R+- and S(-)-warfarin, respectively. The estimated GMRs of maximum plasma concentration (Cmax) (90% CIs) were 1.13 (1.02, 1.26) and 1.11 (0.99, 1.24) for R+- and S(-)-warfarin, respectively. The estimated GMRs of area under the prothrombin time INR curve from 0 to 168 hours on day 21 (INR AUC0-168 h) and average maximum observed prothrombin time INR (INRmax) were 1.02 (0.99, 1.05) and 1.04 (0.98, 1.10), respectively. There was no evidence of clinically meaningful alterations in the pharmacokinetics and pharmacodynamics (ie, INR) of R(+)- or S(-)-warfarin after coadministration of multiple-dose LRPT and single-dose warfarin.

Warfarin-Associated Fetal Intracranial Hemorrhage in Woman with Mitral Valve Replacements: A Case Report

Warfarin-associated fetal hemorrhage is a fatal event. We report the case of a 39-year-old woman who had been taking warfarin for 23 years since undergoing mitral valve replacement. Thereafter, when she was found to be pregnant, the medication was switched to heparin from 6 to 21 weeks of gestation. Following this, she was prescribed oral warfarin again (3.5 mg per day), with a strict control of prothrombin time/international normalized ratio (PT/INR). At 23 weeks of gestation, fetal intracranial hemorrhage occurred because of maternal exposure to warfarin. Maternal PT/INR does not correlate well with the activity of warfarin in the fetus and currently, there is no direct way to prevent fetal intracranial hemorrhage. Hence, further research on the optimal coagulation therapy in pregnant women with valve replacement should be encouraged.

Comparability of the results of PT–INR with local MNPT and APTTR with MNAPTT on different coagulation analyzers in China

The prothrombin time (PT), International normalized ratio (INR) and activated partial thromboplastin time (APTT) are the most used coagulation tests in China, where more than one type of automated coagulation analyzer is often used in the clinical laboratory. The PT-INR results of 109 samples were compared with local mean normal PT (MNPT) and APTT ratio (APTTR) with mean normal APTT (MNAPTT) on two different coagulation analyzers in the same laboratory. The two different coagulation analyzers showed no significant difference (P > 0.05) in PT and INR determination, but there was a significant difference (P < 0.01) for APTT. The INR with local MNPT and APTTR with MNAPTT, obtained with the ACL Futura and CA 510, showed much better agreement; 98.8% (82/83) of bias for INR with local MNPT was less than 15% compared with 90.4% (75/83) of bias for INR; and 100% of bias for APTTR (62/62) was less than 15% compared with only 6.5% (4/62) of bias for APTT. Meanwhile, there was no significant difference (P = 0.865) for APTTR with MNAPTT compared with APTT (P = 0.002) between the ACL Futura and CA 510. In conclusion, these analyzers showed very poor agreement for both the PT and APTT, but the calculation of ratios significantly improved agreement.

Coagulant activity during one year after bioprosthetic aortic valve replacement

Anticoagulant therapy with warfarin is recommended in the early postoperative period after bioprosthetic aortic valve replacement (bAVR). However, some studies have addressed questions about its necessity. We evaluated postoperative coagulant activity data including prothrombin time-international normalized ratio (PT-INR) and thrombin-antithrombin III complex (TAT), measured every month in 21 bAVR patients during the 1st postoperative year. The results were divided into four time intervals after the operation: 1-3 months (P-1), 4-6 (P-2), 7-9 (P-3), and 10-12 (P-4). Warfarin, which was administrated in the first six months, in combination with aspirin, 100 mg, was started targeting PT-INR of 1.75-2.25. The values of TAT in P-1, P-2, P-3 and P-4 were 1.35+/-1.07 (ng/ml), 0.82+/-0.55, 0.81+/-0.78, and 0.72+/-0.62, respectively, showing significantly high values in P-1. Furthermore, the TAT values of P-1 and P-2 within the range of PT-INR from 1.75 to 2.25 were 1.15+/-0.71 (ng/ml) and 0.79+/-0.52; demonstrating statistical difference between them. The coagulant activity assessments suggest that warfarin administration during the first three months is necessary for bAVR patients to keep the TAT within the normal range.

Influence of taranabant, a cannabinoid-1 receptor inverse agonist, on pharmacokinetics and pharmacodynamics of warfarin

The pharmacokinetic/pharmacodynamic effects of warfarin were assessed in the presence and absence of taranabant, an orally active, highly selective, potent, cannabinoid-1 receptor inverse agonist, which was being developed for the treatment of obesity. Twelve subjects were assigned to two open-label treatments in fixed sequence separated by a 14-day washout. Treatment A was single-dose warfarin 30 mg on day 1. Treatment B was multiple-dose taranabant 6 mg each day for 21 days (days -14 to day 7) with coadministration of singledose warfarin 30 mg on day 1. Blood samples were collected predose and up to 168 hours postdose for assay of R(+)-and S(-)-warfarin and prothrombin time/international normalized ratio (PT/INR). The geometric mean ratios (GMR; warfarin+taranabant/warfarin 90% confidence interval [CI] primary endpoints) for area under the curve (AUC)(0-infinity) for R(+)-and S(-)-warfarin were 1.10 (90% CI: 1.03, 1.18) and 1.06 (90% CI: 1.00, 1.13), respectively. The GMRs (warfarin+taranabant/warfarin) for the maximum plasma concentration (C(max)) of S(-)-and R(+)-warfarin were 1.16 (90% CI: 1.05, 1.28) and 1.17 (90% CI: 1.07, 1.29), respectively. For R(+)-and S(-)-warfarin, the 90% CIs for AUC(0-infinity) GMRs fell within the prespecified bounds. Taranabant did not produce a clinically meaningful effect on PT/INR. No clinically significant alterations of the pharmacokinetics of R(+)-and S(-)-warfarin were seen following coadministration of multipledose taranabant 6 mg and single-dose warfarin 30 mg.

Entecavir Therapy in a Hepatitis B-Related Decompensated Cirrhotic Patient

A 58-year-old Arab-American male with HBeAg-negative chronic hepatitis B (HBV), presented with decompensated cirrhosis and a high HBV DNA level. He responded to entecavir with a significant reduction in serum HBV DNA level after 15 weeks of therapy with entecavir. However, he developed a progressive rise in prothrombin time/international normalized ratio (PT/INR) and bilirubin and underwent liver transplantation after receiving 22 weeks of entecavir therapy. Furthermore, with the continued use of combination entecavir and hepatitis B immunoglobulins (HBIG), he showed improvement in his clinical status with a nondetectable serum HBV DNA level 12 weeks after transplantation. He continued to maintain nondetectable serum HBV DNA 2 years following transplantation. To the best of our knowledge, this is the first reported case of a patient with decompensated chronic HBV who responded to entecavir both before and after transplantation without showing any evidence of recurrent HBV. Larger clinical trials are recommended to compare both short-term and long-term efficacy using entecavir among nucleoside-naïve decompensated chronic HBV patients before and after liver transplantation.

Graft size, donor age, and patient status are the indicators of early graft function after living donor liver transplantation

No reliable model for predicting early graft function and patient survival after living donor liver transplantation (LDLT) exists. The aim of this study was to establish a new formula for predicting early graft function and prognosis using technetium-99m galactosyl-human serum albumin (Tc-GSA) liver scintigraphy. The ratio of the hepatic uptake ratio of Tc-GSA to the clearance index of Tc-GSA (LHL/HH) was determined 7 days after LDLT. There were 22 patients with a ratio greater than 1.3 and 6 patients with a ratio less than 1.3. Graft function on the 14th postoperative day (POD) was compared between the 2 groups. A new formula to predict the LHL/HH score was established as follows: LHL/HH (predictive score) = 0.011 x graft weight (%) - 0.016 x donor age - 0.008 x Model for End-Stage Liver Disease score - 0.15 x shunt (if present) + 1.757 (r(2) = 0.497, P < 0.01). This predicted LHL/HH ratio was compared to the graft function on POD 14 for 110 LDLT patients. The total bilirubin (TB) and prothrombin time international normalized ratio (PT-INR) in the group with an LHL/HH score > or = 1.3 were lower than those in the group with an LHL/HH score < 1.3. The TB, PT-INR, and volume of ascites in the group with a predictive score > or = 1.3 (n = 86) were lower than those in the group with a score < 1.3 (n = 24). The 6-month survival probability was improved in the group with a predictive score > or = 1.3. In conclusion, this preoperative calculated LHL/HH score is correlated with graft function and short-term prognosis. Thus, this predictive model may allow transplant surgeons to use a living donor left lobe graft with greater confidence.

Severe Plasmodium falciparum malaria with peripheral gangrene

infection and intravenous quinine therapy was initiated (20 mg salt per kg loading dose infused over 4 h then 10 mg/kg infused over 2–8 h three times a day, total dose 12 g). When the patient was referred to our hospital, he already had multi-organ failure: cerebral malaria, acute renal failure, respiratory failure, diff use intravascular coagulation with thrombocytopenia, and metabolic acidosis were noted. On day 3, acral discolourations of his toes (fi gure) were observed. Low fi brinogen concentration (120 mg/dL; normal 180–350 mg/dL), elevated D-dimers (3000 μg/L; normal <500 μg/L), prolonged prothrombin time (international normalised ratio value 1·3), and a persistently low platelet count (5–15×10³) suggested disseminated intravascular coagulation. Simultaneously, the patient received hydrocortisone (200 mg per day, perfusion pump) and high-dose catecholamines (norepinephrine 1 mg/h and phenylephrine 10 mg/h and fl uid) for hypovolemic shock. After a 7-day course of quinine followed by mefl oquine the patient was extubated and fully recovered from malarial disease. The tips of all toes remained gangrenous and were amputated 2 months later. Peripheral gangrene is a well described complication of severe

The international normalized ratio to prioritize patients for liver transplantation: problems and possible solutions.

The prothrombin time (PT) test once designed by Dr Quick to investigate patients with obstructive jaundice was later adapted and standardized by means of the international normalized ratio (INR) to monitor patients on treatment with vitamin K antagonists (VKA). After more than 70 years from its introduction it is now time to think about its standardization for those very patients for whom it was intended at the beginning of its history. Two studies carried out independently and published recently in the same issue of a specialized journal do exploit the very same idea on how to accomplish this standardization. Both of them confirm previous anecdotal observations that the INR as devised for patients on VKA (INR(vka)) is not valid to harmonize PT results for patients with chronic liver disease. This fact, that at first sight may appear academic, has important consequences because the PT INR is used to construct the model for end-stage liver disease (MELD) scores, which is widely used to prioritize patients for liver transplantation. The two studies further demonstrate that an alternative calibration model, modified from that recommended by the World Health Organization for patients on VKA, may be feasible also for patients with chronic liver disease. This alternative calibration model, which calls for the substitution of plasmas from patients on VKA with those from patients with chronic liver disease, may be highly beneficial to harmonize the calculation of the MELD score, with important implications for the prioritization of patients for liver transplantation.

The international normalized ratio to prioritize patients for liver transplantation: problems and possible solutions

The prothrombin time (PT) test once designed by Dr Quick to investigate patients with obstructive jaundice was later adapted and standardized by means of the international normalized ratio (INR) to monitor patients on treatment with vitamin K antagonists (VKA). After more than 70 years from its introduction it is now time to think about its standardization for those very patients for whom it was intended at the beginning of its history. Two studies carried out independently and published recently in the same issue of a specialized journal do exploit the very same idea on how to accomplish this standardization. Both of them confirm previous anecdotal observations that the INR as devised for patients on VKA (INR(vka)) is not valid to harmonize PT results for patients with chronic liver disease. This fact, that at first sight may appear academic, has important consequences because the PT INR is used to construct the model for end-stage liver disease (MELD) scores, which is widely used to prioritize patients for liver transplantation. The two studies further demonstrate that an alternative calibration model, modified from that recommended by the World Health Organization for patients on VKA, may be feasible also for patients with chronic liver disease. This alternative calibration model, which calls for the substitution of plasmas from patients on VKA with those from patients with chronic liver disease, may be highly beneficial to harmonize the calculation of the MELD score, with important implications for the prioritization of patients for liver transplantation.

ワーファリン内服中に発症した頭蓋内出血性病変への対応

Patients receiving anticoagulants occasionally suffer from intracranial hemorrhage. Initially, it is important to control the coagulation time for such patients, because of the possible need for emergency surgery. Previously, vitamin K and FFP (fresh frozen plasma) were administered to such patients; however, it took 3 to 6 hours to normalize the PT-INR (Prothrombin Time, International Normalized Ratio), and thus the bleeding could increase and the patients’ condition might then become critical. To correct the coagulation time quickly and evacuate the hematoma as soon as possible, ninth factor complex (PPSB-HT) was administered to 5 patients who had taken Warfarin and suffered from intracranial hemorrhage. In all patients, the PT-INR quickly normalized within 10 to 20 minutes, and they were thereafter successfully treated surgically. The administration of PPSB-HT is critical to correct the coagulation time in patients taking Warfarin and requiring emergency surgery.

Oral surgery in patients on oral anticoagulant therapy: a randomized comparison of different intensity targets

To evaluate whether or not it is possible to perform oral surgery in patients on oral anticoagulant therapy (OAT) without stopping treatment. A prospective randomized open-label study was designed to evaluate the outcome of oral surgery in patients on OAT, operated upon in conditions of reduced international normalized ratio (INR), compared with patients maintained in their usual therapeutic ranges of the prothrombin time INR. The INR target in the group with reduced OAT was 1.8, and the INR target of the group without reduced OAT was 2.5 or more in carriers of artificial valves. One hundred thirty-one patients on OAT were randomized to reduced anticoagulation or to full anticoagulation, and 511 teeth were extracted by the same surgeon. Mild bleeding, but excessive enough to warrant adoption of supplementary local hemostatic measures, was observed in 10 cases (15.1%) in the reduced dosage group and in 6 cases (9.2%) in the unmodified dosage group, which was a nonsignificant difference. There were no thrombotic complications in either group. This randomized study shows that, using simple measures for local hemostasis, it is not necessary to reduce OAT in patients undergoing routine dental extractions.

Incidence of Major Bleeding Complication of Warfarin Therapy in Japanese Patients With Atrial Fibrillation

During anticoagulation for prevention of stroke in patients with non-valvular atrial fibrillation (NVAF), bleeding is the most serious complication. In Western countries, the incidences of major bleeding and intracranial hemorrhages with low-dose warfarin are known to occur at a rate of 0.4-1.3% and 0.2% per year, respectively. The purpose of this study was to investigate the incidence and risk factors for major bleeding related with warfarin therapy in Japanese patients with NVAF. From August 2004 to July 2005, 667 NVAF patients treated with warfarin for NVAF were followed-up. The target prothrombin time-international normalized ratio (PT-INR) value was set at 1.6-2.6 (low-dose warfarin). The exposure on warfarin was 503 patient-years (average PT-INR 2.00 +/-0.40). During the follow-up period, 12 major bleeding complications occurred (2.38% per patient-year), which included 3 intracranial hemorrhages (0.60% per patient-year). Among the patients' characteristics, average PT-INR > or =2.27 during the study was identified as an independent risk factor for major bleeding. The incidence of major bleeding and intracranial hemorrhages in Japanese NVAF patients with low-dose warfarin therapy was 2.38% and 0.60% per patient-year, respectively, which is higher than in Westerners.

Drug-Induced Liver Injury

Drug-induced liver injury is a frequent cause of hepatic dysfunction. Reliably establishing whether the liver disease was caused by a drug requires the exclusion of other plausible causes and the search for a clinical drug signature. The drug signature consists of the pattern of liver test abnormality, the duration of latency to symptomatic presentation, the presence or absence of immune-mediated hypersensitivity and the response to drug withdrawal. Determination of causality also includes an evaluation of individual susceptibility to drug-induced liver injury. This susceptibility is governed by both genetic and environmental factors. Components of the drug signature in conjunction with certain risk factors have been incorporated into formal scoring systems that are predictive of the likelihood of drug-induced liver injury. The most validated scoring system is the Roussel-Uclaf causality assessment method, which nonetheless retains certain imperfections. Mitigating the potential for drug-induced liver injury is achieved by the identification of toxicity signals during clinical trials and the monitoring of liver tests in clinical practice. There are three signals of liver toxicity in clinical trials: (i) a statistically significant doubling (or more) in the incidence of serum alanine aminotransferase (ALT) elevation >3 x the upper limit of normal (ULN); (ii) any incidence of serum ALT elevation >8-10 x ULN; and (iii) any incidence of serum ALT elevation >3 x ULN accompanied by a serum bilirubin elevation >2 x ULN. Monitoring of liver tests in clinical practice has shown unconvincing efficacy, but where a benefit-risk analysis would favour continued therapy, monthly monitoring may have some benefit compared with no monitoring at all. With rare exception, treatment of drug-induced liver injury is principally supportive. Drug toxicity is the most common cause of acute liver failure, defined as a prolonged prothrombin time (international normalised ratio > or =1.5) and any degree of mental alteration occurring <26 weeks after the onset of illness in a patient without pre-existing cirrhosis. A patient who meets these criteria must be evaluated for liver transplantation. The pathogenesis of drug-induced liver injury can be examined on the basis of the two principal patterns of injury. The hepatocellular pattern is characterised by a predominant rise in the level of transaminases and results from the demise of hepatocytes by means of either apoptosis or necrosis. The cholestatic pattern is characterised by a predominant rise of the serum alkaline phosphatase level and usually results from injury to the bile ductular cells either directly by the drug or its metabolite, or indirectly by an adaptive immune response.

PT and INR Interference by the Antibiotic Daptomycin in Commercial Thromboplastin Reagents: Dependence on Phospholipid Composition.

The antibiotic, daptomycin (brand name Cubicin, Cubist Pharmaceuticals) is approved in the US for treatment of complicated skin and skin structure infections caused by gram-positive pathogens (e.g., MRSA, methicillin-resistant Staphylococcus aureus). Recently, this antibiotic has been shown to interfere with prothrombin time (PT) assays, resulting in a prolongation of clotting times and artificial increases in the INR (International Normalized Ratio). The level of interference varies with Daptomycin concentration in the plasma, the brand of prothrombin time reagent as well as the type (normal or abnormal) of patient sample being analyzed. The bactericidal action of the antibiotic is known and is through a depolarization of bacterial membranes in the presence of physiologic calcium (Silverman, et al, Antimicrobial Agents and Chemotherapy, Aug 2003); therefore, daptomycin interference with the PT clotting assay is likely mediated through the phospholipid component of the thromboplastin formulations. To examine the dependence of daptomycin interference for a number of commercial PT formulations, testing was performed with daptomycin spiked samples of normal pooled plasma as well as abnormal samples from oral anticoagulant therapy (OAT) patients. For spiked normal samples, a small degree of prolongation in clotting times was observed with most PT reagents, with one reagent showing a significant prolongation. In OAT samples spiked with Daptomycin, the PT prolongation was greater for all formulations, with the one reagent again showing greater prolongation as for the normals. Ultimately, this variation in response was attributed to differences in phospholipid composition among the reagents, supported by previous studies of daptomycin with neutral and acidic phospholipids in the presence of calcium (D. Jung, et al., Chemistry and Biology, Jul 2004). A four-dimensional experimental design matrix was constructed using a mixture of four synthetic phospholipids (DOPC, DOPS, DOPE and DOPG), and the relationship of daptomycin-PT interference to percent composition of the phospholipids was examined. In both normal and OAT plasmas spiked with daptomycin, the major contributor to PT prolongation was the concentration of DOPG (phosphatidylglycerol) in the lipid mixture, with additional contributions correlated with DOPC (phosphatidylcholine). Because of the ubiquitous use of these phospholipids in commercial PT formulations, this work suggests that daptomycin interference should be assessed for each combination of PT reagent and INR range used.

Influence of warfarin therapy on activated factor VII clotting activity

Oral anticoagulant therapy has been widely employed to prevent and treat a variety of thrombotic disorders, although a new generation of antithrombotic drugs, which offer inhibition of clot-bound as well as fluid-phase thrombin, has been developed and tested in several clinical trials. Although most anticoagulant responses to hydroxycoumarin compounds are well established, there are controversial evidences on their influence on activated factor VII (FVIIa). After analyzing the prothrombin time (PT) (International Normalized Ratio reference range, 0.92-1.08), factor VII clotting activity (FVII:C) (reference range, 75-130 U/dl) and activated factor VII clotting activity (FVIIa:C) (reference range, 30-110 U/l) in 46 consecutive patients on stable warfarin therapy for atrial fibrillation, a consistent trend towards decreased values of both FVII:C and FVIIa:C was observed as PT values increased. At moderate-intensity anticoagulation, with international normalized ratios between 2 and 3, the mean activities of FVII:C and FVIIa:C dropped to 28 U/dl (range, 9-61 U/dl) and 5.8 U/l (range, 1-18 U/l), respectively. Results of our investigations indicate that warfarin therapy decreases FVIIa:C, highlighting the potential benefits of oral anticoagulants in thrombotic disorders and other clinical conditions characterized by increased levels of FVIIa. Owing to the good correlation with FVIIa:C, we also hypothesize that the PT and/or FVII:C might be employed for monitoring recombinant FVIIa therapy.