Background and Purpose-Elevated von Willebrand factor (vWF) concentrations are associated with an increased risk of ischemic heart disease. Several factors influence vWF antigen levels and activity, including blood group, genetic variability, acute-phase response, and proteolysis by A Disintegrin and Metalloprotease with ThromboSpondin motif (ADAMTS13), a determinant of proteolytic cleavage of vWF. We assessed how these factors affect the relation between vWF and the occurrence of stroke to understand the underlying mechanism. Methods-In a case-control study of 124 first-ever ischemic stroke patients and 125 age-and sex-matched controls, we studied vWF antigen (vWF:Ag), vWF ristocetin cofactor activity (vWF:RCo), ADAMTS13 activity, the Ϫ1793C/G polymorphism in the vWF gene, and C-reactive protein. Results-vWF antigen and activity levels were significantly higher in cases than in controls. The relative risk of ischemic stroke was highest in individuals in the upper quartile of vWF:Ag (odds ratio, 3.2; 95% CI, 1.4 to 7.5) and vWF:RCo (odds ratio, 2.1; 95% CI, 0.9 to 4.8) compared with individuals in the lowest quartiles. In individuals with ADAMTS13 in the lowest quartile, the relative risk of stroke was 1.7 (95% CI, 0.7 to 3.9) compared with the highest quartile. C-reactive protein, ADAMTS13, and genetic variation did not affect the association between vWF and the relative risk of stroke, whereas blood group did affect the association. Conclusions-vWF antigen and activity are associated with the occurrence of acute ischemic stroke. This relation is unaffected by the severity of the acute-phase response or by genetic variation or degradation.

Summary. Background and objective: Several studies have suggested that thrombin-activatable fibrinolysis inhibitor (TAFI) levels are associated with the risk of arterial thrombosis, but results have been contradictory. We studied functional TAFI levels and TAFI gene polymorphisms in 124 patients with a recent ischemic stroke and 125 age-and sex-matched controls to establish the role of TAFI in ischemic stroke. Methods and results: Functional TAFI levels, defined as TAFI-related retardation (RT), the difference in clot lysis time (LT) in the absence or presence of a specific activated TAFI inhibitor (potato carboxypeptidase inhibitor [PCI]), were higher in patients than controls (19.5 ± 4.2 vs. 17.7 ± 3.7 min, P < 0.005). Clot LTs in the presence of PCI, which were independent of TAFI, were also increased in ischemic stroke patients. This indicates that in these patients fibrinolysis is impaired not only by high TAFI levels, but also by other mechanisms. Individuals with functional TAFI levels in the highest quartile had an increased risk of ischemic stroke compared with the lowest quartile [odds ratio (OR) 4.0, 95% confidence interval (CI): 1.6-9.8]. In an unselected group of 36 of the 125 stroke patients functional TAFI levels were also measured at 3 months, and were persistently high. This indicates that increased functional TAFI levels after stroke are not caused by an acute phase reaction. No difference was found between patients and controls with respect to TAFI genotype distribution. Conclusions: Increased functional TAFI levels, resulting in decreased fibrinolysis, are associated with an increased risk of ischemic stroke.

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Synergism between two antibiotics is usually tested by a checkerboard titration technique, or by time-kill methods. Both methods have the disadvantage that synergism is determined at constant concentrations of the antibiotics, which do not reflect reality in vivo. In the present study we determined whether synergism between tobramycin and ceftazidime can be found at declining concentrations below the MIC, and whether change in dosing sequence of the antibiotics would result in differences in killing. Three monotherapy and six combination therapy schedules were tested in an in vitro pharmacokinetic model, using a Pseudomonas aeruginosa resistant to both antibiotics. During all q8h dosing schedules the peak concentration (Cmax) was adjusted to the MIC for the strain of both antibiotics. During all monotherapy regimens bacterial growth was present, while all six combination therapy schedules showed significant killing. At t = 24 h there were no differences between all combination therapy schedules, but at t = 8 h the two combination therapy schedules with administration of tobramycin once daily showed a significantly faster killing. By using the area under the killing curve (AUKC) as a parameter for synergistic killing, simultaneous combination therapy starting with tobramycin once daily was significantly better than all other regimens. We conclude that there is synergism between tobramycin and ceftazidime at declining antibiotic concentrations below the MIC, resulting in a pronounced killing of a resistant Pseudomonas strain. Infections due to resistant Pseudomonas strains could possibly be treated by a synergistic combination of these drugs.

Background: To determine whether 2148 C/T fibrinogen gene promoter polymorphism increases stroke risk by modifying the fibrinogen level. Design: A case-control study of patients with first ever ischaemic stroke, confirmed by computed tomography. Methods: Venous blood samples were collected for fibrinogen and routine coagulation tests one week after the stroke, and after three months in about half the patients. Population controls were age and sex matched. 2148 C/T fibrinogen polymorphism was determined by polymerase chain reaction followed by digestion with restriction enzymes HindIII/AluI. Results: There were 124 patients and 125 controls, mean age 56 years (range 18 to 75); 34 patients (27%) and 41 controls (33%) were heterozygous for 2148 C/T fibrinogen polymorphism; six patients (5%) and five controls (4%) had the T/T genotype. The odds ratio of ischaemic stroke associated with CC homozygotes v T carriers was 0.8 (95% confidence interval, 0.5 to 1.4). Relative risk for ischaemic stroke associated with fibrinogen levels in the highest quartile was 3.9 (1.9 to 8.4) at one week, decreasing to 1.4 (0.6 to 3.3) at three months. Conclusions: 2148 C/T fibrinogen gene polymorphism was not a strong risk factor for ischaemic stroke. High fibrinogen levels early after acute stroke probably represent an acute phase response.

In spite of our small number of outcome events we found a significant association at the 95% confidence level between homocysteine level and the risk of recurrent vascular events in young patients with an ischaemic stroke or TIA. The association is of the same magnitude as in elderly people.

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The kinetics of the postantibiotic effect (PAE) during one dosing interval of tobramycin against Staphylococcus aureus and Pseudomonas aeruginosa was investigated. We determined the PAE at different time points during this dosing interval of 12 h in an in vitro pharmacokinetic model simulating human pharmacokinetics in which the half-life of tobramycin was adjusted to 2.4 +/- 0.2 h. Using an enzymatic method to inactivate tobramycin, we determined PAEs in samples extracted from the model at 1, 5, 8, and 12 h, corresponding with tobramycin concentrations of 20, 5, 2, and 1 times the MIC for the test organism. The PAE decreased significantly from 2.5 h at 1 h to 0 h at 12 h. No change in MIC was observed for the strains during the experiments. We conclude that the PAE decreases with decreasing tobramycin concentrations during a 12-h dosing interval and completely disappears after the concentration has reached the MIC for the test organism. On the basis of these observations, the emphasis that is placed on the PAE in discussions about the optimal dosing interval in aminoglycoside therapy is questionable.