抗血小板药物治疗的实验室检测

基于一级和二级预防实验结果,当前国内外的缺血性心脑血管疾病防治指南均推荐应用抗血小板药物（Ⅰ级证据）。但值得注意的是约一半患者对抗血小板药物存在＂抵抗＂或＂无效＂的认识,针对上述患者的临床发现存在滞后性。本文重点讨论一些当前国内外用于抗血小板药物（阿司匹林和氯吡格雷）疗效评价实验室方法的优缺点。一些方法已应用于基础和临床研究且有证据支持可预测抗血小板药物的疗效。但至今尚无任何一项研究是通过上述实验室方法检测抗血小板药物来说明改变治疗的临床转归。因此未来的发展应是寻找更加有药物特异性和非特异性的实验室方法,并探讨这些实验室指标与药物临床效果的量化联系。     

Effective antiplatelet drug concentrations in experimental arterial thromboembolism

Although drugs that modify platelet function have been widely studied as antithrombotic agents in experimental and clinical studies, there is limited information regarding the relationship between in vivo drug blood concentrations and antithrombotic efficacy. This study compared the pharmacokinetics of three antiplatelet agents with their antithrombotic effects in an experimental model of arterial thromboembolism in baboons. Thrombus formation was measured as steady-state platelet utilization induced by thrombogenic arteriovenous cannulae. The drugs studied were aspirin, dipyridamole and sulfinpyrazone. Aspirin was administered in daily doses of 20 mg/kg, dipyridamole in daily doses of 2.5 and 10 mg/kg, and sulfinpyrazone in daily doses of 20 and 100 mg/kg; each drug was given in two equal doses per day. Multiple blood samples were collected for drug analysis after steady-state had been reached. The average concentrations of dipyridamole at steady-state were 26 +/- 15 and 79 +/- 69 ng/ml after 2.5 and 10 mg/kg/day. These concentrations were associated with 28 and 87% inhibition of cannula platelet consumption, respectively. The average steady-state concentrations of acetylsalicylic and salicylic acids were 0.67 +/- 0.80 and 3.76 +/- 2.60 micrograms/ml, respectively, after 20 mg/kg/day. Aspirin had no effect on platelet consumption. Average concentrations of sulfinpyrazone were 1.05 +/- 0.45 and 12.25 +/- 5.73 micrograms/ml after 20 and 100 mg/kg/day, with significant concentrations of the sulfide metabolite. These concentrations were associated with 23 and 85% inhibition of platelet consumption, respectively. No significant pharmacokinetic interactions were observed after concurrent administration of aspirin and dipyridamole or sulfinpyrazone. As the experimental model used involves thrombus formation on an artificial surface, it is likely that these results are most relevant to patients with arterial prosthetic devices.     

Ticlopidine - An antiplatelet drug: Effects in human volunteers

Ticlopidine, 500–1000mg daily, was given to 7 healthy volunteers for 5 to 6 days. By the 5th day the bleeding time was significantly prolonged, on average from 3.9 to 11 min and primary aggregation of platelets induced by ADP as well as collagen-induced aggregation were significantly decreased; that induced by thrombin and serotonin was decreased at least in some individuals. Maximal stimulation of platelets in plasma by thrombin caused a two-fold increase in malondialdehyde production and the Stypven clotting time was significantly prolonged. The heparin thrombin clotting time may also have been prolonged. The degree of inhibition was dependent on the strength of the aggregating agent. After stopping the drug the effects persisted for 4 to 8 days. The response to the drug varied considerably between different individuals. It is postulated that this drug may alter the platelet membrane, thereby blocking a number of receptor sites and that its mechanism is independent of inhibition of prostaglandin metabolism.     

Dose- and time-dependent antiplatelet effects of aspirin

Aspirin is widely used, but dosages in different clinical situations and the possible importance of "aspirin resistance" are debated. We performed an open cross-over study comparing no treatment (baseline) with three aspirin dosage regimens--37.5 mg/day for 10 days, 320 mg/day for 7 days, and, finally, a single 640 mg dose (cumulative dose 960 mg)--in 15 healthy male volunteers. Platelet aggregability was assessed in whole blood (WB) and platelet rich plasma (PRP). The urinary excretions of stable thromboxane (TxM) and prostacyclin (PGI-M) metabolites, and bleeding time were also measured. Platelet COX inhibition was nearly complete already at 37.5 mg aspirin daily, as evidenced by >98% suppression of serum thromboxane B2 and almost abolished arachidonic acid (AA) induced aggregation in PRP 2-6 h after dosing. Bleeding time was similarly prolonged by all dosages of aspirin. Once daily dosing was associated with considerable recovery of AA induced platelet aggregation in WB after 24 hours, even after 960 mg aspirin. Collagen induced aggregation in WB with normal extracellular calcium levels (hirudin anticoagulated) was inhibited <40% at all dosages. TxM excretion was incompletely suppressed, and increased <24 hours after the cumulative 960 mg dose. Aspirin treatment reduced PGI-M already at the lowest dosage (by approximately 25%), but PGI-M excretion and platelet aggregability were not correlated. Antiplatelet effects of aspirin are limited in WB with normal calcium levels. Since recovery of COX-dependent platelet aggregation occurred within 24 hours, once daily dosing of aspirin might be insufficient in patients with increased platelet turnover.     

The antiplatelet aggregation effects of aspirin suppositories

To confirm that aspirin suppositories are an effective treatment for acute ischemic stroke, we examined the suppressive effects of 200-mg aspirin suppositories on platelet aggregation. Aspirin suppositories suppressed platelet aggregation induced by ADP or collagen, and the suppression continued for 24 h. There was no significant difference in suppression of platelet aggregation between aspirin administered by suppository and orally given aspirin. These results suggest that aspirin suppositories are a useful treatment for acute ischemic stroke.     

Differential antiplatelet effects of various glycoprotein IIb-IIIa antagonists

The blockade of platelet glycoprotein IIb-IIIa (GPIIb-IIIa) was recently introduced as a new antiplatelet strategy. At present, various GPIIb-IIIa inhibitors are available to treat patients with acute coronary syndrome or when undergoing percutaneous coronary interventions. The current study systematically evaluates the antiplatelet effects of GPIIb-IIIa inhibitors in clinical use. Using conformation-dependent monoclonal antibodies [ligand-induced binding sites (LIBS-1), PMI-1] and flow cytometry, we showed that the GPIIb-IIIa antagonists abciximab, integrelin, lamifiban, and tirofiban, but not EMD 122347 or YM 337, induced LIBS activity of platelet GPIIb-IIIa. The LIBS activity of GPIIb-IIIa antagonists correlates with a proaggregatory response of fixed platelets pretreated with GPIIb-IIIa antagonists (intrinsic activity). All tested GPIIb-IIIa antagonists completely inhibit concentration-dependent ADP (20 micromol/l)-induced aggregation. In contrast, substantial TRAP (25 micromol/l)-induced platelet aggregation still occurs even at high inhibitor concentrations of the tested GPIIb-IIIa antagonists. In addition, we show that GPIIb-IIIa antagonists are poor inhibitors of platelet release reaction (ATP and P-selectin secretion) especially when strong agonists such as TRAP are used to activate platelets. Inhibition of platelet procoagulant activity (thrombin generation) by GPIIb-IIIa antagonists is dependent on the type and concentration of antagonists and on the strength of stimulus (thrombin, tissue factor) used to induce platelet-dependent thrombin generation. The present data show that significant pharmacological differences exist between GPIIb-IIIa antagonists that may have consequences for antithrombotic strategies and for future drug development.     

Whole blood aggregometry for evaluation of the antiplatelet effects of clopidogrel

INTRODUCTION: The marked interindividual variability in platelet inhibition even after administration of high loading doses of clopidogrel raised the question whether monitoring of antiplatelet effects in patients undergoing percutaneous coronary intervention (PCI) can improve clinical outcome. Established methods for monitoring antiplatelet drug activity such as optical aggregometry and determination of surface protein expression are not suitable for routine bedside testing. MATERIAL AND METHODS: We therefore compared the applicability of whole blood impedance aggregometry (20 micromol/L ADP) and the whole blood bedside ULTEGRA assay with ADP-cartridges (20 micromol/L) with optical aggregometry in platelet-rich plasma and determination of surface protein expression (P-Selectin and activated GPIIb/IIIa) by flow cytometry. We analyzed samples obtained from 27 patients scheduled for elective PCI who received a loading dose of 600 mg of clopidogrel. Blood samples were withdrawn before clopidogrel, before PCI and 24h thereafter. RESULTS: Platelet aggregation assessed by optical aggregometry (20 micromol/L ADP) declined from 65+/-9% (baseline) to 42+/-12% (PCI) and 45+/-13% (24h; p<0.01). Expression of surface proteins displayed a similar time course. Platelet aggregation determined by impedance aggregometry decreased from 4.6+/-4.0 Omega (baseline) to 0.1+/-0.3 Omega (PCI) and 0.5+/-1.1 Omega (24h) with no detectable residual platelet aggregation during PCI in 88% of patients. The ULTEGRA assay showed only slight changes after administration of clopidogrel. Correlation analysis between the various assays revealed significant correlations only between optical aggregometry and flow cytometry. CONCLUSIONS: The results indicate that both of the whole blood assays cannot substitute for optical aggregometry or determination of surface proteins in the assessment of clopidogrel-induced platelet inhibition.     

Thromboxane receptor blockade versus cyclooxigenase inhibition: antiplatelet effects in patients

In a randomized pilot study we compared the antiplatelet effects of aspirin and BM 13.177 in two groups of 7 patients each undergoing PTCA. As compared with the pretreatment values template bleeding time was prolonged and collagen induced aggregation was inhibited in PRP and WB in all patients. In the course of angiography and PTCA a rise in platelet factor 4 and beta thromboglobulin was observed in both groups, followed by a decrease below the baseline levels. Thromboxane B2 in plasma and serum decreased in the aspirin group but remained unchanged during BM 13.177 treatment. In PRP and WB aggregation induced by U 46 619 was inhibited after ingestion of BM 13.177 but not following ASA. After three months a control coronary angiography was done. There was no difference in regard to the degree of restenosis between both groups. Medication was well tolerated, compliance was good and no side effects were noted.     

Effects of BM 13.177, a new antiplatelet drug in patients with atherosclerotic disease

Seven males with atherosclerotic disease received daily 1.6 g of the thromboxane antagonist BM 13.177 in two separate oral dosages over a period of four days. The drug significantly reduced elevated plasma levels of thromboxane B2, beta-thromboglobulin and platelet factor 4, whereas thromboxane B2 generation was only slightly depressed. BM 13.177 inhibited platelet aggregation by collagen, and to a minor degree the second wave of ADP induced aggregation. Platelet sensitivity to prostacyclin and aggregation by ristocetin were not altered. Bleeding time was prolonged. All effects disappeared within 24 hours after the last application of the drug. No side effects were noted. Thus BM 13.177 appears to be a safe and effective new antiplatelet drug.     

Lack of antiapoptotic effects of antiplatelet drug, aspirin and clopidogrel, and antioxidant, MCI-186, against focal ischemic brain damage in rats

OBJECTIVES: This study evaluated the antiapoptotic effect of antiplatelet drugs, aspirin and clopidogrel, and the antioxidant drug, MCI-186, against focal cerebral ischemic rat brain damage. METHODS: Cerebral ischemia was mechanically induced by 2-hour occlusion of the left middle cerebral artery (MCA) using an intraluminal filament followed by 24-hour reperfusion. RESULTS: The cerebral infarct size was little affected by oral administration of 300 mg/kg aspirin, 30 mg/kg clopidogrel or 100 mg/kg MCI-186, but was significantly reduced by 30 mg/kg cilostazol. However, intravenous administration of 10 mg/kg MCI-186 suppressed the infarct size. DNA fragmentation observed in the cortical tissues corresponding to the penumbral zone was not suppressed by aspirin, clopidogrel or MCI-186, but was significantly suppressed by cilostazol. Increased phosphorylation of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) and Bax protein, and decreased Akt/cyclic AMP response element binding protein (CREB) phosphorylation, including Bcl-2 protein in the vehicle-treated group were not affected by treatment with aspirin, clopidogrel and MCI-186, whereas those effects were reversed by cilostazol. CONCLUSION: Thus, it is suggested that antiplatelet drugs, aspirin and clopidogrel, and antioxidant drug, MCI-186, showed little antiapoptotic effect in contrast to cilostazol.     

急性脑梗死溶栓出血性转化后抗血小板药物选择

目的 探讨急性脑梗死静脉溶栓后发生无症状性出血性转化(HT)后应用阿司匹林的剂量.方法 收集符合条件的患者60例,随机分为应用阿司匹林组(治疗组)和未应用阿司匹林组(对照组)各30例.对照两种治疗方案引起继续出血增加的风险及再梗死的风险.结果 治疗组溶栓后未引起无症状性HT患者出血量的增加,且可减少再梗死的比率.结论 急性脑梗死静脉溶栓后发生无症状性HT后应用小剂量阿司匹林较为安全,不引起出血量增加,减少再梗死发生率,未增加病死率,可改善患者预后.     

Measuring the effects of antiepileptic medications on balance in older people

BACKGROUND: Dizziness and ataxia are among the most common adverse events associated with antiepileptic medications. Despite this, few studies have attempted to quantitatively assess the effects of antiepileptic therapies on equilibrium. This study was undertaken to prospectively compare quantitative measures of balance in older people taking carbamazepine, gabapentin and lamotrigine. METHODS: Thirty patients on monotherapy for idiopathic partial or generalized epilepsy were enrolled after giving informed consent. Patients had to be at least 50 years old, able to give consent, and on a stable dose of carbamazepine, gabapentin or lamotrigine for at least 30 days. Since this was a study of asymptomatic patients, all patients had to be without complaint of dizziness or imbalance. Patients with a history of alcohol or drug abuse or any medical or neurological condition expected to adversely affect equilibrium were excluded. Each patient underwent a history and examination, computerized dynamic posturography, the activities-specific balance confidence (ABC) scale, Fregly ataxia battery, and the Berg balance scale. Serum drug levels of carbamazepine were obtained to eliminate patients with toxic levels upon enrollment. Two-tailed paired t-tests were used to determined statistical significance among those on each antiepileptic medication. RESULTS: Thirty patients were enrolled: 10 on gabapentin, 10 on lamotrigine and 10 on carbamazepine monotherapy for epilepsy. There were no differences in age or sex among those in each treatment group. The average dosages were 1,120 mg/day for those on gabapentin, 335 mg for lamotrigine, and 640 mg for carbamazepine. There were no differences in the activities-specific balance confidence (ABC) or the Berg balance scale scores. All patients had normal vestibular function by quantitative testing. Posturography showed no statistically significant differences. The Fregly ataxia battery includes the sum of timed trials in the sharpened Romberg (SR) position, standing on one leg with eyes closed (SOLEC), and when walking in tandem with eyes closed (WITEC). The patients on lamotrigine exhibited ability to maintain balance in these positions significantly longer than did those on carbamazepine: SR (P<0.05), SOLEC (P<0.05) and WITEC (P<0.05). CONCLUSIONS: The effects of antiepileptic medications on equilibrium in asymptomatic older people may require more dynamic and challenging measures of equilibrium than are commonly employed in physical therapy to monitor risk of falls. Although the sample size is small, this study suggests that lamotrigine may induce less disequilibrium than does carbamazepine in older people on monotherapy for epilepsy. Further study in this area is needed, particularly given the risks of falling from imbalance in the elderly.     

Measuring drug occupancy in the absence of a reference region: the Lassen plot re-visited

Quantitative estimation of neuroreceptor occupancy by exogenous drugs using positron emission tomography is based on the reduction in the total volume of distribution (V_T) of site-specific radioligands after drug administration. An estimate of the distribution volume of free and nonspecifically bound radioligand (V_ND) is also required to distinguish specific from total binding. However, a true reference region, devoid of specific binding, is often not available. We present a transformation of a graphical method, originally introduced by Lassen, using regional estimates of V_T alone to determine occupancy, together with an extension that does not require baseline data.     

Organic nitrates: direct antiplatelet effects and synergism with prostacyclin. Antiplatelet effects of organic nitrates

Isosorbide dinitrate inhibits platelet function in vivo at concentrations about 10 times lower than in vitro (10(-7)-10(-6) vs. 10(-6)-10(-5) M). We investigated two possible reasons for this difference. Isosorbide dinitrate and its in vivo longer-lived metabolites, isosorbide-2- and isosorbide-5-mononitrate were incubated for 5 min with human platelet-rich plasma or washed platelets; irreversible aggregation was induced with threshold doses of ADP, adrenaline, collagen, arachidonic acid and thrombin, and thromboxane (TX) B2 production was measured by radioimmunoassay. Moreover, the concentration of exogenous prostacyclin required to inhibit platelet aggregation by 50% (IC50) after preincubation with isosorbide dinitrate or vehicle was determined. At 10(-7) M, only isosorbide-2-mononitrate inhibited aggregation (-12%, p less than 0.05) and TX production (-36%, p less than 0.01) by ADP. At 10(-6) M isosorbide-2-mononitrate inhibited aggregation by adrenaline more than the dinitrate (-41% vs. -25%, p less than 0.05). In addition, at supra-threshold doses of all the aggregating agents, isosorbide dinitrate decreased IC50 of prostacyclin from 2.7 +/- 1.2 to 0.36 +/- 0.2 nM. Generation of a platelet-active metabolite and synergism with prostacyclin are new properties of isosorbide dinitrate that may account for antiplatelet effects in vivo.     

Measuring the effects of failure with learning disabled children

The effects of failure on performance for children diagnosed as learning disabled (reading) and normal children were compared with a simple clinical measure. As hypothesized, learning disabled children stressed with failure scored significantly (p less than .05) poorer than stressed normals on a reading posttest. Learning disabled children were seen to have developed a learned helplessness response mode and experienced greater difficulty in recovering from failure than normal cohorts. The results were interpreted as lending support to the use of a clinical measure in assessing the role played by failure in children's learning disorders.