Therapeutic benefit of low-dose clopidogrel in patients undergoing carotid surgery is linked to variability in the platelet adenosine diphosphate response and patients' weight

Unfractionated heparin reverses aspirin inhibition of platelets during coronary artery bypass graft surgery

Unfractionated heparin (UFH) is an effective antithrombotic during surgery but has known adverse effects, in particular on platelets. A marked increase in platelet responsiveness has previously been observed in patients within minutes of receiving UFH, despite adequate inhibition by aspirin prior to heparin. We studied this phenomenon in patients undergoing cardiac artery bypass grafting (n = 17) to determine whether the effects of heparin were systemic or platelet-specific. All patients' platelets were fully inhibited by aspirin prior to surgery, but within 3 min of receiving heparin spontaneous aggregation and responses to arachidonic acid (AA) and ADP increased significantly (p ≥ 0.0002), and activated platelets were found in the circulation. While there was no rise in thromboxane in the plasma following heparin, levels of the major platelet 12-lipoxygenase product, 12-HETE, rose significantly. Mixing experiments demonstrated that the changes caused by heparin resided primarily in the platelets, while addition of AA pathway inhibitors, and analysis of oxylipins provided evidence that, following heparin, aggregating platelets regained their ability to synthesise thromboxane. These findings highlight potentially unrecognised pro-thrombotic and pro-inflammatory changes during CABG surgery, and provide further evidence of adverse effects associated with UFH.

Platelet Function Testing in Patients with Acute Ischemic Stroke: An Observational Study

BACKGROUND

The measurement of platelet reactivity in patients with stroke undergoing antiplatelet therapies is not commonly performed in clinical practice. We assessed the prevalence of therapy responsiveness in patients with stroke and further investigated differences between patients on prevention therapy at stroke onset and patients naive to antiplatelet medications. We also sought differences in responsiveness between etiological subtypes and correlations between Clopidogrel responsiveness and genetic polymorphisms.

METHODS

A total of 624 stroke patients on antiplatelet therapy were included. Two different groups were identified: "non-naive patients", and "naive patients". Platelet function was measured with multiple electrode aggregometry, and genotyping assays were used to determine CYP2C19 polymorphisms.

RESULTS

Aspirin (ASA) responsiveness was significantly more frequent in naive patients compared with non-naive patients (94.9% versus 82.6%, P < .0010). A better responsiveness to ASA compared with Clopidogrel or combination therapy was found in the entire population (P < .0010), in non-naive patients (P < .0253), and in naive patients (P < .0010). Multivariate analysis revealed a strong effect of Clopidogrel as a possible "risk factor" for unresponsiveness (odds ratio 3.652, P < .0001). No difference between etiological subgroups and no correlations between responsiveness and CYP2C19 polymorphisms were found.

CONCLUSION

In our opinion, platelet function testing could be potentially useful in monitoring the biological effect of antiplatelet agents. A substantial proportion of patients with stroke on ASA were "resistant", and the treatment with Clopidogrel was accompanied by even higher rates of unresponsiveness. Longitudinal studies are needed to assess whether aggregometry might supply individualized prognostic information and whether it can be considered a valid tool for future prevention strategies.

Weight-based dosing in medication use: what should we know?

BACKGROUND

Weight-based dosing strategy is still challenging due to poor awareness and adherence. It is necessary to let clinicians know of the latest developments in this respect and the correct circumstances in which weight-based dosing is of clinical relevance.

METHODS

A literature search was conducted using PubMed.

RESULTS

Clinical indications, physiological factors, and types of medication may determine the applicability of weight-based dosing. In some cases, the weight effect may be minimal or the proper dosage can only be determined when weight is combined with other factors. Medications within similar therapeutic or structural class (eg, anticoagulants, antitumor necrosis factor medications, P2Y12-receptor antagonists, and anti-epidermal growth factor receptor antibodies) may exhibit differences in requirements on weight-based dosing. In some cases, weight-based dosing is superior to currently recommended fixed-dose regimen in adult patients (eg, hydrocortisone, vancomycin, linezolid, and aprotinin). On the contrary, fixed dosing is noninferior to or even better than currently recommended weight-based regimen in adult patients in some cases (eg, cyclosporine microemulsion, recombinant activated Factor VII, and epoetin α). Ideal body-weight-based dosing may be superior to the currently recommended total body-weight-based regimen (eg, atracurium and rocuronium). For dosing in pediatrics, whether weight-based dosing is better than body surface-area-based dosing is dependent on the particular medication (eg, methotrexate, prednisone, prednisolone, zidovudine, didanosine, growth hormone, and 13-cis-retinoic acid). Age-based dosing strategy is better than weight-based dosing in some cases (eg, intravenous busulfan and dalteparin). Dosing guided by pharmacogenetic testing did not show pharmacoeconomic advantage over weight-adjusted dosing of 6-mercaptopurine. The common viewpoint (ie, pediatric patients should be dosed on the basis of body weight) is not always correct. Effective weight-based dosing interventions include standardization of weight estimation, documentation and dosing determination, dosing chart, dosing protocol, order set, pharmacist participation, technological information, and educational measures.

CONCLUSION

Although dosing methods are specified in prescribing information for each drug and there are no principal pros and cons to be elaborated, this review of weight-based dosing strategy will enrich the knowledge of medication administration from the perspectives of safety, efficacy, and pharmacoeconomics, and will also provide research opportunities in clinical practice. Clinicians should be familiar with dosage and administration of the medication to be prescribed as well as the latest developments.

Obesity and intracranial in-stent thrombosis

A morbidly obese, diabetic, hypertensive patient, with severe intracranial left middle cerebral artery (MCA) stenosis, suffered recurrent stereotyped transient ischemic attacks over 2 months, despite taking daily antiplatelet agents, high dose statin, insulin and an angiotensin converting enzyme inhibitor. A left MCA (M1) Wingspan stent-assisted angioplasty was performed after standard loading, and daily doses of clopidogrel were given 3 days prior to the procedure. Immediately after the procedure, the patient developed a left hemispheric ischemic stroke syndrome. Urgent re-angiography identified an acute intracranial in-stent thrombosis. This complication was immediately treated successfully with abciximab and balloon angioplasty. The patient had persistent residual stroke despite complete recanalization of the thrombosed stent within 3 h of occlusion. The patient was subsequently found to have incomplete inhibition of platelet activity despite being on clopidogrel 150 mg and aspirin 81 mg daily and having a normal CYP-2C19 genotype, suggesting that suboptimal antiplatelet inhibition, secondary to morbid obesity, contributed to his in-stent thrombosis. Obese patients undergoing coronary artery stenting routinely receive larger loading and maintenance doses of clopidogrel. Our case suggests that obese patients undergoing intracranial stenting may also benefit from higher than conventional clopidogrel doses prior to intracranial stenting, to decrease risk of acute in-stent occlusion.

Combined clopidogrel and aspirin therapy in patients undergoing carotid endarterectomy is associated with an increased risk of postoperative bleeding

This present study investigated the influence of combined preoperative clopidogrel and aspirin (ASA) administration on adverse postoperative outcomes and bleeding risk in patients undergoing carotid endarterectomy (CEA). A retrospective cohort study of all consecutive patients undergoing isolated CEA ( n = 1488) between 1998 and 2005 was performed. Patients were classified into three groups: patients receiving combined preoperative clopidogrel/ASA therapy ( n = 315), patients receiving preoperative ASA only ( n = 639) and patients receiving no preoperative antiplatelet therapy ( n = 518). Multivariate logistic regression was performed to determine if combined preoperative clopidogrel and ASA therapy is independently associated with improved perioperative outcomes after CEA in the absence of significant bleeding risk. Clopidogrel/ASA therapy was independently associated with a five-fold increased risk of postoperative bleeding after CEA (odds ratios = 5.1; 95% confidence intervals: 1.8–14.2; P < 0.002). No increase in bleeding risk or reoperation was observed in patients receiving ASA alone. However, the postoperative length of hospital stay (PLOHS) was significantly shorter ( P = 0.01) for patients receiving combined clopidogrel/ASA therapy (2.5 ± 2.3 days) versus those receiving no antiplatelet agents (3.2 ± 5.9 days). Preoperative clopidogrel/ASA therapy increases risk of postoperative bleeding after CEA, yet reduces overall PLOHS.

Using risk models to improve patient selection for high-risk vascular surgery

Vascular surgeons frequently perform procedures aimed at limiting death, stroke, or amputation on patients who present with diseases such as aortic aneurysms, carotid atherosclerosis, and peripheral arterial occlusive disease. However, now more than ever surgeons must balance the potential benefits associated with these interventions with the risks of physiologic insult for these elderly patients, who often have significant comorbidity burdens and the potential for costly complications. In this paper, we highlight how regional and national datasets can help surgeons identify which patients are most likely to benefit from vascular operations and which patients are most likely to suffer complications in the postoperative period. By using these guidelines to improve patient selection, our risk models can help patients, physicians, and policymakers improve the clinical effectiveness of surgical and endovascular treatments for vascular disease.

Blood loss and complications following carotid endarterectomy in patients treated with clopidogrel

This study assessed the effect of uninterrupted antiplatelet therapy on perioperative blood loss and complications in patients undergoing carotid endarterectomy. The files of 107 consecutive patients (mean age 69.5 ± 9 years; range 47–88; 78 men) who underwent carotid endarterectomy were reviewed. Twenty-six patients had been treated with clopidogrel (16 of whom were on combined clopidogrel and aspirin treatment) and compared with non-clopidogrel patients. Antiplatelet treatment was continued until the day of surgery without interruption. Perioperative blood loss and complications were studied. The mean hemoglobin decrease was 1.64 ± 1.2 mg/dL and was not significantly affected by clopidogrel. Surgical time was significantly longer among patients treated with clopidogrel (205 ± 52 minutes on combined treatment and 201 ± 68 minutes on clopidogrel alone versus 165 ± 33 minutes, P < 0.0001). Postoperative complications were similar for all groups and included five strokes, five neck hematomas, one nerve injury and one wound infection. In conclusion, patients treated with clopidogrel before carotid endarterectomy can be expected to have prolonged surgical time. Large cohorts are required to determine whether these patients have more complications.

Safety of carotid endarterectomy while on clopidogrel (Plavix)

Object

Many patients undergoing carotid endarterectomy (CEA) regularly take clopidogrel, a permanent platelet inhibitor. The authors sought to determine whether taking clopidogrel in the period before CEA leads to more bleeding or other complications.

Methods

The authors performed a retrospective, institutional review board–approved review of 182 consecutive patients who underwent CEA. Clinical, radiographic, and surgical data were gleaned from hospital and clinic records. Analysis was based on the presence or absence of clopidogrel in patients undergoing CEA and was performed twice by considering clopidogrel use within 8 days and within 5 days of surgery to define the groups.

Results

Taking clopidogrel within 8 days before surgery resulted in no statistical increase in any measure of morbidity or death. Taking clopidogrel within 5 days was associated with a small but significant increase in operative blood loss and conservatively managed postoperative neck swelling. No measure of permanent morbidity or death was increased in either clopidogrel group.

Conclusions

Findings in this study support the safety of preoperative clopidogrel in patients undergoing CEA.

Perioperative Microemboli and Platelet Aggregation in Patients Undergoing Carotid Endarterectomy

In carotid endarterectomy (CEA) patients, platelet aggregation is increased despite heparinization. We investigated whether this phenomenon correlates with the occurrence of perioperative microemboli. Of 27 CEA patients, 18 (67%) used aspirin and 9 also used clopidogrel. Blood was collected at multiple time points before, during, and after CEA. Platelet aggregation and P-selectin expression were determined. Transcranial Doppler monitoring was used to measure microemboli. Platelet aggregation showed a significant increase 5 minutes postheparinization compared with preheparinization (19.7 ± 2.8% vs 8.9 ± 0.9% in the aspirin group and 22.5 ± 4.4% vs 8.7 ± 1.2% in the clopidogrel group; p < .01 and p < .05, respectively). P-selectin expression showed a tendency to increase postheparinization in both groups ( p = .07 and p = .09, respectively). The number of microemboli ranged from 0 to 50. Clopidogrel patients displayed fewer microemboli than aspirin patients (4.1 ± 2.3 vs 17.6 ± 18.2; p < .01). Patients with a high number of microemboli displayed had a tendency toward higher baseline platelet aggregation than patients with a low number of microemboli ( p = .08). In conclusion, platelet aggregation is transiently increased during CEA despite the administration of antiplatelet agents. Clopidogrel is associated with a decreased number of perioperative microemboli. The exact relationships between these findings, postoperative microemboli formation, and the risk for thromboembolic complications after CEA remain to be determined.