Investigation into the causes of aspirin resistance in healthy dogs

Antiplatelet effects of acetylsalicylic acid (ASA, aspirin) may be poor in some individuals. Additionally, no method exists for predicting poor ASA response (resistance) in individual dogs. This study's main objective was to determine whether poor ASA response results from pharmacodynamic or pharmacokinetic causes. ASA concentrations causing 50% inhibition of platelet aggregation (in vitro IC50) were determined using whole blood collected from 21 drug-free healthy dogs to evaluate intrinsic sensitivity of platelets to ASA. Dogs were then administered ASA at 4 mg/kg once orally. Percent decrease in platelet aggregation from baseline, and plasma ASA and salicylic acid (SA) concentrations (expressed as AUC values) were measured for up to 3 hr. By 3 hr, 13/21 (62%) dogs showed >50% aggregation inhibition, while 8/21 (38%) dogs showed <50% inhibition. Aggregation inhibition values were negatively correlated with in vitro IC50 values (Rs = -0.49; p = 0.028) and positively correlated with ASA concentrations (Rs = 0.48; p = 0.03). Furthermore, ASA concentrations were strongly negatively correlated (Rs = -0.88; p < 0.001) with SA/ASA concentration ratios, an index of ASA metabolism to SA by esterase enzymes. Multiple linear regression analysis indicated that 59% (p < 0.001) of interindividual variability in aggregation inhibition was explained by in vitro IC50 values (29% of variability) and ASA concentrations (29% of variability). Consequently, poor in vivo ASA response in these dogs resulted from both pharmacodynamic (decreased platelet sensitivity) and pharmacokinetic (lower ASA concentrations) causes. Lower ASA concentrations may be explained by reduced bioavailability associated with higher esterase activities.

Effectiveness and Safety of Antiplatelet in Stroke Patients with End-Stage Renal Disease Undergoing Dialysis

Background

Antiplatelet therapy is known to decrease the risk of secondary ischemic stroke. However, the effectiveness and safety of antiplatelet therapy in patients with end-stage renal disease are uncertain, especially in dialysis.

Aims and/or hypothesis

We estimated the effectiveness and safety of antiplatelet drugs (aspirin and clopidogrel) for the prevention of recurrent ischemic stroke in end-stage renal disease patients undergoing dialysis during long-term follow-up after first-time ischemic stroke.

Methods

The cases were identified from the National Health Insurance Research Database. Antiplatelet therapy was administered for 11 years to patients experiencing a first ischemic stroke between 1998 and 2006. Primary outcomes, including death and readmission to hospital for stroke, and secondary outcomes, including death, stroke, and acute myocardial infarction or bleeding, were examined.

Results

In total, 1936 patients experienced a first ischemic stroke during the follow-up. In a time-dependent analysis, the hazard ratio for primary outcomes in patients treated with aspirin was 0·671 ( P < 0·001) and that for clopidogrel was 0·933 ( P = 0·497). At secondary outcomes, patients treated with aspirin, hazard ratio for readmission for stroke was 0·715 ( P = 0·002) and that for bleeding was 0·885 ( P = 0·291). Independent risk factors for mortality and readmission due to ischemic stroke included age, diabetes mellitus, and administration of proton pump inhibitors.

Conclusions

Antiplatelet therapy, especially aspirin, still offers safe and effective treatment for ischemic stroke prevention in patients with end-stage renal disease undergoing dialysis.