Effect of enteric coating on antiplatelet activity of low-dose aspirin in healthy volunteers

Department of Clinical Pharmacology, Royal College of Surgeons, 123 St Stephens Green, Dublin 2, Ireland.
Stroke (Impact Factor: 6.02). 09/2006; 37(8):2153-8. DOI: 10.1161/
Source: PubMed

ABSTRACT Aspirin resistance may be relatively common and associated with adverse outcome. Meta-analysis has clearly shown that 75 mg plain aspirin is the lowest effective dose; however, it is not known whether the recent increased use of enteric-coated aspirin could account for aspirin resistance. This study was designed to determine whether enteric-coated aspirin is as effective as plain aspirin in healthy volunteers.
Seventy-one healthy volunteers were enrolled in 3 separate bioequivalence studies. Using a crossover design, each volunteer took 2 different aspirin preparations. Five aspirin preparations were evaluated, 3 different enteric-coated 75-mg aspirins, dispersible aspirin 75 mg and asasantin (25-mg standard release aspirin plus 200-mg modified-release dipyridamole given twice daily). Serum thromboxane (TX) B2 levels and arachidonic acid-induced platelet aggregation were measured before and after 14 days of treatment.
All other aspirin preparations tested were inferior to dispersible aspirin (P<0.001) in their effect on serum TXB(2) level. Treatment failure (<95% inhibition serum TXB2 formation) occurred in 14 subjects, none of whom were taking dispersible aspirin. Mean weight for those demonstrating treatment failure was greater than those with complete TXB2 (>99%) inhibition (P<0.001). Using logistic regression analysis an 80-kg subject had a 20% probability of treatment failure. Asasantin was the most potent preparation in terms of inhibition of platelet aggregation.
Equivalent doses of the enteric-coated aspirin were not as effective as plain aspirin. Lower bioavailability of these preparations and poor absorption from the higher pH environment of the small intestine may result in inadequate platelet inhibition, particularly in heavier subjects.


Available from: Ronán Michael Conroy, Jun 06, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Low-dose acetylsalicylic acid (ASA) is widely used as antithrombotic prophylaxis. Enteric-coated ASA has been developed in order to decrease the risk of gastrointestinal side effects. The consequences of enteric coating on pharmacokinetics and antiplatelet effect of ASA have not systematically been assessed. This MiniReview demonstrates that data from clinical trials indicate that enteric coating can reduce the antiplatelet effect of ASA compared to plain ASA. This is possibly due to decreased bioavailability of ASA caused by prolonged solvation and absorption of the enteric-coated formulations. Therefore, low-dose enteric-coated ASA might not be bioequivalent to plain ASA, entailing the risk of insufficient cardiovascular prophylaxis. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Basic & Clinical Pharmacology & Toxicology 12/2014; 116(3). DOI:10.1111/bcpt.12362 · 2.29 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The integrin αIIbβ3 on resting platelets can bind to immobilised fibrinogen resulting in platelet spreading and activation but requires activation to bind to soluble fibrinogen. αIIbβ3 is known to interact with the general integrin-recognition motif RGD (arginine-glycine-aspartate) as well as the fibrinogen-specific γ-chain dodecapeptide; however, it is not known how fibrinogen binding triggers platelet activation. NGR (asparagine-glycine-arginine) is another integrin-recognition sequence present in fibrinogen and this study aims to determine if it plays a role in the interaction between fibrinogen and αIIbβ3. NGR-containing peptides inhibited resting platelet adhesion to fibrinogen with an IC50 of 175 µM but failed to inhibit the adhesion of activated platelets to fibrinogen (IC50> 500 µM). Resting platelet adhesion to mutant fibrinogens lacking the NGR sequences was reduced compared to normal fibrinogen under both static and shear conditions (200 s⁻¹). However, pre-activated platelets were able to fully spread on all types of fibrinogen. Thus, the NGR motif in fibrinogen is the site that is primarily responsible for the interaction with resting αIIbβ3 and is responsible for triggering platelet activation.
    Thrombosis and Haemostasis 11/2014; 113(2). DOI:10.1160/TH14-04-0366 · 5.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Evidence from the literature suggests diminished acetylsalicylic acid (ASA) treatment efficacy in type 2 diabetes (DM2). High on-aspirin platelet reactivity (HAPR) in DM2 has been linked to poor glycemic and lipid control. However, there are no consistent data on the association between HAPR and insulin resistance or adipose tissue metabolic activity. The aim of this study was to assess the relationship between laboratory response to ASA and metabolic control, insulin resistance and adipokines in DM2.MethodsA total of 186 DM2 patients treated with oral antidiabetic drugs and receiving 75 mg ASA daily were included in the analysis. Response to ASA was assessed by measuring serum thromboxane B2 (TXB2) concentration and expressed as quartiles of TXB2 level. The achievement of treatment targets in terms of glycemic and lipid control, insulin resistance parameters (including Homeostatic Model Assessment-Insulin Resistance, HOMA-IR, index), and serum concentrations of high-molecular weight (HMW) adiponectin, leptin and resistin, were evaluated in all patients. Univariate and multivariate logistic regression analyses were performed to determine the predictive factors of serum TXB2 concentration above the upper quartile and above the median.ResultsSignificant trends in age, body mass index (BMI), HOMA-IR, HMW adiponectin concentration, C-reactive protein concentration and the frequency of achieving target triglyceride levels were observed across increasing quartiles of TXB2. In a multivariate analysis, only younger age and higher BMI were independent predictors of TXB2 concentration above the upper quartile, while younger age and lower HMW adiponectin concentration were predictors of TXB2 concentration above the median.Conclusions These results suggest that in DM2, the most important predictor of HAPR is younger age. Younger DM2 patients may therefore require total daily ASA doses higher than 75 mg, preferably as a twice-daily regimen, to achieve full therapeutic effect. Higher BMI and lower HMW adiponectin concentration were also associated with less potent ASA effect. This is the first study to demonstrate an association of lower adiponectin concentration with higher serum TXB2 level in patients treated with ASA.
    Cardiovascular Diabetology 08/2014; 13(1):112. DOI:10.1186/s12933-014-0112-0 · 3.71 Impact Factor