Antiplatelet effects of a 600 mg loading dose of clopidogrel are not attenuated in patients receiving atorvastatin or simvastatin for at least 4 weeks prior to coronary artery stenting

Olga Gorchakovaa, Nicolas von Beckerathb,*, Meinrad Gawaza, Adrienne Moczb, Alexander Joostb, Albert Schömiga,b and Adnan Kastratib

a Medizinische Klinik rechts der Isar, Technische Universität München, Munich, Germany
b Department of Cardiology, Deutsches Herzzentrum, Technische Universität München, Lazarettstrasse 36, 80636 Munich, Germany

Received October 2, 2003; revised October 11, 2003; accepted October 13, 2003 * Corresponding author. Tel.: +49 89 1218 4011; fax: +49 89 1218 4593 (E-mail: beckerath{at}dhm.mhn.de).


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 References
 
AIMS: To test prospectively whether the antiplatelet effect of a 600 mg loading dose of clopidogrel is attenuated in patients receiving atorvastatin and simvastatin for at least 4 weeks prior to coronary artery stenting.

METHODS AND RESULTS: Blood samples were obtained at least 2 h after receiving 100 mg aspirin and 600 mg clopidogrel and prior to coronary stenting from 90 patients without statin therapy and 90 patients with statin (atorvastatin and simvastatin) therapy for at least 4 weeks. Maximal and residual platelet aggregation was evaluated with optical aggregometry in response to ADP (5 and 20 µmol/l). Surface expression of IIb/IIIa (CD61) and P-selectin (CD62) was assessed with whole blood flow-cytometry at baseline and following stimulation (5 and 20 µmol/l ADP). Inhibition of ADP-induced platelet aggregation was not impaired in the presence of concomitant statin therapy. Moreover, patients with and without statin therapy did not differ in respect to all flow-cytometric parameters obtained.

CONCLUSION: The antiplatelet effect of a high, 600 mg loading dose of clopidogrel is not diminished in patients receiving atorvastatin and simvastatin for at least 4 weeks prior to coronary stenting.


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 References
 
Dual antiplatelet therapy with clopidogrel and aspirin is now the standard regimen to prevent thrombosis following coronary stent insertion. Clopidogrel is a prodrug that is extensively metabolised in the liver. The active short-lived metabolite is a thiol derivate that is formed by oxidation to 2-oxo-clopidogrel and subsequent hydrolysis.1 Statins, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, were consistently effective in randomised trials for primary and secondary prevention of cardiovascular events. Since statins also reduce the incidence of adverse events following coronary stenting,2 clopidogrel and statins are often given together in this clinical setting. In a recent report on a large consecutive series of patients undergoing coronary stenting from 1995 to 1999 roughly 80% of the patients received statins.2

Lau and coworkers reported a concerning attenuation of the antiaggregatory effect of clopidogrel due to concomitant maintenance therapy with atorvastatin.3 Patients in that study received a 300 mg loading dose clopidogrel before stenting. ADP-induced platelet aggregation was assessed before administration of the loading dose and 24 h later with a point-of-care test. The authors also provided evidence that the observed drug–drug interaction was related to the cytochrome P450 3A4 (CYP3A4) pathway.3 Simvastatin, another CYP3A4-metabolised statin, is believed to exert the same drug–drug interaction with clopidogrel as atorvastatin.4

Administration of a high, 600 mg loading dose clopidogrel before coronary stenting exerts the maximal antiaggregatory effect of clopidogrel within 2 h,5 has the potential to overcome individual differences in response to clopidogrel6,7 and has been shown to be clinically useful in patients undergoing percutaneous coronary interventions.8 Recently, no attenuation of the antiaggregatory effect of 600 mg has been described after administration of single doses of the CYP3A4-metabolised statins, atorvastatin and simvastatin.9 Since CYP3A4-mediated drug–drug interactions may occur only at steady state,10 it is not known whether this high dose of clopidogrel is capable of overcoming the interfering action of long-term therapy with CYP3A4-metabolised statins.

This prospective study was planned to test whether the antiplatelet effect of the 600 mg loading dose of clopidogrel is attenuated in patients receiving atorvastatin or simvastatin for at least 4 weeks prior to elective coronary stenting.


    Methods
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 References
 
Study population
Eligible for this prospective study were patients scheduled for elective coronary stenting for symptomatic coronary artery disease. Patients with a history of myocardial infarction (MI) within 14 days and stroke within 3 months as well as patients with haemodynamic instability, malignancies, active bleeding and bleeding diathesis, oral anticoagulation therapy with a coumarin derivate, recent treatment (less than 14 days) with a GP IIb/IIIa antagonist or a platelet count <100x109/l were not included. This also applied to patients that presented with chest pain at rest and ST-segment changes in >2 ECG leads and/or troponin-T level >0.03 ng/ml. Additional exclusion criteria were concomitant medication with known CYP3A4 inducers or inhibitors11 except calcium channel blockers12 as well as an impaired renal function resulting in a serum creatinine >2 mg/dl and any liver disease resulting in a bilirubin >2 mg/dl. The first study group comprised 90 consecutive patients who were not on statin therapy. The second study group consisted of 90 consecutive patients treated with atorvastatin or simvastatin for at least the previous 4 weeks. Enrolment was done before knowing the results of platelet function evaluation. The study complies with the Declaration of Helsinki. Approval from the institutional ethics committee and written informed consent from all subjects participating in this study had been obtained. Patients received 100 mg aspirin and a 600 mg loading dose of clopidogrel orally at least 2 h before the intervention.

Aggregometry
Citrated blood samples were obtained from the arterial sheath immediately before the intervention and then processed within 60 min by operators unaware of the patients medication. Platelet aggregation was evaluated by optical aggregometry in platelet-rich plasma (PRP) using a Chrono-log lumi-aggregometer (Probe & go Labordiagnostica, Endingen, Germany) with a constant stirring rate of 1000 rpm at 37 °C as previously described.13 The final platelet count was adjusted to 300x109/l with autologous platelet-poor plasma. Platelet-rich plasma (0% light transmission) and platelet-poor plasma (100% light transmission) served as references. After baseline adjustment ADP (5 or 20 µmol/l) was added and aggregation recorded for 5 min. The analysed parameters were maximal aggregation (%) and aggregation after 5 min=residual aggregation (%).

Flow-cytometry
The evaluation of surface expression of platelets receptors was performed in whole blood.14 The following monoclonal antibodies were used: anti-CD61 PE (anti-GP IIb/IIIa labelled with phycoerythrine; Serotec, Düsseldorf, Germany) and anti-CD62 FITC (anti-P-selectin labelled with fluorescein isothiocyanate; Beckman Coulter, Krefeld, Germany). In brief, citrated blood (10 µl) was diluted with 490 µl phosphate buffered saline (PBS) and gently mixed. Both antibodies (5 µl each) and ADP or PBS (5 µl) were added to 35 µl diluted citrated blood and incubated at room temperature for 20 min. The samples were fixed with 300 µl of 1% buffered paraformaldehyde and then analysed on a Becton Dickenson FACScan flow-cytometer. Mean intensity of immunofluorescence was used as an index of antibody binding and receptor surface expression.

Statistical analysis
The primary endpoint of the study was maximal ADP (5 µmol/l)-induced aggregation immediately before the intervention and at least 2 h after ingestion of the 600 mg loading dose clopidogrel and 100 mg aspirin. The number of patients included in the study was based on the assumption that concomitant therapy with atorvastatin or simvastatin results in a 25% increase (from 40±20% to 50±20% [mean±standard deviation]) of maximal ADP (5 µmol/l)-induced aggregation. Choosing a power of 90% and a two-sided α value of 0.05 we calculated that a sample size of at least 86 was required in each group (nQuery advisor, version 5.0). Continuous variables are expressed as mean±S.D. The unpaired t-test or Wilcoxon rank-sum test were used for 2-group comparisons. One-way analysis of variance (ANOVA) was used for multiple group comparisons. Categorical variables were compared using {chi}2 test. Statistical analyses were performed using S-Plus software (Mathsoft Inc., Seattle, WA). Statistical significance was accepted for P values <0.05.


    Results
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 Abstract
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 Methods
 Results
 Discussion
 Conclusion
 References
 
Table 1 shows the baseline clinical characteristics and concomitant cardiovascular medication of the patients without statin therapy and those with atorvastatin or simvastatin therapy.


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Table 1. Clinical characteristics of patients according to statin treatment
 
Treatment with aspirin and the high loading dose clopidogrel resulted in a pronounced inhibition of ADP-induced platelet aggregation. Maximal ADP-induced platelet aggregation was 41.8±19.8% and 50.7±21.3% for 5 and 20 µmol/l, respectively (n=180). Table 2 shows all obtained aggregometric and flow-cytometric parameters according to the presence or absence of concomitant statin therapy. Inhibition of ADP-induced platelet aggregation was not impaired in the presence of concomitant statin therapy (see also Fig. 1a). Patients with and without statin therapy did not differ in respect to all flow-cytometric parameters obtained (Table 2). Maximal aggregation in response to 5 µmol/l ADP was similar in patients without statin therapy and those concomitantly treated with atorvastatin or simvastatin (Fig. 1b). The antiaggregatory effect clopidogrel was not diminished even in the presence of high doses of atorvastatin and simvastatin (Fig. 1c). We also assessed the potential influence of calcium channel blockers, another group of CYP3A4 substrates, on the antiplatelet effect of clopidogrel. ADP (5 µmol/l)-induced aggregation was similar in patients with and without calcium channel blocker therapy (42.0±17.2% vs. 41.8±20.1%; P=0.96).


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Table 2. Effect of the 600 mg clopidogrel loading dose on ADP-induced platelet aggregation and receptor surface expression in the absence and presence of statin therapy
 


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Fig. 1 Mean±standard error of the mean (S.E.M.) of maximal aggregation in response to ADP (5 µmol/l) in patients with and without statin therapy (a), in patients with atorvastatin and simvastatin therapy and without statin therapy (b) and according to atorvastatin and simvastatin dosages (c).

 

    Discussion
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 References
 
Recently, Lau et al. reported an inhibition of the antiaggregatory effect of clopidogrel by concomitant therapy with atorvastatin, a CYP3A4-metabolised statin.3 In the first part of their study 44 patients (16 without, 9 with pravastatin and 19 with atorvastatin therapy) were studied that received a 300 mg loading dose of clopidogrel before coronary stenting. In addition, all patients received 325 mg aspirin15 and adjunctive therapy with eptifibatide. Platelet aggregation was measured before clopidogrel (and eptifibatide) administration and 24 h later (after cessation of the eptifibatide effect) as well as 6 to 8 days later. The effect of concomitant atorvastatin therapy was dose-dependent. Treatment with 40 mg atorvastatin almost completely inhibited the antiplatelet effect of clopidogrel. Moreover, the attenuation of the antiaggregatory effect of clopidogrel persisted until day 6 to 8. In the second and third part of the study in which altogether 27 volunteers were involved and in a recent in vitro study evidence was provided that CYP3A4 is the major cytochrome metabolising clopidogrel.3,4

In our study, we did not observe an attenuation of the antiplatelet effect of clopidogrel in the presence of atorvastatin and simvastatin therapy as demonstrated by all aggregometric and flow-cytometric parameters obtained. In addition to maximal aggregation, we also evaluated residual aggregation. Residual aggregation is particularly helpful in assessing the secondary phase of ADP-induced platelet aggregation that is predominantly mediated by ADP-binding to the P2Y12 receptor.16 We also did not find an influence of concomitant calcium channel blocker therapy on platelet inhibition achieved by the 600 mg loading dose of clopidogrel. These data, though, have to be interpreted with caution since only 15 out of the 180 patients received these drugs. It is important to note the most important difference between the study of Lau et al.3 and our study: the different loading dose of clopidogrel. The high, 600 mg loading dose of clopidogrel may overcome differences in drug-response and drug–drug interactions observed with the 300 mg loading dose used in the study of Lau et al.3 The findings of the present study conducted in clinical settings common to patients undergoing coronary artery stenting complement the data provided recently by Müller and colleagues who did not find any reduction of the antiplatelet effects of 600 mg clopidogrel after single 20 mg doses of atorvastatin or simvastatin.9

Other recent studies have evaluated patients on long-term clopidogrel therapy and did not find a significant interaction between statins and clopidogrel. In the CREDO (clopidogrel for the reduction of events during observation) study, the 1-year adverse event rate in the clopidogrel group was 7.6% for those treated with CYP3A4-metabolised statins and 5.4% for those treated with other statins (P=0.51).17 In the MITRA PLUS (maximal individual therapy of acute myocardial infarction PLUS) registry, the long term mortality was 3.2% in the group receiving atorvastatin and 2.7% in the group that received other statins (p=0.49).18

Two limitations of the present study deserve consideration: the lack of randomisation between patients with and without statin therapy and the assessment of platelet function at a single time point prior to the intervention. Although this time point is probably most useful in the clinical setting of percutaneous coronary intervention, baseline measurements before loading might have provided additional information.


    Conclusion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 References
 
The antiplatelet effect of a high, 600 mg loading dose of clopidogrel is not diminished in patients receiving atorvastatin and simvastatin for at least 4 weeks prior to coronary stenting.


    Acknowledgments
 
The invaluable and skilful contribution of M. Eichinger is highly appreciated


    References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusion
 References
 

  1. Savi P, Pereillo JM, Uzabiaga MF, et al. Identification and biological activity of the active metabolite of clopidogrel Thromb Haemost 2000;84:891-896.[Medline]
  2. Schömig A, Mehilli J, Holle H, et al. Statin treatment following coronary artery stenting and one-year survival J Am Coll Cardiol 2002;40:854-861.[CrossRef][Medline]
  3. Lau WC, Waskell LA, Watkins PB, et al. Atorvastatin reduces the ability of clopidogrel to inhibit platelet aggregation: a new drug–drug interaction Circulation 2003;107:32-37.[Abstract/Free Full Text]
  4. Clarke TA, Waskell LA. The metabolism of clopidogrel is catalyzed by human cytochrome p450 3A and is inhibited by atorvastatin Drug Metab Dispos 2003;31:53-59.[Abstract/Free Full Text]
  5. Müller I, Seyfarth M, Rüdiger S, et al. Effect of a high loading dose of clopidogrel on platelet function in patients undergoing coronary stent placement Heart 2001;85:92-93.[Free Full Text]
  6. Gurbel PA, Bliden KP, Hiatt BL, et al. Clopidogrel for coronary stenting. Response variability, drug resistance, and the effect of pretreatment platelet reactivity Circulation 2003;9:9.[CrossRef]
  7. Müller I, Besta F, Schulz C, et al. Prevalence of clopidogrel non-responders among patients with stable angina pectoris scheduled for elective coronary stent placement Thromb Haemost 2003;89:783-787.[Medline]
  8. Kastrati A, Mehilli J, Schühlen H, et al. A clinical trial of abciximab in patients undergoing elective percutaneous coronary interventions after pretreatment with clopidogrel N Engl J Med 2004;350:232-238.[Abstract/Free Full Text]
  9. Müller I, Besta F, Schulz C, et al. Effects of statins on platelet inhibition by a high loading dose of clopidogrel Circulation 2003;20:20.
  10. Dresser GK, Spence JD, Bailey DG. Pharmacokinetic-pharmacodynamic consequences and clinical relevance of cytochrome P450 3A4 inhibition Clin Pharmacokinet 2000;38:41-57.[Medline]
  11. Knopp RH. Drug treatment of lipid disorders N Engl J Med 1999;341:498-511.[Free Full Text]
  12. Flockhart DA, Tanus-Santos JE. Implications of cytochrome P450 interactions when prescribing medication for hypertension Arch Intern Med 2002;162:405-412.[Abstract/Free Full Text]
  13. Gawaz M, Ruf A, Neumann FJ, et al. Effect of glycoprotein IIb–IIIa receptor antagonism on platelet membrane glycoproteins after coronary stent placement Thromb Haemost 1998;80:994-1001.[Medline]
  14. Gawaz M, Neumann FJ, Schömig A. Evaluation of platelet membrane glycoproteins in coronary artery disease: consequences for diagnosis and therapy Circulation 1999;99:E1-E11.[Medline]
  15. Martin PT, Denman R. Atorvastatin–clopidogrel interaction Circulation 2003;107:e223author reply e223.[Free Full Text]
  16. Foster CJ, Prosser DM, Agans JM, et al. Molecular identification and characterization of the platelet ADP receptor targeted by thienopyridine antithrombotic drugs J Clin Invest 2001;107:1591-1598.[Abstract/Free Full Text]
  17. Saw J, Steinhubl SR, Berger PB, et al. Lack of adverse clopidogrel-atorvastatin clinical interaction from secondary analysis of a randomized, placebo-controlled clopidogrel trial Circulation 2003;108:921-924.[Abstract/Free Full Text]
  18. Wienbergen H, Gitt AK, Schiele R, et al. Comparison of clinical benefits of clopidogrel therapy in patients with acute coronary syndromes taking atorvastatin versus other statin therapies Am J Cardiol 2003;92:285-288.[CrossRef][Medline]