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40 mg of Aspirin Are Not Sufficient to Inhibit Platelet Function under Conditions of Limited Compliance
Thrombosis Research 97 (2000) 365–367
BRIEF COMMUNICATION
40 mg of Aspirin Are Not Sufficient to Inhibit Platelet Function under Conditions of Limited Compliance Artur-Aron Weber, Sven Liesener, Thomas Hohlfeld and Karsten Schro¨r Institut fu¨r Pharmakologie und Klinische Pharmakologie, Heinrich-Heine-Universita¨t, Du¨sseldorf, Germany. (Received 10 May 1999 by Editor D.L. Heene; accepted 21 August 1999)
Key Words: Aspirin; Platelet aggregation; Thromboxane A2
1. Materials, Methods, and Subjects Studied
A
1.1. Subjects
spirin is the “gold standard” antiplatelet agent for prevention of atherothrombotic vessel occlusions [1,2]. By acetylation of platelet cyclooxygenase, aspirin induces a longlasting inhibition of platelet-dependent thromboxane A2 biosynthesis. Because of the permanent platelet inactivation, the inhibitory effects of repeated doses (⬍100 mg) of aspirin have been shown to be cumulative [3]. Assuming that patients strictly adhere to the daily treatment regime, the administration of 30 to 50 mg of aspirin should almost completely (⬎90%) inhibit platelet thromboxane A2 synthesis after 7 to 10 days. However, adherence to medical treatment with aspirin is poor. For example, elderly patients adhered to treatment with less than 70% compliance. In elderly patients with major depression, the adherence to aspirin treatment was less than 50% compliance [4]. Thus, an effective treatment concept designed to prevent atherothrombotic events should be able to compensate for missed doses. To simulate patient noncompliance, we have conducted a study comparing 40 and 100 mg of aspirin administered every second day to healthy volunteers.
Corresponding author: Karsten Schro¨r, Institut fu¨r Pharmakologie und Klinische Pharmakologie, Moorenstr. 5, D-40225 Du¨sseldorf, Germany. Tel: ⫹49-211-81-12500; Fax: ⫹49-211-81-14781. E-mail: ⬍[email protected]⬎.
This study was conducted according to the Helsinki Declaration and was approved by the Ethics Committee of the Heinrich-Heine-Universita¨t of Du¨sseldorf. Twenty healthy male volunteers (aged 21 to 37 years) gave informed written consent to participate in the study. All participants were advised to abstain from any medication for at least 2 weeks prior to and during the study. Complete data collection was possible in 18 volunteers.
1.2. Drug Administration The effects of acetylsalicylic acid (aspirin, Bayer, Leverkusen, Germany) (40 vs. 100 mg, every second day) on platelet function were studied in a randomized cross-over design (14 days treatment; 14 days washout) under double-blind conditions. Compliance was monitored by tablet counts. Platelet analyses were performed prior to and at the end of the respective treatment (24 hours after the last aspirin intake). No adverse effects were observed throughout the study.
1.3. Platelet Function Platelet-rich plasma, prepared from citrate (1:9)anticoagulated blood and collagen (0.3–5 g/mL)induced platelet aggregation, as well as thromboxane formation (measured as thromboxane B2) were determined according to standard methods as pre-
0049-3848/00 $–see front matter 2000 Elsevier Science Ltd. All rights reserved. PII S0049-3848(99)00171-1
366
A.-A. Weber et al./Thrombosis Research 97 (2000) 365–367
1.4. Statistics Data are means⫾SEM. For statistical significance, areas under the concentration-response curves from each individual experiment were calculated to avoid repeated measurements. Statistical analysis was performed using one-way analysis of variance, followed by the Bonferroni test for multiple comparisons.
2. Results Fig. 1. Effects of aspirin (40 vs. 100 mg, every second day for 14 days) on collagen (0.3–5 g/mL)-induced platelet thromboxane formation (measured as thromboxane B2).
viously described [5]. Briefly, 400 L of plateletrich plasma were incubated with 90 L of HEPESbuffered Tyrode solution [6] in a two-channel aggregometer (LAbor, Hamburg, Germany) for 1 minute at 37⬚C, followed by a stimulation with 10 L of collagen (Nycomed, Mu¨nchen, Germany). Five minutes after the addition of collagen, thromboxane formation was stopped by adding 80 M indomethacin/4.8 mM EDTA. Platelet aggregates were sedimented by centrifugation at 10,000⫻g for 3 minutes and platelet-free supernatants were stored at ⫺20⬚C until radioimmunoassay for thromboxane B2 as previously described [7].
Fig. 2. Effects of aspirin (40 vs. 100 mg, every second day for 14 days) on collagen (0.3–5 g/mL)-induced platelet aggregation.
Collagen-induced thromboxane formation was significantly (p⬍0.001) inhibited by both aspirin dose regimes (Figure 1). However, in contrast to the 100mg dose that almost completely (⬎90%) blocked platelet thromboxane formation, only a partial (60– 70%) inhibition was seen with 40 mg of aspirin. These findings were paralleled by functional data, demonstrating a markedly reduced inhibition of collagen-induced platelet aggregation by 40 mg of aspirin compared to the 100-mg dose (Figure 2).
3. Discussion Although the clinical efficacy of aspirin in the secondary prevention of atherothrombotic vessel occlusions is well established, there still exist controversies regarding the optimal dose (for review see Patrono [1] and Schro¨r [2]). It is generally accepted that for a clinically relevant effect of aspirin, an inhibition of platelet cyclooxygenase activity by ⬎90% must be achieved [8,9]. To reduce side effects, a reduction of aspirin dose below 100 mg/day is being recommended [10]. This is based on the assumption that a daily intake of 30 mg of aspirin would cumulatively block platelet thromboxane formation [3]. However, noncompliance is common, especially in elderly patients [4]. Thus, a treatment concept that would compensate for missed aspirin doses would clearly be advantageous. In the present study, noncompliance was simulated by an alternate-day dosing regime. This model should reflect the actual dosing frequency in elderly patients [4]. This study demonstrates that 100 mg of aspirin sufficiently (⬎90%) inhibit platelet thromboxane formation even under conditions of limited compli-
A.-A. Weber et al./Thrombosis Research 97 (2000) 365–367
ance. In contrast with the 40-mg dose, a marked reduction of the inhibitory effects on platelet thromboxane formation was observed. This was paralleled by a significantly reduced inhibition of collagen-induced platelet aggregation. It is concluded that under conditions of limited patient compliance, a reduction of aspirin doses below 100 mg/day might result in an impairment of its antithrombotic efficacy. The authors thank Erika Lohmann for competent secretarial work and Irmhild Ru¨ter for technical assistance.
5.
6.
7.
References 1. Patrono C. Aspirin as an antiplatelet drug. N Engl J Med 1994;330:1287–94. 2. Schro¨r K. Aspirin and platelets: The antiplatelet action of aspirin and its role in thrombosis treatment and prophylaxis. Sem Thromb Hemost 1997;23:349–56. 3. Patrignani P, Filabozzi P, Patrono C. Selective cumulative inhibition of platelet thromboxane production by low-dose aspirin in healthy subjects. J Clin Invest 1982;69:1366–72. 4. Carney RM, Freedland KE, Eisen SA, Rich
8.
9.
10.
367
MW, Jaffe AS. Major depression and medication adherence in elderly patients with coronary artery disease. Health Psychol 1995;14: 88–90. Braun M, Kramann J, Strobach H, Schro¨r K. Incomplete inhibition of platelet secretion by low-dose aspirin. Platelets 1994;5:325–31. Weber A-A, Strobach H, Schro¨r K. Direct inhibition of platelet function by organic nitrates via nitric oxide formation. Eur J Pharmacol 1993;247:29–37. Schro¨r K, Seidel H. Blood-vessel wall arachidonate metabolism and its pharmacological modification in a new in vitro assay system. Naunyn-Schmiedeberg’s Arch Pharmacol 1988; 337:177–82. Reilly IA, FitzGerald GA. Inhibition of thromboxane formation in vivo and ex vivo: Implications for therapy with platelet inhibitory drugs. Blood 1987;69:180–6. Patrono C. Aspirin and human platelets: From clinical trials to acetylation of cyclooxygenase and back. Trends Pharmacol Sci 1989;10:453–8. Fo¨rster W, Parratt JR. The case of low-dose aspirin for the prevention of myocardial infarction: but how low is low? Cardiovasc Drugs Ther 1997;10:727–34.
BRIEF COMMUNICATION
40 mg of Aspirin Are Not Sufficient to Inhibit Platelet Function under Conditions of Limited Compliance Artur-Aron Weber, Sven Liesener, Thomas Hohlfeld and Karsten Schro¨r Institut fu¨r Pharmakologie und Klinische Pharmakologie, Heinrich-Heine-Universita¨t, Du¨sseldorf, Germany. (Received 10 May 1999 by Editor D.L. Heene; accepted 21 August 1999)
Key Words: Aspirin; Platelet aggregation; Thromboxane A2
1. Materials, Methods, and Subjects Studied
A
1.1. Subjects
spirin is the “gold standard” antiplatelet agent for prevention of atherothrombotic vessel occlusions [1,2]. By acetylation of platelet cyclooxygenase, aspirin induces a longlasting inhibition of platelet-dependent thromboxane A2 biosynthesis. Because of the permanent platelet inactivation, the inhibitory effects of repeated doses (⬍100 mg) of aspirin have been shown to be cumulative [3]. Assuming that patients strictly adhere to the daily treatment regime, the administration of 30 to 50 mg of aspirin should almost completely (⬎90%) inhibit platelet thromboxane A2 synthesis after 7 to 10 days. However, adherence to medical treatment with aspirin is poor. For example, elderly patients adhered to treatment with less than 70% compliance. In elderly patients with major depression, the adherence to aspirin treatment was less than 50% compliance [4]. Thus, an effective treatment concept designed to prevent atherothrombotic events should be able to compensate for missed doses. To simulate patient noncompliance, we have conducted a study comparing 40 and 100 mg of aspirin administered every second day to healthy volunteers.
Corresponding author: Karsten Schro¨r, Institut fu¨r Pharmakologie und Klinische Pharmakologie, Moorenstr. 5, D-40225 Du¨sseldorf, Germany. Tel: ⫹49-211-81-12500; Fax: ⫹49-211-81-14781. E-mail: ⬍[email protected]⬎.
This study was conducted according to the Helsinki Declaration and was approved by the Ethics Committee of the Heinrich-Heine-Universita¨t of Du¨sseldorf. Twenty healthy male volunteers (aged 21 to 37 years) gave informed written consent to participate in the study. All participants were advised to abstain from any medication for at least 2 weeks prior to and during the study. Complete data collection was possible in 18 volunteers.
1.2. Drug Administration The effects of acetylsalicylic acid (aspirin, Bayer, Leverkusen, Germany) (40 vs. 100 mg, every second day) on platelet function were studied in a randomized cross-over design (14 days treatment; 14 days washout) under double-blind conditions. Compliance was monitored by tablet counts. Platelet analyses were performed prior to and at the end of the respective treatment (24 hours after the last aspirin intake). No adverse effects were observed throughout the study.
1.3. Platelet Function Platelet-rich plasma, prepared from citrate (1:9)anticoagulated blood and collagen (0.3–5 g/mL)induced platelet aggregation, as well as thromboxane formation (measured as thromboxane B2) were determined according to standard methods as pre-
0049-3848/00 $–see front matter 2000 Elsevier Science Ltd. All rights reserved. PII S0049-3848(99)00171-1
366
A.-A. Weber et al./Thrombosis Research 97 (2000) 365–367
1.4. Statistics Data are means⫾SEM. For statistical significance, areas under the concentration-response curves from each individual experiment were calculated to avoid repeated measurements. Statistical analysis was performed using one-way analysis of variance, followed by the Bonferroni test for multiple comparisons.
2. Results Fig. 1. Effects of aspirin (40 vs. 100 mg, every second day for 14 days) on collagen (0.3–5 g/mL)-induced platelet thromboxane formation (measured as thromboxane B2).
viously described [5]. Briefly, 400 L of plateletrich plasma were incubated with 90 L of HEPESbuffered Tyrode solution [6] in a two-channel aggregometer (LAbor, Hamburg, Germany) for 1 minute at 37⬚C, followed by a stimulation with 10 L of collagen (Nycomed, Mu¨nchen, Germany). Five minutes after the addition of collagen, thromboxane formation was stopped by adding 80 M indomethacin/4.8 mM EDTA. Platelet aggregates were sedimented by centrifugation at 10,000⫻g for 3 minutes and platelet-free supernatants were stored at ⫺20⬚C until radioimmunoassay for thromboxane B2 as previously described [7].
Fig. 2. Effects of aspirin (40 vs. 100 mg, every second day for 14 days) on collagen (0.3–5 g/mL)-induced platelet aggregation.
Collagen-induced thromboxane formation was significantly (p⬍0.001) inhibited by both aspirin dose regimes (Figure 1). However, in contrast to the 100mg dose that almost completely (⬎90%) blocked platelet thromboxane formation, only a partial (60– 70%) inhibition was seen with 40 mg of aspirin. These findings were paralleled by functional data, demonstrating a markedly reduced inhibition of collagen-induced platelet aggregation by 40 mg of aspirin compared to the 100-mg dose (Figure 2).
3. Discussion Although the clinical efficacy of aspirin in the secondary prevention of atherothrombotic vessel occlusions is well established, there still exist controversies regarding the optimal dose (for review see Patrono [1] and Schro¨r [2]). It is generally accepted that for a clinically relevant effect of aspirin, an inhibition of platelet cyclooxygenase activity by ⬎90% must be achieved [8,9]. To reduce side effects, a reduction of aspirin dose below 100 mg/day is being recommended [10]. This is based on the assumption that a daily intake of 30 mg of aspirin would cumulatively block platelet thromboxane formation [3]. However, noncompliance is common, especially in elderly patients [4]. Thus, a treatment concept that would compensate for missed aspirin doses would clearly be advantageous. In the present study, noncompliance was simulated by an alternate-day dosing regime. This model should reflect the actual dosing frequency in elderly patients [4]. This study demonstrates that 100 mg of aspirin sufficiently (⬎90%) inhibit platelet thromboxane formation even under conditions of limited compli-
A.-A. Weber et al./Thrombosis Research 97 (2000) 365–367
ance. In contrast with the 40-mg dose, a marked reduction of the inhibitory effects on platelet thromboxane formation was observed. This was paralleled by a significantly reduced inhibition of collagen-induced platelet aggregation. It is concluded that under conditions of limited patient compliance, a reduction of aspirin doses below 100 mg/day might result in an impairment of its antithrombotic efficacy. The authors thank Erika Lohmann for competent secretarial work and Irmhild Ru¨ter for technical assistance.
5.
6.
7.
References 1. Patrono C. Aspirin as an antiplatelet drug. N Engl J Med 1994;330:1287–94. 2. Schro¨r K. Aspirin and platelets: The antiplatelet action of aspirin and its role in thrombosis treatment and prophylaxis. Sem Thromb Hemost 1997;23:349–56. 3. Patrignani P, Filabozzi P, Patrono C. Selective cumulative inhibition of platelet thromboxane production by low-dose aspirin in healthy subjects. J Clin Invest 1982;69:1366–72. 4. Carney RM, Freedland KE, Eisen SA, Rich
8.
9.
10.
367
MW, Jaffe AS. Major depression and medication adherence in elderly patients with coronary artery disease. Health Psychol 1995;14: 88–90. Braun M, Kramann J, Strobach H, Schro¨r K. Incomplete inhibition of platelet secretion by low-dose aspirin. Platelets 1994;5:325–31. Weber A-A, Strobach H, Schro¨r K. Direct inhibition of platelet function by organic nitrates via nitric oxide formation. Eur J Pharmacol 1993;247:29–37. Schro¨r K, Seidel H. Blood-vessel wall arachidonate metabolism and its pharmacological modification in a new in vitro assay system. Naunyn-Schmiedeberg’s Arch Pharmacol 1988; 337:177–82. Reilly IA, FitzGerald GA. Inhibition of thromboxane formation in vivo and ex vivo: Implications for therapy with platelet inhibitory drugs. Blood 1987;69:180–6. Patrono C. Aspirin and human platelets: From clinical trials to acetylation of cyclooxygenase and back. Trends Pharmacol Sci 1989;10:453–8. Fo¨rster W, Parratt JR. The case of low-dose aspirin for the prevention of myocardial infarction: but how low is low? Cardiovasc Drugs Ther 1997;10:727–34.