Cumulative antiplatelet effect of low-dose enteric coated aspirin

Bleeding in patients who underwent scheduled second-look endoscopy 5 days after endoscopic submucosal dissection for gastric lesions

Background

Bleeding after endoscopic submucosal dissection (ESD) in antithrombotic drug users is still one of the important issues to be solved. We performed scheduled second-look endoscopy (SLE) 5 days after ESD, when the resumption of antithrombotic agents is assumed to have achieved a steady state, rather than on the day after ESD. We investigated bleeding incidence and the status of ulcers.

Methods

A total of 299 lesions in 299 patients subjected to ESD for gastric neoplasms were enrolled. A double dose of proton pump inhibitors was administered after ESD. SLE was planned 5 days after ESD. Post-ESD bleeding occurring before SLE was defined as early phase post-ESD bleeding, whereas bleeding after SLE was defined as later phase post-ESD bleeding. Forrest IIa and IIb ulcers are defined as high-risk ulcers requiring prophylactic hemostasis. We investigated risk factors for post-ESD bleeding, particularly focusing on the use of antithrombotic agents and the presence of high-risk ulcers requiring prophylactic hemostasis during SLE.

Results

Under a double dose of proton pump inhibitors, early phase post-ESD bleeding occurred in 2.3% of non-users (5/218) and 6.2% of users of antithrombotic agents (5/81). High-risk ulcers were found in 19.0% of the cases during scheduled SLE (55/289). Later phase bleeding occurred in 5.5% of cases [2.8% of non-users (6/213) and 13.2% of users of antithrombotic agents (10/76)]. Cox regression analysis revealed that the risk factor for post-ESD bleeding was antithrombotic treatment (HR: 3.56; 95% CI: 1.63–8.02, p = 0.002) alone. Among patients with high-risk ulcers, a statistically significant increase in bleeding was observed in the later phase in patients under antithrombotic therapy, compared to those not receiving any antithrombotic agents (p = 0.001).

Conclusions

Antithrombotic treatment is a risk factor for post-ESD bleeding despite SLE being scheduled 5 days after ESD. Later phase post-ESD bleeding was observed in 13.2% of the patients under antithrombotic treatment even after prophylactic hemostasis for high-risk ulcers.

Trial registration

This study was registered in the UMIN Clinical Trials Registry System (000023306). Retrospectively registered on 23rd July 2016.

Transfer of Low Dose Aspirin Into Human Milk

BACKGROUND

Aspirin has antipyretic and anti-inflammatory properties and is frequently used by pregnant and lactating women. However, its transfer in human milk when administered at low dose has not been reported. Research aim: This study aimed to evaluate the transfer of acetylsalicylic acid and its metabolite, salicylic acid, into human milk following the use of low dose aspirin.

METHODS

In this study, milk samples were collected at 0, 1, 2, 4, 8, 12, and 24 hours from seven breastfeeding women after a steady-state daily dose of 81 mg of aspirin. Milk levels of acetylsalicylic acid and salicylic acid were determined by liquid chromatography-tandem mass spectrometry.

RESULTS

Acetylsalicylic acid levels were below the limit of quantification (0.61 ng/ml) in all the milk samples, whereas salicylic acid was detected at very low concentrations. The average concentration of salicylic acid observed was 24 ng/ml and the estimated relative infant dose was 0.4%.

CONCLUSION

Acetylsalicylic acid transfer into milk is so low that it is undetectable even by highly sophisticated methodology. Salicylic acid does appear in the human milk in comparatively low amounts, which are probably subclinical in infants. Thus, the daily use of an 81-mg dose of aspirin should be considered safe during lactation.

Influence of nonsteroidal anti-inflammatory drugs on aspirin's antiplatelet effects and suggestion of the most suitable time for administration of both agents without resulting in interaction

Background

Low-dose aspirin irreversibly inhibits platelet cyclooxygenase-1 (COX-1) and suppresses platelet aggregation. It is effective for secondary prevention of cardiovascular events. Because nonsteroidal anti-inflammatory drugs (NSAIDs) reversibly bind with COX-1, the antiplatelet effects of aspirin may be suppressed when NSAIDs are co-administered. This interaction could be avoided by avoiding simultaneous administration; however, the minimum interval that should separate the administration of aspirin and loxoprofen is not well known. In this study, we investigated how to avoid the influence of NSAIDs on the antiplatelet effects of aspirin. An in vitro experiment was performed to investigate the influence of ibuprofen and loxoprofen at various concentrations on aspirin’s antiplatelet action.

Methods

Platelet aggregation and thromboxane B₂ (TXB₂) levels were measured after addition of aspirin only and NSAIDs plus aspirin to platelet-rich plasma. NSAIDs were used at their maximum plasma concentrations, the assumed concentration after 6 h (for loxoprofen only), and the assumed concentration after 12 h of taking one clinical dose. Platelet aggregation threshold index (PATI), defined as the putative stimulus concentration giving 50% aggregation, was calculated as an index of aggregation activity.

Results

PATI decreased in ibuprofen plus aspirin group compared to that in the aspirin only group, regardless of ibuprofen concentration. Furthermore, PATI significantly decreased when aspirin was added after loxoprofen-trans-OH addition at the maximum concentration (4.1 ± 0.1 μg/mL), compared to that in aspirin only group (5.9 ± 0.1 μg/mL). PATI showed no significant difference after addition of loxoprofen at the assumed concentration after 6 h (aspirin only group, 5.0 ± 0.5 μg/mL; loxoprofen-trans-OH plus aspirin group, 4.9 ± 0.4 μg/mL).In addition, TXB₂ concentration tended to decrease with increasing PATI.

Conclusions

It is desirable to avoid ibuprofen co-administration with the usual once-daily low-dose aspirin therapy; however, a 6-h interval between loxoprofen and aspirin could avoid this potential interaction when loxoprofen is taken before aspirin.

Antiplatelet Effects of the Addition of Acetylsalicylic Acid 40 Mg Daily to Ticlopidine in Human Healthy Volunteers

Clinical studies have shown that acetylsalicylic acid (ASA) or ticlopidine (T) bring a partial clinical benefit in a subset of patients threatened by thrombosis on atherosclerotic plaques. Acetylsalicylic acid and T have different impacts on platelet function and the combination of the drugs seems logical to achieve a greater antiplatelet effect. Healthy volunteers were randomly allocated to any of the three treatment groups: T 250-placebo; T 250-T 250; placebo-placebo (treatment was administered in a double blind manner). Acetylsalicylic acid 40 mg was openly administered once a day to the subjects of the three groups after the first week of treatment. Simplate I bleeding time and platelet aggregation testing were performed before treatment and at the end of the two treatment periods. We confirmed that T alone prolongs bleeding time and impairs, in a dose-dependent manner, ADP-induced aggregation; platelet responses that depend on released ADP were also affected. Inhibition of thromboxane-dependent aggregation, associated with a doubling of the bleeding time, was observed after one week of low-dose ASA inhibition of thromboxane synthesis. An additive effect of ASA 40 mg to T 250 mg on the bleeding time was evidenced. There was also a wider alteration of platelet aggregation, with a trend towards an inhibition of the response to a high concentration of collagen as compared to ASA or T used alone. Such a powerful, logical drug combination is in good agreement with preliminary encouraging results obtained after coronary stent implantation and deserves further studies in patients at high risk for arterial thrombosis to define its benefit-risk profile. Key Words: Aspirin—Ticlopidine— Drug combination—Bleeding time—Platelet aggregation.

Screening for deep vein thrombosis after periacetabular osteotomy in adult patients: is it necessary?

BACKGROUND

The periacetabular osteotomy has become a common procedure for treating symptomatic acetabular dysplasia. Like other major hip procedures, there is concern regarding the risk of associated venous thromboembolic disease. Nevertheless, there is limited information regarding the need for screening, and optimal prophylactic measures have not been established.

QUESTIONS/PURPOSES

We sought to determine the frequency of thromboembolic events (deep vein thrombosis [DVT] and symptomatic pulmonary embolism [PE]) associated with the periacetabular osteotomy in in patients receiving aspirin and mechanical compression prophylaxis.

METHODS

We performed a retrospective review of 134 adult patients (149 hips) treated with the periacetabular osteotomy during an 8-year period. During this period, 136 (91%) of the hips treated with a periacetabular osteotomy were screened within 1 week for DVT, whereas 13 (9%) could not be evaluated for various reasons. The mean age of the patients at the time of surgery was 30 years (range, 18-60 years), and no patients were lost to followup during the 4 to 6 months after surgery. The same thromboembolic prophylactic regimen was used for all patients. This consisted of 325 mg aspirin twice a day and compression stockings for 6 weeks and lower extremity pneumatic compression devices while hospitalized. Screening bilateral lower extremity ultrasonography was performed within 1 week (mean, 4 days) of the procedure to detect asymptomatic DVTs.

RESULTS

Of the 134 patients, two patients (two hips) with negative postoperative screening ultrasounds presented at 14 and 38 days postoperatively with clinical symptoms of DVT. Repeat ultrasound confirmed this diagnosis in both cases. There were no symptoms of PE. Screening venous ultrasonography did not identify any DVTs during the early postoperative period before discharge. These two patients were treated with 3 to 6 months of warfarin anticoagulation. Neither patient had persistent symptoms related to the DVT.

CONCLUSIONS

These data indicate that the risk of symptomatic DVT associated with periacetabular osteotomy is low (1%) with use of aspirin and mechanical compression prophylaxis. Furthermore, routine postoperative screening did not detect any patients with an asymptomatic DVT.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

A phase 1 study of prasugrel in patients with sickle cell disease: pharmacokinetics and effects on ex vivo platelet reactivity

AIMS

Prasugrel is a novel thienopyridine P2Y12 adenosine diphosphate (ADP) receptor antagonist that inhibits ADP-mediated platelet activation and aggregation. Accordingly, it may be useful in reducing platelet-related ischaemia in sickle cell disease (SCD). Exposure to prasugrel's active metabolite (Pras-AM) and its antiplatelet activity in SCD have not been investigated.

METHODS

Thirteen adult patients with SCD and an equal number of matched healthy control subjects were studied before and after 12 days of 5.0 or 7.5 mg day(-1) prasugrel treatment. Platelet reactivity was assessed by light transmission aggregometry (LTA), impedance aggregometry (MEA), VerifyNow® P2Y12, vasodilator-stimulated phosphoprotein (VASP) phosphorylation and Plateletworks. Exposure to Pras-AM was also assessed.

RESULTS

At baseline, patients with SCD showed increased platelet reactivity vs. healthy control subjects with VerifyNow (408 vs. 323 P2Y12 reaction units (PRU), respectively, P = 0.003) and MEA (106 vs. 77 area under the aggregation curve (AU.min), P = 0.002); lower platelet reactivity index with VASP flow cytometry (59 vs. 79% platelet reactivity index (PRI), P = 0.018); and no significant differences with LTA, VASP enzyme-linked immunosorbent assay or Plateletworks. Relative to baseline, prasugrel significantly reduced platelet reactivity by all assays in both populations (all P < 0.05). Prasugrel was well tolerated, with no bleeding-related events in patients with SCD. The mean concentration-time profiles of Pras-AM were comparable between healthy subjects and patients with SCD following a single 10 mg prasugrel dose and following the 12th dose of 7.5 or 5 mg prasugrel.

CONCLUSIONS

Results demonstrate that in response to prasugrel, patients with SCD and healthy subjects have similar degrees of platelet inhibition and exposure to Pras-AM, and provide a basis for further study of prasugrel in patients with SCD.

Aspirin discontinuation syndromes: clinical implications of basic research studies

Abrupt discontinuation of many drugs used in medicine causes withdrawal syndromes, some of which can be fatal. Discontinuation of a number of cardiovascular drugs can increase the risk of cardiovascular events. Whereas aspirin administration is known to decrease the risk of vascular ischemic problems, aspirin withdrawal may temporarily increase the risk of thrombotic events. Indeed, aspirin withdrawal has been associated with an increased risk of thrombosis both in clinical and fundamental research studies. Such complications occur within the first month after interrupting aspirin therapy and their mechanism remains unexplained. We have previously demonstrated that aspirin, when injected as a single high dose (100 mg/kg), induces a prothrombotic state in the rat, similar to that described above, 8 and 10 days after administration. This effect in the rat may be reproduced 1 hour after a single injection of ultra-low-dose aspirin. Caution is therefore required regarding the possibility of drug discontinuation effects within the framework of drug safety evaluation.

High-dose aspirin in dogs increases vascular resistance with limited additional anti-platelet effect when combined with potent P2Y12 inhibition

INTRODUCTION

With the arrival of the potent P2Y12 antagonists, ticagrelor and prasugrel, the need for co-treatment with aspirin in acute coronary syndromes must be re-examined. This study assessed whether high-dose aspirin: a) provides additional anti-platelet efficacy, assessed in vivo and ex vivo, when combined with P2Y12 inhibition; and/or b) has a negative effect on vascular function.

MATERIALS AND METHODS

Using an anaesthetized dog model of thrombosis, the effects of aspirin (50mg/kg) in addition to clopidogrel and ticagrelor were evaluated at two levels of P2Y12 inhibition, maximal (≥96%) and sub-maximal (~80%), as assessed by ex vivo ADP-induced whole blood impedence aggregometry.

RESULTS

In the absence of aspirin, maximal and sub-maximal P2Y12 inhibition inhibited arachidonic acid-induced platelet aggregation by approximately 80% and 24%, respectively, without affecting platelet TXA2 formation. During maximal P2Y12 inhibition, aspirin provided less additional inhibition of ex vivo arachidonic acid- and collagen-induced platelet aggregation, as compared with sub-maximal P2Y12 inhibition, without additional anti-thrombotic effect in vivo. Aspirin significantly decreased in vivo PGI2 production (27%) and increased vascular resistance (16%), independently of P2Y12 antagonism.

CONCLUSION

In the dog, P2Y12 antagonists inhibit TXA2-mediated platelet-aggregation independently of aspirin. Aspirin provides less additional anti-platelet effects during maximal compared with sub-maximal P2Y12 inhibition but increases vascular resistance.

Monitoring the effectiveness of antiplatelet therapy: opportunities and limitations

Previous clinical studies have shown heterogeneity in individual patient responses to antiplatelet therapy and high residual platelet reactivity is associated with increased risk of adverse clinical events. Monitoring response to antiplatelet therapy and tailoring treatment accordingly is currently not recommended in routine clinical practice largely due to the lack of a standardized definition of antiplatelet therapy hyporesponse and the need for a widely accepted point-of-care platelet function test that can be reliably utilized in frontline clinical practice. Recent data have shown that titrating the dose of clopidogrel in patients undergoing percutaneous coronary intervention significantly reduces the incidence of major adverse cardiovascular events and large-scale clinical trials are currently underway to investigate whether individually tailored treatment based on results of platelet function testing leads to improved clinical outcome. Furthermore, genetic testing has demonstrated a link between CYP2C19 genetic polymorphisms, altered clopidogrel metabolite concentrations and adverse clinical events. Clinical studies are currently underway to investigate the potential clinical benefit associated with genotype-guided tailoring of antiplatelet therapy. With the advent of newer, more potent antiplatelet agents and their associated increased bleeding risks, it will become imperative in the future to select the most appropriate, safe and effective drug.

Metabolism and disposition of the thienopyridine antiplatelet drugs ticlopidine, clopidogrel, and prasugrel in humans

Ticlopidine, clopidogrel, and prasugrel are thienopyridine prodrugs that inhibit adenosine-5'-diphosphate (ADP)-mediated platelet aggregation in vivo. These compounds are converted to thiol-containing active metabolites through a corresponding thiolactone. The 3 compounds differ in their metabolic pathways to their active metabolites in humans. Whereas ticlopidine and clopidogrel are metabolized to their thiolactones in the liver by cytochromes P450, prasugrel proceeds to its thiolactone following hydrolysis by carboxylesterase 2 during absorption, and a portion of prasugrel's active metabolite is also formed by intestinal CYP3A. Both ticlopidine and clopidogrel are subject to major competing metabolic pathways to inactive metabolites. Thus, varying efficiencies in the formation of active metabolites affect observed effects on the onset of action and extent of inhibition of platelet aggregation (IPA). Knowledge of the CYP-dependent formation of ticlopidine and clopidogrel thiolactones helps explain some of the observed drug-drug interactions with these molecules and, more important, the role of CYP2C19 genetic polymorphism on the pharmacokinetics of and pharmacodynamic response to clopidogrel. The lack of drug interaction potential and the absence of CYP2C19 genetic effect result in a predictable response to thienopyridine antiplatelet therapy with prasugrel. Current literature shows that greater ADP-mediated IPA is associated with significantly better clinical outcomes for patients with acute coronary syndrome.

The pharmacokinetics and pharmacodynamics of prasugrel in healthy Chinese, Japanese, and Korean subjects compared with healthy Caucasian subjects

PURPOSE

Prasugrel is a novel thienopyridine prodrug metabolised to an active metabolite that binds irreversibly to the platelet P2Y(12) receptor and inhibits adenosine diphosphate (ADP)-induced platelet aggregation. We compared prasugrel pharmacokinetics, pharmacodynamics, and tolerability in healthy Chinese, Japanese, Korean and Caucasian subjects.

METHODS

In an open-label, single-centre, parallel-design study, 89 healthy subjects (25 Chinese, 20 Japanese, 22 Korean and 22 Caucasian) aged 20-65 years were given a prasugrel 60-mg loading dose (LD) followed by daily 10-mg maintenance doses (MD) for 7 days and then 5-mg MD for 10 days. Plasma concentrations of prasugrel's active metabolite and inhibition of ADP-induced platelet aggregation (IPA) were determined.

RESULTS

Mean exposure to prasugrel's active metabolite in all treatment regimens was higher in each of the Asian groups than in the Caucasian group, although there was considerable overlap between individual exposure estimates in Asians and Caucasians. The mean IPA was also higher in Asians than in Caucasians following a prasugrel 60-mg LD, although the difference did not consistently achieve statistical significance. Prasugrel 10-mg or 5-mg MD produced statistically significantly higher IPA in each Asian group compared with that in the Caucasians. Prasugrel was well tolerated during the LD and MD regimens by all groups.

CONCLUSIONS

Mean exposure to the prasugrel active metabolite following prasugrel 60-mg LD and during daily 10-mg or 5-mg MD was higher in each of the Asian groups than in the Caucasian group, which resulted in greater platelet inhibition.

Effect of rifampin on the pharmacokinetics and pharmacodynamics of prasugrel in healthy male subjects

OBJECTIVE

Prasugrel is a thienopyridine antiplatelet agent for the prevention of atherothrombotic events in patients with acute coronary syndrome undergoing percutaneous coronary intervention. Since cytochrome P450 enzymes CYP3A4 and CYP2B6 play a major role in prasugrel's active metabolite formation, the effect of potent CYP induction by rifampin on the pharmacokinetics of prasugrel and on the pharmacodynamic response to prasugrel was evaluated in healthy male subjects.

RESEARCH DESIGN AND METHODS

This was an open-label, two-period, fixed-sequence study conducted at a single clinical research center. In the first treatment period, subjects received prasugrel as an oral 60-mg loading dose (LD) on the first day followed by ten oral, 10-mg daily maintenance doses. After a 2-week washout period, subjects received oral rifampin alone (600 mg once daily) for 8 days, followed by coadministration of oral rifampin with prasugrel, given as a 60-mg LD on the first day followed by five daily 10-mg MDs. Blood collection for pharmacokinetic and pharmacodynamic analyses occurred after the LD and fifth MD of prasugrel in both periods. CLINICAL TRIAL SYNOPSIS: clinicalstudyresults.org ID #8976

RESULTS

Rifampin coadministration (600 mg daily) did not affect exposure to prasugrel's active metabolite (R-138727). However, at 2 and 4 h after the prasugrel loading dose (60 mg), rifampicin coadministration was associated with a 6-9 percentage point decrease (p < 0.01) in the magnitude of platelet inhibition; similarly, a 5-17 percentage point decrease (p < 0.05) was observed with rifampin coadministration during the prasugrel maintenance dose (10 mg) period. Post hoc in vitro experiments demonstrated a dose-dependent R-138727-rifampin interaction at the P2Y(12) level unrelated to enzyme induction. A limitation of this study is that while results of the in vitro post hoc study indicate a pharmacodynamic interaction with rifampin, the mechanism underlying this interaction has not been elucidated.

CONCLUSIONS

Dose adjustment should not be necessary when prasugrel is administered with CYP inducers since formation of prasugrel's active metabolite is not affected by potent enzyme induction with rifampin.

Effect of atorvastatin on the pharmacokinetics and pharmacodynamics of prasugrel and clopidogrel in healthy subjects

STUDY OBJECTIVE

To investigate the potential effect of atorvastatin 80 mg/day on the pharmacokinetics and pharmacodynamics of the thienopyridines prasugrel and clopidogrel.

DESIGN

Open-label, randomized, crossover, two-arm, parallel-group study.

SETTING

Single clinical research center in the United Kingdom.

PARTICIPANTS

Sixty-nine healthy men aged 18-60 years. Intervention. Subjects received either a loading dose of prasugrel 60 mg followed by a maintenance dose of 10 mg/day or a loading dose of clopidogrel 300 mg followed by 75 mg/day. The drug was given as monotherapy for 10 days, and after a 6-day run-in period with atorvastatin 80 mg/day, the same dosage of atorvastatin was continued with the respective thienopyridine for 10 days. A 14-day washout period separated the treatment regimens.

MEASUREMENTS AND MAIN RESULTS

Blood samples were collected before and at various time points after dosing on days 1 and 11 for determination of plasma concentrations of metabolites and for measurement of platelet aggregation induced by adenosine 5'-diphosphate 20 microM and vasodilator-stimulated phosphoprotein (VASP). Coadministration of atorvastatin did not alter exposure to active metabolites of prasugrel or clopidogrel after the loading dose and thus did not alter inhibition of platelet aggregation (IPA). During maintenance dosing, atorvastatin administration resulted in 17% and 28% increases in the area under the plasma concentration-time curve (AUC) values of prasugrel's and clopidogrel's active metabolites, respectively. These small changes in AUC did not result in a significant change in IPA response to prasugrel but did result in a significant increase in IPA during clopidogrel maintenance dosing at some, but not all, of the time points on day 11. Coadministration of atorvastatin with either prasugrel or clopidogrel had no effect on VASP phosphorylation relative to the thienopyridine alone after the loading dose.

CONCLUSION

Coadministration of atorvastatin 80 mg/day with prasugrel or clopidogrel did not negatively affect the antiplatelet response to either drug after a loading dose or during maintenance dosing. The lack of a clinically meaningful effect of high-dose atorvastatin on the pharmacodynamic response to prasugrel after the loading or maintenance dose indicates that no dosage adjustment should be necessary in patients receiving these drugs concomitantly.

Fast platelet suppression by lysine acetylsalicylate in chronic stable coronary patients. Potential clinical impact over regular aspirin for coronary syndromes

BACKGROUND

The rapid utilization of fibrinolytics following Q-wave myocardial infarction has clearly modified the evolution of this disease. However, it is still not known whether the immediate inhibition of platelet aggregation (PA) during the coronary event improves outcomes.

HYPOTHESIS

The present study was designed to test, in patients with known coronary artery disease (chronic stable angina), whether the particular kinetic pattern of lysine acetylsalicylate (LA) compared with aspirin may affect the time to onset of inhibition of platelet aggregation.

METHODS

Ten patients suffering from chronic stable angina participated in this study to compare the efficacy and speed of the inhibition of PA with 320 mg of LA versus 320 mg of aspirin. All patients discontinued the use of aspirin and any other anti-inflammatory agents for 15 days prior to the beginning of the study. They were randomly assigned to LA or aspirin. Blood specimens were obtained to measure the PA at admission, and 5, 10, 20, 30, and 60 min after ingestion. Patients continued to take the assigned drug once a day for the following 4 days. On Day 5, a new blood sample was taken. After this, patients underwent a 15-day wash-out period, and then crossed over to the opposite drug. The samples were analyzed immediately using platelet-rich plasma stimulated with adenosine diphosphate (ADP) 2 mumol/l, collagen 1 microgram/ml, epinephrine 20 mumol/l, and sodium arachidonate acid 0.75 mm/l.

RESULTS

The same level of PA inhibition after 30 and 60 min of aspirin administration can be obtained with LA 5 min following ingestion (sodium arachidonate acid: LA: 16.3 +/- 25.9 vs. aspirin 57.6 +/- 8.2; p = 0.00014; collagen: LA 18.9 +/- 20.1 vs. aspirin 47.2 +/- 10.5; p = 0.00092; ADP: LA 27.3 +/- 18.4 vs. aspirin 39.7 +/- 21.8, p = 0.18; epinephrine: LA 22.0 +/- 9.9 vs. aspirin 55.4 +/- 10.9, p = 0.00002.

CONCLUSIONS

Platelet aggregation inhibition immediately following LA may have significant clinical implications for the treatment of coronary syndromes.

Switching directly to prasugrel from clopidogrel results in greater inhibition of platelet aggregation in aspirin-treated subjects

Prasugrel, a novel P2Y(12) antagonist, achieves faster onset and greater inhibition of platelet aggregation than clopidogrel 300 and 600 mg loading doses (LD). We studied the safety, time course, and level of platelet inhibition when switching directly from clopidogrel 75 mg maintenance dose (MD) to a prasugrel 60 mg LD/10 mg MD or 10 mg MD regimen. Healthy subjects (n = 39) on aspirin (81 mg/d) received a clopidogrel 600 mg LD followed by 10 days of clopidogrel MD (75 mg/d). Subjects were then randomized without a washout period to prasugrel 60 mg LD (n = 16) followed by 10 days of prasugrel MD (10 mg/d) or to prasugrel MD (10 mg/d, n = 19) for 11 days. Maximal platelet aggregation (MPA) to 20 microM ADP was measured by turbidimetric aggregometry. In subjects on clopidogrel 75 mg MD, mean MPA decreased from 39 to 12% by 30 minutes, and to 5% by 1 hour after a prasugrel 60 mg LD (p < 0.001 for both) and from 37 to 28% (p < 0.001) by 1 hour after a prasugrel 10 mg MD. During prasugrel MD, a new pharmacodynamic steady state MPA of approximately 24% (p < 0.01 vs. clopidogrel MD) occurred within four to five days of switching from clopidogrel. Changing from clopidogrel to prasugrel did not increase bleeding episodes or other adverse events. Switching directly from clopidogrel MD to either prasugrel LD or MD was well tolerated and resulted in significantly greater levels of platelet inhibition than a clopidogrel 75 mg MD.

Increased active metabolite formation explains the greater platelet inhibition with prasugrel compared to high-dose clopidogrel

Prasugrel pharmacodynamics and pharmacokinetics after a 60-mg loading dose (LD) and daily 10-mg maintenance doses (MD) were compared in a 3-way crossover study to clopidogrel 600-mg/75-mg and 300-mg/75-mg LD/MD in 41 healthy, aspirin-free subjects. Each LD was followed by 7 days of daily MD and a 14-day washout period. Inhibition of platelet aggregation (IPA) was assessed by turbidometric aggregometry (20 and 5 microM ADP). Prasugrel 60-mg achieved higher mean IPA (54%) 30 minutes post-LD than clopidogrel 300-mg (3%) or 600-mg (6%) (P < 0.001) and greater IPA by 1 hour (82%) and 2 hours (91%) than the 6-hour IPA for clopidogrel 300-mg (51%) or 600-mg (69%) (P < 0.01). During MD, IPA for prasugrel 10-mg (78%) exceeded that of clopidogrel (300-mg/75-mg, 56%; 600-mg/75-mg, 52%; P < 0.001). Active metabolite area under the concentration-time curve (AUC0-tlast) after prasugrel 60-mg (594 ng.hr/mL) was 2.2 times that after clopidogrel 600-mg. Prasugrel active metabolite AUC0-tlast was consistent with dose-proportionality from 10-mg to 60-mg, while clopidogrel active metabolite AUC0-tlast exhibited saturable absorption and/or metabolism. In conclusion, greater exposure to prasugrel's active metabolite results in faster onset, higher levels, and less variability of platelet inhibition compared with high-dose clopidogrel in healthy subjects.

A multiple dose study of prasugrel (CS-747), a novel thienopyridine P2Y12 inhibitor, compared with clopidogrel in healthy humans

AIMS

This double-blind, placebo-controlled trial was designed to evaluate the pharmacodynamics, pharmacokinetics, safety, and tolerability of prasugrel (CS-747, LY640315), a novel thienopyridine P2Y(12) ADP receptor antagonist compared with clopidogrel, during multiple oral dosing in healthy subjects.

METHODS

Thirty subjects received placebo, prasugrel 5 mg, 10 mg, or 20 mg, or clopidogrel 75 mg orally, daily for 10 days. Platelet aggregation, bleeding time, and prasugrel metabolites were measured and adverse events were recorded.

RESULTS

Inhibition of ADP-induced platelet aggregation reached steady state by day 3 following prasugrel 10 and 20 mg compared with 5 days for clopidogrel 75 mg or prasugrel 5 mg. Compared with placebo, at 24 h after the last dose of study drug, inhibition of platelet aggregation using (20 microm) ADP was significantly higher in the prasugrel 10 mg group (58.2 +/- 4.9% vs. 9.2 +/- 4.0%, P < 0.001) with no difference in the clopidogrel group (15.7 +/- 6.8% vs. 9.2 +/- 4.0%, P = 0.78). With 5 microm ADP, inhibition of platelet aggregation with prasugrel 10 mg and clopidogrel 75 mg was significantly higher than with placebo (prasugrel 10 mg, 70.5 +/- 4.7%; clopidogrel 75 mg, 36.5 +/- 9.0%; vs. placebo, 11.3 +/- 5.1%; P < 0.0001 and P = 0.02). On day 10 at 4 h postdose, bleeding time was prolonged with prasugrel 10 mg (prasugrel 10 mg, 706 +/- 252 s vs. placebo, 221 +/- 38 s, P = 0.05) but not with clopidogrel (283 +/- 56 s, P = 0.98). There were no clinically significant bleeding events, serious adverse events, or discontinuations of the study drug.

CONCLUSIONS

Compared with clopidogrel 75 mg, prasugrel 10 mg and 20 mg daily for 10 days resulted in more rapid, more consistent, and higher levels of platelet inhibition.

Cytochrome P450 3A inhibition by ketoconazole affects prasugrel and clopidogrel pharmacokinetics and pharmacodynamics differently

Prasugrel and clopidogrel inhibit platelet aggregation through active metabolite formation. Prasugrel's active metabolite (R-138727) is formed primarily by cytochrome P450 (CYP) 3A and CYP2B6, with roles for CYP2C9 and CYP2C19. Clopidogrel's activation involves two sequential steps by CYP3A, CYP1A2, CYP2C9, CYP2C19, and/or CYP2B6. In a randomized crossover study, healthy subjects received a loading dose (LD) of prasugrel (60 mg) or clopidogrel (300 mg), followed by five daily maintenance doses (MDs) (15 and 75 mg, respectively) with or without the potent CYP3A inhibitor ketoconazole (400 mg/day). Subjects had a 2-week washout between periods. Ketoconazole decreased R-138727 and clopidogrel active metabolite Cmax (maximum plasma concentration) 34-61% after prasugrel and clopidogrel dosing. Ketoconazole did not affect R-138727 exposure or prasugrel's inhibition of platelet aggregation (IPA). Ketoconazole decreased clopidogrel's active metabolite AUC0-24 (area under the concentration-time curve to 24 h postdose) 22% (LD) to 29% (MD) and reduced IPA 28% (LD) to 33% (MD). We conclude that CYP3A4 and CYP3A5 inhibition by ketoconazole affects formation of clopidogrel's but not prasugrel's active metabolite. The decreased formation of clopidogrel's active metabolite is associated with reduced IPA.

Effects of different aspirin formulations on platelet aggregation times and on plasma salicylate concentrations

BACKGROUND

Early aspirin treatment is widely used to inhibit platelet activity and to reduce morbidity and mortality in patients presenting with an acute myocardial infarction or a stroke. A number of different aspirin formulations have been used for this purpose; however, a comparison of their effectiveness in inhibiting early platelet aggregation has not been determined.

METHODS

In this study, we determined plasma salicylate concentrations and platelet inhibitory activities at various times after ingestion of three commonly used aspirin formulations: soluble aspirin (Alka-Seltzer), 325 mg, chewed baby aspirin, 324 mg, and whole compressed non-enteric coated aspirin, 324 mg. Twenty-four healthy volunteers, 18-39 years of age, participated in the prospective single-blinded triple-crossover study. Plasma salicylate concentrations and inhibition of arachidonic acid-induced platelet aggregation were determined on post-dose blood samples collected at 2.5, 5.0, 7.5, 10, 15, 20, 25, 30, and 40 min. All subjects crossed over to the other two formulations with at least 2 weeks between ingestions.

RESULTS

The median platelet inhibition times for the chewed, soluble, and whole aspirin formulations were 7.5, 7.5, and 10.0 min, respectively. Soluble and chewed aspirin were found to inhibit platelet aggregation faster than whole aspirin (p<0.001); however, there were no significant differences in platelet aggregation times between the soluble and chewed formulations (p<0.163). Inhibition of platelet aggregation was found to occur at an average plasma salicylate concentration of 2.46 microg/mL, regardless of method of ingestion.

CONCLUSION

The results indicate that soluble and chewed aspirin inhibit platelet aggregation in a shorter period of time than does whole aspirin. The results suggest that chewing baby aspirin or taking soluble buffered aspirin may be the preferred route of administration for early platelet inhibition.

Duration of increased bleeding tendency after cessation of aspirin therapy

BACKGROUND

Aspirin has a significant effect on hemostasis, so it is often recommended that patients taking aspirin discontinue treatment before elective surgery. While off aspirin, these patients may be at risk of thrombosis. The optimum period of time that aspirin should be withheld is controversial. The aim of this study was to establish the duration of the antihemostatic effect of prolonged aspirin therapy.

STUDY DESIGN

In a prospective study, 51 healthy volunteers were randomly assigned into 3 groups, each receiving an identical tablet for 14 days. One group received a placebo tablet; individuals in the other two groups received either 75 mg or 300 mg of aspirin once a day. Template bleeding times and specific platelet function testing (using the PFA-100; Dade Behring) were carried out on subjects before therapy and again after its completion until they returned to baseline.

RESULTS

Thirty-eight volunteers complied sufficiently with the protocol to provide useful results. All bleeding times normalized within 96 hours and all platelet function tests within 144 hours after stopping aspirin. There was no demonstrable hemostatic defect in any volunteer persisting by or beyond the sixth day after treatment cessation. There was no apparent difference in duration of effect between those taking either 75 mg or 300 mg of aspirin.

CONCLUSIONS

This study uses sensitive measures of platelet function to demonstrate the duration of increased bleeding tendency after withdrawal of aspirin therapy. It supports discontinuation of aspirin therapy 5 days before elective surgery (with the operation being performed on the sixth day).

Effects of enteric-coated, low-dose aspirin on parameters of platelet function

BACKGROUND

Aspirin is widely used as an anti-thrombotic drug; however, it has been suggested that enteric-coated formulations of aspirin may be less bioavailable and less effective as anti-thrombotic agents.

AIM

To assess the effect of a formulation of enteric-coated, low-dose (81 mg) aspirin on serum generated thromboxane B2 and platelet aggregation in healthy subjects.

METHODS

Twenty-four subjects participated in a double-blind, randomized, placebo-controlled, parallel-group, multiple-dose study. Twelve subjects in each of two groups received a daily oral dose of enteric-coated aspirin (81 mg) or matching placebo for 7 days. Serum thromboxane B2 and platelet aggregation (using 1 mm arachidonic acid and 1 microg/mL collagen as agonists) were measured 1-3 days prior to day 1, on day 1 (prior to therapy) and 4 h after the last dose on day 7.

RESULTS

After seven daily doses of enteric-coated aspirin, the mean percentage inhibition from baseline of ex vivo generated serum thromboxane B2 was 97.4%, compared with a 7.8% increase after placebo treatment. The mean percentage inhibition of arachidonic acid- and collagen-induced platelet aggregation was 97.9% and 70.9%, respectively, following enteric-coated aspirin, compared with - 1.0% and 2.7%, respectively, after placebo.

CONCLUSIONS

The anti-platelet effects of multiple, daily, low-dose aspirin (as assessed by inhibition of serum thromboxane B2 and platelet aggregation) are not adversely affected by enteric coating.

A high level of cyclooxygenase-2 inhibitor selectivity is associated with a reduced interference of platelet cyclooxygenase-1 inactivation by aspirin

Both nonsteroidal anti-inflammatory drugs, such as ibuprofen, and the prototypical selective cyclooxygenase (Cox)-2 inhibitors DuP-697 and NS-398 block the inhibition of Cox-1 by aspirin in vitro. However, clinical studies have shown that the Cox-2 selective drugs (or coxibs) rofecoxib and etoricoxib, at therapeutic doses, do not interfere with the antiplatelet effect of aspirin, in contrast to ibuprofen. Here, we have evaluated the relative potential of ibuprofen and various coxibs to interfere with the inactivation of Cox-1 by aspirin by using purified enzyme and calcium ionophore-activated human platelets. The irreversible inactivation of Cox-1 by aspirin can be antagonized by ibuprofen and coxibs, albeit with widely different potencies. The rank order of potencies for this process (ibuprofen > celecoxib > valdecoxib > rofecoxib > etoricoxib) parallels that obtained for the inhibition of Cox-1-mediated thromboxane B(2) production by calcium ionophore-stimulated platelets. The antagonism of aspirin therefore likely involves a competition at the enzyme active site. The EC(50) value for the antagonism against 10 microM aspirin for each drug is approximately 10- to 40-fold lower than the corresponding IC(50) value for inhibition of platelet Cox-1 activity, consistent with the much weaker initial binding of aspirin to Cox-1 as compared with arachidonic acid. These results show that a low affinity for Cox-1 and a high degree of Cox-2 selectivity confers a low potential to block aspirin inhibition of platelet Cox-1, consistent with the results of clinical studies.

Prevention of pulmonary embolism and deep vein thrombosis with low dose aspirin: Pulmonary Embolism Prevention (PEP) trial

BACKGROUND

Previous trials of antiplatelet therapy for the prevention of venous thromboembolism have individually been inconclusive, but a meta-analysis of their results indicated reductions in the risks of deep-vein thrombosis and of pulmonary embolism in various high-risk groups. The aim of this large randomised placebo-controlled trial was to confirm or refute these apparent benefits.

METHODS

During 1992-1998, 148 hospitals in Australia, New Zealand, South Africa, Sweden and the UK randomised 13,356 patients undergoing surgery for hip fracture, and 22 hospitals in New Zealand randomised a further 4088 patients undergoing elective arthroplasty. Study treatment was 160 mg daily aspirin or placebo, started preoperatively and continued for 35 days. Patients received any other thromboprophylaxis thought necessary. Follow-up was of mortality and of in-hospital morbidity up to day 35.

FINDINGS

Among the patients with hip fracture, allocation to aspirin produced proportional reductions in pulmonary embolism of 43% (95% CI 18-60; p=0.002) and in symptomatic deep-vein thrombosis of 29% (3-48; p=0.03). Pulmonary embolism or deep-vein thrombosis was confirmed in 105 (1.6%) of 6679 patients assigned aspirin compared with 165 (2.5%) of 6677 assigned placebo, which represents an absolute reduction of 9 (SE 2) per 1000 and a proportional reduction of 36% (19-50; p=0.0003). Similar proportional effects were seen in all major subgroups, including patients receiving subcutaneous heparin. Aspirin prevented 4 (1) fatal pulmonary emboli per 1000 patients (18 aspirin-group vs 43 placebo-group deaths), representing a proportional reduction of 58% (27-76; p=0.002), with no apparent effect on deaths from any other vascular cause (hazard ratio 1.04 [95% CI 0.86-1.26]) or non-vascular cause (1.01 [0.84-1.23]). Deaths due to bleeding were few (13 aspirin vs 15 placebo), but there was an excess of 6 (3) postoperative transfused bleeding episodes per 1000 patients assigned aspirin (p=0.04). Among elective-arthroplasty patients, rates of venous thromboembolism were lower, but the proportional effects of aspirin were compatible with those among patients with hip fracture.

INTERPRETATION

These results, along with those of the previous meta-analysis, show that aspirin reduces the risk of pulmonary embolism and deep-vein thrombosis by at least a third throughout a period of increased risk. Hence, there is now good evidence for considering aspirin routinely in a wide range of surgical and medical groups at high risk of venous thromboembolism.

Development of dual-acting agents for thromboxane receptor antagonism and thromboxane synthase inhibition. 3. Synthesis and biological activities of oxazolecarboxamide-substituted omega-phenyl-omega-(3-pyridyl)alkenoic acid derivatives and related compounds

A novel series of oxazolecarboxamide-substituted omega-phenyl-omega-(3-pyridyl)alkenoic acid derivatives was discovered as potent dual-acting agents to block the TXA2 receptor and to inhibit the thromboxane synthase (TRA/TSI). Synthesis, structure-activity relationship (SAR), and in vitro and in vivo pharmacology of this series of compounds are described. Modification of the series revolved around the oxazole moiety to increase the hydrophilicity of the compounds and to correlate the biological activity with lipophilicity of the compounds. The most potent in the series was (E)-7-[4-[4-[[(4-cyclohexylbutyl)amino]carbonyl]-2-oxazolyl] phenyl]-7 -(3-pyridyl)hept-6-enoic acid (14) with Kd = 9.9 +/- 0.4 nM for the thromboxane receptor antagonism and IC50 = 55.0 +/- 17.9 nM for thromboxane synthase inhibition. The compound 14 was a selective TRA/TSI which exhibited desirable characteristics for oral activity, "shunt" effect to elevate PGI2 level, and absence of agonist activity.

Controversies in Antithrombotic Therapy in Cardiovascular Diseases

Antithrombotic treatment became an important point in human medical treatment. Dicoumarols, heparin, aspi rin, and more recently, direct antithrombins and platelet glyco protein IIb/IIIa receptor blockers are the most frequent medi cations used as antithrombotics. The role of these drugs in the treatment of cardiovascular diseases remains controversial. Low-dose aspirin (80-100 mg/day) should be used for second ary prevention in patients with a history of coronary disease. Primary prevention in patients with no risk factors is not rec ommended. Studies using oral anticoagulant therapy indicated that long-term therapy achieves substantial benefit in arterial complications in patient survivors of myocardial infarction. Combined therapy of aspirin and a higher dose of oral antico agulant than that used in the CARS trial seem necessary after myocardial infarction, and further studies should be under taken. In the treatment of unstable angina, the combined use of aspirin and unfractioned heparin (UFH) is widely accepted. Low molecular weight heparin (LMWH) was also proposed for the treatment of these patients, but the beneficial effect of LMWH over UFH is a matter of discussion, and more prospec tive studies with different LMWHs should be undertaken be fore reaching a definitive answer. The use of hirudin needs additional studies because its superiority over heparin is un- proved. The initial clinical experience with blockers/inhibitors of platelet glycoprotein IIb/IIIa receptors has been promising, although some increase of bleeding was reported. According to published trials on the use of antiplatelet drugs and antithrom botic therapy in the prevention of acute closure after PTCA or after stent implantation, antithrombotic therapy decreased the incidence of abrupt closure or reocclusion at 30 days postan gioplasty, but neither antiplatelet agents nor other pharmaco logical agents have been shown to reduce significantly the rate of restenosis. Finally, oral anticoagulant in a target INR of 2.0 to 3.0 together with aspirin 100 mg/day provide good protec tion from thromboembolism and diminish the rate of minor bleeding complications in patients with cardiac valve replace ment.

Human group II 14 kDa phospholipase A2 activates human platelets

Recombinant human group II phospholipase A2 (sPLA2) added to human platelets in the low microg/ml range induced platelet activation, as demonstrated by measurement of platelet aggregation, thromboxane A2 generation and influx of intracellular free Ca2+ concentration and by detection of time-dependent tyrosine phosphorylation of platelet proteins. The presence of Ca2+ at low millimolar concentrations is a prerequisite for the activation of platelets by sPLA2. Mg2+ cannot replace Ca2+. Mg2+, given in addition to the necessary Ca2+, inhibits sPLA2-induced platelet activation. Pre-exposure to sPLA2 completely blocked the aggregating effect of a second dose of sPLA2. Albumin or indomethacin inhibited sPLA2-induced aggregation, similarly to the inhibition of arachidonic acid-induced aggregation. Platelets pre-treated with heparitinase or phosphatidylinositol-specific phospholipase C lost their ability to aggregate in response to sPLA2, although they still responded to other agonists. This suggests that a glycophosphatidylinositol-anchored platelet-membrane heparan sulphate proteoglycan is the binding site for sPLA2 on platelets. Previous reports have stated that sPLA2 is unable to activate platelets. The inhibitory effect of albumin and Mg2+, frequently used in aggregation studies, and the fact that isolated platelets lose their responsiveness to sPLA2 relatively quickly, may explain why the platelet-activating effects of sPLA2 have not been reported earlier.

Use of early aspirin in suspected acute myocardial infarction by General Practitioners in Sri Lanka

Early low dose aspirin therapy is beneficial in myocardial infarction (MI). This study investigated the use of early aspirin therapy in patients with suspected MI by General Practitioners (GP). Patients with MI who were referred to our unit by GPs were studied to see whether aspirin therapy had been initiated before referral. A questionnaire was sent to GPs to test their attitudes and practices regarding early aspirin therapy in suspected MI. Our results indicate that few patients with MI had been given early aspirin therapy. Only a minority of GPs were aware of the benefits of early aspirin therapy in MI, and very few prescribed it. Even when it was prescribed, the dose and route of administration were wrong in most instances.

Prothrombotic effects of erythrocytes on platelet reactivity. Reduction by aspirin

BACKGROUND

Aspirin effectively reduces the incidence of secondary vascular occlusive events in only 25% of patients. Low-dose aspirin as currently used blocks platelet production of prothrombotic thromboxane A2 and allows endothelial synthesis of antithrombotic prostacyclin. This regimen minimizes gastrointestinal toxicity. We previously showed that intact erythrocytes markedly enhance platelet reactivity. Therefore we investigated whether supplementation of low-dose aspirin with a single high dose at 2-week intervals could more effectively block erythrocyte promotion of platelet reactivity.

METHODS AND RESULTS

Effects of different aspirin regimens on erythrocyte enhancement of platelet reactivity in normal volunteers were measured with the use of an assay that evaluates both platelet activation and recruitment. After 15 days of daily ingestion of 50 mg aspirin, reactivity of platelets alone was inhibited. However, erythrocyte promotion of platelet activation and recruitment was only inhibited by approximately 50% and persisted in the total absence of thromboxane synthesis. In contrast, if 50 mg/d aspirin was preceded by a single loading dose of 500 mg aspirin, the erythrocyte prothrombotic effect was strongly inhibited (approximately 90%) for 2 to 3 weeks. However, over time, erythrocytes "escaped" from this inhibition, and once again became prothrombotic, even on a daily regimen of 50 mg aspirin.

CONCLUSIONS

For clinical purposes, we recommend a loading dose of aspirin (500 mg), followed by daily administration of 50 mg. The loading dose should be repeated at 2-week intervals. This regimen blocks recovery of the erythrocyte capacity to promote platelet reactivity and may amplify the therapeutic potential of aspirin in cardiovascular disease.

p38 mitogen-activated protein kinase phosphorylates cytosolic phospholipase A2 (cPLA2) in thrombin-stimulated platelets. Evidence that proline-directed phosphorylation is not required for mobilization of arachidonic acid by cPLA2

The Ca2+-sensitive 85-kDa cytosolic phospholipase A2 (cPLA2) is responsible for thrombin-stimulated mobilization of arachidonic acid for the synthesis of thromboxane A2 in human platelets. We have previously shown that thrombin activates p38 kinase, a recently discovered new member of the mitogen-activated protein kinase family (Kramer, R. M., Roberts, E. F., Strifler, B. A., and Johnstone, E. M. (1995) J. Biol. Chem. 270, 27395-27398) and also induces phosphorylation of cPLA2, thereby increasing its intrinsic catalytic activity. In the present study we have examined the role of p38 kinase in the phosphorylation and activation of cPLA2 in stimulated platelets. We have observed that activation of p38 kinase accompanies receptor-mediated events in platelets and coincides with cPLA2 phosphorylation. Furthermore, in the presence of inhibitors of p38 kinase, the proline-directed phosphorylation of cPLA2 was completely blocked in platelets stimulated with the thrombin receptor agonist peptide SFLLRN and was suppressed during the early (up to 2 min) phase of platelet stimulation caused by thrombin. Unexpectedly, we found that prevention of proline-directed phosphorylation of cPLA2 in stimulated platelets did not attenuate its ability to release arachidonic acid from platelet phospholipids. We conclude that: 1) cPLA2 is a physiological target of p38 kinase; 2) p38 kinase is involved in the early phosphorylation of cPLA2 in stimulated platelets; and 3) proline-directed phosphorylation of cPLA2 is not required for its receptor-mediated activation.

Differential activation of cytosolic phospholipase A2 (cPLA2) by thrombin and thrombin receptor agonist peptide in human platelets. Evidence for activation of cPLA2 independent of the mitogen-activated protein kinases ERK1/2

The thrombin receptor agonist peptide SFLLRN was less effective than thrombin in eliciting the liberation of arachidonic acid and the generation of thromboxane A2 by human platelets. We found that while SFLLRN evokes an initial transient increase in cystolic free calcium concentration ([Ca2+]i) of similar magnitude as that caused by thrombin, the SFLLRN-induced elevation of [Ca2+]i declines more rapidly to near resting levels than that evoked by thrombin, suggesting that disparate levels of [Ca2+]i may contribute to the attenuated arachidonic acid release. Furthermore, we observed that SFLLRN is less effective than thrombin in mediating the "activating" phosphorylation of cytolic phospholipase A2 (cPLA2). Both thrombin and SFLLRN rapidly and transiently activated kinases that phosphorylate the 21-residue synthetic peptide Thr669 derived from the epidermal growth factor receptor, but the maximal activation of proline-directed kinases by SFLLRN was less pronounced than that by thrombin. MonoQ chromatography and immunoblot analysis of extracts from stimulated platelets revealed that while thrombin induced a prominent activation of the mitogen-activated protein kinases ERK1 and ERK2, SFLLRN completely failed to do so. On the other hand, SFLLRN, like thrombin, stimulated the activity of a proline-directed kinase distinct from ERK1/2, but the activation of this kinase was less pronounced following stimulation of platelets with SFLLRN compared with thrombin. We conclude 1) that the partial activation of cPLA2 and the subsequent attenuated mobilization of arachidonic acid in response to SFLLRN may be the consequence of a less prolonged elevation of [Ca2+]i and insufficient activation of proline-directed kinase(s) by SFLLRN and 2) that the ability of SFLLRN to mediate the activating phosphorylation of cPLA2 in the absence of ERK1/2 stimulation suggest that, at least in human platelets, proline-directed kinases other than ERK1/2 may phosphorylate and activate cPLA2.

Effects of nonsteroidal antiinflammatory drugs on platelet function and systemic hemostasis

Aspirin and nonaspirin nonsteroidal antiinflammatory drugs (NSAIDs) inhibit platelet cyclooxygenase, thereby blocking the formation of thromboxane A2. These drugs produce a systemic bleeding tendency by impairing thromboxane-dependent platelet aggregation and consequently prolonging the bleeding time. Aspirin exerts these effects by irreversibly blocking cyclooxygenase and, therefore, its actions persist for the circulating lifetime of the platelet. Nonaspirin NSAIDs inhibit cyclooxygenase reversibly and, therefore, the duration of their action depends on specific drug dose, serum level, and half-life. The clinical risks of bleeding with aspirin or nonaspirin NSAIDs are enhanced by the concomitant use of alcohol or anticoagulants and by associated conditions, including advanced age, liver disease, and other coexisting coagulopathies.

Development of dual-acting agents for thromboxane receptor antagonism and thromboxane synthase inhibition--I. Synthesis, structure-activity relationship, and evaluation of substituted omega-phenyl-omega-(3-pyridyl)alkenoic acids

A series of arylsulfonamido-substituted omega-phenyl-omega-(3-pyridyl)alkenoic acids were synthesized and evaluated in vitro for their ability to act as both a thromboxane A2 receptor antagonist (TRA) and thromboxane synthase inhibitor (TSI). Variations of alkenoic acid chain length, olefin geometry, substituent effect on the benzenesulfonamido group, and conformational flexibility of the substituted arylsulfonamido group were examined. Among the various substituents, iodo-substitution gave the most potent compound. Conformational flexibility between the arylsulfonamido group and the phenyl ring attached to the alkenoic acid side chain significantly enhanced the dual activities. The compound (E)-21c was identified as the most potent TRA/TSI (TRA: Kd = 53 nM; TSI: IC50 = 23 nM) in the series studied. The compounds 9c and 10c have indicated that these series of compounds are orally active and are specific TSIs as exhibited by the so-called 'shunt' effect on prostacyclin synthesis in vitro.

Influence of various doses of aspirin (in vivo) on platelet arachidonic acid metabolism (ex vivo) and function

The influence of various doses of enteric-coated aspirin was evaluated for its in vivo effect on ex vivo platelet arachidonic acid metabolism and function. 24 h after ingestion of the drugs compromised platelet response to the action of agonists such as epinephrine and arachidonate could be demonstrated with as low a dose as 50 mgs aspirin. However, platelets with compromised function were still capable of producing significant quantities of thromboxane. On the other hand, platelets with almost total inhibition of cyclooxygenase activity were capable of aggregating irreversibly when challenged with epinephrine and arachidonate.

Low dose acetylsalicylic acid in the antithrombotic treatment of patients with stable angina pectoris and acute coronary syndromes (unstable angina pectoris and acute myocardial infarction)

Acetylsalicylic acid has an antithrombotic effect by inhibition of thromboxane A2 synthesis in platelets. Thromboxane A2 is a potent stimulator of platelet aggregation and vasoconstriction and synthesis may be completely inhibited by a single oral dose of 150 mg acetylsalicylic acid or an intravenous dose of 100 mg. A daily maintenance dose of 75 mg acetylsalicylic acid is sufficient to effectively inhibit thromboxane A2 synthesis in long-term treatment. Acetylsalicylic acid therapy reduces acute myocardial infarction and sudden death in patients with stable angina pectoris and the drug is equally effective in patients with symptomatic and 'silent' angina pectoris. Early intervention with acetylsalicylic acid in patients with unstable angina pectoris reduces the risk of acute myocardial infarction and death. In patients with acute myocardial infarction, acute therapy with acetylsalicylic acid significantly reduces mortality both in monotherapy and in combination with thrombolytics. In the secondary prophylaxis following acute myocardial infarction, acetylsalicylic acid reduces the incidence of reinfarction and coronary death. Treatment of 100 patients with acute coronary syndrome (unstable angina pectoris or acute myocardial infarction) for 2 years may hinder the development of 3-4 fatal and 4 non-fatal vascular events. The risk of gastrointestinal side-effects and bleeding during acetylsalicylic acid therapy is dose-dependent and the incidence is low with a daily dose of 75-150 mg.

Single-dose effect of enteric-coated aspirin on platelet function and thromboxane generation in middle-aged men

OBJECTIVE

To evaluate the effect of a single dose of enteric-coated aspirin (ECA) in three different dosages on platelet function and thromboxane generation in middle-aged men.

DESIGN AND METHODS

In a nonblind, nonplacebo-controlled, crossover study, a single dose of ECA (50, 250, or 1000 mg) was given in a tablet form to a group of healthy, middle-aged men. Ten subjects, aged 50-67 years, volunteered to participate in this study. Platelet functions including bleeding time, platelet aggregation, adenine nucleotides, beta-thromboglobulin, platelet factor 4, thromboxane generation, and aspirin measurement were determined.

RESULTS

Before ECA ingestion, the intracellular adenine nucleotides (adenosine triphosphate, adenosine diphosphate) were decreased, and both beta-thromboglobulin and platelet factor 4 were increased. These observations suggested that platelets were activated in vivo in middle-aged men. These findings returned to normal within 8 hours after the ingestion of ECA, and maintained normal for at least two days. Bleeding time was significantly prolonged at 8 and 24 hours compared with that before ingestion of ECA 1000 mg (p < 0.05). The generation of platelet thromboxane was maximally inhibited by approximately 40 percent in the samples 8 hours after ECA ingestion. Abnormal values of adenine nucleotides, beta-thromboglobulin, and platelet factor 4 returned to normal within 8 hours. Arachidonic acid-induced platelet aggregation was inhibited compared with that before treatment (p < 0.01) and the inhibitory effect was maintained for at least three days. Adenosine diphosphate- and epinephrine-induced aggregations were less inhibited than those induced by arachidonic acid. Inhibitory effects of ECA on platelet aggregation were dose dependent.

CONCLUSIONS

Our study indicates that platelets are activated in middle-aged men and that a single dose of ECA 50 mg is safe and can inhibit thromboxane synthesis and platelet aggregation. These results suggest that a daily dose of ECA 50 mg may be useful for blocking platelet activation and preventing thrombosis.

Rapidity and duration of platelet suppression by enteric-coated aspirin in healthy young men

The recent demonstration of aspirin's ability to prevent and reduce the severity of myocardial infarction has led to a marked increase in its use and to a need for information regarding the time-course of onset and offset of its antiplatelet effect. A study of healthy men was conducted to determine (1) the rapidity of onset of inhibition of platelet aggregation in response to adenosine diphosphate, and thromboxane A2 production after chewed enteric-coated aspirin (325 mg, n = 10); and (2) the duration of platelet inhibition after cessation of enteric-coated aspirin (325 mg) every other day for 14 days (n = 10). When chewed, enteric-coated aspirin greatly inhibited platelet aggregation response to adenosine diphosphate and thromboxane A2 production within 15 minutes. Complete recovery of platelet aggregation occurred in half of the subjects by day 3, and in 80% of the subjects by day 4; the platelet response was not affected by exercise. This study demonstrates a rapid onset of aspirin's antiplatelet effect and provides information relevant for optimal timing of initiation of aspirin for acute conditions such as myocardial infarction and unstable angina, and cessation of aspirin before surgery.

Thrombolysis: the need for a critical review

The (Thrombolysis in Myocardial Infarction) TIMI-I trial led to the hypothesis that the greater reperfusion rate seen with recombinant tissue-type plasminogen activator (rt-PA) versus streptokinase would result in greater reductions in infarct size and mortality in patients with acute myocardial infarction. Despite extensive investigation, no trial comparing rt-PA with streptokinase (European Cooperative Study Group, Plasminogen Activator Italian Multicenter Study [PAIMS], Gruppo Italiano per lo Studio della Sopravvivenze nell'Infarto Miocardico [GISSI-2], International Study on Infarct Survival [ISIS-3], even TIMI-I itself) nor rt-PA and anisoylated plasminogen-streptokinase activator complex (APSAC or anistreplase) (Bassand, TEAM-3, ISIS-3), have confirmed this hypothesis. In a reversal of traditional scientific method, the studies, rather than the unconfirmed hypothesis, have been rejected. A lack of independent review of this subject may have contributed to this outcome. It is proposed that standards of review and editorial comment mandating true critical distance and independence be followed, permitting greater independence of scientific inquiry, review and debate.

Two year Cottbus reinfarction study with 30 mg aspirin per day

All 701 heart infarction patients admitted to 15 hospitals in the district of Cottbus between 1981 and 1983 were randomly administered 30, 60 or 1000 mg aspirin daily according to the territorial affiliation of their local hospitals. The physical and drug therapy during the 2 years follow-up was highly standardized; deviations--as far as they occurred--were documented. Lower all-cause mortality was statistically demonstrated in patients over 60 and a lower fatal reinfarction rate in patients over 50 as well as in men. Deaths and fatal reinfarctions were significantly lower among patients with a history of angina pectoris, marked ST-depression, with an infarction location except for the posterior wall and among hypercholesterolemic patients. The preventive effect of 60 mg aspirin daily was less than that of 30 mg in comparison to the 1000 mg group. Side effects were seen in 4 and 8% (first and second year), respectively, of the patients administered 30 mg aspirin as opposed to 22 and 17% in patients allocated 1000 mg. We conclude that the optimum dose of aspirin for preventing reinfarctions could be as low as 30 mg daily.