Clinical tolerance and profile of cytokine induction in healthy volunteers following the simultaneous administration of ifn-alpha and the synthetic immunomodulator murabutide

As the therapeutic use of interferon-alpha (IFN-alpha) is limited by a dose-dependent toxicity and variable efficacy, ways of improving the therapeutic index of the cytokine are being sought. Murabutide (N-acetyl muramyl-L-alanyl-D-glutamine-O-n-butyl-ester) (ISTAC Biotechnology, Lille, France) is a safe synthetic and clinically acceptable immunomodulator that enhances the biologic activities of IFN-alpha in different experimental models. We evaluated in healthy human volunteers tolerance of the coadministration of Murabutide with increasing doses of IFN-alpha. The simultaneous administration of the two drugs was well tolerated without any increased or prohibiting toxicity, and all recipients experienced side effects that were similar to those observed after the administration of IFN-alpha alone. We also profiled the serum levels of cytokines induced following coinjection of the two drugs. We mostly detected an induction of anti-inflammatory cytokines and of human immunodeficiency virus type 1 (HIV-1)-suppressive beta-chemokines, in the absence of release of key proinflammatory cytokines. Therefore, the simultaneous administration of Murabutide and IFN-alpha is well tolerated and does not lead to increased toxicity. In addition, the selectivity in the profile of cytokines and chemokines induced following the coadministration of Murabutide and IFN-alpha points to the potential use of this combination in the treatment of inflammatory diseases and chronic viral infections.

Single-dose pharmacodynamics of clopidogrel

The inhibition of platelet aggregation by clopidogrel, a novel platelet ADP-receptor antagonist, was evaluated in healthy male volunteers in two single-dose studies. In one study, 10 subjects received, in increasing order, single doses of 100, 200, 400 and 600 mg of clopidogrel or placebo in five study periods, according to a randomized, doubleblind, protocol design. In the second study, 12 subjects received a single 400 mg dose of clopidogrel as capsules and as tablets, according to an open-label, randomized, crossover design. The interval between the two administrations was seven days. Platelet aggregation induced by ADP (2, 5 and 10 microM) and by collagen (0.5 and 1 microg/mL; rising-dose study only) was assessed from blood samples collected over a period of 24 hours to 72 hours postdose. The inhibition of platelet aggregation was expressed as the mean percent change from baseline in maximum platelet aggregation. The effect of clopidogrel on bleeding time was also assessed. Clopidogrel induced a statistically significant inhibition of ADP-induced platelet aggregation at all doses. With 5 microM of ADP, the inhibition was dose-related up to a dose of 400 mg, with no further increase at a dose of 600 mg. At 2 hours, mean inhibition ranged from 12+/-6% (100 mg) to 42 +/-6% (400 mg), and at 24 hours, it ranged from 17+/-7% (100 mg) to 43+/-9% (400 mg). After 400 mg, the inhibition of platelet aggregation remained stable from 2 hours up to 72 hours, with mean percentages of inhibition ranging from 49 to 39%. Clopidogrel only showed a slight-to-moderate inhibitory effect on collagen-induced platelet aggregation. A mean bleeding time prolongation of 1.7 was observed 5 hours after the 400 mg and 600 mg doses; it was statistically significant only following the higher dose. Individual bleeding time prolongations ranged from 1 to 2.85. Clopidogrel was well tolerated at all doses. The results of these studies were part of the rational for the choice of the loading dose.

Repeated-dose pharmacodynamics of clopidogrel in healthy subjects

The effect of repeated doses of clopidogrel, a novel platelet ADP-receptor antagonist, on platelet aggregation and its tolerance were assessed in two randomized, double-blind studies in healthy male adults. In each of the four successive dose groups in Study I, 6 subjects received either clopidogrel 25, 50, 100, or 150 mg once daily and 2 received placebo for 16 days, according to a rising dose design. In each of the three successive treatment groups of Study II, 9 subjects received clopidogrel (50, 75, or 100 mg once daily) in the morning, 3 received triclopidine 250 mg twice daily and 3 received placebo for 14 days. In both studies, the inhibition of platelet aggregation induced by 5 microM of ADP was measured before dosing (baseline), then at regular intervals during and after treatment. Bleeding time was generally assessed at the same time points as platelet aggregation. In both studies, the inhibition of platelet aggregation reached steady state after day 6 dosing. Mean steady-state percent inhibition of platelet aggregation was 30%, 46%, 53%, and 73% for clopidogrel 25, 50, 100, and 150 mg, respectively, in Study I; and 54%, 52%, 47%, and 43% for clopidogrel 50, 75, 100 mg, and for ticlopidine, respectively, in Study II. After treatment discontinuation, statistically significant inhibition of platelet aggregation persisted for up to 8 days. In Study I, up to 75 mg repeated doses, mean bleeding time prolongation factor did not exceed 2, but increased further to 3.5 and 5.5 at a clopidogrel dose of 100 mg and 150 mg, respectively. In study II, prolongation factors during treatment did not exceed 2.2 for clopidogrel (in the 75 mg dose group) and 1.6 for ticlopidine 500 mg. Recovery of bleeding time was observed within 7-8 days. Treatments were well tolerated, and no serious clinical events or important changes in laboratory parameters were recorded. These data were consistent with those obtained in atherosclerotic patients and showed that the plateau response for the inhibition of platelet aggregation was reached at the 75 mg dose, for which bleeding time prolongation was approximately 2.

Clopidogrel does not affect the pharmacokinetics of theophylline

The potential influence of clopidogrel on the pharmacokinetics of theophylline was evaluated in 15 healthy male subjects during the pharmacokinetic steady state of theophylline, after single and multiple doses. Theophylline was administered orally as one 300-mg capsule in the morning before breakfast and one in the evening before dinner for 13 days (day 1 through day 13), and one capsule on the morning of day 14. Clopidogrel was administered orally as one 75-mg tablet in the morning before breakfast from day 5 through day 14. Plasma concentration of theophylline was determined at the following times: before the morning dose on days, 1, 6-9, and 12; before administration, then at 0.5, 1,2, 3, 4, 5, 6, 7, 8, 10, and 12 hours after administration on days 4, 5, and 14. Tests of hemostasis (ADP-induced platelet aggregation and bleeding time) were carried out 2 hours after clopidogrel dosing on days 5, 7, 9, 11, and 14. The curves of the mean plasma concentration of theophylline over 12 hours post-morning dose on day 4 (drug alone), day 5 (after a single dose of clopidogrel), and day 14 (after 10 days of clopidogrel coadministration) were superimposable, indicating the absence of an effect of clopidogrel on the steady-state pharmacokinetics of theophylline. There were no statistically significant differences between the days of administration for the log-transformed values of theophylline C(bt) (concentration before treatment) Cmax, AUC(0-12h), and Cmin; and the 90% confidence intervals of the day 5/day 4, day 14/day 4, and day 14/day 5 ratios of the geometric means of C(bt) all fell within the (0.80; 1.25) interval. These results show that the administration of clopidogrel during steady state theophylline administration had no effect on the plasma concentration of the latter drug. The average steady-state (days 11-14) percentage of inhibition of ADP-induced platelet aggregation by clopidogrel with respect to day 1 was 46%. The geometric mean of the bleeding time prolongation factor was about 2 at steady state. The latter results indicate that the pharmacodynamics of clopidogrel were not affected by concomitant theophylline.

Pharmacokinetics of estradiol and of estrone during application of three strengths of an estradiol transdermal patch with active matrix

The pharmacokinetic pattern of estradiol (CAS 50-28-2) and of estrone (CAS 53-16-7) during and after application of three strengths of a new transdermal estradiol patch (Dermestril) with active matrix was investigated in a cross-over study in 24 women in natural or surgical menopause. Free estradiol and estrone were assayed by GC-MS on plasma samples obtained during a 4-day application on the upper buttocks of the patches with 3 strengths and release rates of 25, 50 and 100 micrograms/day estradiol. The estradiol concentrations in plasma increased from 0-10 pg/ml typical of menopause to average concentrations of 23, 40 and 79 pg/ml during the application of the new estradiol transdermal patches with the three strengths. The concentrations of estradiol are in the range of those during the early follicular phase in women in fertile age. The increases were linearly related with the strength of the patches. Upon removal of the patches the estradiol concentrations returned to the basal low values in 8-24 h. Retarded with regard to estradiol, there was also an increase of estrone, from basal average concentrations of 22-32 pg/ml up to 31, 39 and 60 pg/ml. The increase of estrone was less pronounced than that of estradiol. Also estrone returned to its basal concentrations 24 h after removal of the patches. The estradiol/ estrone ratio from very low values typical of postmenopause increased to values of about 1, i.e. in the range of those found during the fertile age of woman. The adhesion of the patches was satisfying, provided that direct rough frictions were avoided. The patches were locally well tolerated, with rare mild and transient irritating effects on the skin. Also the systemic tolerability was good, with occasional mild or moderate side effects typical of estradiol (headache, mastodynia and pelvic heaviness) which in the practical use can be easily avoided by the application of patches of lower strength.

Comparative wheal and flare study of mizolastine vs terfenadine, cetirizine, loratadine and placebo in healthy volunteers

1. Mizolastine, a new benzimidazole derivative with potent selective, non-sedative H1-histamine antagonist activity was compared with terfenadine, cetirizine and loratadine using the histamine-induced wheal and flare model in healthy volunteers. 2. Study design was a five way double-blind crossover design using a single dose of mizolastine 10 mg, terfenadine 120 mg, cetirizine 10 mg, loratadine 10 mg and placebo. 3. Histamine tests were performed on 10 occasions up to +24 h after dosing using an intradermal injection of histamine 2 micrograms with concommittant contralateral injection of a saline control. 4. Mizolastine, terfenadine, cetirizine and loratadine significantly (P < 0.001 vs placebo) inhibited the wheal and flare formation starting 1 to 2 h after dosing up to 24 h after dosing. 5. Mizolastine was significantly more active than loratadine on the wheal (P < 0.01) and flare (P < 0.05) inhibition from 3 up to 6 and 8 h respectively, as active as terfenadine on both parameters and as active as cetirizine on wheal inhibition while less active (P < 0.01) than cetirizine on flare inhibition at 2 and 12 h post-dosing.

Pharmacokinetics of sparfloxacin in humans after single oral administration at doses of 200, 400, 600, and 800 mg

The pharmacokinetics of sparfloxacin at oral doses of 200, 400, 600, and 800 mg were studied in 12 healthy volunteers in a randomized double-blind crossover study. Each dose administration was separated by a 1-week washout period. Plasma and urine samples were collected up to 120 hours postdosing, for determination of free and total (free plus glucurono-conjugated) sparfloxacin levels by high-performance liquid chromatography assay and ultraviolet detection. Mean Cmax values ranged from 705 +/- 158 to 1966 +/- 620 ng/mL for the 200 to 800 mg doses, at median tmax ranging from 4 to 5 hours. A slight decrease of sparfloxacin bioavailability with increasing dose was observed because AUC was 87% to 88% of the expected area when the dose was doubled. The elimination half-life values were constant over the dose range (with values ranging from 18 to 21 hours) as well as the renal clearance. The metabolic ratio conjugated/free drug was not modified by increasing dose.

EEG profile of intravenous zolpidem in healthy volunteers

Zolpidem is an imidazopyridine which binds specifically to the omega 1 receptor. Zolpidem demonstrated potent hypnotic activity at a dose of 10 mg. Pharmacodynamics and pharmacokinetics of zolpidem were studied after daytime administration in a randomised, double-blind, placebo-controlled, cross-over trial. Single doses of zolpidem (10 mg IV as a 3-min infusion and 20 mg orally) and placebo were firstly tested in 12 healthy young male volunteers. Two other doses (5 mg IV and orally) were then evaluated in 6 out of these 12 subjects. EEG (4 leads = Fp2-T4, Fp1-T3, T4-02 and T3-01), and Stanford Sleepiness Scale (SSS) were measured up to 5 h postdosing. Blood samples were also collected up to 24 h. The time course of the hypnotic activity of zolpidem, assessed by the score obtained on SSS, showed a similar profile whatever the route or the dose administered: slightly earlier onset after IV but sedative scores were reached at 30 min and the effect peaked between 1 and 1.5 h and lasted 4 h in both conditions. The EEG profile of zolpidem was characterised by a decrease of alpha activity and an increase in delta and in beta activity. The effect on beta activity was marked within the first hour and then disappeared. The time course of delta and alpha activities indicated a rapid onset (10 min after IV, 30 min after oral route) and a duration of 3-4 h. The amplitude of these relative EEG changes and their duration were independent of the route of administration and the dose administered. AUC and Cmax increased proportionally to the administered dose and elimination half life (2h), clearance and volume of distribution did not change according to the dose or the route of administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of 2-(alpha-thenoylthio)-propionylglycine (TTPG) in healthy volunteers--an oral dose-proportionality investigation

The dose linearity of 2-(alpha-thenoylthio)-propionylglycine (TTPG) pharmacokinetics after a single oral administration at three different TTPG doses (180, 540 and 1080 mg) was evaluated in 12 healthy volunteers according to an open, randomized, cross-over study with a 1-week wash-out period between each administration. The duration of the study, for each subject, was 4 weeks. Plasma concentration and urinary excretion of TTPG and its two systemic metabolites, namely propionylglycine (tiopronin) and thiophenecarboxylic acid (TCA) were assayed by a previously well validated HPLC method. Due to differences in the physical and chemical properties of these compounds, two assays were needed, one to measure TTPG and TCA as such, and one to measure derivatized tiopronin. Both used UV detection. TTPG, tiopronin and TCA were quickly detected in plasma, suggesting that the drug administered is rapidly absorbed and biotransformed, in part, in the systemic circulation into the two metabolites noted above. Time-to-peak for all three analytes showed a trend to increase with increasing doses of TTPG, being: 0.42, 0.40 and 0.67 h (P < 0.01) with TTPG; 0.53, 0.47 and 0.73 h (P < 0.05) with TCA; and 1.33, 2.13 and 2.58 h (P < 0.01) with tiopronin. Cmax showed the opposite behaviour with values (ng ml-1) normalized to the dose of 540 mg: 1235, 905 and 513 (P < 0.001) with TTPG; 888, 547 and 383 (P < 0.001) with TCA; and 7290, 6950 and 5170 (P < 0.01) with tiopronin.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacodynamics and pharmacokinetics of mizolastine (SL 85.0324), a new nonsedative H1 antihistamine

The antihistaminic activity, clinical safety, and pharmacokinetics of mizolastine (SL 85.0324) were studied in a 5-way, double-blind crossover study of ten healthy volunteers with doses of 1 to 75 mg. Inhibition of the histamine-induced wheal and flare showed clear dose-dependent antihistaminic activity beginning from the 2-mg dose with a maximum attained between 10 and 20 mg. The onset of action was rapid (one hour) and the effect persisted for more than 24 hours after a 10-mg dose or more. Mizolastine was well tolerated at doses up to 75 mg; subjective and objective signs of transient sedative activity were not observed at doses below 30 mg. The pharmacokinetic profile (rapid absorption with Tmax congruent to 1 h and elimination T1/2 of about eight hours) parallels the pharmacodynamic activity. Within the considered dose range, the pharmacokinetics was linear with no saturation phenomena.

A single blind normal volunteer bioavailability study of a new microencapsulated potassium chloride tablet compared with two reference potassium formulations

A single blind placebo controlled, cross-over study comparing a new microencapsulated potassium chloride tablet (MET) with two reference formulations of oral potassium, potassium chloride solution (PS) and potassium chloride wax-matrix tablets (WMT), was performed in 12 normal healthy volunteers. Urinary potassium excretion was the main criterion of comparison. Results showed that all three formulations have excellent bioavailability. This indicates that potassium absorption in the stomach is similar to that in more distant portions of the gut. The slow-release characteristics of both MET and WMT were confirmed. Clinical and pharmacological tolerance was excellent and no side-effects were reported with any of the potassium formulations studied.

Modulation of allogenic reaction by ticlopidine treatment

Ability of response in proliferation and cytotoxicity of lymphocytes, after in vitro allogeneic reaction was tested in three independent series of experiments, before and after seven days of ticlopidine treatment (500 mg daily) taken by normal adult individuals. In the third experiment, blood samples were taken twice before treatment and twice during the treatment. In two of the three series of experiments the ability of proliferation of responding cells in a mixed lymphocyte reaction was decreased (P less than 0.01). Cytotoxicity was reduced in the three series of experiments when the combination effector/target cells after treatment was compared with the combination before treatment (P less than 0.01 - 0.001), at various effector to target cells ratios for one target (50:1 and 100:1).

Comparative bioavailability study of cefixime administered as tablets or aqueous solution

The relative bioavailability of cefixime was studied in 24 healthy male volunteers, with each subject receiving a single 400mg dose of cefixime administered as an aqueous solution, a 400mg tablet and two 200mg tablets, in a randomised crossover sequence. Serum and urine samples were analysed using high-performance liquid chromatography. Peak cefixime levels were achieved 3 hours after administration of the solution vs 4 hours for the 2 tablet formulations; however, the extent of absorption was only slightly improved with the solution (by 14 and 7% compared with the 1 x 400 and 2 x 200mg tablets, respectively). The 400mg and 2 x 200mg tablets were found to be bioequivalent. The pharmacokinetic profile of the 400mg cefixime tablet (mean maximum plasma concentrations of 4.4 mg/L at 4 hours, area under the concentration-time curve of 34.4 mg/L.h, and apparent terminal elimination half-life of 3.7 hours) supports the clinical evaluation of a 400mg once-daily dosage regimen for cefixime.

[Pharmacokinetics of cefixime in healthy volunteers after a single oral administration of 200 mg]

The antibacterial activity of cefixime is identical with that of parenteral third generation cephalosporins. Its kinetics were studied in 24 healthy male volunteers who received one single 200 mg tablet. Cmax was 3.25 mg/l and Tmax was 4 h. After 12 hours, serum concentrations were still as high as 0.70 mg/l. Half-life was 3.3 h and urinary excretion was not predominant. Thus, cefixime was characterized by its relatively long serum half-life as compared with other cephalosporins. Despite some degree of individual variations, serum and urine concentrations of the antibiotic remained for 12 hours above the MIC of susceptible pathogens.

Pharmacokinetics of nicorandil

This report presents the findings of some studies on single intravenous and oral dosing performed in healthy volunteers to determine the pharmacokinetics and preliminary metabolism of nicorandil, a new vasodilator acting via increase of both membrane potassium conductance and intracellular cyclic guanosine monophosphate in vascular smooth muscle. Nicorandil (5 to 40 mg) is rapidly and completely absorbed after oral administration. Absolute bioavailability is 75 +/- 23% (mean +/- standard deviation) indicating that no significant hepatic first-pass effect exists; peak plasma levels occur within 0.30 to 1.0 hours after dosing. Maximal concentration and area under the plasma concentration time curve of the parent drug are linearly related to a dose range of 5 to 40 mg, which covers the therapeutic regimen proposed for the treatment of patients with angina pectoris. The apparent distribution volume is about 1.4 liters/kg and the plasma concentrations decline according to 2 different processes: (1) a rapid elimination phase (apparent t1/2 beta congruent to 1 hour) that involves about 96% of the dose found in plasma, and a slower phase between the eighth and twenty-fourth hour that could be the consequence of the vascular affinity of the compound. Nicorandil is weakly bound to human plasma proteins (free fraction greater than 75%) and its mean residence time is close to 1.25 hour. Both in animals and in humans, preliminary metabolic studies show that the main biotransformation pathways are denitration and then introduction into the nicotinamide metabolism. However, unchanged nicorandil and denitrated metabolite excreted into the urine represent only about 1 and 4% of the dose, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of food on the bioavailability of a slow release theophylline preparation

Food-induced changes in the absorption of Theostat 300, a controlled release formulation of theophylline, have been studied in healthy volunteers. This open, randomised, 3-way, single-dose study involved 12 volunteers who received the drug either while fasting, or with a standardised low-fat (10g), or high-fat (60g) breakfast. Each subject was studied over a 3-week period, with 3 separate days of oral treatment and a 7-day washout period between treatments. The results showed no differences in AUC0-24 and tmax values between the 3 kinds of diet. The only differences observed concerned absorption. Food intake increased Cmax values by 20%. The steady-state peak concentration obtained by means of simulated plasma levels was not influenced by food intake. This slight food-drug interaction of Theostat 300 seemed to be of no clinical significance.

Pharmacokinetics of ornidazole in patients with severe liver cirrhosis

Pharmacokinetics of ornidazole, a nitroimidazole derivative, was studied after intravenous injection in 10 patients with severe alcoholic cirrhosis and 10 healthy volunteers. Plasma concentrations of ornidazole and its two major hydroxylated metabolites, M1 (alpha-(chloromethyl)-2-hydroxymethyl-5-nitroimidazole-1-ethanol) and M4 (3-(2-methyl-5-nitroimidazole 1-yl) 1,2 propane diol), were measured by HPLC. The t1/2 of ornidazole was 14.1 +/- 0.5 hours for normal subjects and 21.9 +/- 2.9 hours for patients with cirrhosis. Mean plasma clearance was 50.6 +/- 2.1 ml/min in control subjects and 34.9 +/- 4.9 ml/min in patients, whereas apparent V SS was not modified in hepatic insufficiency. In healthy volunteers, M1 and M4 levels are well below levels of the parent drug; in cirrhosis both metabolites accumulate in plasma as a result of decreased elimination. Hepatic cirrhosis prolongs ornidazole elimination, and to avoid cumulation the interval between repeated doses could be doubled.

A priori lithium dosage regimen using population characteristics of pharmacokinetic parameters

The important problem of initiation of long-term lithium treatment is tackled by means of the selection of an a priori dosage regimen based on the presumed efficacy of lithium and absence of toxicity. The pharmacokinetics of Li+ ion is represented by a four-compartment open model including the supposed first-order processes for the release of the active compound from the dosage form and its absorption. Experimental protocols for measurements of serum concentrations and of urinary amounts after single and multiple dosing to healthy volunteers were derived with several oral dosage forms. Estimation of the pharmacokinetic parameters for each subject made it possible to validate the model for the various dosage forms. The interindividual variability of these parameters is taken into account by estimating the characteristics of the statistical distribution for the whole population. A dosage regimen is considered optimum when serum concentration profiles at steady state range from the threshold of efficacy (0.8 mmol/liter) to the threshold of toxicity (2.0 mmol/liter). When the number of daily intakes is fixed, the search for the optimum dose for the whole population is effected by minimizing the expected value of the random variable which characterizes the risks of excursion out of the therapeutic range. By this means universal dosages are shown to be unsatisfactory. However, certain dosage regimens individualized with respect to the renal clearance value of lithium and based on two or three daily intakes can give excellent results even when conventional dosage forms are used.

Clinical pharmacology of flurbiprofen: a novel inhibitor of platelet aggregation

Studies are reviewed of the inhibitory effect of flurbiprofen, given in doses ranging from 50 mg to 200 mg per day for 1 week, on platelet aggregation measured by biological tests (adenosine diphosphate and collagen methods). Flurbiprofen at doses of 50 mg and 100 mg daily had a peak time of action of between 1 and 2 hours, the effects usually disappearing after 24 hours, and 100 mg flurbiprofen caused a similar decrease in platelet aggregation to 1 g aspirin daily. In a clinical study of 72 patients with chronic glomerulonephritis treated with doses of flurbiprofen up to 200 daily there was a significant correlation between the parameters of aggregation measured and treatment, and between proteinuria and adenosine disphosphate aggregation when the flurbiprofen dose did not exceed 100 mg daily.

Effects of ticlopidine, a new platelet aggregation inhibitor in man

Ticlopidine is a new platelet aggregation inhibitor. The effect of this drug was studied on 55 subjects, healthy volunteers and hospitalized patients. The action requires 24 to 48 hr to appear, and lasts more than 3 days. A dose-effect relationship was studied with oral daily doses ranging from 250 to 1,000 mg during 1 wk; it showed a 50% inhibition on adenosine diphosphate (ADP)-induced aggregation at 2 muM concentration on an oral daily dose of 450 mg. No action was found on collagen-induced aggregation, and a mild effect was observed on platelet adhesiveness. Clinical tolerance was assessed in patients given ticlopidine in oral doses up to 500 mg/day during several weeks, showing no overt side effects and no change in the safety parameters.

The interactions of ticlopidine and aspirin in normal subjects

This trial was performed on 24 health volunteers in order to study the possible interactions between aspirin and ticlopidine. The results confirm the inhibitory activity of aspirin on collagen-induced aggregation and that of ticlopidine on ADP-induced aggregation. If aspirin does not modify the inhibitory effect of ticlopidine on ADP-induced aggregation, ticlopidine on the other hand potentiates the effect of aspirin on collagen-induced aggregation.