Absorption kinetics of low-dose chewable aspirin--implications for acute coronary syndromes.

BACKGROUND: This study describes the implications of the pharmacokinetics of low-dose chewable aspirin for acute coronary syndromes. Current guidelines recommend the administration of 162-325 mg aspirin chewing tablets for the treatment of acute myocardial infarction. Although aspirin is widely used and a cornerstone in myocardial infarction, there is no information available on the pharmacokinetics of low doses of chewable aspirin. MATERIALS AND METHODS: This prospective trial assessed the pharmacokinetics of acetylsalicylic acid and its metabolite salicylic acid after intake of 162 mg chewable low-dose aspirin in 35 healthy volunteers. Plasma drug and metabolite levels were analysed using high-performance liquid chromatography, and corresponding pharmacodynamics were determined by impedance aggregometry. RESULTS: Acetylsalicylic acid was rapidly absorbed with a mean Tmax of 27 ± 8 min. Tmax of salicylic acid was 69 ± 21 min. Mean Cmax was 1·8 ± 0·6 mg/L and 7·6 ± 1·4 for acetylsalicylic acid and salicylic acid, respectively. Arachidonic acid-induced aggregation showed maximum platelet inhibition 30 min after drug ingestion. CONCLUSIONS: The characterization of the plasma-time profile fills the gap between the lack of data on pharmacokinetics and the pharmacodynamics and the recommendation for using low-dose chewable aspirin for acute coronary syndromes. We describe for the first time that a 162-mg dose of chewable aspirin is rapidly absorbed and achieves plasma concentrations of the active metabolite salicylic acid required to maximally inhibit platelet aggregation. However, a 162-mg dose is truly a minimum, and doubling this dose might be better for patients with myocardial infarction.

Simultaneous determination of acetylsalicylic acid and salicylic acid in human plasma by isocratic high-pressure liquid chromatography with post-column hydrolysis and fluorescence detection.

A selective, sensitive and rapid high-performance liquid chromatography method with post-column hydrolysis and fluorescence detection was developed for the simultaneous quantification of acetylsalicylic acid and its metabolite salicylic acid in human plasma. Following the addition of 2-hydroxy-3-methoxybenzoic acid as internal standard and simple protein precipitation with acetonitrile, the analytes were separated on a ProntoSIL 120 C18 ace-EPS column (150 × 2 mm, 3 µm) protected by a C8 guard column (5 µm). The mobile phase, 10 mm formic acid in water (pH 2.9) and acetonitrile (70:30, v/v), was used at a flow rate of 0.35 mL/min. After on-line post-column hydrolysis of acetylsalicylic acid (ASA) to salicylic acid (SA) by addition of alkaline solution, the analytes were measured at 290 nm (λex ) and 400 nm (λem ). The method was linear in the concentration ranges between 0.05 and 20 ng/µL for both ASA and SA with a lower limit of quantification of 25 pg/µL for SA and 50 pg/µL for ASA. The limit of detection was 15 pg/µL for SA and 32.5 pg/µL for ASA. The analysis of ASA and SA can be carried out within 8 min; therefore this method is suitable for measuring plasma concentrations of salicylates in clinical routine.

Multisite analytical evaluation of the Abbott ARCHITECT cyclosporine assay.

The objective of this study was to evaluate the analytical performance of the Abbott ARCHITECT Cyclosporine (CsA) immunoassay in 7 clinical laboratories in comparison to liquid chromatography/tandem mass spectrometry (LC/MS/MS), Abbott TDx, Cobas Integra 800, and the Dade Dimension Xpand immunoassay. The ARCHITECT assay uses a whole blood specimen, a pretreatment step with organic reagents to precipitate proteins and extract the drug, followed by a 2-step automated immunoassay with magnetic microparticles coated with anti-CsA antibody and an acridinium-CsA tracer. Imprecision testing at the 7 evaluation sites gave a range of total % coefficient of variations of 7.5%-12.2% at 87.5 ng/mL, 6.6%-14.3% at 411 ng/mL, and 5.2%-10.7% at 916 ng/mL. The lower limit of quantification ranged from 12 to 20 ng/mL. Purified CsA metabolites AM1, AM1c, AM4N, AM9, and AM19 were tested in whole blood by the ARCHITECT assay and showed minimal cross-reactivity at all 7 sites. In particular, AM1 and AM9 cross-reactivity in the ARCHITECT assay, ranged from -2.5% to 0.2% and -0.8% to 2.2%, respectively, and was significantly lower than for the TDx assay, in which the values were 3.2% and 16.1%, respectively. Comparable testing of metabolites in the Dade Dimension Xpand assay at 2 evaluation sites showed cross-reactivity to AM4N (6.4% and 6.8%) and AM9 (2.6% and 3.6%) and testing on the Roche Integra 800 showed cross-reactivity to AM1c (2.4%), AM9 (10.7%), and AM19 (2.8%). Cyclosporine International Proficiency Testing Scheme samples, consisting of both pooled specimens from patients receiving CsA therapy as well as whole-blood specimens supplemented with CsA, were tested by the ARCHITECT assay at 6 sites and showed an average bias of -24 to -58 ng/mL versus LC/MSMS CsA and -2 to -37 ng/mL versus AxSYM CsA. Studies were performed with the ARCHITECT CsA assay on patient specimens with the following results: ARCHITECT CsA assay versus LC/MSMS, average bias of 31 ng/mL; ARCHITECT versus the Dade Dimension assay (4 sites), average biases of -7 to -228 ng/mL; ARCHITECT versus AxSYM and TDx, average biases of -4 and -53 ng/mL, respectively. Spearman correlation coefficients were >or=0.89. The ARCHITECT CsA assay has significantly reduced CsA metabolite interference relative to other immunoassays and is a convenient and sensitive semiautomated method to measure CsA in whole blood.

Multi-site analytical evaluation of a chemiluminescent magnetic microparticle immunoassay (CMIA) for sirolimus on the Abbott ARCHITECT analyzer.

OBJECTIVE: This study evaluated a new chemiluminescent magnetic microparticle immunoassay (CMIA) for sirolimus on the ARCHITECT analyzer. DESIGN AND METHODS: Patient and laboratory proficiency samples were tested at three European sites and one site in the United States. RESULTS: The CMIA total %CV's were all <8% and the Limit of Quantification (LOQ) was <1.52 ng/mL across the four sites. It cross-reacts to sirolimus metabolites F4 and F5 and showed no hematocrit interference over a range of 25% to 55%. Patient specimen correlations to three LC/MS/MS methods gave R>or=0.91 at three sites and mean biases of 14%, 25% and 39%. CMIA patient specimen correlations to the Abbott IMx gave R>or=0.94 at 2 sites and mean biases of 5.4% and 6.9%. CONCLUSIONS: CMIA is a precise and sensitive immunoassay method without hematocrit interference. It correlates well to both LC/MS/MS and immunoassay results, but shows an expected positive bias to LC/MS/MS.

Multi-site analytical evaluation of the Abbott ARCHITECT tacrolimus assay.

The objective of this study was to evaluate the analytical performance of the Abbott ARCHITECT Tacrolimus immunoassay. Proficiency panels and specimens from a population of organ transplant recipients were analyzed in 6 clinical laboratories in Europe and the United States, and the results were compared with other methods. The ARCHITECT assay requires a whole blood specimen pretreatment step with methanol/zinc sulfate to precipitate protein and extract the drug, followed by a 30-minute immunoassay using anti-tacrolimus antibody-coated paramagnetic microparticles and an acridinium-tacrolimus tracer. The assay was free from hematocrit interference in the range 25%-55% and from interference by extremes of cholesterol, triglycerides, bilirubin, total protein, and uric acid. The total percent of coefficient of variations of the assay were 4.9%-7.6% at 3 ng/mL, 2.9%-4.6% at 8.6 ng/mL, and 3.1%-8.2% at 15.5 ng/mL. Limit of detection was < or =0.5 ng/mL and limit of quantification (LOQ) ranged from 0.69 to 1.07 ng/mL across the 6 sites (based on the upper 95% confidence interval concentrations). The 2007 European Consensus Conference on Tacrolimus Optimization recommended the use of assay methods with an LOQ around 1 ng/mL, based upon the need to measure trough tacrolimus blood concentrations precisely down to 3 ng/mL during low-dose tacrolimus regimens. Tacrolimus International Proficiency Testing Scheme samples were measured by the ARCHITECT immunoassay at 5 sites and showed an average bias of -0.28 to +0.85 ng/mL versus IMx Tacrolimus II immunoassay historical values and -0.21 to +0.68 ng/mL versus liquid chromatography/tandem mass spectrometry (LC-MSMS) Tacrolimus historical values. Method comparison studies were performed with the ARCHITECT Tacrolimus immunoassay on patient specimens with the following results: ARCHITECT Tacrolimus assay versus the Abbott IMx Tacrolimus II immunoassay (4 sites) yielded average biases between -0.94 and +0.26 ng/mL; ARCHITECT assay versus the Dade Dimension Tacrolimus immunoassay (2 sites) yielded average biases of -0.46 and +0.11 ng/mL; and ARCHITECT assay versus LC-MSMS methods at 2 sites yielded average biases of +0.51 and +1.63 ng/mL. Spearman correlation coefficients were >/=0.90 on all method comparisons. The ARCHITECT Tacrolimus assay is a semiautomated, robust, and highly sensitive immunoassay, representing an alternative approach for laboratories not equipped with LC-MSMS, and meets the 1 ng/mL recommendation of LOQ by the European Consensus Conference on Tacrolimus Optimization.

Contribution of nicotine to acute endothelial dysfunction in long-term smokers.

OBJECTIVES: The aim of this study was to determine whether nicotine, a constituent of cigarette smoke, contributes to acute endothelial dysfunction after smoking one cigarette. BACKGROUND: Animal studies suggest that nicotine might cause an impairment of endothelium-dependent vasodilation via an increase in oxidative stress. METHODS: Sixteen healthy smokers were entered into a randomized, observer-blinded crossover study comparing the effects of nicotine nasal spray (1-mg nicotine) and cigarette smoke (1-mg nicotine, 12 mg tar) on vascular reactivity in the brachial artery. Using high-resolution ultrasound, flow-mediated dilation (FMD) and endothelium-independent, nitroglycerin-induced dilation were assessed at baseline and 20 min after the administration of nicotine (spray or cigarette). RESULTS: In response to similar increases in nicotine serum levels, FMD values declined from 10.2 +/- 4.4% to 6.7 +/- 4.0% after the spray (mean difference: -3.6 +/- 2.0%, 95% confidence interval: -4.6; -2.5, p < 0.0001) and from 9.4 +/- 3.8% to 4.3 +/- 2.8% after the cigarette (-5.1 +/- 2.6%, -6.5; -3.7, p < 0.0001). Nitroglycerin-induced dilation remained similar within both periods. Performing a period effect analysis of variance, a significant influence on FMD was found for the mode of administration (p = 0.017) and the baseline value (p = 0.021). The effect on FMD was more pronounced after the cigarette than after the spray (estimated average effect difference: 1.9% FMD). Oxidation parameters did not increase significantly after nicotine spray or tobacco exposure. CONCLUSIONS: These results demonstrate that nicotine alone causes acute endothelial dysfunction, although to a lesser extent than smoking a cigarette of the same nicotine yield. However, the precise mechanisms by which nicotine leads to this altered vascular reactivity remain unclear.