Determination of aspirin and salicylic acid in uremic patients' plasma using reversed-phase high-performance liquid chromatography

Review of HPLC methods and HPLC methods with mass spectrometric detection for direct determination of aspirin with its metabolite(s) in various biological matrices

Aspirin, the most widely used drug in the world, has been known to mankind for over a century. It is not only the pharmacologically active entity, but is also biotransformed into a major metabolite, i.e. salicylic acid, which also exhibits similar pharmacologic/pharmacodynamic properties. Hence it is necessary to quantitate aspirin along with its metabolite(s) in various biological matrices accurately and precisely to correlate with pharmacological/pharmacodynamic activity. This paper provides a comprehensive overview of various bioanalytical methods (HPLC and LC-MS/MS) that have been reported for direct quantitation of aspirin along with its metabolite(s). The review also provides general information on sample collection, sample processing, internal standard selection, conditions for chromatographic separation, succinct validation data and applicable conclusions for reported assays in a structured manner.

Aspirin extrusion from human platelets through multidrug resistance protein-4-mediated transport: evidence of a reduced drug action in patients after coronary artery bypass grafting

OBJECTIVES

In this study we investigate: 1) the role of multidrug resistance protein-4 (MRP4), an organic anion unidirectional transporter, in modulating aspirin action on human platelet cyclooxygenase (COX)-1; and 2) whether the impairment of aspirin-COX-1 interaction, found in coronary artery bypass grafting (CABG) patients, could be dependent on MRP4-mediated transport.

BACKGROUND

Platelets of CABG patients present a reduced sensitivity to aspirin despite in vivo and in vitro drug treatment. Aspirin is an organic anion and could be a substrate for MRP4.

METHODS

Intracellular aspirin concentration and drug COX-1 activity, measured by thrombin-induced thromboxane B2 (TxB2) production, were evaluated in platelets obtained from healthy volunteers (HV) and hematopoietic-progenitor cell cultures reducing or not reducing MRP4-mediated transport. Platelet MRP4 expression was evaluated, in platelets from HV and CABG patients, by dot-blot or by immunogold-electromicrographs or immunofluorescence-microscopy analysis.

RESULTS

Inhibition of MRP4-mediated transport by dipyridamole or Mk-571 increases aspirin entrapment and its in vitro effect on COX-1 activity (142.7 ± 34.6 pg/10(8) cells vs. 343.7 ± 169.3 pg/10⁸ cells TxB2-production). Platelets derived from megakaryocytes transfected with MRP4 small interfering ribonucleic acid have a higher aspirin entrapment and drug COX-1 activity. Platelets from CABG patients showed a high expression of MRP4 whose in vitro inhibition enhanced aspirin effect on COX-1 (349 ± 141 pg/10⁸ cells vs. 1,670 ± 646 pg/10⁸ cells TxB2-production).

CONCLUSIONS

Aspirin is a substrate for MRP4 and can be extruded from platelet through its transportation. Aspirin effect on COX-1 is little-related to MRP4-mediated aspirin transport in HV, but in CABG patients with MRP4 over-expression, its pharmacological inhibition enhances aspirin action in an efficient way.

Sensitive determination of aspirin and its metabolites in plasma by LC-UV using on-line solid-phase extraction with methylcellulose-immobilized anion-exchange restricted access media

We describe a sensitive determination of aspirin (ASA) and its three metabolites (salicylic acid [SA], 2,3-dihydroxybenzoic acid [2,3-DHBA], and 2,5-dihydroxybenzoic acid [gentisic acid (GA)]) in rat plasma. Analysis was carried out by on-line solid-phase extraction (SPE) using a methylcellulose-immobilized-strong anion-exchanger (MC-SAX), followed by liquid chromatography (LC) coupled with UV detection. The lower limits of quantitation for ASA and SA were 60 ng/mL in 100 microL of plasma, respectively. This method was validated with respect to intra- and inter-day precision, accuracy, and linearity up to concentrations of 20,000 ng/mL for ASA, SA, 2,3-DHBA and gentisic acid, respectively. The method was successfully applied to an analysis of the pharmacokinetics of ASA and SA in rats.

Pharmacokinetic and pharmacodynamic differences between two low dosages of aspirin may affect therapeutic outcomes

BACKGROUND

Meta-analyses of the prevention of major vascular events by aspirin suggest therapeutic equivalence of all dosages. However, the optimal dosage still remains problematic, and a recent trial found aspirin 160 mg/day to be more effective than 80 mg/day for secondary prevention of ischaemic stroke.

OBJECTIVE

To evaluate two low dosages of aspirin in terms of pharmacokinetics and pharmacodynamics (inhibition of platelet thromboxane generation and urinary excretion of thromboxane and prostacyclin metabolites).

DESIGN AND PARTICIPANTS

A randomised cross-over study was performed in 16 healthy volunteers (9 women and 7 men, 33.8 +/- 5.1 years old) given enteric-coated aspirin 80 or 160 mg/day for 7 days.

METHODS

Plasma concentrations of salicylate and aspirin were measured by high-performance liquid chromatography (HPLC) after both the first and the last dose (days 1 and 7). The usual pharmacokinetic parameters were then derived. Serum thromboxane B2 (TxB2) was measured by radioimmunoassay. The urinary excretion of 11-dehydro-TxB2 and 2,3-dinor-6-keto-prostaglandin F1alpha were measured on 8-hour urine samples by immunoassay after extraction and HPLC separation, both before and after 7 days of drug administration.

RESULTS

With the 160 mg dosage, but not with the 80 mg dosage, higher concentrations of aspirin were found at day 7 compared with day 1. For aspirin 80 mg/day, 24-hour area under the concentration-time curve (AUC24) was similar on days 1 and 7 (569 +/- 339 vs 605 +/- 377 microg. h/L), but increased from 904 +/- 356 microg. h/L on day 1 to 1355 +/- 883 microg. h/L on day 7 with the higher dosage. Similarly, the AUC24 for salicylate was similar on days 1 and 7 with the lower dosage, but significantly increased from day 1 to day 7 after the higher dosage. This paralleled inhibition of serum TxB2 levels (99% vs 95% average inhibition by 160 and 80 mg/day) and of urinary excretion of thromboxane metabolite (77% vs 61% average inhibition by 160 and 80 mg/day), without altering the excretion of prostacyclin metabolite.

CONCLUSIONS

Inhibition of serum TxB2 generation and of thromboxane metabolite urinary excretion by the lower dosage of aspirin, although substantial, still appeared incomplete. The small but significant further increase of serum TxB2 inhibition by the higher dosage was accompanied by an even greater inhibition of urinary excretion. We suggest that in some instances this difference would translate into a greater clinical benefit with the higher aspirin dosage. Our findings may also contribute to better definition of the recent concept of 'aspirin resistance'.

Determination of salicylic acid in human serum with capillary zone electrophoresis

The determination of salicylic acid (SA), a metabolite of aspirin, in human serum was developed using capillary zone electrophoresis (CZE) with diode array detection. The reproducibility of separation and quantification with CZE analysis of the extract of SA from human serum was appropriate for the intra- and inter-day assay coefficients. A high correlation was revealed between the serum SA levels in volunteers determined by CZE and those determined by a fluorescence polarization immunoassay (r=0.973, n = 12), although the former values were slightly higher than the latter. There were no peaks interfering with the assay of SA by internal standard method. This CZE method could provide a simple and efficient method for monitoring SA in patients.

Determination of aspirin and salicylic acid in human plasma by column-switching liquid chromatography using on-line solid-phase extraction

A column-switching liquid chromatographic method is described for the simultaneous determination of aspirin and salicylic acid in human plasma. Blood samples are taken into chilled tubes containing a fluoride anticoagulant, and the plasma is isolated by centrifugation. Following a simple acidification step, a 200 microL aliquot of the sample is injected directly onto the HPLC system. The C-18 extraction column is washed with acidified water for 2 min, after which time the compounds are removed by back-flushing directly onto the analytical column (C-8 Nucleosil, 5 microns, 250 mm x 4.6 mm). The flow rate through both columns is 1 mL/min, and the analytes are quantified by measurement of their UV absorbance at 225 nm. The mobile phase is a mixture of water-methanol-acetonitrile-orthophosphoric acid (650:200:150:1 v/v/v/v). The method is linear in the concentration ranges 0.10-5.00 micrograms/mL for aspirin and 0.25-15.00 micrograms/mL for salicylic acid. Both compounds have a limit of quantitation of 0.10 microgram/mL and a limit of detection of 0.04 microgram/mL. Extensive stability tests have been carried out, and validation studies reveal the method to be reproducible and repeatable. Excellent recoveries from plasma obviate the need for an internal standard. The procedure is easier to execute and requires less sample handling than methods currently described in the literature. It has been successfully applied to the investigation of the levels of aspirin and salicylic acid in a healthy, nonfasting volunteer following a 600 mg oral dose of aspirin.

Influence of antacid administrations on aspirin absorption in patients with chronic renal failure on maintenance hemodialysis

In order to investigate the possible interaction between oral aspirin and antacids in uremic patients on chronic hemodialysis, we administered to 5 uremic patients: (1) aspirin alone; (2) aluminum-magnesium hydroxide with aspirin; (3) aluminum-magnesium hydroxide followed (two hours) by aspirin; (4) calcium carbonate simultaneously with aspirin; and (5) calcium carbonate followed (two hours) by aspirin. In all the occasions, aspirin was given two hours after a standard lunch. Both antacid preparations induced comparable changes in aspirin mean peak plasma concentration (Cmax), if given simultaneously with aspirin, whereas no difference was found in other pharmacokinetic parameters. When antacids were followed (two hours) by aspirin, both Cmax and time of maximum concentration (Tmax) were significantly altered in respect to the value with aspirin alone. No changes in the time course of post aspirin serum thromboxane B2 were detected when aspirin and antacids were administered simultaneously, but the inhibition of serum thromboxane B2 was delayed when antacids were followed (two hours) by aspirin. These results indicate that the administration of antacids to uremic patients interferes with absorption of oral aspirin. This interference can be minimized if aspirin and antacids are given simultaneously.