A simultaneous determination of acetylsalicylic acid, salicylic acid and salicylamide in plasma by gas liquid chromatography

Decreased cyclooxygenase inhibition by aspirin in polymorphic variants of human prostaglandin H synthase-1

OBJECTIVES

Aspirin (ASA), a major antiplatelet and cancer-preventing drug, irreversibly blocks the cyclooxygenase (COX) activity of prostaglandin H synthase-1 (PGHS-1). Considerable differences in ASA effectiveness are observed between individuals, and some of this variability may be due to PGHS-1 protein variants. Our overall aim is to determine which, if any, of the known variants in the mature PGHS-1 protein lead to functional alterations in COX catalysis or inhibition by ASA. The present study targeted four PGHS-1 variants: R53H, R108Q, L237M, and V481I.

METHODS

Wild-type human PGHS-1 and the four polymorphic variants were expressed as histidine-tagged, homodimeric proteins in insect cells using baculovirus vectors, solubilized with a detergent, and purified by affinity chromatography. The purified proteins were characterized in vitro to evaluate COX and peroxidase (POX) catalytic parameters and the kinetics of COX inhibition by ASA and NS-398.

RESULTS

Compared with the wild type, several variants showed a higher COX/POX ratio (up to 1.5-fold, for R108Q), an elevated arachidonate Km (up to 1.9-fold, for R108Q), and/or a lower ASA reactivity (up to 60% less, for R108Q). The decreased ASA reactivity in R108Q reflected both a 70% increase in the Ki for ASA and a 30% decrease in the rate constant for acetyl group transfer to the protein. Computational modeling of the brief ASA pulses experienced by PGHS-1 in circulating platelets during daily ASA dosing predicted that the 60% lower ASA reactivity in R108Q yields a 15-fold increase in surviving COX activity; smaller, approximately two-fold increases in surviving COX activity were predicted for L237M and V481I. NS-398 competitively inhibited COX catalysis of the wild type (Ki=6 µmol/l) and inhibited COX inactivation by 1.0 mmol/l ASA in both the wild type (IC50=0.8 µmol/l) and R108Q (IC50=2.1 µmol/l).

CONCLUSION

Of the four PGHS-1 variants examined, R108Q exerts the largest functional effects, with evidence for impaired interactions with a COX substrate and inhibitors. As Arg108 is located on the protein surface and not in the active site, the effects of R108Q suggest a novel, unsuspected mechanism for the modulation of the PGHS-1 active site structure. The lower intrinsic ASA reactivity of R108Q, V481I, and L237M, combined with the rapid hydrolysis of ASA in the blood, suggests that these variants decrease the antiplatelet effectiveness of the drug. These PGHS-1 variants are uncommon but ASA is used widely; hence, a considerable number of individuals could be affected. Further examination of these and other PGHS-1 variants will be needed to determine whether PGHS-1 genotyping can be used to personalize anti-COX therapy.

Simultaneous determination of salicylic acid and salicylamide in biological fluids

A new methodology for the simultaneous determination of salicylic acid and salicylamide in biological fluids is proposed. The strong overlapping of the fluorescence spectra of both analytes makes impossible the conventional fluorimetric determination. For that reason, the use of fluorescence decay curves to resolve mixtures of analytes is proposed; this is a novel technique that provides the benefits in selectivity and sensitivity of the fluorescence decay curves. In order to assess the goodness of the proposed method, a prediction set of synthetic samples were analyzed obtaining recuperation percentages between 98.2 and 104.6%. Finally, a study of the detection limits was done using a new criterion resulting in values for the detection limits of 8.2 and 11.6 μg L(-1) for salicylic acid and salicylamide respectively. The validity of the method was tested in human serum and human urine spiked with aliquots of the analytes. Recoveries obtained were 96.2 and 94.5% for salicylic acid and salicylamide respectively.

Rapid and sensitive determination of acetylsalicylic acid and salicylic acid in plasma using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic study

A simple and sensitive analytical method using liquid chromatography-tandem mass spectrometry (LC/MS/MS) for determination of acetylsalicylic acid (aspirin, ASA) and its major metabolite, salicylic acid (SA), in animal plasma has been developed and validated. Both ASA and SA in plasma samples containing potassium fluoride were extracted using acetonitrile (protein precipitation) with 0.1% formic acid in it. 6-Methoxysalicylic acid was used as the internal standard (IS). The compounds were separated on a reversed-phase column. The multiple reaction monitoring mode was used with ion transitions of m/z 178.9 --> 136.8, 137.0 --> 93.0 and 167.0 --> 123.0 for ASA, SA and IS, respectively. The lower limits of quantification for ASA and SA were 3 and 30 ng/mL, respectively. The developed method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after p.o. and i.v. administration of 1 mg/kg to rats.

Determination of acetylsalicylic acid and its major metabolite, salicylic acid, in human plasma using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic study of Astrix in Korean healthy volunteers

The first liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for determination of acetylsalicylic acid (aspirin, ASA) and one of its major metabolites, salicylic acid (SA), in human plasma using simvastatin as an internal standard has been developed and validated. For ASA analysis, a plasma sample containing potassium fluoride was extracted using a mixture of ethyl acetate and diethyl ether in the presence of 0.5% formic acid. SA, a major metabolite of ASA, was extracted from plasma using protein precipitation with acetonitrile. The compounds were separated on a reversed-phase column with an isocratic mobile phase consisting of acetonitrile and water containing 0.1% formic acid (8:2, v/v). The ion transitions recorded in multiple reaction monitoring mode were m/z 179 --> 137, 137 --> 93 and 435 --> 319 for ASA, SA and IS, respectively. The coefficient of variation of the assay precision was less than 9.3%, and the accuracy exceeded 86.5%. The lower limits of quantification for ASA and SA were 5 and 50 ng/mL, respectively. The developed assay method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after single oral administration of Astrix (entero-coated pellet, 100 mg of aspirin) to 10 Korean healthy male volunteers.

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.

False-high blood salicylate levels in neonates with hyperbilirubinemia

Drug assays may yield false-positive results caused by cross-reacting compounds. After finding a serum salicylate concentration of 81 microg/mL by using Trinder's colorimetric method, in a comatose child admitted to the authors' pediatric intensive care unit, in the absence of reported salicylate intake, the authors aimed to compare this situation with the phenomenon involving endogenous digoxin-like substances, which cross-react with the routine assay of digoxin. None of the participants in the study had been exposed to salicylate. Salicylate concentration was measured in all patients using Trinder's colorimetric method and in the second stage of the study also by AxSYM salicylate assay. Salicylate concentration using Trinder's method was 18 +/- 25 (4-81) microg/mL among nine seriously ill children in the pediatric intensive care unit, of whom two children with extensive burns had salicylate levels of 30 and 81 microg/mL, respectively. Salicylate concentrations were 107 +/- 24 (45-143) microg/mL and 60 +/- 25 (28-92) microg/mL, among 18 premature newborns and 18 term newborns, with hyperbilirubinemia, respectively. In the second stage, which involved 22 jaundiced term newborns and cord blood from 21 pregnant women, Trinder's method yielded elevated salicylate blood levels among the hyperbilirubinemic infants: 82 +/- 5 (73-89) microg/mL; however, the AxSYM assay yielded significantly lower blood levels: 2.5 +/- 3.4 (0-10.9) microg/mL (P < 0.0001). Among the pregnant women, salicylate cord blood levels were found to be low-within the limit error of the assay with both assay methods. In conclusion, when salicylate intoxication is suspected, particularly during the neonatal period, it is advisable to measure salicylate levels by immunoassay technology.

Comparative bioavailability of aspirin and paracetamol following single dose administration of soluble and plain tablets

In this study, the bioavailability of aspirin and paracetamol was compared in plain and soluble combination formulations in fasting, healthy volunteers. Blood samples were taken and Cmax, Tmax and AUC measured at various times following administration of single doses of the two formulations in 12 subjects. The rapidity of uptake of aspirin following administration of a soluble formulation suggests significant absorption from the stomach. There was no significant difference in the pharmacokinetic parameters of paracetamol derived from a soluble or plain formulation. A comparison of the uptake of aspirin from the soluble aspirin formulation with paracetamol from either plain or soluble tablets showed that aspirin entered the plasma and achieved peak levels significantly more quickly. However, the half life of paracetamol was significantly longer than that of aspirin. These findings suggest that onset of analgesia should be more rapid following dosing with soluble aspirin, a conclusion supported by comparative efficacy studies conducted with differing formulations of aspirin.

Laser induced resonance energy transfer--a novel approach towards achieving high sensitivity in capillary electrophoresis. I. Clinical diagnostic application

Most of the procedures currently performed by capillary zone electrophoresis (CZE) with laser induced fluorescence detection requires prior derivatization. This increases cost, the turn-around-time and chances of extraneous contaminations. CZE with laser induced resonance energy transfer is demonstrated as a viable alternative for detecting non-fluorescent compounds with no prior derivatization. The feasibility of this approach is demonstrated by separating and directly detecting salicylic acid (2,4-dihydroxybenzoic acid), gentisic acid (o-methoxybenzoic acid), salicyluric acid (o-hydroxyhippuric acid) and 4-aminosalicylic acid in urine. The detection of salicylate in serum is also shown. The method is highly sensitive with detection limits in the 1.10(-7) M range. Importantly it requires no prior preconcentration or sample preparation and can be used with complex sample matrices such as serum and urine.

Prostacyclin production at the human microvascular anastomosis: its effect on initial platelet deposition

The human microvascular anastomosis represents a localized environment with strongly thrombotic tendencies. In previous studies, an increase in initial platelet deposition at a human ex vivo anastomosis was measured. It is postulated that this increase in anastomotic platelet deposition was due to a reduction in anastomotic prostacyclin production as a consequence of local endothelial cell injury or loss. Instead, in this study, an increase in anastomotic prostacyclin production over unsutured controls (control 1093 +/- 222 pg/ml of 6-keto prostaglandin F (PGF) 1-alpha, n=21; anastomosis 2494 +/- 414, n=21, mean +/- 1 SEM, p=0.005) is demonstrated. Anastomotic prostacyclin production was augmented by addition of arachidonic acid (0.1 mM) (39,000 +/- 11,300 pg/ml of 6-keto PGF 1-alpha, n=7, p<0.001) and suppressed by the preincubation of vessel segments with aspirin in a dose-dependent fashion (1mM) (83+/-22 pg/ml of 6-keto PGF 1-alpha, n=21, p<0.001); aspirin (0.1 mM) (312 +/- 56 pg/ml of 6-keto PGF 1-alpha, n=7, p<0.001). In further studies using a perfusion apparatus of human blood pumped through human placental artery segments, suppression of prostacyclin production did not augment initial platelet deposition (control anastomosis 4.9 +/- 2.2 x10(6) platelets per cm2, aspirin treatment 6.0 +/- 2.8 x 10(6) platelets per cm2, n=5, mean +/- 1 SEM, p>0.05). Suppression of platelet function with aspirin (0.1 mM) also did not decrease initial platelet deposition onto the anastomosis (5.8 +/- 2.8 x 10(6) platelets per cm2, n=r, p>0.05). In this model system, initial platelet deposition at the anastomosis may not be dependent upon cyclooxygenase pathways.

Determination of salicylic acid in plasma by gas chromatography using steam as carrier gas

A gas chromatography method using steam as the carrier gas was established for the determination of salicylic acid in plasma. A 0.5 mL plasma sample was mixed with 0.5 mL of 6N HCl and then extracted with 2 mL of dichloromethane. The dichloromethane was evaporated to dryness and the residue was redissolved in 0.5 mL of water and then analysed by gas chromatography using steam as the carrying gas. The result was calculated by external standardization.

An evaluation of buffered aspirin and aspirin tablets in postoperative pain after third molar surgery

1. Single doses (500 and 1000 mg) of both buffered aspirin and aspirin tablets were compared with placebo in a randomised double-blind trial of parallel design in patients with postoperative pain after third molar surgery. 2. Only buffered aspirin 500 mg provided significant pain relief (P = 0.016) during the 5 h investigation period. 3. A significant correlation (P = 0.004) was observed between overall pain scores after the various aspirin treatments and aspirin esterase activity. 4. Buffered aspirin preparations afforded a slight advantage over aspirin tablets in the control of postoperative pain after third molar surgery. However, the duration of analgesia was short (approximately 2 h). 5. Aspirin esterase activity appears to be an important determinant of the drug's efficacy in postoperative dental pain.

An evaluation of different doses of soluble aspirin and aspirin tablets in postoperative dental pain

1. The efficacy of three different single doses (600, 900 and 1200 mg of soluble aspirin and aspirin tablets) was determined in a randomized placebo-controlled parallel study in 140 patients (70 females) with postoperative pain after removal of impacted third molars. 2. Patients treated with soluble aspirin 600 mg, 900 mg, 1200 mg and aspirin tablet 1200 mg reported significantly less pain (P less than 0.01) throughout the investigation period than those treated with placebo. 3. Overall pain scores after treatment with aspirin tablets 600 and 900 mg did not differ significantly from those after treatment with placebo (P greater than 0.05). 4. On a comparative dose basis, soluble aspirin was significantly more potent (P less than 0.05) than aspirin tablets.

Automated flow injection determination of salicylates using Trinder reaction for clinical analysis, assays and dissolution studies of formulations

An automated flow-injection technique is described for salicylate (25-250 or 80-800 mg l(-1)), salicylamide (30-300 mg l(-1)), methylsalicylate (100-1000 mg l(-1)) and acetylsalicylic acid (after alkaline hydrolysis), based on their colour reaction with iron (III) in weak acid medium. The method was evaluated for the determination of salicylate in serum, the assay of the drugs in commercial formulations and automated dissolution studies of drug tablets. There were decreased interferences because of the short reaction time. The precision was good with RSD less than 1% in all cases. Recoveries of salicylate from spiked sera (100-1000 mg l(-1)) varied from 96.4-102.5% (mean 99.3%), and from spiked sample solutions of acetylsalicylic acid, 97.8-103.0% (mean 99.6%). The results of the analysis of commercial drug formulations obtained with the proposed method agreed well with the current USP and BP procedures, with differences of 0.4-1.5% (mean 0.8%). High measurement rates of 180 or 95 per hour were achieved using manifolds without and with predilution respectively.

Comparative efficacy of soluble aspirin and aspirin tablets in postoperative dental pain

The efficacy of single doses (1.2 g) of soluble aspirin and aspirin tablets was determined in a randomised, placebo-controlled, double-blind, parallel study in 90 patients (45 females) with postoperative pain after removal of impacted lower third molars. Also investigated was the relationship between plasma aspirin esterase activity and overall pain scores after both aspirin preparations. Patients reported significantly less pain (p less than 0.001) after treatment with aspirin than after treatment with placebo. However, patients receiving soluble aspirin reported both an earlier onset and a longer duration of pain relief than those who received aspirin tablets. A significant correlation was observed between plasma aspirin esterase activity and overall pain scores after both soluble aspirin (r = 0.57, p less than 0.01) and aspirin tablets (r = 0.51, p less than 0.02). It is concluded that soluble aspirin is the preferred aspirin formulation for treating postoperative pain after third molar surgery and that plasma aspirin esterase activity is determinant of a patient's analgesic response to aspirin in postoperative dental pain.

Determination of salicylamide and five metabolites in biological fluids by high-performance liquid chromatography

Two high-performance liquid chromatographic (HPLC) assay procedures were developed for the determination of salicylamide and its metabolites in serum, urine, and saliva. One method involves reverse-phase ion-pair chromatography and UV detection, and is used to determine salicylamide, salicylamide glucuronide, and salicylamide sulfate. The other method, with a different mobile phase and without the ion-pairing reagent, is used to determine gentisamide (the hydroxylated metabolite of salicylamide), gentisamide glucuronide, and gentisamide sulfate. The assays are performed by direct injection of the sample after protein precipitation with ethanol containing the internal standard. Increased sensitivity for the determination of low concentrations of salicylamide is obtained by organic extraction of this drug from serum or saliva. Calibration curves for the conjugates of salicylamide and gentisamide were obtained, in the absence of authentic standards, by partial enzymatic hydrolysis, using the decrease of the conjugate peaks and the concomitant increase of free salicylamide or gentisamide concentrations to determine peak area ratio-concentration relationships. Application of the HPLC assay procedures to the determination of salicylamide excretion products in the urine of three normal human subjects resulted in 98.6% (range:97.1-100.1%) recovery of a 1-g oral dose of the drug. All five metabolites of salicylamide were found in urine, but only salicylamide glucuronide, salicylamide sulfate, and gentisamide glucuronide were found consistently and in appreciable quantities. Salicylamide and all of its metabolites except gentisamide sulfate were found in human and rat serum, and unconjugated salicylamide as well as gentisamide were found in human saliva.

Systemic availability of acetylsalicylic acid in human subjects after oral ingestion of three different formulations

Systemic availability of acetylsalicylic acid (ASA) in normal human subjects after oral ingestion of 1 g in three different formulations was determined by using high-pressure liquid chromatography for ASA assay. For an effervescent, a plain and a sustained release preparation systemic availabilities expressed in percent of the ingested dose were 16.9 +/- 3.2, 8.6 +/- 1.2 and 2.6 +/- 0.4%, respectively. All subjects had clearly measureable amounts of ASA in plasma after oral intake of a sustained release preparation with an average peak concentration of 15 mumol/l. Peak concentration after an effervescent and plain formulation was on the average 80 and 40 mumol/l, respectively. Half-life of ASA in plasma was 18.1 +/- 1.2 min. for the effervescent and 28.7 +/- 5.3 min. for the plain preparation, while the elimination phase was too ill defined for the sustained release formulation. Average plasma half-life of salicylic acid (SA) was similar after the three different administration forms with values between 3.0 and 3.7 hrs. Further, no difference in SA distribution volumes or amounts of SA absorbed was found. The present study demonstrates that oral ingestion of ASA in effervescent, plain and sustained release formulations gives rise to significant amounts of ASA in plasma. Concentrations found indicate that long-term antithrombotic therapy with ASA in a sustained release formulation may be possible.

Efficacy and pharmacokinetics of aspirin in post-operative dental pain

1 Soluble aspirin, 600 mg and 1200 mg, and placebo were compared in a double-blind, cross-over study in 12 patients with post-operative pain following removal of impacted lower third molars. 2 Significant analgesia after 600 mg aspirin occurred only at 45 min after administration, whereas significant analgesia after 1200 mg aspirin occurred from 45 to 240 min. The 1200 mg dose produced greater analgesia than the 600 mg dose and is to be recommended in clinical practice. 3 Plasma concentrations of salicylate and acetylsalicylate were measured after both doses. A significant correlation (rs = 0.876, P less than 0.01) was observed between analgesia and plasma salicylate concentration after 1200 mg aspirin.

Platelet aggregation induced by arachidonic acid and thromboxane generation in patients with hypertension or cerebrovascular disease

The aggregability of platelets to arachidonic acid (AA) was investigated in 26 control subjects, 40 patients with essential hypertension, 20 patients with ischemic cerebrovascular diseases (CVD) not taking aspirin and 11 patients with CVD taking aspirin. The aggregability of platelets was evaluated on the basis of threshold concentrations of AA to induce irreversible platelet aggregation. The enhanced sensitivity of platelets to AA was observed more frequently in hypertensives and/or CVD patients not taking aspirin than in the controls. The relationship between platelet aggregation induced by AA and thromboxane B2 (TXB2) formation from AA or prostaglandin H2 (PGH2) in platelets was also studied in the subjects taking or not taking aspirin. It was proposed that the assessment of platelet aggregability with AA could provide a tool for identifying a subgroup of patients who might substantially benefit from the secondary preventive treatment with aspirin or other anti-platelet drugs. The clinical usefulness of this aggregation test for the management of the patients taking aspirin was also discussed.

Relative bioavailability of aspirin gum

The bioavailability of aspirin gum relative to unbuffered aspirin tablets was determined in six normal volunteers. Twenty-four hours following the administration of two aspirin tablets, 91.2 +/- 1.7% (SE) of the 648-mg dose was recovered in the urine. The relative bioavailability of aspirin gum was 69.5 +/- 3.4% (SE), based on cumulative 4-hr urinary excretion of total salicylate after the chewing of three gum tablets for 15 min. The chewed gum was analyzed for total salicylate and contained an average of 37.8% of the administered dose. When added to the cumulative amount of total salicylate excreted in the urine at 24 hr after dosing, the salicylate contained in the chewed gum accounted for essentially 100% of the dose administered. Chewing aspirin gum for up to 30 min did not significantly (p greater than 0.05) reduce the amount of salicylate entrapped in the gum base when compared to chewing times of 5, 10, and 15 min. Based on the results of this study, four pieces of aspirin gum would be needed to provide the same amount of salicylate to the general circulation as two 324-mg aspirin tablets.

Simultaneous GLC analysis of aspirin and nonaspirin salicylates in pharmaceutical tablet formulations

The analysis of aspirin and nonaspirin salicylates in buffered and plain tablet formulations employing nearly nonaqueous extraction is described. The results obtained compare favorably with those obtained from USP procedures. A simultaneous assay for aspirin and nonaspirin salicylates in buffered tablets involves the use of an acidified chromatographic siliceous earth column for the separation of the aspirin and nonaspirin salicylates from various buffers or antacids. The methods described here have definite advantages over USP XX procedures, and the buffered aspirin tablet procedures also is adaptable to aspirin formulations containing codeine, acetaminophen, propoxyphene, caffeine, and many antihistamines.

Interactions of aspirin with acetaminophen and caffeine in rat stomach: pharmacokinetics of absorption and accumulation in gastric mucosa

To study the pharmacokinetic interactions between aspirin (250 mg/kg) and simultaneously administered oral acetaminophen (125 mg/kg) or caffeine (50 mg/kg) in male rats, noninterfering GLC assays for these drugs were developed. Acetaminophen and caffeine both retarded the appearance of salicylate in plasma. During the elimination phase, acetaminophen enhanced plasms salicylate levels whereas caffeine did not. Aspirin reduced the plasms levels of both acetaminophen and caffeine during absorption and elimination. Regardless of whether the drugs had been administered separately or in combination, higher concentrations of salicylate, acetaminophen, and caffeine were found in the glandular part of the stomach compared to the nonglandular part (rumen). In both parts, the absorption of acetaminophen increased in the presence of aspirin. Simultaneous administration of aspirin with caffeine did not influence the absorption of either drug in the glandular and ruminal parts. The inhibitory action of acetaminophen and the potentiating action of caffeine on the erosive activity of aspirin are not due to any effects of these drugs on salicylate accumulation in glandular tissue.

Solid-state acetylation of codeine phosphate by aspirin

A nonsolvolytic (solid-state) acetylation of codeine phosphate in the presence of aspirin to yield acetylcodeine phosphate is reported. GLC assays for the simultaneous determination of aspirin and salicylic acid and codeine and acetylcodeine are described. The apparent heat of activation for codeine phosphate is estimated, and the possible reaction mechanisms are discussed.

GLC determination of purity of Schiff bases bakrine and saddamine

GLC methods were developed for the investigation of impurities in bakrine and saddamine. The method used for bakrine was unsuitable for saddamine since two possible saddamine impurities, benzylamine and salicylaldehyde, reacted very readily in solution to form saddamine, thus giving a false low value for the original concentration of these impurities. The method devised for saddamine involved silylation, which greatly reduced the possibility of saddamine formation from its precursors and also enabled the detection of another possible impurity, salicylic acid. The method described has an obvious application to the determination of other Schiff bases.

Influence of food and fluid ingestion on aspirin bioavailability

The influence of test meals and accompanying fluid volume on aspirin bioavailability from commercial tablets was determined following single oral doses to healthy male volunteers. Plasma aspirin and salicylate levels were determined simultaneously using a GLC end-point. Area analysis indicated that approximately 5--8% of absorbed drug entered the systemic circulation as unchanged aspirin in nonfasted subjects compared to 16--18% in fasted individuals. Food tended to reduce the appearance rate of aspirin into the circulation, resulting in lower and somewhat more sustained levels than with fasting. Plasma salicylate levels were not influenced markedly by the various treatments, although levels were higher in fasted than in nonfasted subjects during the 1st hr after dosing. After this time, fat pretreatment tended to produce higher levels than other treatments.

Simple and rapid high-pressure liquid chromatographic simultaneous determination of aspirin, salicylic acid, and salicyluric acid in plasma

A rapid and sensitive high-pressure liquid chromatographic assay was developed for aspirin, salicylic acid, and salicyluric acid in plasma. The procedure involves the solvent extraction of these compounds from plasma and separation using a reversed-phase column eluted by acidified aqueous acetonitrile. Small quantitites of aspirin can be assayed directly in the presence of a large quantity of salicylic acid. The assay is also free from blank interference.

Rapid direct determination of trace amounts of salicylic acid in deproteinized serum by means of high-pressure liquid--liquid chromatography

A simple method for the quantitative analysis of salicylic acid in blood serum is described. A liquid--liquid chromatographic system, consisting of a long-chain aliphatic amine as the stationary phase and dilute aqueous perchloric acid as the mobile phase, enables the direct injection of deproteinized serum into the system. No change in the chromatographic properties of the system was noticed after 2000 injections of deproteinized serum. Quantitative analysis is possible using peak area or peak height measurements. The method has a high precision: relative standard deviations of 0.4% and 5% are found for samples containing 10 micrograms and 10 ng injected salicylic acid respectively. The detection limit is found to be about 1 ng slicylic acid, corresponding to 40 ppb salicylic acid in serum. Simultaneously administered drugs such as indomethacin, acetylsalicylic acid, caffeine and phenacetin, and metabolites of salicylic acid do not interfere with the analysis. The time course of the concentration of salicylic acid in serum is demonstrated after oral administration of 1 g sodium-salicylate. The phase system was also found to be suitable for the analysis of salicylic acid in urine.

Direct analysis of salicylic acid in keratolytic plaster by gas-solid chromatography

A rapid gas-solid chromatographic method is reported for the direct analysis of salicylic acid in keratolytic plaster. The method requires no preseparation or derivatization and takes about 14 min. Since it requires only 2-7 mg of sample, it can determine the salicylic acid concentration in a particular area of plaster. The analyzing column is packed with porous polymer beads of 2,6-diphenyl-1,4-phenylene oxide. An automatic solid sampling system is used to connection with the gas chromatograph employing dual flame-ionization detectors. The average recovery of salicylic acid in synthetic samples containing 400-2700 microgram was 100.6 +/-1.6%. The average correlation coefficient of the peak area against the standard was +0.9995 +/- 0.0003 for samples in the 300-3000-microgram range.

Application of gas-liquid chromatography and high-performance liquid chromatography to the analysis of trace amounts of salicylic acid, acetylsalicylic anhydride and acetylsalicylsalicylic acid in aspirin samples and aspirin formulations

The gas-liquid chromatographic (GLC) determination of salicylic acid (SA) in 12 commercial acetylsalicylic acid (aspirin, ASA) samples and 12 ASA formulations is reported. The GLC determination of SA as an impurity in ASA, utilising methylation with methyl iodide in the presence of potassium carbonate, requires a column chromatographic separation of SA prior to derivatization. Trace amounts of SA in ASA have also been determined by high-performance liquid chromatography (HPLC) on a Sil-X-I adsorption column using light petroleum-ethyl acetate-acetic acid as the mobile phase. Acetylsalicylic anhydride (ASN) and acetylsalicylsalicylic acid (ASSA) were determined by HPLC on a reversed-phase C18 column with water-methanol mixtures as the mobile phase. GLC was also applied to the determination of ASN as an impurity in ASA formulations.