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

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.

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.

Stable isotope dilution analysis of salicylic acid and hydroquinone in human skin samples by gas chromatography with mass spectrometric detection

A sensitive and accurate gas chromatographic-mass spectrometric (GC-MS) method has been developed for the quantitative determination of salicylic acid (SA) and hydroquinone (HQ) from human skin samples and cosmetic emulsions. Deuterium labeled SA-d(6) and HQ-d(6) were used as internal standards (IS). The samples were extracted with methanol, dried under nitrogen and derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)+1% trimethylchlorosilane (TMCS). Quantification was performed in SIM mode with a limit of quantification (LOQ) of 50 ng ml(-1) for SA and 10 ng ml(-1) for HQ. The inter-day variation (R.S.D.) was less than 5% and the accuracy was better than 13.3% for both compounds. The recoveries from the different matrices ranged between 93.1 and 103.3% for SA, and 97.3 and 100.8% for HQ.

Spectrofluorimetric determination of paracetamol in pharmaceuticals and biological fluids

A spectrofluorimetric method for the determination of paracetamol is presented, based on the oxidation of the analyte to give the fluorophore 2,2'-dihydroxy-5,5'-diacetyldiaminebiphenyl. Sodium hypochlorite was used as an oxidizing reagent and the optimum pH was found to be 10.0 (sodium carbonate-boric acid buffer solution). The linear concentration range of application was 0.1-100.0 micrograms ml-1 of paracetamol, the detection limit 0.01 micrograms ml-1 and the relative standard deviation 1.2%. The method has been satisfactorily applied to the determination of paracetamol in pharmaceutical formulations and biological fluids.

High-performance liquid chromatographic method for the determination of salicylic acid and its metabolites in urine by direct injection

A direct injection method has been developed for the determination of salicylic acid and its metabolites in urine. Urine samples are treated with hydroxylamine to convert salicyl acyl glucuronide to salicylhydroxamic acid, which can be accurately quantitated by direct injection into a high-performance liquid chromatographic system along with salicylic acid, gentisic acid and salicyluric acid. Salicyl phenolic glucuronide is quantitated by difference after hydrochloric acid hydrolysis at 65 degrees C with no loss of salicylic acid by sublimation or hydrolytic loss of salicyluric acid. This method has been applied to urine samples from human subjects and the results are discussed.

Modification of transplacental distribution of salicylate in rats by acidosis and alkalosis

1. The basis for the existence of a lower concentration of salicylate in the foetal than in the maternal blood was investigated in rats on day 20 of gestation. 2. Bolus injections of sodium salicylate were made into the mother and of [14C]-salicylic acid into its foetuses and serial maternal and foetal blood samples were collected. When derived on the basis of serum salicylic acid uncorrected for differences in ionization in the maternal and foetal blood, the placental clearance was 2.2 fold greater from the foetal to maternal side than that from the maternal to foetal side. 3. The greater foetal placental clearance relative to the maternal placental clearance was not due to any active placental transfer, since there was no evidence of saturation of this process and it was not affected by pretreatment with probenecid. Moreover, salicylic acid was not concentrated by placental slices in vitro and its placental uptake was not affected by dinitrophenol or by cooling. 4. Maternal blood pH was 0.19 units higher than the foetal blood pH. Administration of ammonium chloride or of sodium bicarbonate into the mother increased the foetal to maternal ratio of salicylic acid from 0.6 to approximately 1. 5. It is concluded that a foetal to maternal serum salicylate concentration-ratio of less than 1 simply reflects lower ionization in the foetus than in the mother, because foetal blood pH is lower than the maternal blood pH.

Clinical assessment of an enzyme immunoassay (EMIT) for measurement of serum salicylate

Salicylic acid concentrations in serum were compared using a homogenous enzyme immunoassay (EMIT) and an automated colorimetric analysis (ACA) technique. Analysis of samples showed similar within-day and day-to-day coefficients of variation (CV): 1.3% and 4.6% by EMIT and 1.0% and 2.6% by ACA, respectively. Quantification of serum containing added salicylate and serum from patients receiving salicylate therapy showed a slight positive bias towards the ACA method over the range of 0-600 mg/l. No significant difference in reliability was found between the two methods. The EMIT assay showed no interference from other antiflammatory drugs being taken by patients who were not taking salicylates. If decisions to alter salicylate dosage are made with due regard to the drug's saturation kinetics, measurements using either EMIT or ACA should allow the clinician to titrate patients' serum concentrations accurately within the narrow therapeutic range.

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.

Therapeutic potential of choline magnesium trisalicylate as an alternative to aspirin for patients with bleeding tendencies

We have compared the effects of acetyl salicylic acid (ASA, aspirin) and choline magnesium trisalicylate (CMT), a non-acetylated salicylate product, on platelet aggregation in human whole blood ex-vivo. Using a whole blood platelet counter, platelet aggregation was quantified by measuring the fall in the number of single platelets at peak aggregation in response to collagen, arachidonic acid (AA), as well as spontaneous aggregation. In double blind and random order, 12 healthy volunteers received, on two separate occasions 10 days apart, a single oral dose of 652 mg ASA or 655 mg CMT. Despite a comparable absorption of salicylic acid from the two drugs, ingestion of ASA resulted in a marked inhibition of platelet aggregation induced by collagen (p less than 0.005), AA (p less than 0.01) and spontaneous aggregation (p less than 0.01), whereas such effects were not observed after CMT ingestion. We suggest that CMT may have therapeutic potential as an alternative to aspirin when inhibition of platelet aggregation can induce bleeding complications.

Presence of salicylic acid in standardbred horse urine and plasma after various feed and drug administrations

Plasma and urinary levels of salicylic acid were examined in Standardbred mares after administration of various feeds, containing different compositions of hay. In addition, horses were administered acetylsalicylic acid orally and methyl salicylate topically. Elevated salicylic acid levels were observed in horse urine and plasma in animals fed lucerne hay. The plasma and urinary elimination of salicylic acid exhibited a diurnal pattern which was related to the type of feed and the feeding schedule. Within 24 h after oral administration of acetylsalicylic acid, plasma and urine salicylic acid levels were consistent with residual levels observed after feeding lucerne hay. Elimination of salicylic acid was rapid and complete, with a half-life between 5 and 7 h. Topical administration of methyl salicylate (8.4 g) produced elevated urinary salicylic acid levels for 6 h. A smaller dose of methyl salicylate (3.4 g) did not elevate plasma or urine salicylic acid levels above those observed following administration of lucerne hay.

The extracellular control of intracellular aspirin hydrolysis

We have previously presented evidence that an intra-erythrocyte arylesterase is primarily responsible for the deacetylation of aspirin to salicylate. We now report studies on extracellular control factors. The fractional acetylsalicylic acid (ASA) hydrolysis at the completion of 20-minute incubations in suspensions of washed red blood cells (RBC) with human serum albumin (HSA) decreased sharply, from 0.6 at 0 gm/dl HSA to 0.2 at 5.0 gm/dl HSA. In RBC suspensions with oleic, linoleic, and lauric acid, ASA hydrolysis increased as fatty acid:HSA ratios increased. The addition of salicylate (SA) also resulted in an increase in the fraction hydrolyzed. In a separate, more direct, ultracentrifugation assay, unbound ASA levels were similarly affected by HSA and the other ligands. When SA and oleic acid were incubated with ASA in RBC, additive competition for binding sites was apparent at relatively low levels of the fatty acid. In the presence of increasing concentrations of sodium SA, 5-amino SA, and 4-amino SA, ASA hydrolysis in RBC suspensions was increased by an average of 137%, 75%, and 54%, respectively. The most reasonable explanation for these findings is that the intact ASA molecule binds to albumin and that the binding of competing ligands can modulate the levels of free ASA in the circulation. This, in turn, affects the amount of drug available as substrate for penetration into the RBC and reaction with the intracellular hydrolase which catalyzes ASA deacetylation. Such factors controlling drug availability, if validated in vivo, could be important with regard to the antiinflammatory and anti-platelet properties of aspirin.

Salicylate measurement: clinical usefulness and methodology

The salicylates are the most commonly used analgesic, antipyretic, and anti-inflammatory drugs. They are available in hundreds of preparations, many of which are over-the-counter medications. The easy access to large quantities of the drug and the widespread perception that the drug is harmless have contributed to salicylate intoxication becoming a serious and common problem, particularly among the pediatric and geriatric populations. Salicylate is still the major drug for the treatment of rheumatic diseases. The use of salicylate in high doses for the management of these patients requires close monitoring of serum salicylate levels because of the large interindividual variation in dose-serum level relationships and the narrowness of the therapeutic range. Thus, both for the management of patients intoxicated with salicylate and patients who are on high-dose salicylate therapy, the measurement of serum salicylate levels is an important clinical laboratory service. Recent research on the inhibitory effect of aspirin on platelet aggregation has led to the prophylactic use of aspirin in low doses as an antithrombotic drug. This new therapeutic use of aspirin can be aided by monitoring low serum levels of salicylate and perhaps aspirin itself. This article reviews the current state of the knowledge of the pharmacokinetics and clinical toxicology of salicylate, the clinical usefulness of salicylate measurement by the clinical laboratory, and recent development in the analytical technology for salicylate analysis.

Separation and identification of non-steroidal antirheumatic drugs containing a free carboxyl function using high-performance liquid chromatography

Different methods for the separation and identification of eighteen non-steroidal antirheumatics (non-steroidal, anti-inflammatory drugs) and the application of these methods for systematic toxicological analysis are reviewed. A method for separating these compounds by high-performance liquid chromatography using an RP-18 column and mixtures of acetonitrile and acetate buffers as eluents is presented and the detectability of these substances with respect to their different UV maxima is discussed.

High-performance liquid chromatographic determination of certain salicylates and their major metabolites in plasma following topical administration of a liniment to healthy subjects

The liniment used is a topical analgesic and anti-inflammatory preparation containing two active constituents, 3-phenylpropylsalicylate and ethyl-5-methoxysalicylate, in solution in isobutyl decanoate. It is known that 3-phenylpropylsalicylate is metabolised to salicylic acid and salicyluric acid and ethyl-5-methoxysalicylate is metabolised to 5-methoxysalicylic acid and gentisic acid. In the present study the separation of the salicylates and their metabolites was carried out on a Waters mu Bondapak C18 column using two different mobile phases, methanol-water (80:20) for the parent drugs and methanol-5% aqueous acetic acid (27:73) for their metabolites. The salicylates and their metabolites were detected by absorption at 310 nm. The limits of detection for parent drugs and metabolites were respectively 0.2 and 0.1 microgram/ml in plasma, using a 1-ml plasma sample and a 20-microliter injection from a reconstituted volume of 250 microliter. Mean percentage coefficients of variation for intra-assay and inter-assay precision were between 3.3 +/- 1.9% to 9.1 +/- 3.7% and 6.8 +/- 2.2% to 15.7 +/- 10.1%, respectively. Linearity, as measured by the correlation coefficient of intra-assay linear regression curves, was better than 0.998 in all cases.

Influence of intravenous acetylsalicylic acid and sodium salicylate on human renal function and lithium clearance

The influence of intravenous acetylsalicylic acid (ASA; D,L-lysine-mono-acetylsalicylate), equimolar doses of sodium salicylate (SA) and placebo (P) on renal function has been studied in 6 healthy female volunteers, in 150 mmol sodium balance, and in lithium (Li) steady state with a plasma Li between 0.6 and 0.8 mmol/l. Following a bolus injection of 0.5 g ASA, 0.444 g SA or P (50 ml saline) given over 10 min and a subsequent continuous infusion of 1.5 g ASA, 1.332 SA or P (150 ml saline) over 170 min, urine was collected for 3 h as well as 6 plasma samples at 30-min intervals. Plasma ASA levels were between 13.8 and 22.1 micrograms/ml and for SA they were 20.8 to 82.6 microgram/ml during ASA infusion, and between 22.5 and 108.9 microgram/ml for SA during SA infusion. Neither ASA nor SA caused a significant change in urine volume, in the renal clearances of Na, K, free water, osmolality, creatinine, inulin and p-aminohippurate (PAH) or in plasma Li level. Renal Li clearance was slightly reduced by SA, from 37.8 to 29.4 ml/min (p less than 0.05). Since renal prostaglandin (PG) synthesis (urinary PGE2 excretion) was 60.6% suppressed by ASA and was not affected by SA, the decrease in Li clearance cannot be related to inhibition of cyclooxygenase in the kidney.

Improved method for the determination of aspirin and its metabolites in biological fluids by high-performance liquid chromatography: applications to human and animal studies

An improved method has been developed for the determination of acetylsalicylic acid, salicylic acid, gentisic acid, and salicyluric acid in plasma and urine of rabbits and man. Samples are extracted with dichloromethane containing mephenytoin as an internal standard, the solvent is evaporated under reduced pressure, the residue reconstituted and analyzed by high-performance liquid chromatography. Extraction efficiencies, linearity and assay precision were determined. This method has been applied to human bioavailability studies and the data are presented.

Aspirin metabolites causing misinterpretation of paracetamol results

The inadequacy of single, simple arithmetic corrections for salicylate interference in the widely employed Glynn and Kendal technique for plasma paracetamol assay is highlighted by reference to an actual case of combined salicylate/paracetamol intoxication in an infant. Attention is drawn for the first time to the not insubstantial contribution to such interference made by even the minor metabolites of salicylate. The conclusion is reached that is necessary, particularly in the assessment of paracetamol toxicity, to determine the presence of salicylate, and when present, to employ a specific method for the estimation of paracetamol.

Rapid and sensitive determination of acetylsalicylic acid and its metabolites using reversed-phase high-performance liquid chromatography

A rapid and sensitive high-performance liquid chromatographic technique was developed for the simultaneous determination of gentisic acid, salicyluric acid, acetylsalicylic acid and salicylic acid in plasma and serum. The method involved a single deproteinization step and separation using a reversed-phase column eluted with a buffered methanol (35%) mobile phase. Detection was achieved with a variable-wavelength ultraviolet detector set at 235 nm and a given chromatographic analysis could be completed in less than 10 min. The method was tested in both human and animal (rat) models given a single dose of acetylsalicylic acid.

Indirect inhibition of vitamin K epoxide reduction by salicylate

Salicylate antagonizes the vitamin K-dependent biosynthesis of clotting factors in the rat and produces an elevation of the ratio of vitamin K epoxide to vitamin K in the liver. Vitamin K epoxide is reduced to vitamin K by a vitamin K epoxide reductase, and 1 mM salicylate was required to cause a 50% inhibition of the dithiothreitol-dependent in-vitro reduction of vitamin K epoxide by this enzyme. This enzyme was, however, inhibited 50% by as little as 70-80 microM salicylate when reducing equivalents for the reaction were furnished by endogenous cytosolic reductants. This effect on the cytosolic reductant supply was shown to be unrelated to a previously demonstrated inhibition of DT-diaphorase by salicylate. The concentrations of salicylate at which significant inhibitory effects are exerted in-vitro (50-100 microM) are below the 200 microM levels observed in the livers of rats given an anticoagulating dose of salicylate.

Choline magnesium trisalicylate: comparative pharmacokinetic study of once-daily and twice-daily dosages

This randomized crossover study compared the pharmacokinetics of choline magnesium trisalicylate tablets administered once daily (3000 mg of salicylate) or twice daily (1500 mg of salicylate) for six d. Serum salicylate levels were measured by HPLC. Mean "trough" concentrations fell within the therapeutic range (5-30 mg/dL) with either regimen and were relatively constant, indicating that the steady state had been reached. The 24-h area under the salicylate curve (AUC0-24 h) after the final 3000-mg salicylate dose averaged about twice the mean 12-h AUC after the last 1500-mg dose, indicating that the two dosing regimens were equally bioavailable. Clinical observations and results of laboratory safety studies indicate that both dosage schedules of the drug are well tolerated. The present findings support the once-daily therapeutic use of choline magnesium trisalicylate.

Influence of age, sex, pregnancy and protein-calorie malnutrition on the pharmacokinetics of salicylate in rats

The influence of age, sex, pregnancy and protein-calorie malnutrition (PCM) on the plasma t1/2, plasma clearance (Clp) and apparent volume of distribution (Vd) of sodium salicylate (62 mumol kg-1) was determined in Sprague-Dawley rats. Female and male rats of five different age groups (ages in weeks: pups 1, weanling 3, young 8-9, adult including pregnant 14-15, old 56-60) including three age groups with PCM (8-9, 14-15 and 56-60 weeks old) were used. Plasma and urinary salicylates were assayed by h.p.l.c. Plasma t1/2 was longer and Clp smaller in pups than in weanling and young rats and comparable to values for old rats; Vd of salicylate in pups was larger than in any other group of rats. Plasma t1/2 was longer and Clp as well as Vd of salicylate were smaller in adult females than in males of comparable age. Relative to nonpregnant adult females, Vd of salicylate in pregnant rats was larger but plasma t1/2 and Clp were unchanged. In all groups of rats studied, PCM decreased the plasma t1/2 and increased the Clp of salicylate; Vd was unchanged. Changes in salicylate pharmacokinetics were not due to any differences in serum protein-salicylate binding or to serum testosterone levels. Ovariectomy decreased the plasma t1/2 of salicylate but castration of male rats had no significant effect. Administration of testosterone to ovariectomized female rats exerted no significant effect on salicylate pharmacokinetics. It is concluded that the physiological state and the nutritional status can modify salicylate pharmacokinetics; in so far as the rat model reflects the human situation, these variables should be taken into account for a rational salicylate therapy.

The relative roles of hydrolases of the erythrocyte and other tissues in controlling aspirin survival in vivo

The rate of aspirin (acetylsalicylic acid, ASA) deacetylation to salicylate in vivo determines the availability of the intact molecule for therapeutically important transacetylation reactions. Experiments were carried out to assess the relative contribution of a previously isolated human erythrocyte ASA esterase to the overall hydrolysis rate in vivo, as opposed to similar enzymes in other tissues. In vitro, the rates of ASA hydrolysis were relatively slow in plasma from humans and dogs. The hydrolysis rates were significantly greater in whole blood in dogs, rabbits, and humans. In human and canine whole blood, the rate of hydrolysis correlated positively with hematocrit. In vivo studies with dogs showed that ASA decay rates conform to a 2-compartment model. After reduction of hematocrit by a mean of 49% in 4 dogs without previous splenectomy, the "availability" of ASA increased. In 4 dogs with previous splenectomy, this measurement was increased even more after comparable hematocrit reduction. In 2 dogs that underwent a sub-total hepatectomy, ASA availability increased by only 35% and 12.8%, respectively. These results suggest a significant role for the erythrocyte esterase in vivo in the dog and possibly in humans.

Stabilized normal-phase high-performance liquid chromatographic analysis of aspirin and salicylic acid in solid pharmaceutical dosage forms

A simultaneous analysis of aspirin and nonaspirin salicylates in solid pharmaceutical dosage forms is described. Two separate extraction procedures are employed, one for plain aspirin tablets and one for tablets containing aspirin plus buffers or antacids. The analyses of the extracted samples are accomplished by a stabilized normal-phase high-performance liquid chromatographic (HPLC) procedure. Prepared samples and standards are stable for up to 24 h, and the methodology is suitable for an automated HPLC system.

High-performance liquid chromatographic determination of aspirin and its metabolites in plasma and urine

A simple quantitative method for the rapid determination of aspirin and its metabolites, salicylic acid, salicyluric acid, and gentisic acid, in plasma and urine using o-toluic and o-anisic acids, respectively, as internal standards was developed. Plasma proteins were precipitated by the addition of acetonitrile and, after centrifugation, the supernatant fluid was injected directly onto a reverse-phase column. The mobile phase consisted of an isocratic mixture of water, methanol, and glacial acetic acid (64:25:1, v/v/v) and the separated components were detected at 238 nm using a UV detector. Concentrations greater than or equal to 0.5 microgram/ml could be quantitated for aspirin or its metabolites in plasma. The peak heights and peak height ratios to the internal standard, o-toluic acid, were linear for the concentration range of 0.5-200 micrograms/ml. The aspirin metabolites in urine were isolated by extracting the acidified urine with either and then reextracting the material into an aqueous buffer solution at pH 7.0. Twenty microliters of the buffer extract was directly injected onto the column. The separated components were detected and quantitated at 305 nm. Concentrations greater than or equal to 5 micrograms/ml of salicyluric acid, salicylic acid, and gentisic acid could be determined accurately. The peak heights and peak height ratios to the internal standard, o-anisic acid, were found to be linear for the concentration range of 5-200 micrograms/ml in urine.

Identification and partial purification of the major aspirin hydrolyzing enzyme in human blood

In normal whole human blood in vitro, the source of the enzyme controlling the hydrolysis of aspirin (ASA) was found to be the erythrocyte (RBC). Experiments were carried out to determine whether this enzyme was membrane-bound or free in the lysate. The mean rates of ASA hydrolysis in comparable concentrations of intact RBC (1.61 +/- 0.20 mumole/liter/minute, n = 12 and 1.23 +/- 01.7 mumole/liter/minute, n = 5) were much faster than that measured in isolated RBC membranes (0.23 +/- 0.08 mumole/liter/minute, n = 6, P = less than 0.001). Detailed study showed that the RBC-related ASA esterase is located intracellularly and is not related to membrane acetylcholinesterase. The ASA esterase from crude lysate was purified 900-fold by means of DEAE Sephacel chromatography of active enzyme recovered from a 50% saturated ammonium sulfate fraction. Non-SDS polyacrylamide gel electrophoresis (pH 8.3 and 9.0) resulted in one major band and one or more small minor protein bands. When esterase activity was assayed in a non-stained gel, ASA depletion and salicylate production corresponded exactly to the major stained band. This band was eluted from another unstained gel, concentrated, and applied to an SDS gel. This yielded a single band with a molecular weight of approximately 95,000. The partially purified enzyme had a mean Km of 66.6 +/- 3.5 microM and a mean Vmax of 4.0 +/- 0.9 mumole/liter/minute/mg under the assay conditions. The results of inhibition studies suggested that this enzyme's activity is sulfhydryl group dependent, does not require divalent cations for activity, and is different from the RBC type D "nonspecific" esterases.

Propranolol and acetylsalicylic acid in migraine prophylaxis. Double-blind crossover study

The aim of this double-blind crossover study was to compare the prophylactic effect of acetylsalicylic acid (ASA) with that of propranolol (PRP) in the treatment of migraine. Plasma concentrations of the two drugs were measured in order to investigate a possible relationship to the clinical effect. Compared to the pretreatment period, PRP and ASA reduced migraine index, frequency, duration, severity of attacks and headache days. Due to the limited number of patients, our results should be cautiously interpreted, however relevant the clinical improvement seemed. Improvement of migraine index was not related to different plasma levels of the two drugs.

Determination of acetylsalicylic acid and metabolites in biological fluids by high-performance liquid chromatography

A new method has been developed for the determination of acetylsalicylic acid, salicylic acid, salicyluric acid and gentisic acid in plasma, urine and tissue homogenates by simple extraction with ethyl acetate, evaporation and redissolution and measuring by high-performance liquid chromatography. Linearity, reproducibility and recovery were determined. Experiments were carried out to investigate the decomposition of acetylsalicylic acid in plasma with fluoride at different temperatures. The method has been used for pharmacokinetic experiments and an example is given.