Monitoring plasma concentrations of salicylate

Salicylate intoxication: a clinical review

Salicylates are widely used and are easily available as over-the-counter medications; thus, they can be readily abused. Although acute toxicity can be readily diagnosed if an ingestion history is provided, both acute and chronic salicylate toxicity often goes unrecognized, with high mortality when the patient is not treated properly. Salicylates should be considered in the differential diagnosis of an adult patient with acid-base abnormalities of uncertain cause, especially when there are concurrent neurologic symptoms. Patients with salicylate toxicity are treated with alkaline diuresis and sometimes dialysis. The prognosis depends on prompt recognition and treatment. Delayed diagnosis results in increased morbidity and mortality, particularly in the elderly.

Combined liquid and solid-surface room temperature fluorimetric determination of naproxen and salicylate in serum

A rapid and sensitive method for the determination of naproxen and salicylate in serum is presented. The employed strategy combines solid-phase extraction on a reverse-phase membrane with spectrofluorimetry. Solid-phase extraction under optimum pH conditions makes NX to be retained over the solid surface (where it is directly determined by a fluorimetric technique). Salicylate passes through the disk and is also fluorimetrically determined, but in solution. The linear calibration ranges for NX in the membrane and salicylate in solution were 0.014-0.250 and 0.010-0.250 microg ml(-1), respectively. The lowest value, in each case, is the corresponding limit of quantitation. The performance of the method is demonstrated with the successful determination of both drugs in spiked and real human serum samples.

Non-steroidal anti-inflammatory drugs and prostaglandin effects on pepsinogen secretion by dispersed human peptic cells

The effects of aspirin and ibuprofen on pepsinogen secretion were studied in isolated human peptic cells prepared from endoscopically obtained biopsy specimens after collagenase digestion, mechanical disruption, and percoll gradient centrifugation. Pharmacological concentrations of aspirin and ibuprofen (10(-8)-10(-4) M), potentiated histamine (10(-6)-10(-4)M) and forskolin (10(-5)M) stimulated pepsinogen secretion without affecting basal secretion, acetylcholine (10(-6)M) stimulated pepsinogen secretion or cell vitality. Augmentation of secretagogue stimulated pepsinogen secretion was dependent on extracellular calcium because potentiation was abolished by calcium depletion of the medium. Cimetidine inhibited the potentiation effect on histamine but not on forskolin stimulated pepsinogen secretion, thus suggesting that this augmentation was independent of histamine H2 receptors. Of interest, potentiation was also independent of endogenous prostaglandin inhibition because exogenous addition of prostaglandin E2 and D2 increased both basal and acetylcholine stimulated pepsinogen secretion in a dose dependent way, but they did not modify histamine or histamine plus aspirin or ibuprofen stimulated pepsinogen secretion. In conclusion, aspirin and ibuprofen potentiate secretagogue stimulated pepsinogen secretion by dispersed human peptic cells and this might be an additional mechanism of non-steroidal anti-inflammatory drug (NSAID) induced gastric injury. This potentiation effect is regulated by calcium, independent of endogenous prostaglandin inhibition and seems to act on pepsinogen secretion at a post-receptor site.

Ingestion of aspirin prevents platelet-induced human fibroblast growth. Implications for peptic ulcer healing

Because aspirin (ASA) may affect peptic ulcer healing through actions on platelets (for example, by inhibiting release of growth factors), human foreskin fibroblast mitogenesis was used for two bioassays (24-h growth with 3H-thymidine incorporation and 5- to 6-day cell proliferation) for serum derived from collagen-aggregated platelet-rich plasma (PRP) or platelet-poor plasma (PPP) or from clotted whole blood (WBS). Blood was taken from five normal subjects before and 6 h after ingestion of ASA. After ASA ingestion serum (WBS or PRP) was less mitogenic (p < 0.01) by both bioassays, whereas PPP serum was not mitogenic either before or after ASA. In vitro, neither ASA nor salicylic acid alone at levels normally found in plasma with ASA use inhibited fibroblast growth. We conclude that ASA ingestion inhibits the mitogenic action of platelets on fibroblast culture by inhibiting the release of putative growth factors. Such an effect might explain the adverse effects of ASA on ulcer healing.

Salicylic acid disposition in children with rheumatoid arthritis

The plasma level profile of SA and SUA after a single oral dose of ASA was studied in 8 children with juvenile rheumatoid arthritis, aged 3.5-15.0 years. Pharmacokinetic parameters were on average similar to those reported in the literature for adult subjects, although a somewhat larger intersubject variability was found.

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.

Salicyl phenolic glucuronide pharmacokinetics in patients with rheumatoid arthritis

The pharmacokinetics of salicyl phenolic glucuronide (SPG) and other salicylic acid (SA) metabolites were studied at three aspirin dosage regimens in eight patients with rheumatoid arthritis. Each patient received 1, 2 and 4 g enteric coated aspirin (ASA) daily in ascending order. At the end of each 2-week dosage period, plasma and urine were collected over a dosage interval for the estimation of various pharmacokinetic parameters. With increasing ASA dosage, mean clearance of SA to SPG was approximately constant (1.8 +/- 0.3, 1.7 +/- 0.2, and 1.5 +/- 0.2 ml/min at 1, 2 and 4 g/day, respectively) when related to plasma concentrations of total SA. The percentage of the ASA dosage recovered in urine as SPG increased from 5.2 +/- 1.1 to 7.1 +/- 1.1 to 10.5 +/- 1.7 at 1, 2 and 4 g/day, respectively. It was concluded, however, that the conversion of SA to SPG is saturable, since the mean clearance of SA to SPG decreased when calculated with respect to the plasma concentration of unbound SA (13.4 +/- 1.6, 11.0 +/- 1.4, and 6.6 +/- 1.9 ml/min at 1, 2 and 4 g/day, respectively). The kinetics of the formation and excretion of salicylurate and the excretion of gentisate were similar to those found in previous studies.

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.

Influence of age, gender, and obesity on salicylate kinetics following single doses of aspirin

Salicylate kinetics following single, 650-mg intravenous and oral doses of aspirin were evaluated in humans in 2 studies. Complete conversion of aspirin to salicylate was assumed. The first study involved 25 young (25-40 years) and 21 elderly (66-89 years) healthy male and female volunteers. Mean salicylate clearance was lower in elderly females compared with that in young females; however, the difference between young men and elderly men was not significant. Salicylate free fraction in plasma increased significantly with age in men and women. After correction for free fraction, unbound mean clearance was reduced in elderly men compared with young men, and in elderly women compared with young women. Peak plasma salicylate concentrations after taking oral aspirin were not significantly influenced by age, and systemic availability of salicylate in all groups was complete. The second study compared 20 obese subjects (mean weight 113 kg) with 20 normal weight controls (mean weight 67 kg) matched for age, sex, height, and smoking habits. Small differences between obese and control groups were observed in total salicylate volume of distribution (Vd), unbound Vd, and mean clearance of total or unbound salicylate. Following normalization for total weight, however, values of total Vd and mean clearance were significantly smaller in obese subjects than in normal weight subjects. Rate and completeness of salicylate absorption were not influenced by obesity when aspirin was ingested, although peak levels were lower in obese subjects. If applied to multiple doses, the reduced unbound clearance of salicylate in the elderly would imply increased accumulation unless doses are appropriately adjusted downward. During long-term therapy, salicylate dosage for obese individuals should not be adjusted upward in proportion to total weight.

The pharmacokinetics of timegadine and two of its metabolites after multiple oral dosing, and the effects of concomitant administration of ibuprofen

A 250 mg tablet of timegadine was given twice daily for 15 days to 13 healthy volunteers. On Day 16 a single morning dose of timegadine was supplemented by two 200 mg tablets of a proprietary brand of ibuprofen. Serum concentrations of timegadine were measured by high pressure liquid chromatography, and steady state was achieved between Days 5 and 8. Serum concentrations of two metabolites of timegadine, MI and MII were measured by thin layer chromatography by Leo Pharmaceutical Products, Denmark. Ibuprofen did not significantly affect the serum half-time of timegadine, but did reduce the maximum measured serum timegadine concentration, the area under the serum concentration versus time curve and the time to achieve maximum measured serum concentration. Serum liver enzymes remained within the normal ranges and there were no changes in hepatic microsomal enzyme activity as assessed by urinary excretion of D-glucaric acid.

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.

Plasma protein binding of dipyrone metabolites in man

Four metabolites of dipyrone, 4-methylaminoantipyrine (MAA), 4-aminoantipyrine (AA), 4-formylaminoantipyrine (FAA) and 4-acetylaminoantipyrine (AAA) can be identified in human plasma after its oral administration. The plasma protein binding of the metabolites in samples from 20 healthy volunteers was determined by ultrafiltration. None of the metabolites were found to be extensively bound to plasma proteins. The binding of MAA and AA was relatively higher than of FAA and AAA, as expected from their chemical structure. The mean percentage plasma protein binding was 57.6% for MAA, 47.9 for AA, 17.8 for FAA and 14.2% for AAA. The correlation between the unbound concentration in plasma and the total concentrations of MAA, AA, FAA and AAA was linear. No association was evident between the total protein plasma concentration and the extent of binding. The possible therapeutic implications related to protein binding of several analgesic and non-steroidal anti-inflammatory drugs are discussed.

Factors determining efficacy of NSAIDs

This article reviews the efficacy of NSAIDs and their pharmacokinetic and pharmacodynamic properties. The assumption that classic pharmacokinetic dose/plasma concentration response relationships can be applied to NSAIDs has tenuous support in the biomedical literature. Comparative efficacy studies, using ASA and indomethacin as the standards for comparison, ignore the fact that the major outcome variables are subjective responses among patients, not among drugs. Comparing inhibition of platelet malonyldialdehyde, synovial drug concentrations, urinary prostaglandin metabolites, and plasma free and total concentration with the clinical outcome provides no guidelines to serve as predictors of response. The individual agents, indomethacin, salicylates, sulindac, piroxicam, and naproxen, illustrate the complexities of NSAID pharmacotherapy. Recent proliferation of newer NSAIDs will not add significantly to the efficacy of these agents in the treatment of pain and inflammatory disease states. However, knowledge of pharmacokinetic population parameters for the individual NSAIDs will increase the likelihood of therapeutic success and diminish the possibilities for adverse reactions.

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.

Pharmacokinetics of aspirin and salicylate in elderly subjects and in patients with alcoholic liver disease

Plasma aspirin, salicylate and salicyluric acid concentrations were monitored in young, elderly and alcoholic subjects after ingestion of a single 1.2 g dose of soluble aspirin. The plasma aspirin, salicylate and unbound salicylate concentration-time profiles varied considerably between individual subjects. Most of the pharmacokinetic parameters derived from these profiles were not significantly different between young subjects, elderly subjects and subjects with alcoholic liver disease. Individual plasma albumin concentrations provided a better index of the unbound plasma salicylate clearances and salicylate plasma protein binding than the age of the subject or the presence of alcoholic liver disease. Highest unbound plasma salicylate concentrations were found in subjects with the lowest plasma albumin concentrations.

The influence of food intake on the bioavailability of timegadine, a novel non-steroidal anti-inflammatory drug

The effects of food ingestion on the absorption of timegadine, a recently synthesised non-steroidal anti-inflammatory drug, was studied in ten healthy volunteers. It was found that food enhanced the absorption of timegadine as shown by increased peak plasma concentrations (Cmax), decreased time taken to achieve these concentrations (tmax), and increased area under the plasma concentration time curve (AUC).

The metabolism of [carboxyl-14C]aspirin in man

1. [carboxyl-14C]Aspirin has been orally administered to four male volunteers and the urinary metabolites examined by paper chromatography, t.l.c., h.p.l.c. and mass spectrometry. 2. 14C Radioactivity was eliminated rapidly in the urine, 94 to 98% of the dose in the first 24 h and approx. 1% in 24-48 h. 3. The major urinary metabolite was salicyluric acid (56-68% dose). In addition, free salicylic and gentisic acids were also detected as were both the acyl and phenolic glucuronides of salicylate. 4. A phenolic glucuronide of salicyluric acid has also been identified. The importance of this metabolite in relation to analytical methods for salicylphenolic glucuronide determination is discussed. 5. The presence of other di- and tri-hydroxybenzoic acids or gentisuric acid could not be demonstrated.

High-pressure liquid chromatographic determination of acetylsalicylic acid, salicylic acid, diflunisal, indomethacin, indoprofen and indobufen

A high-pressure liquid chromatographic technique was developed which allowed concurrent measurement of acetylsalicylic acid (ASA) and salicylic acid (SA) in plasma. ASA was extensively deacetylated to SA not only in vivo but also in vitro, even in frozen plasma. The in vitro conversion could be prevented by physostigmine. In vivo, ASA was eliminated within few hours, whereas SA was continuously present following daily administration of conventional doses of ASA. A slight modification of a similar method, originally developed for naproxen determination [9], was found appropriate for measurement of the SA derivative diflunisal, of two non-SA antiinflammatory agents, indomethacin and indoprofen, and of a related anti-platelet agent, indobufen.