Decreasing serum salicylate concentrations during long-term administration of acetylsalicylic acid in healthy volunteers. Discussion of possible clinical implications

Investigation of the influence of acetylsalicylic acid on the steady state of long-term therapy with theophylline in elderly male patients with normal renal function

The risk inherent in the clinical control of patients with theophylline is widely recognized. Elderly patients may present an additional risk because of altered pharmacokinetics and the use of concomitant medication. Acetylsalicylic acid has been proposed for primary and secondary prevention of myocardial infarction and possible strokes. This investigation was undertaken to determine if concomitant administration of acetylsalicylic acid in elderly patients would alter steady-state levels of theophylline. A population of smoking male patients older than 60 years of age under long-term control of chronic obstructive pulmonary disease (COPD) with theophylline were evaluated for a baseline period of 3 days. Serum levels were measured at 6:00 AM and 6:00 PM. An enteric-coated acetylsalicylic acid preparation, 650 mg by mouth, was added to the daily slow-release theophylline, 6:00 AM hour dose regimen for 4 weeks. The serum levels of theophylline and salicylates were measured at 6:00 PM after dosing and at 6:00 AM the following day, at weekly intervals for 4 weeks. Urine specimens collected before administration of medication at 6:00 AM were analyzed for salicylates to further confirm dosage compliance. All volunteers continued to be clinically controlled throughout the treatment period and no symptoms of either overdose or underdose of either medication occurred. Plateau or trough theophylline serum levels did not change significantly during the salicylate treatment period. Salicylate serum levels did show during treatment self-induced metabolism. It is concluded that in elderly male patients, a daily concomitant therapeutic salicylate regimen does not alter steady-state serum theophylline levels and therefore does not per se necessitate the assay of theophylline blood levels in elderly patients.

Salicylate pharmacokinetics in patients with rheumatoid arthritis

1. The pharmacokinetics of salicylic acid (SA) and its major metabolite salicyluric acid (SU) were studied in nine patients with rheumatoid arthritis following a 900 mg oral dose of acetylsalicylic acid and during 6 weeks of chronic administration of enteric coated aspirin (3,900 mg day). Response to therapy was also monitored. 2. The various pharmacokinetic parameters determined in the study were similar to those observed in other single dose salicylate studies amongst healthy volunteers but were not predictive of salicylate concentration in the chronic dose study. 3. Plasma concentrations of SA (total and unbound) were found to decline significantly over the 6 weeks and plasma SU concentrations increased. 4. During the chronic dosing study, there was a significant increase in the Vmax (total and unbound) for the formation of SU, whilst the Km and SU clearance remained constant. Also, the elimination rate constant (k) for salicylate was not significantly affected. 5. Therapeutic response to salicylate therapy was not significantly affected by the decline in SA concentrations.

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.