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Unit Code 4925:
Salicylate, Serum, NIH Units

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Useful For

Assessing toxicity

Clinical Information

Acetyl salicylate (aspirin, ASA) remains one of the most commonly

used therapeutic agents, both alone or in combination with other

therapeutic agents(1).  

 

Inhibits prostaglandin synthesis, acts on the hypothalamus heat-

regulating center to reduce fever, blocks prostaglandin synthetase

action which prevents formation of the platelet-aggregating substance

thromboxane A2(2).  Aspirin is rapidly absorbed has a bioavailability

or 50% to 75% and a volume of distribution (Vd) of 10 L (2). 

 

Aspirin is metabolized to salicylate (active drug) by esterases in GI

mucosa, red blood cells, synovial fluid, and blood; metabolism of

salicylate occurs primarily by hepatic conjugation; metabolic pathways

are saturable (1, 2)  The half-life elimination of acetyl salicylate (parent

drug) is 5-20 minutes while the half-life for the active drug salicylate is

dose dependent and ranges from 3 hours at lower doses (300-600 mg)

to 20 hours with higher doses (1, 2).  

 

Stimulation of the respiratory center in the central nervous system and

uncoupling of oxidative phosphorylation are direct effects of salicylate

that lead to many of the toxic symptoms observed in overdose situations (3). 

Clinical manifestations of salicylism depend on the dose of salicylate

ingested, duration of exposure, and age of the patient. In general, acute

ingestion of less than 150 mg/kg may produce "mild" toxicity, with nausea,

vomiting, and GI irritation, but significant toxicity is not expected. Acute

ingestion of 150 to 300 mg/kg may produce "mild to moderate" toxicity, with

vomiting, hyperpnea, diaphoresis, tinnitus, and acid-base disturbances.

Acute ingestion of more than 300 mg/kg may produce "severe" toxicity. 

The presentation can range form metabolic acidosis to a mixed disturbance

with respiratory alkalosis and increased anion-gap metabolic acidosis(1, 3, 4)

Reference Values

Adult therapeutic concentration:  20-200 mg/L

Toxic concentration:  > or =500 mg/L

Interpretation

Adult therapeutic concentration: 20-200 mg/L

 

Toxic concentration: > or =500 mg/L

Clinical Reference

1.   Baselt RC:  Disposition of Toxic Drugs and Chemicals in Man.

      7th ed. Foster City, CA: Biomedical Publications, 2004:1254

 

2.   Physician's Desk Reference. 61th ed. Montvale, NJ:

      Thomson PDR, 2007

 

3.   Goodman & Gilman's:  The Pharmacological Basis of

      Therapeutics. 10th ed. New York, NY: McGraw-Hill

      Professional, 2001

 

4.   Tietz Textbook of Clinical Chemistry and Molecular

      Diagnostics. Fourth ed. St. Louis, MO: Elsevier

      Saunders, 2006:1091

Key