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Subject: Salicylates (Aspirin)
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An acidic drug that is rapidly metabolized to an active metabolite, salicylate; also known as acetylsalicylic acid (ASA). Included in aspirin, sodium salicylate, oil of wintergreen, methyl salicylate.
Normal therapeutic range (serum):
Analgesic/antipyretic use: <60 μg/mL
Anti-inflammatory use: 150–300 μg/mL
ASA and salicylate have analgesic, antipyretic, and anti-inflammatory properties; used in the treatment of RA.
ASA also inhibits platelet aggregation and, therefore, prolongs bleeding time.
See discussion of salicylate poisoning in Chapter 14.
Requires specific test request; not usually detected in routine screens:
Limit of detection: 40–50 μg/mL
Suitable for blood, serum, plasma, urine
Not recommended for quantitative purposes due to interferences from metabolites, AND plasma constituents
With a Limit of quantitation: 50 μg/mL.
Not whole blood.
Anticoagulants (heparin, citrates, oxalates, EDTA) do not interfere.
Do not use sodium azide in collection tubes.
Hemolysis produces false-negative results.
Hemoglobin concentrations >100 mg/dL may interfere.
Sample pretreatment required
Gas chromatography: derivatization may be necessary
HPLC: preferred technique for distinguishing metabolites
Limit of quantitation: 50 μg/mL