5-Aminosalicylic acid (5-ASA) is an important maintenance drug for patients with ulcerative colitis. A proportion of the ingested dose is excreted in the urine. Measuring 5-ASA and its metabolites in urine requires mass spectrometry, which is not widely available for this purpose. Urinary 5-ASA can be measured by colorimetry using the serum salicylic acid assay and is a surrogate marker of recent 5-ASA ingestion. We evaluated whether measuring 5-ASA in first morning voids or in random spot urine samples correctly identifies teenagers with poor adherence to oral 5-ASA.Methods:
Teenagers who were prescribed a current regimen including >40 mg · kg−1 · day−1 of 5-ASA were invited to collect their spot urine with various time lapses since their last presumed 5-ASA ingestion. Classification of adherence was based on a composite method that included a patient-reported adherence scale and 6-thioguanine levels in erythrocytes.Results:
Teenagers who were classified as “good adherers” had 66 of 69 (96%; 95% confidence interval 87%–99%) spot urine samples with detectable 5-ASA levels. “Poor adherers” had 30 of 45 (67%; 95% confidence interval 52%–79%) spot urine samples with undetectable 5-ASA levels. The “good adherers” with false-negative urine tests were on a once daily dosing regimen and had collected a spot urine sample shortly before the next dosage. Their first morning voids had detectable 5-ASA levels.Conclusions:
Undetectable 5-ASA levels in the first morning void confirms short-term nonadherence to oral 5-ASA.