Simple Urine Test to Evaluate Adherence to Oral 5-ASA in Teenagers With Ulcerative Colitis: Proof of Concept

Objectives: 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 patientreported 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.