ASA) and sulfapyridine, followed by acetylation to form acetyl-5-amino- salicylic acid and acetylsulfapyri- dine, respectively. Solutions of both sulfasalazine.
Sulfasalazine Interference with HPLC Assay of 5-Hydroxyindole-3acetic Acid To the Editor: An increase in the urinary excretion of 5-hydroxytryptamine (5HT; serotonin) and of its major metabolite 5-hydroxyindole-3-acetic acid (5HIAA) is one of the biochemical features of the carcinoid syndrome. The most consistent clinical feature is attacks of facial flushing, a feature that also may occur with pheochromocytoma, making the differential diagnosis important (1). The diagnosis of pheochromocytoma is indicated by increased urinary excretion of 4-hydroxy-3-methoxymande]ic acid (HMMA; vanillyhuandelic acid). Homovanillic acid (HVA), a metabolite of dopamine, can be detected in the urine in increased amounts in patients with neuroblastoma (2) and may also be increased in patients with carcinoid syndrome (3). Measurement of the three metabolites HMMA, 5HIAA, and HVA by HPLC in the urine of patients with unexplained facial flushing is useful in the differential diagnosis of these conditions. A simultaneous assay of HMMA, 5HIAA, and HVA described by Richards and Titheradge (4) involves extraction of the metabolites from acidified urine into ethyl acetate, with 5-hydroxyindole-2-carboxylic acid as
the internal standard. The extract is evaporated to dryness under nitrogen and reconstituted with mobile phase [methanol:potassium phosphate-phosphoric acid buffer (0.1 mol/L, pH 3.0), 18:82 by vol]. Separation is achieved with a 15 cm X 4.6 mm Hypersil ODS reversed-phase column (5-pm particles; Jones Chromatography, Hengoed, UK) with isocratic elution and amperemetric detection (+0.75 V). This study was carried out in accordance with the rules of the ethical committee of King’s Healthcare. In investigating paroxysmal hypertension in a young man (patient A) who had been admitted with a fractured neck of femur, we screened for HMMA/5HIAAJHVA in 24-h urine. Quantitation of the chromatogram (Fig. 1A) gave the following results: HMMA, 21 pmol/24 h (normal
