C. HARVENGT, M.D., PH.D.
To the editor: The recent editorial on labetalol (1), released in Belgium several years ago, does not mention the interference of the drug with the fluorimetric determination of urinary catecholamines and metanephrines (2). We have seen marked apparent elevation of these pressor metabolites in hypertensive patients on labetalol. Some patients, referred to our hospital for further study, have had aortic arteriography done to exclude a secreting pheochromocytoma. This spurious elevation of the urinary metanephrines was not confirmed by gas-liquid chromatography (3).
The mechanism of this interference lies in adsorption of the drug itself or one of its metabolites to alumina,
HARVENGT C. Labetalol and Determinations of Pressor Hormones. Ann Intern Med. ;100:314. doi: 10.7326/0003-4819-100-2-314_1
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Published: Ann Intern Med. 1984;100(2):314.
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