Studies on the Intestinal Excretion of Doxycycline

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Abstract
A study of the biliary excretion of doxycycline was performed in 2 patients. Doxycycline appeared rapidly in the bile in concentrations up to 14 μg/ml but the daily excretion in the bile was only a few per cent of the given dose. In 3 other patients a comparison was performed between concentrations in fluids from the intestines after intravenous infusions of oxytetracycline and doxycycline. When renal function was impaired doxycycline appeared in higher concentration, whereas no obvious change was observed for oxytetracycline. No evidence of liver metabolism of doxycycline or tetracycline hydrochloride was found as judged by levels in the serum and urinary excretion before and after medication with phenobarbitone. The increased diffusion of doxycycline into the intestinal tract in uremia may not prevent accumulation when intravenous hyperalimentation is used over long periods of time.