STUDIES ON THE FATE OF CARBON-14 LABELED PHENOLPHTHALEIN

¹ Department of Pharmacology, University of Chicago

Carbon-14 labeled phenolphthalein was administered in solution to mice and dogs. Absence of C¹⁴O₂ in the expired air of mice was interpreted as an indication that the phenolphthalein molecule was not broken down.

Mice excreted 96 per cent of the administered radioactivity in the feces and urine within 48 hours; tissue distribution studies in this species showed that the level of radioactivity paralleled the concentration in the blood stream. The drug was not concentrated in any of the organs studied. In mice phenolphthalein crossed the placental barrier in both directions, with radioactivity in the fetuses paralleling that in the maternal blood and showing no evidence of retention in the maternal tissue or the fetuses.

Normal dogs excreted 51 per cent of the orally administered radioactivity in the feces and 36 per cent in the urine in 72 hours. Corresponding values following intravenous administration were 54 per cent and 37 per cent. Subsequently these dogs were surgically treated making quantitative bile collection possible. In 72 hours the recovery of orally administered radioactivity was as follows: feces, 31 per cent; urine, 38 per cent; and bile, 22 per cent. Corresponding values for intravenous administration were: feces, 11 per cent; urine, 35 per cent; and bile, 43 per cent.

To what extent the solvents used influenced the behaviour of phenolphthalein was not determined. In our studies we did not observe any adverse effects such as tissue irritation, toxic symptoms or interference with the normal physiological functions of the digestive system, kidneys, liver, or any other organs.