BALANCE EXCRETION OF H-3 AND C-14 TYLOXAPOL IN THE MALE RABBIT AFTER INTRATRACHEAL ADMINISTRATION

1. Tyloxapol, trace-labelled (50-100 mu Ci/animal) with H-3 or C-14, w as administered intratracheally in a surfactant formulation (EXOSURF N eonatal) to the male rabbit in a total tyloxapol dose of 5 mg/kg. Urin e, faeces, expired air, and blood were collected for up to 10 days fol lowing tyloxapol administration.2. Over 5 days, H-3-tyloxapol-related radioactivity in the urine (13.4%) and faeces (27.4%) accounted for a major fraction of the labelled dose. However, urine also contained an additional 13% of the dose as tritiated water. Expired air accounted f or only 4.2% of the dose. At the end of the study, an additional 35.6% of the radioactive dose was found in tissues and the carcass, mainly in the lung (27.4%) and to a lesser extent in the liver (2.8%) and kid ney (0.4%). Levels of radioactivity in other tissues, including whole blood, were low. 3. Over a separate 10-day study, faecal (30.4%) and r enal (9.7%) elimination of C-14-tyloxapol accounted for 40% of the rad ioactive dose, with expired air accounting for much less (2.7%). At th e end of the study, additional radioactivity was recovered from the lu ng (43.9%) and to a lesser extent from the liver (3.8%) and kidney (0. 3%). The half-life for the elimination of total radioactivity from the lung was estimated to be 10-12 days. 4. These data indicate that, fol lowing intratracheal administration, tyloxapol and metabolites were re tained by the lung, released slowly into the systemic circulation, and eliminated through faecal and renal excretion.