Occurrence of myeloid bodies in rats following two-year administration of imipramine hydrochloride.

Sprague-Dawley CD rats received daily oral doses (45 mg/kg) of the cationic amphiphilic tricyclic antidepressant imipramine HCl (Tofranil) for up to two years. Representative specimens of liver, lung, spleen, mesenteric lymph node, retina and dorsal root ganglion were examined for myeloid bodies (MB). The extent that MB affected a given cell or group of cells was qualitatively determined. Myeloid bodies were observed in a variety of cell types after one year of administration to treated rats. They were less common after a subsequent three month recovery period. Fewer MB were observed in rats treated for one year than were previously reported in short term studies. Fewer MB were seen after two years of treatment than after one year although the same organs were affected. Thus, MB appear to decrease in number with increasing time of compound administration. This may result from a more efficient metabolism of the drug or because of decreased levels of phospholipid in aged rats.