MECHANICAL, HISTOLOGIC, AND BIOCHEMICAL EFFECTS OF CANINE RECTAL FORMALIN INSTILLATION

Instillation of 4 percent formalin effectively treats radiation hemorr hagic proctitis; however, little is known regarding its side effects. PURPOSE: The study contained herein was undertaken to determine rectal compliance and collagen content, mucosal and vascular histologic chan ges, and kinetics of formalin absorption following instillation. METHO DS: Fifteen mongrel dogs (50-60 pounds) were randomized into five expe rimental groups according to time elapsed from formalin treatment: con trol, acute, one week, two weeks, and four weeks. Formalin was instill ed in 30-ml aliquots to a total volume of 400 mi. Rectal compliance (c losed manometry system) was assessed pre-formalin and post-formalin at the designated time interval. Serum formalin metabolites were determi ned at time 0, 0.5, 1, and 3 hours. A segment of rectal wall was analy zed for collagen content, mucosal injury, and blood vessel density. RE SULTS: Serum formalin levels peaked within 30 minutes, returning to no rmal by 3 hours. With the exception of one dog, toxic levels were not reached at any time during the study. No dogs experienced sepsis, feve r, or altered gastrointestinal function. Acute and one-week dogs showe d mild diffuse proctitis and mucosal slough, which healed within two w eeks. Rectal compliance and collagen content were unchanged. Mucosal b lood vessels decreased in number early (P = 0.03). CONCLUSIONS: Instil lation of 4 percent formalin in sequential aliquots of a small volume that is kept in contact for a short period of time is safe. Serum form alin levels generally do not reach toxic levels, and the slight elevat ion in formalin concentration that was seen returns to normal within t hree hours. Formalin-induced proctitis heals within two weeks, and no long-term changes in rectal compliance or collagen content were seen.