Rectal formalin instillation - a practical and safe therapy for hemorrhagic proctitis

Hemorrhagic proctitis is a rare, but severe complication of radiation thera py in the treatment of several pelvic malignancies. Administration of topic al steroids, anti-inflammatory agents or laser therapy and rectal instillat ion of 4% formalin have been described as a method of treating this complic ation. A dog model was established to study the safest volume and duration of administration of formalin, the histological changes in the rectal mucos a, and rectal compliance following this treatment. Method: Twenty-one mongr el dogs were assigned randomly to seven groups. Three dogs received a recta l formalin bolus of 400 mi for 1 h; in the other six groups formalin was in stilled in 30 mi aliquots to a total volume of 400 mi. Serum levels of form alin were obtained at designated time intervals, rectal compliance was eval uated pre- and post-formalin instillation, and rectal mucosa was analyzed f or blood-vessel density and mucosal injury at different time points. Result s: Serum formalin in the bolus group reached toxic levels, while sequential instillation caused no serum toxicity in any dog. Rectal compliance and mu cosal thickness were not affected by formalin, but there was a decrease in the angiogenesis score, and mild proctitis was seen in the acute and 1-week group.