Absorption Kinetics of Rectal Formalin Instillation

Abstract

Formalin instillation has become an accepted treatment of radiation-induced hemorrhagic cystitis and proctitis since the initial report by Brown in 1969 (Med. J. Aust. 1:23, 1969). Although its use is widespread, no studies have been performed to determine the safest, volume or duration of formalin exposure. The purpose of our study was to determine the optimum technique for instillation and the safety margin regarding the maximum time that formalin can be in contact with the rectal mucosa without causing serum toxicity. In a pilot canine study, 4% neutral buffered formalin was instilled into the rectum in 30 ml aliquots for 60 seconds each after which each aliquot was withdrawn; a total volume of 400 ml was used. Our subsequent experiment involved rectal instillation of a single formalin bolus of 100 ml for 1 hour without removal during this time. Formalin metabolites were measured in the blood and urine to assess toxicity. Results indicate that with the latter technique serum formic acid reaches toxic levels within 15 minutes of instillation and may stay elevated for several hours. Metabolites in the urine similarly increase within 15 minutes, lagging only shortly behind the rise in serum levels. Performing formalin instillation in a series of 30 ml aliquots appears to be a safer treatment, as toxic serum levels were not reached and their slight rise above baseline returned to normal within 3 hours.

Treatment of Hemorrhagic Radiation Proctitis With 4 Percent Formalin

“…[21][22][23] The safety of formalin has also been established with absorption studies. 24 The present study showed that, after 15 minutes of instillation of 100 ml of 4 percent formalin in the rectum, the toxic metabolite of formic acid started to have increased levels in the bloodstream. Smaller aliquots with shorter instillation time in the rectum were shown to be safer.…”

The utilization of intraluminal formalin for intractable rectal haemorrhage in advanced rectal cancer: a case report

“…As most patients with radiation proctitis are successfully treated with formalin, surgery is conducted more for non-bleeding manifestations of chronic radiation damage to the rectum 50 such as stricture and fistula [12]. Despite some authors recommending rectal formalin as a first-line therapy in transfusion-dependent radiation proctitis [13], there is considerable debate concerning the technique (irrigation, enema or contact) and the dose which is most likely to be efficacious and safe [14,15]. Its use in intractable bleeding for a fixed rectal tumour has been only reported once before by Kelly and Nugent [2].…”

Formalin Instillation for Control of Rectal Hemorrhage in Advanced Pelvic Malignancy

“…4 A recent study examining absorption kinetics of rectal formalin instillation in a canine model showed that formalin metabolites reached toxic levels within 15 minutes when formalin was instilled as a bolus for one hour, but formalin instillations in a series of 30-ml aliquots for 60 seconds each failed to reach toxic serum levels, making this a safer treatment technique. 6 …”