Safety and efficacy of acetarsol suppositories in unresponsive proctitis.

In a prospective open study, 10 patients with intractable proctitis were treated with acetarsol suppositories (250 mg b.d. for 4 weeks) and were monitored clinically, biochemically and toxicologically. Proctitis resolved symptomatically and sigmoidoscopically within 2 weeks in nine patients; one patient was unaffected. The only side-effect was of transient thrombocytosis in a single patient. Maximal blood and urinary arsenic concentrations occurred after 1 week's treatment with a total inorganic arsenic in the hazardous range in six patients; subsequent concentrations fell despite continuing therapy and at 4 weeks potentially hazardous values persisted in only two patients. Continued renal excretion and diminished absorption across an improved rectal mucosa is thought to be responsible for this paradox. Arsenic levels fell rapidly when acetarsol was withdrawn and were indistinguishable from pretreatment values within 4 weeks. Short-term acetarsol therapy offers a useful additional measure when local steroids have failed to control ulcerative proctitis; it appears to be safe and formal controlled comparisons with other therapeutic options are therefore legitimate.