The present study of metronidazole in perineal Crohn's disease includes 26 
patients, and is composed of 17 of 21 patients who were previously reported and 
9 additional consecutive patients. The course of these patients was evaluated to 
determine if the drug could be reduced or stopped, whether or not it continued 
to be effective for prolonged periods, and what long-term side effects were 
encountered. Dosage reduction was associated with exacerbation of disease 
activity in all patients, but in all, the perineal manifestations of disease 
healed promptly when the full dosage of metronidazole was reinstituted. The drug 
could be successfully discontinued in only 28% of those in whom cessation was 
attempted; in those patients whose perineal disease worsened with cessation of 
therapy, rapid healing was achieved if the drug was reintroduced. Sixteen 
patients received metronidazole for at least 12 mo including 7 for 18-36 mo. 
Eight of these 16 patients, including 4 on and 4 off the drug, remain healed; 
the other 8 patients had advanced healing. The only major side effect observed 
was paresthesias. These occurred in 50% of the patients and developed in the 
patients at a mean of 6.5 mo after the onset of treatment. They appeared to be 
dose related and nonprogressive but tended to persist for prolonged periods even 
after discontinuance of the drug.