Evaluation of Topical 10% Metronidazole Ointment for the Treatment of Active Perianal Crohn's Disease

Inclusion Criteria: * Have Crohn's disease (diagnosed by radiology, endoscopy and pathology), with anorectal involvement. * Have had perianal symptoms for longer than 3 months * Have a PCDAI of 5 or above at baseline * Subjects can be on concomitant medication. Acceptable regimes are:- * Aminosalicylates at a dosage that has been stable for more than 4 weeks before screening; * Oral corticosteroids \<40mg per day that has been stable for more than 3 weeks; * Methotrexate given for at least 3 months that has been stable for more than 4 weeks; Azathioprine or mercaptopurine given for at least 6 months at dosage that has been stable for more than 8 weeks; * Antibiotics at a dosage that has been stable for 4 weeks (subjects may be on oral metronidazole but on a dose not more than 750mg per day), * Cycolsporin for more than 3 months and on a stable dose for more than 4 weeks; * Patients who have been treated with Infliximab must have received their initial dose 3 months before starting study medication and their most recent dose at least 8 weeks before starting study medication and not receive an infusion whilst in the double-blind treatment phase of the study for 4 weeks. During the second 4 week open stage of the study patients can commence again a maintenance regime with Infliximab treatment if deemed necessary * Any patients not on concurrent medication must have been off medication for at least 4 weeks before screening. * If patients have Setons these must have been in place for at least 4 weeks prior to screening. * Subjects must be aged 18 years or over and of the legal age of consent. * If female, the subject must not be lactating and must be (a) post- menopausal, (b) surgically sterilised, or (c) have a negative pregnancy test result prior to entry into the study and will use double- barrier methods of contraception (two separate methods of birthcontrol one of which may include oral contraception) for the duration of the study. * Must have provided written informed consent to participate. Exclusion Criteria: * They have had surgery to the anus or rectum in the past 4 weeks; * They have a perianal abscess requiring incision and drainage; * They have a stoma of less than 6 months duration; * Allergic to metronidazole; * Are taking any prohibited medication. * Deemed mentally incompetent. * Considered by their physician unlikely to be able to comply with the protocol. * Taken part in an experimental drug study in the preceding three months.