Effect of Oral Administration of Methylene Blue MMX Tablets on Double Stranded DNA

Inclusion Criteria:

* Males or females, aged between 18 and 75.
* Outpatients scheduled for screening or surveillance colonoscopy
* Subjects must be identified as having the clinical requirement for second colonoscopy within 2weeks of the initial colonoscopy.
* Women of childbearing potential must use at least one reliable method of contraception, be surgically sterilised or be abstinent.
* For female subjects, a negative serum pregnancy test is required before Methylene Blue MMX® tablets are dispensed to the subject.
* Post menopausal patients need to have a period of greater than 1year since last menstrual period.
* Subjects must be able to comprehend the full nature and purpose of the study, including possible risks and side effects.
* Subjects must be able to co-operate with the investigator and to comply with the requirements of the entire study.
* Signed written informed consent prior to inclusion in the study.

Exclusion Criteria:

* No Pregnant or lactating women, or women undergoing fertility treatment.
* No previous medical history of, or suspected hypersensitivity to the Methylene Blue and/or this formulations ingredients.
* No previous medical history of, or suspected hypersensitivity to the PEG based bowel cleansing preparation and/or this formulations ingredients.
* No previous medical history of gastrointestinal obstruction or perforation, toxic megacolon, major colonic resection, severe diverticulitis, heart failure (Class III or IV), serious cardiovascular disease.
* No ALT, AST, GGT, Bilirubin, Creatinine or Urea greater than 2.5 x the upper limit for normal, based on local laboratory testing.
* No clinical alarm symptoms or history of anaemia (previously recorded haemoglobin of less than 10mg/dL) or frank blood in the stool within the last 30 days prior to enrolment.
* No known deficiency of glucose-6-phosphate dehydrogenase.
* No known deficiency of NADPH reductase.
* No treatment within 5 weeks prior to randomisation with Fluoxetine (Prozac).
* No concurrent treatment, or previous treatment within 2 weeks with any of the prohibited psychiatric medications that may interact with Methylene Blue as listed in the Prohibited Medications section; Selective Serotonin Reuptake Inhibitors (SSRI), Serotonin-Norepinepherine Reuptake Inhibitors (SNRI's), listed Tricyclic anti-depressants or Monoamine oxidase A inhibitors.
* No concurrent treatment with anticoagulants, or antiaggregants, inducing an INR \> 1.5.
* No current enrolment in any other clinical trial, or previous enrolment in a clinical trial within the last 30 days.
* No other medical condition that in the investigators opinion would make the administration of the study drug or procedures hazardous to the subject.

Exclusion Criteria:

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