The purpose of this study is to determine whether Propionyl-L-carnitine administration may ameliorate the illness in patients affected by mild to moderate ulcerative colitis already in treatment with one of the standard treatments (corticosteroids excluded).

The trial foresees the administration of 2 different dosages of Propionyl-L-carnitine (ST261) colon release tablets, 1 g/die and 2 g/die. The primary objective of this trial is to evaluate the clinical/endoscopic response defined as a lowering of the Disease Activity Index (DAI score) of at least 3 points ot the reaching of remission, the clinical/endoscopic remission (DAI score <= 2 with no individual subscore > 1) and histological efficacy of the two combined dosages of PLC (i.e. PLC 1 g/die + 2 g/die) in comparison to placebo, defined as an improvement of the Histological Index (HI) of at least 1 point at the end of the study (a final HI score of <= 1 will be defined as an histological remission).

The secondary objective is to evaluate the clinical/endoscopic and histological efficacy of the two dosages of PLC individually considered in comparison to Placebo, in order to gather information on the dosage to be used in subsequent trials. The safety and tolerability of the regimens studied will also be objectives of the study.

Inclusion Criteria:

• Have read the Information for the Patient and signed the Informed Consent Form.

• Age comprised between 18 and 75 included.

• If female, not pregnant or nursing.

• For women of childbearing potential, willingness to avoid a pregnancy during the treatment period and for at least 1 month from the last dose of drug.

• Availability of a pancolonoscopy and histology both confirming the diagnosis of active ulcerative colitis.

• Disease Activity Index comprised between 3 and 10, inclusive, (mild to moderate ulcerative colitis).

• On one of the following treatments for ulcerative colitis prior to baseline visit:

  1. Stable background oral aminosalicylates (mesalazine, balsalazide, olsalazine) or sulfasalazine therapy for greater than or equal to 4 weeks prior to baseline assessments.
  2. Stable background mercaptopurine or azathioprine for greater than or equal to 12 weeks prior to baseline assessments.

Exclusion Criteria:

• First diagnosis of ulcerative colitis.
• Crohn's disease.
• Current or previous (in the last 10 days preceding the screening) use of systemic corticosteroids.
• Use of antibiotics in the last 10 days preceding the screening.
• Use of NSAID's in the last 10 days preceding the screening.
• Use of probiotics in the last 10 days preceding the screening
• Positive stool culture (when performed, according to Investigator's judgment, to assess possible parasitologic infection(s)).
• Significantly impaired liver, renal, pulmonary or cardiovascular function.
• History of colon resection.
• Diverticulitis.
• Diagnosis of proctitis
• Stable rectally administered therapy in the last 10 days.
• Active or chronic infection(s).
• Simultaneous participation in another clinical trial, or participation in any clinical trial involving investigational drugs within 3 months from enrolment into the present study.
• Any physical or psychological condition in a patient that could let the investigator suspect his/her poor compliance.