Patients suffering from Irritable Bowel Syndrome with predominant constipation will be provided with the study medication. The study medication will be evaluated for its efficacy in relieving the symptoms

Inclusion Criteria:

1. Male or female patient fulfilling the Rome III criteria for IBS-C
2. Signed informed consent at screening visit

Exclusion Criteria:

1. Patients having significant diarrhea at least 25% of the time during the past 3 months
2. Patients having alarm symptoms or signs
3. Chronic diarrhea
4. History of gastrointestinal haemorrhage, mechanical obstruction or perforation
5. Patient with clinically relevant ECG abnormalities (prolonged QT interval)
6. Active psychiatric disorder that would interfere with the study objectives
7. Health conditions (e.g. age related impairment of cognitive functions) that would interfere with the study objectives or might impair the compliance of the patient
8. Severe hepatic, renal, cardiac, metabolic, haematological or malignant diseases (including prolactin dependent tumours) or clinically relevant deviations in laboratory values (AST/ALT greater than twice the upper limit of normal, serum creatinine * 2 mg/dl [177 µmol/l] according to the medical judgement of the investigator
9. Patient with hypokalemia (serum potassium < 3.5 mmol/l).
10. History of any known hypersensitivity to the ingredients of the investigational drug
11. Pregnancy or lactation
12. Women with childbearing potential who do not apply a medically accepted method of contraception.