Patient description: The patient is a 57-year-old man with abdominal pain and vomiting. The pain started gradually about 20 hours ago in the epigastric and periumbilical regions, radiating to his back. He drinks around 60 units of alcohol per week and smokes 22 cigarettes per day. He is healthy with no history of allergies or using any medications. His family history is positive for type 2 diabetes (his father and sister). He lives alone and has no children. The abdomen is tender and soft. His bowel sounds are normal. His heart rate is 115/min and blood pressure 110/75 mmHg. The lab results are remarkable for leukocytosis (19.5), urea of 8.5, high CRP (145), high amylase (1200) and Glc level of 15. Cross-sectional imaging was negative for obstructive pancreatitis.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  Psoriasis Type 2 Diabetes Mellitus People who satisfy all of the following may be included in the study: 1. Have a diagnosis of generalized chronic plaque and/or guttate psoriasis; 2. Are male or female aged between 18 and 75 years inclusive; 3. Have a psoriasis area and severity index (PASI) greater than 7; 4. Have a diagnosis of type 2 diabetes; 5. Have a glycated haemoglobin (HbA1c) level between 48mmol/mol and 69mmol/mol; 6. Are able and willing to stop sulphonylurea, dipeptidyl peptidase-4 (DPP-4) inhibitor and glucagon-like peptide-1 (GLP-1) analogue therapy for the duration of the study; 7. Have a negative pregnancy test at screening (women of child bearing potential only); and 8. Are willing to voluntarily sign a statement of informed consent to participate in the study  People with any of the following conditions will be excluded from the study: 1. Allergy or hypersensitivity to sitagliptin (Januvia®) or gliclazide (Diamicron®); 2. Current or recent (within 8 weeks) receipt of phototherapy; 3. Type 1 diabetes; 4. Severe kidney disease as defined by a previous diagnosis of chronic kidney disease in the presence of an estimated glomerular filtration rate (eGFR) of less than 30ml/min/1.73 m2; 5. Severe heart disease as defined by a previous diagnosis of heart disease and a left ventricular ejection fraction which is known to be less than 35% (as measured by echocardiogram or cardiac catheterisation study); 6. Severe lung disease as defined by a previous diagnosis of chronic lung disease and a forced expiratory volume in 1 second (FEV1) or a forced vital capacity (FVC) that is known to be less than 50% that which would be estimated for a person of that age and gender; 7. Severe liver disease as defined by a previous diagnosis of chronic liver disease in the presence of an alanine transferase concentration greater than 150 international units (IU)/L (greater than three times the upper limit of the normal reference range); 8. Any other contraindications, as stated in the SPCs for sitagliptin (Januvia®) or gliclazide (Diamicron®); 9. Female patients of child bearing potential who are pregnant, breastfeeding, or unwilling to practice an acceptable barrier and/or hormonal method of contraception during participation in the study abstinence will be permitted only if it is in keeping with a person's lifestyle; 10. Any clinically significant chronic disease that might, in the opinion of the investigator, interfere with the evaluations or preclude completion of the trial; 11. Any current or recent (within the past 4 weeks) acute serious illness, acute psychiatric illness or severe uncontrolled/unstable illness; 12. Previous randomisation into this study; 13. Concurrent participation in another clinical trial; and 14. Participation in another clinical trial during the twelve weeks prior to study entry (i.e. screening visit)