Sitagliptin Metformin/PPARg Agonist Combination Therapy Add-on (0431-052)

Sitagliptin 100mg tablet each day for 54 weeks. All subjects will be given placebo to sitagliptin for a 2 week period.

Placebo to sitagliptin 100mg tablet each day for 54 weeks.

Subjects taking 4mg or greater rosiglitazone at screening will enter a 6 week stable dose period followed by a 54 week treatment period. Subjects who are taking less than 4mg/day or no rosiglitazone at screening will be titrated to a stable dose of at least 4mg over a a maximum of 8 weeks followed by a dose stable period of up to 12 weeks then a 54 week treatment period. Total treatment will be up to 77 weeks.

Subjects taking 1500mg or greater metformin at screening will enter a 6 week stable dose period followed by a 54 week treatment period. Subjects who are taking less than 1500mg/day or no metformin at screening will be titrated to a stable dose of at least 1500mg over a a maximum of 8 weeks followed by a dose stable period of up to 12 weeks then a 54 week treatment period. Total treatment will be up to 77 weeks.

Subjects not meeting specific glycemic controls during the 54-week treatment period will use glipizide as rescue therapy. Glipizide will be titrated in 5mg doses up to a maximum 40mg each day. (In Canada, the rescue therapy will be a sulfonylurea agent marketed in that country.)