HYPOTHESIS: Prescription patterns for the newer thiazolidinedione (TZD) drugs, pioglitazone and rosiglitazone, will reflect historic prescription patterns for troglitazone. Predicting what drugs are commonly prescribed in combination with pioglitazone and rosiglitazone might help anticipate the most common drug interactions for these drugs, and possible adverse effects due to additive drug toxicity. This information can be used to design surveillance monitoring to detect toxicity due to additive effects early. If this type of toxicity is detected, recommendations for multidrug regimens can be revised appropriately. METHODS: This retrospective data analysis used data from Solucient’s proprietary Medical Claims Data Warehouse of over 6 million lives. Patients in the troglitazone cohort took troglitazone for at least 4 consecutive months between 9/1/1998 and 6/30/2000, and had at least one other prescription for a diabetic drug written after the last troglitazone prescription. Patients in the pioglitazone and rosiglitazone cohorts took pioglitazone or rosiglitazone for at least 4 consecutive months between 1/1/1999 and 6/30/2000. RESULTS: All three TZDs show similar prescription patterns, even though both newer TZDs are approved as monotherapy and troglitazone was not. The combination of TZD and sulfonylurea occurred most commonly (troglitazone 28%, pioglitazone 26% and rosiglitazone 30%), followed by monotherapy (troglitazone 20%, pioglitazone 23% and rosiglitazone 23%). Combination with insulin (troglitazone 20%, pioglitazone 19% and rosiglitazone 16%) ranked third for all. CONCLUSIONS: Our results suggest that pioglitazone and rosiglitazone are prescribed in a manner similar to troglitazone. This suggests that physicians should be particularly vigilant for drug interactions between sulfonylureas and TZDs, as well as for additive drug toxicities between from these drugs. This analytic approach could be expanded to other drugs frequently used in patients with type II diabetes, particularly antihypertensives, drugs for congestive cardiac failure and antihyperlipidemics.