First 20 months' experience with use of metformin for type 2 diabetes in alarge health maintenance organization

OBJECTIVE - To assess adherence to prescribing guidelines, continuation rat es, population effects on glycemic control, and occurrence of lactic acidos is during the first 20 months of the availability of metformin in a large h ealth maintenance organization. RESEARCH DESIGN AND METHODS - A retrospective cohort study was performed in the 90,000-member diabetes registry of Kaiser Permanente, northern Califor nia. Principal study measures were the proportions of patients started on m etformin who met prescribing guidelines (previously on sulfonylureas, HbA(1 c) obesity, creatinine), the change in HbA(1c), at 6 months after starting metformin, and hospitalization rates for lactic acidosis. RESULTS - A total of 9,875 patients received metformin during this interval . At least 74% were previously treated with sulfonylureas alone, 81% had ba seline HbA(1c) greater than or equal to 8.5%, 71% were obese, and 99% had a serum creatinine less than or equal to 1.5 mg/dl. Among patients on sulfon ylureas at baseline, those starting metformin had significantly lower HbA(1 c) levels 6 months later than those not started, alter adjustment for age, sex, and the higher baseline levels in those started (adjusted difference: 0.5%, P < 0.0001). Patients starting metformin as initial monotherapy also improved significantly, but patients previously treated with insulin (with or without sulfonylureas) had slightly higher follow-up HbA(1c) levels than similar patients not starting metformin. Continuation of metformin at 12 m onths was significantly higher for patients previously treated with sulfony lureas than other groups. One probable case of lactic acidosis was identifi ed during 4,502 person-years on metformin. CONCLUSIONS - Adherence to prescribing guidelines was relatively high durin g metformin's first 20 months of availability. Glycemic control improved su bstantially for patients previously treated with sulfonylureas. Lactic acid osis was rare.