Diabetes Care, Vol 22, Issue 1 38-44, Copyright © 1999 by American Diabetes Association
First 20 months' experience with use of metformin for type 2 diabetes in a large health maintenance organization
JV Selby, B Ettinger, BE Swain and JB Brown
Division of Research, Kaiser Permanente Medical Care Program (Northern California Region), Oakland, USA. jvs@dor.kaiser.org
OBJECTIVE: To assess adherence to prescribing guidelines, continuation
rates, population effects on glycemic control, and occurrence of lactic
acidosis during the first 20 months of the availability of metformin in a
large health maintenance organization. RESEARCH DESIGN AND METHODS: A
retrospective cohort study was performed in the 90,000-member diabetes
registry of Kaiser Permanente, northern California. Principal study
measures were the proportions of patients started on metformin who met
prescribing guidelines (previously on sulfonylureas, HbA1c, obesity,
creatinine), the change in HbA1c 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 baseline HbA1c > or
= 8.5%, 71% were obese, and 99% had a serum creatinine < or = 1.5 mg/dl.
Among patients on sulfonylureas at baseline, those starting metformin had
significantly lower HbA1c levels 6 months later than those not started,
after 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 sulfonyl-ureas) had
slightly higher follow-up HbA1c levels than similar patients not starting
metformin. Continuation of metformin at 12 months was significantly higher
for patients previously treated with sulfonylureas than other groups. One
probable case of lactic acidosis was identified during 4,502 person-years
on metformin. CONCLUSIONS: Adherence to prescribing guidelines was
relatively high during metformin's first 20 months of availability.
Glycemic control improved substantially for patients previously treated
with sulfonylureas. Lactic acidosis was rare.