Metformin Safety Warnings and Diabetes Drug Prescribing Patterns for Older Nursing Home Residents

Abstract

Objective: Diabetes mellitus is common in US nursing homes (NHs), and the mainstay treatment, metformin, has US Food and Drug Administration (FDA) boxed warnings indicating safety concerns in those with advanced age, heart failure, or renal disease. Little is known about treatment selection in this setting, especially for metformin. We quantified the determinants of initiating sulfonylureas over metformin with the aim of understanding the impact of FDA-labeled boxed warnings in older NH residents.

Design and setting: National retrospective cohort in US NHs.

Participants: Long-stay NH residents age ≥65 years who initiated metformin or sulfonylurea monotherapy following a period of ≥6 months with no glucose-lowering treatment use between 2008 and 2010 (n = 7295).

Measurements: Measures of patient characteristics were obtained from linked national Minimum Data Set assessments; Online Survey, Certification and Reporting (OSCAR) records; and Medicare claims. Odds ratios (ORs) comparing patient characteristics and treatment initiation were estimated using univariable and multivariable multilevel logistic regression models with NH random intercepts.

Results: Of the 7295 residents in the study population, 3066 (42%) initiated metformin and 4229 (58%) initiated a sulfonylurea. In multivariable analysis, several factors were associated with sulfonylurea initiation over metformin initiation, including heart failure (odds ratio [OR] 1.2, 95% confidence interval [CI] 1.1-1.4) and renal disease (OR 2.1, 95% CI 1.7-2.5). Compared with those aged 65 to <75 years, residents 75 to <85 (OR 1.3, 95% CI 1.2-1.5), 85 to <95 (OR 2.0, 95% CI 1.7-2.3), and ≥95 (OR 4.3, 95% CI 3.2-5.8) years were more likely to initiate sulfonylureas over metformin.

Conclusions: In response to FDA warnings, providers initiated NH residents on a drug class with a known, common adverse event (hypoglycemia with sulfonylureas) over one with tenuous evidence of a rare adverse event (lactic acidosis with metformin).

Keywords: Nursing home; US Food and Drug Administration; contraindications; diabetes; drug prescribing; treatment choice variation.