According to the results of a case control study published early online in Diabetes Care, metformin-based treatment strategies are preferable in patients with diabetes and heart failure (HF), and may result in lower mortality.

The authors note that diabetes is a common co-morbidity in patients with HF, but the choice of treatment for type 2 diabetes in these individuals remains
controversial.  Patients with HF have generally been excluded from trials of glucose-lowering therapies and the safety of these medicines in HF remains unclear.  Although a number of observational studies have reported prognostic differences between various antidiabetic agents when used in patients with concomitant HF, their various limitations mean that definitive conclusions cannot be drawn.

The purpose of their research was to determine whether outcomes in patients with diabetes and HF are associated with drug therapy.  They conducted a case-control study nested within the prospective United Kingdom General Practice Research Database (UKGPRD) cohort.  The study cohort (n=8,404) consisted of patients aged >35 years with newly diagnosed HF and newly diagnosed type 2 diabetes mellitus, who had at least one year of data prior to their index date.  Cases were those in the cohort who had died (n=1633); these were matched 1:1 with controls from the cohort based on age, sex, clinic site, calendar year, and duration of follow-up. Analyses were adjusted for co-morbidities, A1C, renal function, and body mass index.  For medications, current use was defined as at least one prescription issued in the last 90 days prior to the index date (death for cases and analogous date for controls). 

The mean duration of concurrent diabetes and heart failure was 2.8 years (mean age 78 years, 53% male).  The main findings were as follows:

• After adjustment for covariates, only metformin monotherapy was associated with a lower risk of mortality compared to patients who were not exposed to antidiabetic drugs (adjusted OR 0.65 [0.48 to 0.87])

• When outcomes were examined for ‘any use’ of drugs (whether or not dispensed in combination or as monotherapy), again only metformin was associated with reduced mortality (adjusted OR 0.72 [0.59 to 0.90])

• Use of other antidiabetic drugs or insulin was not associated with any effect on all-cause mortality.

• Use of ACE inhibitors/ARBs (adjusted OR 0.55 [0.45 to 0.68]), beta-blockers (adjusted OR 0.76 [0.61 to 0.95]), aspirin (adjusted OR 0.66 [0.55 to 0.8]), digoxin (adjusted OR 0.74 [0.59 to 0.93]), and statins (adjusted OR 0.59 [0.46 to 0.75]) was associated with reduced mortality.

The authors discuss a number of limitations to their study.  They conclude that “until randomized trial evidence becomes available, we believe our study and the extant published literature support the use of metformin-based strategies for glucose lowering in patients with diabetes and HF.”