Metformin, Black Box Warnings, and Radiologic Studies

ANAHEIM, CALIFORNIA – Do prescribers consistently follow the black box warning on metformin? 

Pharmacists at Good Samaritan Hospital in Los Angeles, California, set out to determine the compliance rate of prescribers following metformin’s black box warning and the rate of patients developing lactic acidosis and/or contrast-induced nephropathy (CIN).

Metformin’s black box warning states that it should be temporarily discontinued before an intravascular radiocontrast study, withheld for 48 hours after the procedure, and reinstituted only after an evaluation of renal function shows that it has resumed normal functioning.

After conducting a retrospective cohort study, the researchers determined that prescribers did not consistently follow the black box warning to discontinue the drug – it was continued in 69.7% of cases. The researchers found that although no patients developed lactic acidosis, 9.1% (3 of 33) developed CIN.

They concluded that pharmacists can contribute to patient safety by educating prescribers about the need to adhere to the black box warning, as well as screening for high-risk patients.

The researchers presented their findings at the 49^th Midyear meeting of the American Society of Health-System Pharmacists.

--Stephanie Vaccaro

Reference:

1. Ly B, Choi J, Eto K. Use of metformin in patients undergoing radiologic studies involving intravenous iodinated contrast media: evaluating compliance with black box warning. Presented at: 49^th Midyear meeting of the American Society of Health-System Pharmacists. December 8, 2014; Anaheim, CA. Poster presentation.