Buffered formulations of exendin (9-39)

Provided herein are liquid pharmaceutical formulations comprising exendin (9-39) or a pharmaceutically acceptable salt thereof and a tonicity modifier in a physiologically acceptable buffer having a pH in the range of about 5 to about 6. In some embodiments, the liquid pharmaceutical formulation comprises exendin (9-39) or a pharmaceutically acceptable salt thereof in an acetate buffer or a citrate buffer. Methods of treating or preventing hyperinsulinemic hypoglycemia in a subject comprising administering to the subject the liquid pharmaceutical formulation are also provided.