Enhanced hypoprothrombinemia with warfarin due to azithromycin.

Objective: To report a case of probable azithromycin-warfarin drug interaction with enhanced hypoprothrombinemic effect of warfarin.

Case Summary: An 83-year-old African American man stabilized on warfarin therapy (10 mg on Wednesdays, 7.5 mg on other days) developed a prolonged prothrombin time one day after starting azithromycin 500 mg.

Lactic acidemia associated with metformin.

Objective: To report 2 cases of lactic acidemia associated with the use of metformin in patients with normal renal function.

Case Summary: An 82-year-old African American man and a 76-year-old white man developed an elevated serum lactic acid concentration a few weeks after initiation of metformin therapy for type 2 diabetes. After the patients discontinued metformin, the serum lactic acid concentration normalized in both cases.