MMP9 and abdominal aortic aneurysm: In patients with abdominal aortic aneurysm, doxycycline treatment at a conventional dose, 200 mg/day, resulted in a mean plasma concentration of doxycycline at 4.6 μg/ml with a range of 1.3 to 14.4 μg/ml in humans, and there was a corresponding reduction in plasma MMP-9 levels [12].