This is a Phase I, placebo-controlled, randomized crossover trial to determine the effects of 4-week treatment with subantimicrobial-dose doxycycline on serum and urine biomarkers of fibrosis in patients with pre-dialysis chronic kidney disease (eGFR\<30ml/min/1.73m2). Doxycycline is a matrix metalloproteinase inhibitor and is approved for use as an anti-fibrotic in the setting of gum and skin disease at low doses (20mgBID). At such a dose, serum levels are too low for antimicrobial effect and chronic usage is not thought to lead to tetracycline resistance. Investigators hypothesize that doxycycline will ameliorate cardiac and renal fibrosis and thus investigators will detect a decrease in fibrotic markers during treatment with doxycycline.
