Eligible participants will be allocated by restricted randomization using the minimization method to the treatment group or to the control group. The treatment group will receive periodontal therapy consisting of instructions of plaque control, supra and subgingival scaling and root planing, oral systemic metronidazole (250 mg) plus amoxicillin (500 mg) tid for 7 days. The control group will receive plaque control instructions, supragingival scaling and two placebos. The study plan to enroll 160 participants, 80 in ech arm, over a 6-month period. Follow-up clinic visits will be scheduled to occur every 3 months after finishing treatment. Baseline and follow-up clinic visits will include periodontal examination, blood collection and medical and dental histories. The following biochemical markers will be determined at baseline and at 3, 6, 9 and 12 months posttherapy: total, LDL and HDL lipoprotein cholesterol and triglycerides, glycemia, high sensitivity C-reactive protein, fibrinogen, erythrocyte sedimentation rate and white blood cells count. In diabetic patients, glycosylated hemoglobin will be also assessed.