Over the last decades, peritoneal dialysis has grown worldwide to become one of the most common modalities of renal replacement therapy, particularly in developing or newly industrialized countries, such as India, China, Korea, Turkey, Malaysia, Mexico and Brazil. Peritoneal dialysis has been associated with an initial survival benefit compared to hemodialysis, although this advantage becomes less apparent over time, likely due to the progressive loss of residual renal function and the development of pathological alterations of peritoneum . Recent results suggest that an antioxidant therapy by N-acetyl-cysteine oral supplementation may improve residual renal function in peritoneal dialysis patients. This finding may have major clinical relevance, as preserving residual renal function in peritoneal dialysis patients has been associated with improved survival . Aim of the present randomized, double-blind, crossover study is to confirm the preliminary evidence of the beneficial effects of antioxidant agents on residual renal function by using the L-enantiomeric form of cysteine in 10 prevalent peritoneal dialysis patients with residual diuresis.

Inclusion Criteria:

• Males and females aged ≥ 18 years;
• Chronic automated peritoneal dialysis;
• Residual 24-hour diuresis ≥ 100 ml with less than 30% changes over the three months preceding randomization;
• Written informed consent.

Exclusion Criteria:

• Chronic automated peritoneal dialysis therapy since less than three months;
• Diabetes mellitus;
• Acute peritonitis during the three months before enrollment;
• Concomitant treatment with other antioxidant agents (including N-acetyl-cysteine and vitamin C);
• Cystinuria;
• Pregnancy or breastfeeding;
• Childbearing potential without reliable contraceptive methods during the whole study period;
• Alcohol or drug (excluding tobacco) abuse;
• Inability to comply with the study procedures during the whole study period, legal incapacity;
• Cancer and any severe systemic disease or clinical condition that may jeopardize data interpretation or completion of the study.