Peritoneal dialysis (PD) is one of the methods of renal replacement therapy (RRT) that can easily perform at home. The declared "PD first" policy from the National Health Security Office causes rapidly expansion of this group of patients. In the year 2013, the current study in Thailand showed that the patients enrolled for peritoneal dialysis accumulated for more than 15,000 people. It works continuously similar to the actual function of the kidneys in normal people. In addition, PD also helps to slow the decline of remaining kidney function (residual renal function), which is very important and affect in decreasing mortality rate in this group of patients. However, PD has several limitations such as complications from the infection and high failure rate associated with a dysfunction of the peritoneal membrane during long-term treatment. Approximately 4-12 percent of patients will have ultrafiltration failure and volume overload in the first couple of years of treatment and soar to 30-50 percent in patients treated for more than six years.

The causes of peritoneal membrane deterioration are exposure to incompatible dialysis solution with hyperosmolar glucose content, acidic pH, reactions to PD catheter material, uremia and peritonitis. The alterations of structural and functional of the peritoneal membrane after exposed to these several insults are epithelial-to-mesenchymal transition (EMT), and increase in peritoneal solute transport, which consequently leading to peritoneal dialysis failure. It has been already demonstrated that the local renin-angiotensin-aldosterone system (RAAS) plays a key role in this regulation by promoting the activation of neoangiogenesis and fibrotic pathways.

According to the pathophysiologic changes of the peritoneal membrane, Angiotensin Converting Enzyme Inhibitors (ACEIs) and Angiotensin Receptor Blockers (ARBs) are adapted to be use in respect of membrane preserving agents. Many studies, both in human and animal models, demonstrate the protective effect against peritoneal membrane deterioration by inhibiting the formation of transforming growth factor beta1 (TGF-β1), vascular endothelial growth factor (VEGF), and decreasing progression rate of small to high transport membrane type. In fact, mineralocorticoid receptor antagonists (MRAs) seem to have higher efficacy than ACEIs/ARBs in some experimental models. The possible mechanism is the effects of mineralocorticoid receptor antagonists that not only inhibit the formation of TGF- β1 and VEGF, but also suppress intracellular Reactive Oxygen Species (ROS) generation, activation of extracellular signal-regulated kinase (ERK) 1/2, and p38 mitogen-activated protein kinase (MAPK), the substrates responsible for aldosterone induces alterations in cell phenotype. A prospective cohort study of 23 CAPD patients was conducted and evaluated the effect of spironolactone on peritoneal membrane. The result showed the possible benefit of spironolactone in slowing the decline of peritoneal function, suppressing the elevation of profibrotic markers, and increasing mesothelial cell mass.

As a result of the clinical practice, most of CAPD patients tend to receive ACEIs/ARBs as prescribe by the clinicians, in order to control blood pressure, raise serum potassium level, and others compelling indications. Thus, the concept of add-on MRAs to ACEIs/ARBs, desiring the synergistic effects of these 2 drugs group, for membrane preservation is challenge. Notwithstanding the fact that current evidence about the combination effects of ACEIs/ARBs with MRAs is limited in term of quality of the study, sample size, inadequate follow-up period, and poor sensitive parameter in assessing the structural and functional changes of the peritoneal membrane. Thereby, this study aims to evaluate the effect of add-on spironolactone to losartan versus losartan alone on membrane preservation in continuous ambulatory peritoneal dialysis patients.