OBJECTIVES: To identify the nature and frequency of DRPs (drug interaction and irrational dose), and their impacts on length of stay (LOS) of patients with chronic  kidney disease (CKD) stage 4 and 5 hospitalized in Haji Adam Malik (HAM) Hospital, Indonesia. METHODS: This retrospective cohort study was conducted on 80 patients based on JAMKESMAS database for 6-month period (October 2009 - March 2010). Inclusion criteria were patients administered antibiotics and GFR of ≤30 mL/min/1.73 m2. Exclusion criteria were patients under 18 years old, patients with cancer, and patient with Human Immunodeficiency Virus (HIV). Data collected include type of drugs administered, laboratory tests, and clinical outcomes. Identification of drug interaction and analysis of antibiotics dose rationality were performed using Stockley’s drug interactions, Medlines, and Handbook of Clinical Drug Data. The impacts of DRPs on LOS were performed by multiple linear regression analysis.  RESULTS: Of the sample, male was 66% and female was 34%; CKD stage 4 was 17% and CKD stage 5 was 83%. Most drug interactions were between NSAIDs and ACE inhibitor, ranitidine and furosemide, ranitidine and ciprofloxacin, metoclopramide and NSAIDs, dexamethasone and furosemide, NSAIDs and furosemide. Mean value of drug interaction was 1 ± 1.31. Most frequent irrational doses of antibiotics involved ceftriaxone, ceftazidime, cefadroxyl, ciprofloxacin, and amoxicillin. Mean value of irrational doses was 0.43 ± 0.67. Means of LOS was 6.64±5.76.  Multiple linear equation obtained: y = 3.91 + 2.16x1 + 0.97x2; y = LOS; x1 = drug interaction; x2= irrational dose of antibiotics.  CONCLUSIONS: This finding must be highlighted and considered to optimize treatment of CKD. Impact of drug interaction on LOS of CKD patients was higher compared to that of irrational dose of antibiotics.