Background: There are limited therapeutic options to slow the progression of autosomal dominant polycystic kidney disease (ADPKD). Recent clinical studies indicate that somatostatin analogues are promising for treating polycystic liver disease and potentially also for the kidney phenotype. We report on the design of the DIPAK 1 (Developing Interventions to Halt Progression of ADPKD 1) Study, which will examine the efficacy of the somatostatin analogue lanreotide on preservation of kidney function in ADPKD. Study Design: The DIPAK 1 Study is an investigator-driven, randomized, multicenter, controlled, clinical trial. Setting & Participants: We plan to enroll 300 individuals with ADPKD and estimated glomerular filtration rate (eGFR) of 30-60 mL/min/1.73 m(2) who are aged 18-60 years. Intervention: Patients will be randomly assigned (1: 1) to standard care or lanreotide, 120 mg, subcutaneously every 28 days for 120 weeks, in addition to standard care. Outcomes: Main study outcome is the slope through serial eGFR measurements starting at week 12 until end of treatment for lanreotide versus standard care. Secondary outcome parameters include change in eGFR from pretreatment versus 12 weeks after treatment cessation, change in kidney volume, change in liver volume, and change in quality of life. Measurements: Blood and urine will be collected and questionnaires will be filled in following a fixed scheme. Magnetic resonance imaging will be performed for assessment of kidney and liver volume. Results: Assuming an average change in eGFR of 5.2 +/- 4.3 (SD) mL/min/1.73 m(2) per year in untreated patients, 150 patients are needed in each group to detect a 30% reduction in the rate of kidney function loss between treatment groups with 80% power, 2-sided a = 0.05, and 20% protocol violators and/or dropouts. Limitations: The design is an open randomized controlled trial and measurement of our primary end point does not begin at randomization. Conclusions: The DIPAK 1 Study will show whether subcutaneous administration of lanreotide every 4 weeks attenuates disease progression in patients with ADPKD. (C) 2014 by the National Kidney Foundation, Inc.