Safety, Pharmacokinetics, Tolerability and Efficacy of Tolvaptan in Children and Adolescents With ADPKD (Autosomal Dominant Polycystic Kidney Disease)

Key Inclusion Criteria: * Male and female participants aged 4 to 17 years (inclusive) with a diagnosis of ADPKD as defined by the presence of family history and/or genetic criteria AND who have at least 10 renal cysts, each of which measure at least 0.5 cm, confirmed upon magnetic resonance imaging (MRI) inspection; participants under the age of 12 years must have at least 4 cysts that are at least 1 cm in size, confirmed by ultrasound. * Weight ≥20 kg. * Participants with estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73m\^2 within 31 days prior to randomization (using the Schwartz formula, eGFR = 0.413 × height \[cm\]/serum creatinine milligrams per deciliter \[mg/dL\]). * Independent in toileting. * Ability to swallow a tablet. Key Exclusion Criteria: * Liver function tests including aspartate aminotransferase (AST), alanine aminotransferase (ALT) \> 1.5 × the upper limit of normal (ULN). * Nocturnal enuresis. * Need for chronic diuretic use. * Participants with advanced diabetes (e.g., glycosylated hemoglobin \>7.5, and/or glycosuria by dipstick, significant proteinuria, retinopathy), evidence of additional significant renal disease(s) (i.e., currently active glomerular nephritides), renal cancer, single kidney, or recent (within 6 months of screening) renal surgery or acute kidney injury. * Participants having disorders in thirst recognition or inability to access fluids. * Participants with critical electrolyte imbalances, as determined by the investigator…