Early Oxybutinin Treatment for Boys With Posterior Urethral Valves

Inclusion Criteria: * Boys * Aged 3 to 6 months * Diagnosed with posterior urethral valves, and having undergone valve resection within the first 3 months of life * Children who have had their valve resection at least 3 months before inclusion * Having undergone urodynamic studies between 10 weeks and 6 months of age andshowing abnormal urodynamics, notably: high voiding pressure (\>60cm H2O)/ small capacity bladder (\<70% expected bladder volume)and for those without pop-off mechanisms, poor compliance (\<10ml/cmH2O)/ * Holders of parental authority affiliated to French national health insurance * With informed consent signed by holders of parental authority Exclusion Criteria: * Boys with posterior urethral valves and normal urodynamics or no urodynamic assessment * Boys in whom urodynamic assessment is not possible for medical or anatomical reasons * Boys requiring dialysis before the age of 3 months * Contra-indication to oxybutynin such as hypersensitivity to oxybutynin or any of the excipients, digestive obstruction, occlusive or sub-occlusive syndrome, megacolon, digestive stasis, intestinal atony, paralytic ileus, ulcerative colitis, Hemorrhagic rectocolitis, Crohn's disease, Inflammatory bowel disease, Inflammatory organic colopathy, myasthenia, congenital glaucoma