What's some medicine for hydronephrosis?

Depends on the cause: Hydronephrosis is a symptom (fluid in the kidney and or ureter) not a disease. Treatment depends on discovering its underlying cause. Potential causes include: obstruction from stones, clots, or tumors, infection, reflux, excess fluid ingestion or excretion, among many others. See your urologist.

Usually intervention: Hyrdonephrosis is an anatomic diagnosis, usually caused by obstruction, less common by reflux of urine from bladder & occasionally by infection. Thus intervention, to relieve blockage, usually required to correct cause, unless mild. Obstruction from narrow or kinked kidney outflow needs pyeloplasty surgery, stones passed or removed + meds if metabolic cause, tumor removed, antibiotics 4 infection.