Are there any interactions between chlorthalidone and oxybutynin.? I am 60yrs. Old, and am being treated for very high bp,, and had been taking the oxybutinin also because I have an overactive bladder as well. I have one kidney, (donated it to brother).. is there anything synergistic between them? It has started to hurt when I urinate, but it s not an infection. It s different; it starts with pressure, then pain and I have to push quite a bit. I ll go a bit, then stops, and this cycle starts again. Usually it s 3x, and I really have to work at it to empty my bladder. Any concerns about this? Thanks for an answer!