My 85 year old mother has been on methotrexate for years for rheumatoid arthritis. She had pulmonary embolus 4 months ago and it was determined she has polycythemia vera ( PV). She was started on warfarin and had a phlebotomy twice. One week ago she had pain with deep breaths and they are concerned it might be new clots to her lung but they can not be sure if the clots are old or new. She was taken off methotrexate and started on hydroxyurea, bably aspirin, and lovenox shots. Two days ago she broke out in itchy hives, so the hydroxyurea has been stopped. Any idea how long it will take for the medicine to get out of her system and for the hives to end. Also wondering the possibility of methotrexate causing the PV?