My 6 year old St Bernard has severe osteoarthritis in her front left leg, she is on Previcox, 4 a day but they have not made any difference. In fact she is worse today, she has already had a SHO operation on it. At first she was brilliant but she has gradually started to limp more and more. I was wondering if I could give her one of my husband's Sevredol tablets which are morphine based. It is just till I can get her back to the vets tomorrow or Tuesday. My vet prescribed the Previcox last Saturday so I have given them a chance to work. Any help or advice would be gratefully appreciated.