Is 112.5mg of aspirin a safe dose for my 50lb dog's pain relief?

Hello there! The amount of aspirin you gave to Whitney is probably not enough to hurt her, however it is my general recommendation to avoid giving aspirin to dogs whenever possible. Aspirin is very hard on a dog's stomach, and can cause gastrointestinal distress and even ulcers or organ failure if given in too large of a dose, or over a long period of time. There are now lots of pain medications available that are made specifically for dogs that have less of an effect of their body, though they are only available through your vet or a veterinary pharmacy. If you have a relationship with a veterinarian, they may be willing to write you a prescription for a dog-safe pain medication if Whitney has been seen at the office recently. You may be required to go in for a visit if it has been a while, however, as there must be a recent client-veterinarian-patient relationship for the vet to dispense or prescribe these drugs safely.

I hope that Whitney feels better soon!