I have a puncture wound from a dog bite. but i am allergic to tetanus shots. so would tetracycline antibiotics be an acceptable alternative to prevent?

No: Antibiotics aren't used for prevention, they are used to treat active tetanus infection, and tetracycline isn't the first choice. Given your conditio, you should be seen by your doctor or go to ER, you need rabies prophylaxis too, if the dog isn't known to you or not itself immunized.Tetanus shot true allergy is very rare, it might only be a side effect, see an allergist and get the shot, goodluck