Is it possible for me to take phenergan (promethazine) if I'm allergic to penicillan?

Yes you can. Phenergan (promethazine) and penicillin are totally different classes of medication. One is a first generation antihistamine, while the other (penicillin) is an antibiotics. You should take Phenergan (promethazine) safely if you have penicillin allergy.