For the treatment of upper respiratory tract infections, including tonsillitis and/or pharyngitis secondary to Streptococcus pyogenes (i.e., primary rheumatic fever prophylaxis). What is the shelf life for Cephalexin 500mg? RX was filled 10/25/05. Can I take it & be effective? I just got laid off from my job, and cannot afford to go to the doctor plus get a prescription for my upper respiratory infection.