I had unprotected oral & protected vaginal sex with a 50 year old married woman. about 6 hours later i took 1g of zithromax & 400mg of suprax. the next morning i took an additional 400mg of suprax. would these meds prevent possible bacterial sti?

Probably, BUT: Taking antibiotics post sexual encounters in an attempt to prevent disease is not a good idea. Yeast, venereal warts, chlamydia, HIV/AIDS are just some of the potential diseases which can be transmitted sexually, and none of these respond to the type of antibiotics you used. (Which are antibacterials). Also, if you truly had an infection, 1-2 doses would not be enough to fully treat the problem.