I just found a prescription of erythromycin 500 mg tablets (quantity 14 & take 1 tablet by mouth twice daily) for my girlfriend under my car seat. I have a strong suspicion she's been cheating on me and she has contracted an std because we haven't had sex in over a month. When I googled this drug chlamydia popped up everywhere. I need to know what this drug in this dosage is used for?