Just to share my anecdotal experience: I tried the tetracycline in high school, and that was a joke. Doxy worked amazingly well for me last year. I was on short-term course because as was mentioned, long-term use of antibiotics promote resistance. It's actually becoming a seriously problem worldwide. In many countries, you can get them without a prescription (e.g., India). I did a 14-day course of 200mg/day, followed up with a 30-day course of 100mg/day. It was great.
Skip to today. It didn't do jack for my cysts. I was on 200mg/day for three week and I was breaking out more than ever. Now I'm on Duricef (part of the cefaflexin family - brand name is Keflex). I have no idea if it will work, but I really hope it does.
I don't know what I'm going to do if I become immune to this. That is the inherent problem with antibiotics. They aren't meant to kill bacteria. So, if you have an infection, they work well. Acne, though it is an infection, is chronic so taking antibiotics long terms can cause it to lose its effectiveness, but also for the individual to have a weakened immunity system.
So yeah, it sucks. I try to use it as a kickstarter in the short term, by the time the long-term medications kick in (i.e., Spiro or BCPs, for women anyway). Part of it also depends on the cause and severity and age of the individual who has acne too.