A little more on doxycycline. You will see it being prescribed more regularly, especially in hospitals. The reason, largely unpublished, for this is the front line drugs such as vancomycin and gentomycin are failing to combat new infectious diseases as well as hoped. Resistance to those drugs is increasing alarmingly- and gent is the top of the line anti-infective. (That should scare you) The general feeling is that in prescribing the older antibiotics, such as doxy, the disease strains may not recognize them and therefore they may help.
Just as an opinion, the reason vanc and gent have reduced potency these days is that they were severely over-prescribed in the hospitals due to how fast they worked for certain conditions. I always thought it was ridiculous to prescribe those drugs when other, cheaper, albeit, slower acting drugs were available. Everyone always wanted the quick fix and vanc, especially bacame a placebo in the ER. I predicted vanc/gent resistance a decade ago and was scoffed at. Sometimes it sucks to be right.