With antibiotic resistance growing I’m going to assume that medicine has various antibiotics they rarely use so the bugs do not get a chance to get adjusted to them. Is that a valid assumption? You have a pyramid of drugs where most people never need the higher tiers of medication?
Is it basically a method of:
‘give him these drugs. If those fail, go to these drugs. If those fail go to these drugs. If those fail, go to these drugs’ each drug stronger and less likely to have resistance than the last?
Is that how antibiotic prescriptions work (I know it varies based on the characteristics of the bacteria and seriousness of the infection too obviously)? If so, what are the classifications/tiers? I know I usually get amoxicillin for ear infections. Is that one of the first given if someone is sick with an infection?
There seems to be two broad divisions in antibiotics. Penicillin derived and the rest (though the rest are not any particular family).
Essentially you get the 'cillin variety for most infections and if you are allergic to them you get some other sort - often tetra-cycline derived like doxycycline. Doctors seem to have personal favourites so the type of 'cillin is not necessarily important.
When it gets interesting* they may give you a cocktail of different types. It only gets hairy when you get MRSA and they have very limited choice of rare antibiotics. Bone infections also are very difficult to treat.
(*Interesting is a word you really don’t want to hear from your specialist. It means they’ve found something nasty and it will shortly cost you a lot of money)
So is the first step a penicilin or tetracycline drug. What if that fails? Do they go straight to multi drug combos or is there a different class of a single drug they use? Like, do they go for the macrolides if the penicillin drugs fail?
What is the last resort (or near last resort)? Is it a cocktail of multiple drugs, or a class of drugs that are rarely used (so the bacteria never have a chance to get used to them)?
Looking on wikipedia, apparently the cephalosporins are used to treat MRSA. I would assume they are like a 3rd or 4th resort after earlier attempts with cheaper/safer/more widely used drugs have failed.
My only serious antibiotic experience was for Cellulitis where i was prescribed one type of 'cillin and when I deteriorated after a week they gave me another four courses of Flucloxacillin / Dicloxacillin - half of them in hospital on a drip. They didn’t seem too concerned to alter the basic treatment - just give more of it. Interestingly you can get MRSA Cellulitis but I didn’t seem to have that.
The decision on what antibiotic to use, and when, can become incredibly complex (and it doesn’t really start simple) very rapidly, and depends on so many factors that Infectious Disease is its own specialty that takes years of training and practice to get really good at.
Suffice it to say that it depends on clinical presentation of the patient (what anatomic location(s) might be infected and how their body is responding to it), their other co-existing morbidities, the local geographic area’s own pattern of bacterial prevalence and resistance patterns, previous history of culture-demonstrated past infections and their sensitivities, cross-reactions with other drugs they may be on, preliminary results of gram stains of tissue/fluid samples, past responses to other antibiotics used, etc. etc. etc.
There are no simple algorithms for antibiotic usage as a whole. There are some simple algorithms for a few select disease processes, such as what to do with strep throat or syphilis, but more often than not, infectious disease choices get real complex real quick.
I got to see my GP every couple of years with a chest infection. I have asthma. He goes through the usual tests and tells me that I have a chest infection. Then he looks at my notes and says, “Ampicillin worked last time, so let’s start with that.” After a couple of days I feel better and keep taking the 'cillin like a good citizen until the end of the course.
There’s also the concept of “spectrum”. Bacteria come in many different types, and each antibiotic is only effective against some types, and useless (or less effective) against others. Broad spectrum antibiotics work on a wide variety of bugs, while narrow spectrum drugs work on just a few specific kinds.
Depending on the disease, the doctor may not be able to tell what kind of bug it is just by looking. He might start you on a broad spectrum drug while running tests to figure it out, then switch you to a more effective narrow spectrum drug when the ID is in, if the first drug isn’t working.