Can some one flesh out for me the types of infection each would address? In which situations would a vet Rx one but not the other?
thanks n
Uniprim is SMZ powder. It contains trimethoprim and sulfadiazine. Both are decent antibiotics but only address gram-positive aerobic organisms and a few gram-negative ones. It will not do anything for an anaerobic infection or for spirochetes. Generally SMZs are safe to use even in very sick animals without a lot of risk of off-target effects to other systems. Because of this and because of their broad-spectrum activity they tend to be used as a first resort for infections that have not had a culture and sensitivity done.
Doxycycline is part of the tetracycline class of antibiotics and is effective against gram-positive and gram-negative bacteria. Its main utility is for treating spirochete bacteria like most tickborne infections, though it can also be used for infections that have not responded to another antibioticâusually as the third or fourth one tried. Itâs hard on the kidneys and liver so unless the vet knows what theyâre treating (i.e. a tickborne illness) this isnât usually the first on the list.
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Doxy is also about twice the cost per dose of uniprim.
IME, uniprim (or smz/tmp tabs) gets used as a general use, first line, abx for snotty stuff, skin infection, cellulitis, etc. Doxy (or mino) gets used for Lyme or Anaplasma.
Iâd expect a culture indicating doxycycline for use outside of tick stuff.
Iâm sure there are some free microbiology classes online, @Sansena, if youâre interested in learning about the different classes of antibiotics and how they work.
My horse was on doxycycline this summer for severe pneumonia (based on bacteria culture. In addition to metronidazole) then we swapped out the doxy for enrofloxacin.
This is what we did last year for Ariesâ clostridium infection (tho no swapping out). It was brutal.
Thank you, Dungrulla. This is exactly the type of information I was seeking. However I was under the impression Doxy didnât treat gram negative bacteria. Off to do more research.
I seem to have a spontaneous healing on my hands⊠fingers crossed it continues 
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Curious, is there something comparable to Doxy that is not âbad for pregnant maresâ? My mare was on Doxy because her health is first priority, but it was advised that Doxy may affect her foal in-utero. So I was curious, if any need for something in the future, what would be better for a pregnant / nursing mare needing Doxy? Also, for a side note, Uniprim from this posting establishes its just a stronger version of an SMZ, are any ages ok on it? My vets didnât have a solid answer for me, so I approached âDrâ Google LOL⊠curious if anyone knew?
