If indeed your little guy has an abscess he may need antibiotics. The vet should have made sure to thoroughly exam the rabbit, including his back molars. An abscess in a rabbit is usually associated with an underlying illness. They are not like cat's and dog's where they are usually caused by a bite wound. He/she should have also prescribed you a medication called Baytril. If the vet did not do any of these things then I strongly suspect that they aren't very knowledgeable about rabbit treatments.
Abscesses in rabbits are extremely difficult to treat. If the underlying illness can be found it makes it much easier. If for example he has over grown spurs on his back molars and you have them ground down then the abscess may heal quicker. Rabbits have the amazing ability to isolate these abscesses from the rest of their bodies. They will develop a thick fibrous capsule of pus almost the consistency of toothpaste. This prevents the pus from moving to other parts of the body but it also makes them extremely difficult to treat.
Antibiotics are always warranted for abscess treatment and it usually means long term antibiotic therapy. The vet should do a culture and sensitivity test to determine what organism is causing the the infection and which antibiotic will best be able to treat it. Basically they take a small bit of the pus out with needle aspiration and they take it to the lab and test it with multiple different rabbit safe antibiotics. When they find the one that kills the bacteria they will then start your rabbit on a course of that mediation. In the meantime Baytril is usually prescribed because it does work fairly well on most problems. If it does happen to be pasturella that is causing it Baytril usually won't work. However pasturella usually causes severe respiratory problems as well. Including snotty nose with white purulent discharge, rattling in the lungs, difficulty breathing, pneumonia and it eventually leads to death. Since you mentioned no other symptoms it is probably not pasturella. However it should still be tested because many rabbits actually carry pasturella but never become ill until they are run down or stressed.
The end result in treating abscesses almost always requires surgery. The entire capsule has to be removed. It is sometimes not possible to surgically remove abscesses on the throat and jaw depending on the location. In this case a surgical procedure where an antibiotic that has been found useful on the sensitivity and culture test is injected right into the abscess itself. Our clinic will do culture and sensitivity testing and will try a course of Baytril while waiting for the tests. If there is no improvement with the Baytril our doctor won't even mess around trying other antibiotics. He will just remove the abscess or surgically inject the antibiotics in the encapsulated wound. I know it is not possible for everyone to be fortunate enough to have a veterinary clinic that has doctors that deal only with rabbits. However there are some very good doctor's out there and it is worth getting a second opinion. Remember that these specialists may be a 2 orXXXXXbut it would be worth it in the end. I will attach some web-sites for you at the end.
Sadly abscesses are extremely difficult to treat and can be very expensive. You need to find a veterinarian that specializes in exotic pets and is well versed in rabbit care. A good doctor will discuss the treatment options with you and talk about costs versus outcomes. They won't just say he has an abscess here is some medicine see you later.
I am going to attach a few web-sites for you that may help you. In my opinion the most important one is the veterinary referral link:
RABBIT SAVVY VETERINARY LISTINGS BY STATE
CULTURE AND SENSITIVITY TESTING
ABCESSES IN RABBITS
I hope this information helps you. I am deeply concerned about your little guy. Remember that a well taken care of rabbit can live well into it's teen years. Your guy is still a youngster and deserves the best care possible.
If you have any further questions at all please feel free to ask. I love rabbits and I have devoted the majority of my life to educating the public on properly caring for them. I would be more than happy to answer any further questions you have.
Thank you for loving your little dutch bunny enough to ask for a second opinion.
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