I first met Sir William in June of 2002. A feisty little potbellied pig, "Wil" came to the hospital as a 6 month old with intestinal problems (he hadn't pooped in days!). He required major abdominal surgery during which a portion of Wil's small intestine was removed which is a fairly complicated and long procedure. After surgery, it took Wil a good deal of time before he felt himself again. Slowly, he regained his appetite and perky attitude and after 10 days of hospitalization he went home with only a prescription of procaine penicillin, which is an antibiotic that is given in the muscle.
I would very much have liked the story to end there with Wil living the rest of his life without any further problems. Unfortunately, about 3 days after he left the hospital, I received a call from Wil's owner. He had broken out in hives soon after having received an injection of the penicillin. Also, a spot on his belly was turning blue and the skin was falling off where he had been injected with a local anesthetic (lidocaine) the day he was brought to the hospital. The skin problem didn't concern me as the skin underneath was healing without any problems. On the other hand, the reaction to the penicillin injection was potentially serious. Luckily, no other symptoms were reported and Wil was treated with an anti-histamine for the hives and the antibiotics were immediately stopped. After this, the little guy recovered without any other problems and is healthy as of the writing of this article (November, 2002).
We all know someone walking around with a Medic Alert bracelet citing they are allergic to penicillin. I must admit that as a veterinarian who routinely treats large animals and barn animals, I consider myself quite well informed on many veterinary topics, however, I was a little bit at a loss in answering this particular client's questions. The truth is that while there is a wealth of knowledge on penicillin itself, the amount of information on penicillin allergies in potbellied pigs is quite limited. Over the next few days I performed some basic research and chatted with several more experienced swine veterinarians. After obtaining as much information on penicillin reactions as I could and sharing this with Wil's owner, she asked me to write this article on this topic. Now, I do not claim to be an expert on this topic. All I learned was through reading general texts, articles and talking to experienced colleagues.
Nevertheless, the purpose of this article is to describe, in general, what penicillin reactions are and what, as a potbellied pig owner, you need to be aware of if you animal is given this medication.Despite all the choices available in veterinary medicine, penicillin is still one of the most effective and useful antibiotics in use. Discovered in 1928 by Alexander Fleming, Penicillin G (benzylpenicillin) is prescribed frequently in both human and veterinary medicine. It is known to effectively kill many types of bacteria, including various strains of Staphylococcus, streptococcus, Clostridium, Fusobacterium, Actinomyces and Erysipelothrix rhusipathiae.
In general, penicillin is considered a very safe medication and adverse side effects are rare and mild, although they have been described in both humans and numerous veterinary species (including swine). Specifically, animal reactions to penicillin can be classified into several categories, including an allergic (anaphylactic) reaction, a toxic (overdose) type reaction, and a
psychotic (neurologic) type reaction. While these problems have been clearly described in humans and certain animal species, specifics on porcine problems related to penicillin are, for the most part, anecdotal. That being said, penicillin reactions seem to be quite universal across species, and there is no reason to think that pigs would not be subject to the same or similar problems.
At this point, I wish to clarify that frequently, penicillin reactions are not caused by penicillin at all! In truth, most of the adverse reactions associated with penicillin are caused by other molecules that are linked to penicillin. These "other molecules" are present in the drug formulation for various purposes such as stabilization of the drug or allowing it to be more properly absorbed and distributed throughout the body. More specifically, procaine, which is a cocaine derived local anesthetic (originally used by dentists to numb the gums), is linked to penicillin to form Procaine Penicillin G (PPG), a very commonly used form of this antibiotic. Procaine' s presence in the formulation is mainly as an anesthetic to decrease pain associated with the injection because this form of penicillin is given under the skin or in the muscle. Along with penicillin itself, procaine is the most frequently implicated molecule associated with penicillin reactions.
When an adverse reaction occurs following a PPG injection, the problem is more likely going to be associated with the procaine than the penicillin, no matter what the species involved. Furthermore, procaine and other cocaine derivatives (such as lidocaine and mepivicaine) are known to be particularly toxic to some pigs, although there is a high degree of individual variation.
A procaine reaction is classified as an intoxication or overdose rather than an allergic reaction and can occur at any time during the course of therapy, even after the very first dose is given. A reaction to procaine typically occurs if it is accidentally injected into the blood stream, which can be prevented by pulling back on the syringe before injecting the drug into a muscle and alternating injection sites between treatments. Also, proper storage of procaine penicillin (in the refrigerator) is imperative, because prolonged exposure of procaine penicillin to warm temperatures is associated with a higher rate of adverse reactions. Clinical signs of procaine toxicity include shivering, vomiting, cyanosis (cold extremities and blue gums) and fever.
Nowadays, the use of procaine as a local anesthetic has been replaced by more effective drugs such as lidocaine (which was used on our infamous "Wil") and mepivicaine. If these other drugs are used, a local reaction to the drug such as the development of a rash or redness at the site of injection is an indication that the animal is sensitive to it. Further use of this class of drug should be discontinued or it should be used with caution (sometimes the veterinarian just doesn't have a choice).
Furthermore, the use of procaine penicillin in such an animal should be pursued with caution and ideally a different form of the drug or a different drug altogether should be considered. Obviously, your veterinarian should be the one making these decisions. Now, back to penicillin. Animals that are truly allergic to penicillin can show a variety of symptoms including behavioral changes, rashes, fever, joint pain (polyarthritis), vomiting, diarrhea, neurologic problems (incoordination), anemia (weakness, palor), enlarged lymph nodes, changes in immune cell populations (requires a blood test to evaluate) or full blown anaphylaxis. An acute allergic reaction (anaphylaxis) can happen almost instantaneously and be life threatening. Fortunately, this is an extremely rare occurrence. Allergic reactions are non-dose dependent so even a small amount of the drug can cause a reaction. Finally, a true allergic reaction usually requires that the animal first be "sensitized" to the drug, so a reaction is only seen after at least one dose has already been given.
A toxic reaction or overdose of penicillin itself is so rare that many scientists don't actually believe this can happen. Some infections are purposefully treated with double the recommended dose of penicillin without any problems. And, if a reaction were to occur, it would not be associated with an overdose of penicillin, but rather one of the other problems described in this article.
The last type of reaction associated with procaine penicillin is a neurologic or psychotic episode that occurs immediately following the injection. This syndrome has been observed in several species and in humans is called "Hoigne's Syndrome". It is typically characterized by a violent physical reaction in horses and a feeling of extreme dread in humans. This type of reaction has not been described in potbellied pigs and I've never personally heard of this type of reaction occurring in swine. Behavioral changes following procaine penicillin injections are suspicious, however, and should be reported to your veterinarian.
Common sense should dictate when procaine penicillin or any form of penicillin that is being given should be stopped. If you are unfortunate enough to have a potbellied pig that requires injections at home (it's hard enough to do in a hospital setting!) you simply need to be aware of your animals normal behavior and appearance, and whether this changes following an injection. Obviously, if your animal has any adverse reactions associated with an injection you should call your veterinarian immediately and do not give any more treatments until the doctor determines that it is safe to do so. As described, a true allergic reaction to penicillin would be rare, and a different formulation of penicillin would probably be safe for animals reacting to procaine penicillin. That being said, careful monitoring is recommended if an animal is to continue receiving penicillin following an obvious drug reaction.
In conclusion, reactions to procaine penicillin are frequently difficult to categorize. The difference in symptoms and timing of the reaction are often similar for both an allergic and a toxic reaction. Furthermore, some reactions don't occur until the animal has already been on the drug for several days, at which point it may be impossible to tell if the animal is experiencing a toxic reaction to procaine or whether he has become sensitized to penicillin. As a veterinarian, trying to make such distinctions can be frustrating. In truth, all we ask is that you, the owner, understand that not all things in medicine are black and white. The best we can do under these circumstances is to make a note in the animal's record of the event (as you should do at home), to discontinue use of the medication and to prevent future reactions by limiting or preventing the animal from ever receiving another treatment with the offending drug.Such has been the case with Sir William. Notes have been made on his charts regarding his documented reactions to procaine penicillin. The Duchess Fund was able to track his treatment from beginning to end, supply us with detailed descriptions of his "allergic episodes", which in turn alerted us to his sensitivity to procaine penicillin. Sir William may be an isolated case, however, it would be prudent to notify owners of his relatives, if possible, to be on the alert for any other reactions.WHAT MAKES US HAPPY
We are happy when through working together we find good loving homes for the animals. This month we have placed 4 dogs,2 pigs and have about 4 pigs in fosters waiting for homes. Thanks to all who have helped.