Veterinary Medicine - February 2008 - (Page MV10) MANAGING VOMITING Dr. Michael Leib Jergens: Yes. Anticholinergics aggravate vomiting patients by their negative e ects on gut motility. Twedt: And give them a dry mouth. Leib: So why are these drugs so ingrained in veterinary practice? I guess they have been utilized for a long time. Jergens: I think certain practitioners grew up with these medications and are more familiar with them. The vomiting probably resolves spontaneously, and the veterinarians attribute it to the medication. Leib: P zer has just released a new antiemetic: maropitant citrate (Cerenia). It has a novel mechanism of action that is di erent from any of the other drugs we have mentioned. Twedt: Yes, Cerenia is an antagonist for neurokinin1 receptors, which are found in peripheral a erent neurons. They are also found in the chemoreceptor trigger zone, and there are apparently high numbers of those receptors in the vomiting center as well. They are stimulated by substance P, a neurotransmitter found throughout the body. Cerenia blocks those neurokinin1 receptors, so it works both peripherally and centrally. Leib: We’ve all used this new product in our clinics. Are there contraindications, side e ects, or administration problems that we should be aware of? Williams: We have not seen any side e ects. It appears to be safe and e ective. (Sponsor’s note: In clinical studies, diarrhea, bloody stools, inappetence, lethargy, hypersalivation, vomiting, muscle tremors, and death have been observed with the use of Cerenia.) “Cerenia has a novel mechanism of action that is different from any of the other drugs we’ve discussed.” therapy induced vomiting prior to 5-HT3 receptor antagonists. Jergens: The best example might be acute pancreatitis. Many times you just put patients on pain medications to treat their discomfort and vomiting markedly decreases. Leib: I believe butorphanol also has been used in some chemotherapy protocols as an antiemetic. Simpson: It would be similar to buprenorphine? Williams: Aminopentamide, under the trade name Centrine, was once widely used in general practice but was rarely used in academic institutions. Leib: So we are talking about the anticholinergic compounds. Does anybody want to comment on their proposed antiemetic actions? Twedt: There are receptors in the chemoreceptor trigger zone, so they may have some e ects there. Some e ects may exist peripherally with e erent receptors in the smooth muscle and glands of the gastrointestinal tract. And the receptors 10 may have some e ect in decreasing gastrointestinal secretions but also decrease gastrointestinal motility. Williams: Which is probably why the receptors may help in the symptomatic control of diarrhea, for example. Leib: They relieve smooth muscle spasms that may be producing pain. The majority of acute, self-limiting vomiting dogs managed as outpatients are going to get better. So over time, clinicians may associate the result with treatment, and that treatment might have no e ect. Practitioners will say they have been using a treatment for years because it works, despite the negative physiologic e ects of that drug class. Twedt: In fact, as far as contraindications, the anticholinergics are probably more contraindicated with an obstruction than metoclopramide. I think they are de nitely contraindicated because they cause decreased gastrointestinal motility. Leib: So if we use anticholinergics to treat a vomiting animal with abnormal gastrointestinal motility, we are promoting ileus and potentially worsening the vomiting.
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