Good, that is positive to hear that he can keep water down. Though if his gums are pale, we need to be very careful as that can be a sign of internal bleeding or circulatory compromise in the gut (from foreign bodies, blockages, etc). Any doubt in the color and you can compare his gums with your other dog's gums. And I have to say that since the other dog had signs as well, we'd be wary of a possible severe bacterial or viral gastroenteritis, pancreatitis (something Paco's breed is very prone to), or shared ingestion (ie toxins, plants, non-edible items). And while we can see gastritis with some lizards, I'd be surprised if both caught one so close together. So, unless the lizards are of a size that both dogs could have had a bit, that would be less likely (and wouldn't explain the paling).
With this all in mind, we can try some home supportive care to try to settle his stomach as we keep a very close eye on him (since any more paling of if he is white we'd need him seen urgently to make sure there is no bleed or damaging blockage). To start, if he hasn’t just vomited (since otherwise we’d need to rest his stomach for a few hours first), then you can consider treating him an OTC pet safe antacid [ie Pepcid (More Info/Dose @http://www.petplace.com/article/drug-library/library/over-the-counter/famotidine-pepcid), Zantac (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/ranitidine-hcl-zantac),Tagamet (More Info/Dose Here @ http://www.petplace.com/article/drug-library/library/over-the-counter/cimetidine-hcl-tagamet)]. Whichever you choose, we’d give this 20 minutes before offering food to allow absorption. Of course, do double check with your vet if he has a known health issues or is on any medications you haven't mentioned. Though if he cannot keep it down due to nausea, that is usually a red flag that we need to bypass his mouth with injectable anti-vomiting medication from his vet.
Afterwards, you can consider starting an easily digestible diet like cooked white rice with boiled chicken, boiled white fish, cottage cheese, scrambled eggs, or meat baby food (as long as its garlic/onion free). There are also OTC vet diets that can be used (ie Hill’s I/D or Royal Canin’s sensitivity) too. The aim of these diets is that they will be better tolerated/absorbed by the compromised gut. Therefore, it should get more nutrients in and result in less GI upset. As long as improvement is being seen, I usually advise continuing this until signs are settled, and then weaning slowly back to your normal diet.
Finally, as dehydration is a risk here, we need to keep an eye on his hydration. To check that he isn't dehydrated, there are a few things you can test. Further to checking for gum moisture, do make sure he doesn’t have sunken eyes and that he doesn’t have a "skin tent" when you lift the skin. To see how to check these parameters for dehydration, you can find a good video HERE (http://www.ehow.com/video_12232503_dog-dehydrated.html). If you are seeing any signs of dehydration already, then that would be our cue to have him seen before this becomes an additional issue (especially as it is often dehydration that makes them feel unwell).
Overall, his signs do raise some concerns here. But the most important thing just now is to compare his gums to the other dog to make sure we don't have a risky situation here. If they are similar colored, then we’d want to start supportive care to settle his stomach. If he cannot keep that or water down at any point, appears dehydrated already, or doesn’t respond to the above by the time his vet is open; then we'd want to get them to assess Paco, rule out fever, make sure there is nothing in his stomach that shouldn't be there or any sinister viruses present. Depending on their findings, his vet can treat him with injectable anti-vomiting medication +/- antibiotics to settle his stomach, and get him back feeling like himself.
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