Sorry to hear Teddy is unwell, however I have worked out an answer for you below ...
1. Claritin D is unsuitable for dogs because it contains pseudoephedrine which can cause side effects in the dog, however regular Claritin is sometimes prescribed for dogs and few side effects have been reported. So of course switch to the regular version of this drug in future.
2. Reported side effects of pseudoephedrine in the dog are said to include vomiting, diarrhoea, panting and agitation, unfortunately there is little you can do to combat the pills already given this week but any remaining drug should naturally drain out of his system over the next 12 hours. But if more serious symptoms other than than just diarrhoea appear or you become further concerned then you should have him checked over by a local vet without delay just to be on the safe side.
3. If he is otherwise bright and happy and the only symptom you are seeing is some degree of diarrhoea then this is very encouraging, there are a number of home remedies for diarrhoea in the dog you may want to try, here are some examples ...
1. I am aware that some owners use Pepto-Bismol to treat their dogs with gastro-enteritis and report success. Here is a link to a web page which has all the information you might need including dose rates : LINK
2. Some owners try and control the situation with diet alone before they try anything else. This is logical and often works, the basis of this is to give the intestinal tract a complete rest and then bring it back slowly to function, resting the alimentary tract is the critical factor. It would go something like this ...
A. Starve him for 24 hours but make sure he has access to water.
B. The next day feed him four or five small light meals in the day. These meals should be the likes of chicken, fish, scrambled egg etc. with a little rice.
C. If he picks up on this diet gradually reintroduce his normal diet over the next few days.
Also I should be available online for you the next four or five hours today so please do not hesitate to get straight back to me if Teddy's condition changes in any way or you would like to talk things over with me further.
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