Welcome to Just Answer! I would like to help you and your dog with this question, but need more information in order to better assist you both.
How long ago did she ingest this pill?
Does she weigh about 50lbs? More? Less?
Does she have any underlying health problems such as kidney disease?
I am going to sign off for the night, but will leave you with an answer before I go...
How is your dog doing?
Is she able to walk?
is she drinking a lot?
When we know within 2 hours that a dog has consumed a pill, it may be ok to make her vomit. ALWAYS CHECK WITH A VET as there are some things that will cause more harm if you make the dog vomit than if you leave it down in the stomach.
For future reference, you can make a dog vomit by using 3% hydrogen peroxide. Give 2 teaspoons per 10lbs body weight. You can repeat in 10 minutes if she has not vomited yet.
More here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx
Also, some hints to make it work better:
1. Feed a small meal or slice of bread first - they are more likely to vomit with some food in the stomach.
2. Dogs will often drink peroxide if you mix it 50:50 with milk or ice cream, and it is just as effective.
3. Dogs are more likely to vomit after getting hydrogen peroxide if they move around - play ball, go for a walk, run up and down stairs - as this heightens the fizzing.
4. Always check the expiration date of the peroxide. If it is old it doesn't fizz very well!
Both hydrochlorothiazide and triamterene are drugs we use in dogs. If she is about 50lbs, then both of those are separately within the dose range we use. However, given together they are likely to cause some problems. I would be concerened about electrolyte imbalances, and dehydration. She could develop lethargy, and even coma or seizures if she has underlying health problems like kidney or heart disease. She may also develop diarrhea and abdominal pain.
If she came to see me, I would give her 50 - 100 grams of activated charcoal to help to prevent her from absorbing more of the drugs that are in her body. In Canada you can buy it in the local pharmacy and I expect you can in the USA as well. It is widely used in human and veterinary medicine to bind up any toxins that have been ingested.
Here are some links about activated charcoal:
Unfortunately, since we are many hours now after ingestion, it is getting to the point where it is almost too late to give this, but you could try. It binds with the drug in the intestines to prevent absorption... but by 4 hours after ingestion, she has probably absorbed whatever she ingested.
Again, if she were my patient, I would monitor her VERY closely for low blood pressure and for dehydration and treat those if they occured.
Given that this is an overdose and that your dog is elderly, I would recommend a visit to your vet to have her checked over. I'm concerned about her!
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