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If this just occurred in the last hour or two you could induce vomiting and attempt to retrieve it and see how much has already been absorbed. Instructions on inducing vomiting can be found here.
The toxic dosage of ibuprofen is 50mg per pound to cause stomack ulceration problems. To cause kidney issues, the dosage would be 150mg per pound. You can read more on this here:
You can use this to determine if there is a chance your dog ingested enough to cause stomach or kidney issues. These are things that are not immediately evident but can show up later. I hope this information is helpful to you.