Hello, although the information you provided is not sufficient for a complete answer, I ll give you two possible explanations of carbamazepine levels elevation on this particular situation. Kidney functionality should be stable for the levels to be stable as well. A dehydrated person is likely to have impaired kidney function which means that less carbamazepine (the active ingredient of tegretol) is excreted to the urine. Keep in mind though that only a small amount of carbamazepine is directly excreted through the kidneys. Another possible explanation is the administration of other drugs (the antibiotics you mentioned). Certain drugs may cause slower clearance of other drugs (or the opposite). This may eventually lead to elevated (or decreased) plasma levels of the drug. Nobody can say for sure if levels will rise in case he gets sick again. It depends. Under the same circumstances though, expect similar results. I hope I ve answered your query. Don t hesitate to ask again, if you need more information. Kind Regards!