Find the medicine name, then google 'name' overdose
Something will pop up.
I found this for Itraconazole overdose.
Overdosage/Acute Toxicity - There is very limited information on the acute toxicity of itraconazole. Giving oral antacids may help reduce absorption. If a large overdose occurs, consider gut emptying and give supportive therapy as required. Itraconazole is not removed by dialysis. In chronic toxicity studies, dogs receiving 40 mg/kg PO daily for 3 months demonstrated no overt toxicity.Drug Interactions - Itraconazole requires an acidic environment for maximal absorption, therefore antacids.