How many mg of zofran (ondansetron) should one take & how often, for a stomach bug, if they already take 8mg at least 3x a week for severe nausea caused by anxiety?

Zofran (ondansetron): http://www.rxlist.com/zofran-drug/indications-dosage.htm Dose for chemotherapy , the initial indication is 8 mg 2 x a day. Rarely up to 24 mg /day . It has a large therapeutic index(can be tolerated ) . Not recommended for nausea due to anxiety or long term use. Caution if used with SSRIs and apomorphine. F/u w/ doc there are other meds for anxiety and can cause serotonin syndrome.