The maximum daily dose of Ondansetron varies according to the condition you’re giving it for, but usually it’s 16-32 mg daily. Some factors can impact your decision, like age, indication, baseline QTc interval, and risk of emesis for chemotherapeutic agents.
Achieving your goal using 2-3 agents with different mode of action would be a good option when you evaluate the risks vs benefits of giving ondansetron at doses > 32 mg/day.
If your recommending Ondansetron as a prophylaxis against CINV, and the emetogenic chemotherapy is high, then it’s recommended to give the patient a loading dose of Ondansetron prior starting chemo (16mg), and two doses subsequently (8 mg each dose).
The previous recommendation I wrote was adopted from NCCN antiemetic guidelines. According to Ondansetron new label, hence, guideline recommendations had changed, the recommendations are as follows:
For CINV prevention, IV route:
0.15 mg/kg over 15 min administered 30 min before chemotherapy, then 4 and 8 hr after first dose; not to exceed 16 mg (32 mg no longer recommended because of increased risk of QT prolongation)
Kindly note that the risk of QT prolongation is additive, and if your patient has a low baseline QT interval, does not receive other medications that might prolong QT internal, negative CVD history, and no other antiemetics are available or contraindicated, then you might follow the 32 mg/day as long as you can monitor your patient.