The best replacement for ondansetron is metoclopramide.

The best alternatives to ondansetron are rated as following:
★★★★★  metoclopramide
★★★★  zofran
★★★★  granisetron
★★★★  promethazine
★★★  phenergan
★★  compazine
★★  palonosetron
★★  prochlorperazine
★★  dimenhydrinate
★  dolasetron
★  cerenia
★  domperidone
★  meclizine

Your alternative for ondansetron is not listed? Suggest!
Speaking about ondansetron, one probably shouldn't forget about dexamethasone.

Other search terms related to ondansetron and their ratings are:

★★★★★ dexamethasone
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