Brief Answer:
please see the detailed answer below...
Detailed Answer:
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I've gone through your query in details...
I can understand your concerns...
Ondansetron can be given at the dose of 0.15mg/KG that is around 4mg of one tablet to your son...the same can be repeated up to twice daily if required. So you can give him 4mg tablet once and observe how he stays. If required, later on, another 4mg tablet (at the gap of 4hours) can also be repeated.
Let me know if I can assist you further.
Take Care
Kind Regards