Brief Answer:
Give him antiemetic with acid reducers

Detailed Answer:
Hello

Sinus drainage into the throat also known as postnasal drip; rarely if ever causes vomiting. The main problem of postnasal drip is irritation in throat and cough.

Sometimes reflux of stomach content into food pipe or upper airway is associated with the postnasal drip.Even some viral infection of stomach may cause the same symptoms.

Repeated vomiting may cause dehydration. Zyrtec contains antiallergic and works well in sinus drainage(postnasal drip).

I would suggest you to give him some antiemetic like ondensetron or domperdone syrup along with the acid reducers like esomoprazole/lansoprazole under supervision of your doctor. It will help in relieving the vomiting.

I will be glad to answer if you have any further query.

Regards

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Brief Answer:
Mucolytic cough syrup will help

Detailed Answer:
Hello

You are right. Vomiting in postnasal drip may occur due to irritation or coughing.
Zyrtec is an antiallergic and it helps in postnasal drip.
I would suggest you to add mucolytics(for thinning of mucus) like ambroxol or guaifenesin syrup under physician supervision.
As reflux may be associated with the postnasal drip, antiemetic with acid reducers will also be helpful.
Regards

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