You have not mentioned the age of your son.
If below 2 years, its better to avoid Rhinathiol.
If he is above 2 years you can give him Butalin
+ Rhinathiol. Butalin is a bronchodilator
that is used in wheeze and Rhinathiol loosens the secretions.
When ever you visit a doctor, inform the doctor about G6PD deficiency
so that drugs contraindicated in G6PD def will not be prescribed.
Be sure that the syrups you administer do not contain any coloring substances/ menthol as these may produce problems in G6PD deficiency patients. If you have any doubts, please have a word with your doctor again.
Hope I have answered your query.
Wish a speedy recovery for your son.