child's dose for Iophen C-NR (Oral)

Hello,

  My son was given Guaifenesin 2 years ago for a bad cough due to cold.  He has another cough due to cold and I can't remember the dosage.  I believe it was 1/2 teaspoon every 4-6 hours.  Could you please let me know?  My son is 9 years old.  Also, can he take regular Dimetapp with it.  He is not taking Dimetapp DM (cough).  Thank you.

        Katherine Hynes