The active ingredient found in the prescription medicine, Claritin- D 12 hour, is 120 mg of pseudoephedrine sulfate.  It is produced in extended release tablets for this particular medicine.  Pseudoephedrine sulfate acts as a nasal decongestant.  This ingredient is added to the medicine to treat seasonal  allergies with temporary relief of nasal and sinus congestion, sneezing, runny nose,  watery eyes, and itchy throat or nose.