my son aadhyan, he is now 4 yr 10 m old. he is suffering from cough(aasthama), so doctor suggested "Montelukast sodium and levocetirizine hydrochloride". we using since 1 and half year, still we using that. if we avoid that medicine, after 24 hrs he attacks by Cough. please tell is it safe by using this medicine for long time period, and suggest me any alternative medication or anything else plz....