I have mild asthma and allergy and I am using singulair (montelukast) 1*1 and seretide diskus 500 1*2, symptoms are well controlled can I reduce the dose

Need to see doctor. Check with your doctor who may test your lung function before trying to reduce the dose of your medication. In general, I do not use the 500 ug seretide for asthma control since the 250 ug one usually does the job .