I would start with 2.5 mg then after 2-3 weeks, go down gradually in dosage each day for 3-4 days--say 2mg, then 1.5mg, then 1mg, then 0.5mg, and then stop. Prednisone should always start with the higher dose and be decreased gradually. Never stop it suddenly. With 20 mg tablets, you could dissolve 1 in 4 ml of water, draw it up in a needless syringe, and after shaking the syringe to mix each time, 1/2 ml would equal 2.5 mg.
