Thanks for putting up your question so nicely. Decreased platelets counts (monocytopenia or thrombocytopenia) is due to many causes and if every test comes normal and no cause is associated, then it is called idiopathic thrombocytopenia which simply means decreased platelets without any cause. If I were attending my patient, and every blood test i did came normal except platelets. I would prescribe the same drug with same frequency. sptra/bactrim is antibiotic which is prescribed by the doctor because steroids (prednisone) reduces immunity. yes you have to take these drugs as prescribed. Please consult your local doctor for followup so that he could repeat blood test after a 3-4days, as steroids has very drastic response. Hope I have answered your question. If you have any further questions, I will be happy to help. If you do not have any clarifications, you can close the discussion and rate the answer. Wish you GOOD HEALTH