An 18-year-old male presents with nephrotic syndrome. 24-hour urinary protein is 4.5g, urine disc electrophoresis shows mid-molecular proteinuria (selective proteinuria), marked edema, normal blood pressure (BP) and renal function. He had similar episodes in childhood which achieved complete remission (CR) with standard steroid therapy, and remained urine test negative until this relapse. Current treatment should be: