A 26-yr girl at 31 weeks gestation C/O a 4-week H/O a pustular eruption that developed initially on the periumbilical skin. Subsequently the eruption spread to involve the breasts, back, flexures and proximal limbs. There was cutaneous pain, fever & malaise. O/E the lesions were pustules were arranged in concentric rings while on the breasts there was coalescence of pustules forming lakes of pus. Treatment of choice in this case?