A 3-year-old child with ARVI had been administered biseptol, paracetamol, nazoferon. On the third day of treatment the baby's condition deteriorated: he developed sore throat, stomatitis, conjunctivitis, hypersalivation, painful dark red spots on the neck, face, chest and legs, then the spots were replaced with vesicles. Examination revealed lesions of mucous membranes around the mouth and anus. What is your provisional diagnosis?