<s>[INST] My aunt is visiting and we took her to the er 2 days ago for a rash. Dr. said it was shingles.  2 days later it is worse and these red blisters are now black and have spread very quickly.  Is this the normal progression- black blisters after starting antiviral meds? [/INST] Hi, Thanks for writing to us. The change in color of the blister suggests either it has become blood filled or has scabbed. In herpes, clear vesicles can later on fill with pus or blood. Usually once the antivirals like acyclovir (800 mg five times in a day) or valaciclovir(1g thrice in a day) are started in appropriate dose, progression of disease stops. If you are having and doubt either consult the doctor again or use ask a specialist feature of this website to upload pics and have an elaborate discussion. Take care </s>