Mystery rash on legs after Bactrim ?

[Joeyzoom56]

My mother recently was treated with Bactrim for a cyst between her buttocks.  She began the meds on Monday morning, and by Tuesday evening she had 3 starburst, silver dollar sized rashes on her legs -- 2 on one leg, 1 on another.  She also complained of a very sore tongue.  Her MD advised her to stop Bactrim, and by Friday's follow-up, they had diminished only slightly.  The MDs in the office had no idea what this was, and stated it was atypical reaction to Bactrim so they were concerned with an infection.   Blood work sent off yesterday for CBC, and ASO -- can we get any insight as to what this may be?  Is it likely to be a reaction to the meds, or perhaps something else going on in the body?  I am uploading 2 images of the legs as well.  No other symptoms, such as fever, cough, sore throat, or GI upset.  

The doctors all went back and forth on this, so it would really be appreciated to get some expert advise.  Thank you !

[Joeyzoom56]

no Jerry, but thank you for your take on this -- it is on both legs, but fading more with each day ... almost definitely a reaction to the Bactrim

[Jerry_NJ]

The problem only on the one leg?  If yes it may be an injury - looks like burn which could be temperature of chemical caused...just to name two.  Also, with age the skin does lose it "beauty"... I'm an old person so I know personally on that matter.

Doesn't look like anything to due with the blood unless it appears to be a bruise due to low blood coagulation condition... is you other taking an "blood thinner".. "coumadin"?