Acetretin and rash

[Donnamackay77]

Hi, my dad has been on acetretin for 6 weeks due to severe psoriasis on the soles of his feet, he has been pretty much housebound for a year due to this, thus week however he has developed a nasty red rash from his throat down to below his ribs... Does anyone know if this is a normal reaction, is it dangerous? 
He has started walking again and he feels his feet have improved, but now we have this rash?! 

Thanks in advance for your help x