Treatment resistance

A search in Medline for treatments when first-line treatment fails:

exp Drug Resistance/ OR exp Treatment Failure/ OR resistan*.mp. OR refractor*.mp. OR intractab*.mp. OR nonrespon*.mp. OR non respon*.mp. OR persisten*.mp.

PsycInfo has:
DE "Treatment Resistant Disorders"
and you can do:
TI ( resistan* OR refractor* OR intractab* OR nonrespon* OR non-respon* OR persisten* ) OR AB ( resistan* OR refractor* OR intractab* OR nonrespon* OR non-respon* OR persisten* )

EMBASE has:
drug resistance/ or multidrug resistance/ or exp treatment failure/

and also, /dr [Drug Resistance] is a subheading, so check your EMTREE terms to see if they provide it, eg. exp posttraumatic stress disorder/dr [Drug Resistance]