Doctor cited case subject to dehydration (9)
I believe the answer is:
desiccate
'subject to dehydration' is the definition.
'doctor cited case' is the wordplay.
'doctor' is an anagram indicator.
'cited'+'case'='citedcase'
'citedcase' with letters rearranged gives 'DESICCATE'.
(Other definitions for desiccate that I've seen before include "dry" , "Remove moisture" , "Preserve by removing all liquids from" , "Preserve by drying (eg coconut)" .)