Case of doctor holding 50% of ribose for pharmacist? (5)

'pharmacist?' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'case of doctor holding 50% of ribose' is the wordplay.
'case of' suggests removing the centre (outsides of).
'holding' means one lot of letters goes inside another.
'50% of' indicates taking half.
'doctor' with its middle taken out is 'dr'.
'ribose' halved is 'ose'.
'dr' placed around 'ose' is 'DOSER'.

'for' is the link.

Can you help me to learn more?