Which of the following vitamin should not be supplemented in a patient of parkinsonism on levodopa therapy
Pyridoxine acts as cofactor for Dapa decarboxylase enzyme that converts levodopa to dopamine. 
As peripheral conversion can cause postural hypotension, nausea & vomitting and also makes the therapy ineffective. Pyridoxine should not be supplemented.
Thiamine
Pyridoxine
Cobalamine
Pantothenic acid