L-Dopa is combined with carbidopa in treatment of parkinsonism because -

Ans. is 'd' i.e., To make more L-Dopa available to cross the blood brain barrier Carbidopa More than 95% of an orally administered levodopa is decarboxylated by dopa-decarboxylase in peripheral tissues. Carbidopa and benserazide are extracerebral (peripheral) dopa decarboxylase inhibitors. Prevent peripheral decarboxylation of levodopa. o They do not penetrate BBB and do not inhibit conversion of levodopa to dopamine in the brain.. o Benefits of levodopa-carbidopa combination are ? 1.Plasma t 1/2 of levodopa is prolonged and its dose is reduced. 2.Nausea, vomiting, cardiac complications and other peripheral side effects are reduced as peripheral dopamine production is reduced. 3.Pyridoxine reversal of levodopa effect does not occur. 4.On-off effect is minimized o Problems not resolved or accentuated are ? Postural hypotension 2.Involuntary movement 3.Behavioral abnormalties. About option 'b' o Peripheral side effects of L-dopa are reduced when given with carbidopa as peripheral dopamine production is reduced. o But this is an additional benefit; Levadop-carbidopa combination is primarily given to reduce peripheral decarboxylation of levodopa so that more of it will be available to cross BBB.