Benserazide

Benserazide (also called Serazide or Ro 4-4602) is a peripherally-acting aromatic L-amino acid decarboxylase (AAAD) or DOPA decarboxylase inhibitor, which is unable to cross the blood-brain barrier.

Indications
It is used in the management of Parkinson's disease in combination with L-DOPA (levodopa) as co-beneldopa (BAN), under the brand names Madopar in the UK and Prolopa in Canada, both made by Roche. Benserazide is not approved for use in the US; carbidopa is used instead for the same purpose. These combinations are also used for the treatment of restless legs syndrome.

Pharmacology
Levodopa is a precursor to the neurotransmitter dopamine which is administered to increase its levels in the central nervous system. However, most levodopa is decarboxylated to dopamine before it reaches the brain, and since dopamine is unable to cross the blood-brain barrier, this translates to little therapeutic gain with strong peripheral side effects.

Benserazide inhibits this decarboxylation, and since it itself cannot cross the blood-brain barrier, this allows dopamine to build up solely in the brain instead. Adverse effects caused by peripheral dopamine, such as nausea and arrhythmia, are minimized. However, benserazide cannot reduce the centrally-mediated side effects of levodopa, particularly dyskinesia.

Benserazide has little therapeutic effect on its own, and is only administered in combination with levodopa.