Benserazide is a peripherally-acting

Peripheral nervous system

The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

 aromatic L-amino acid decarboxylase

Aromatic L-amino acid decarboxylase

Aromatic L-amino acid decarboxylase is a lyase enzyme.-Reactions:It catalyzes several different decarboxylation reactions:* L-DOPA to dopamine - a neurotransmitter* 5-HTP to serotonin - also a neurotransmitter...

 (AAAD) or DOPA decarboxylase inhibitor

Enzyme inhibitor

An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides...

, which is unable to cross the blood-brain barrier

Blood-brain barrier

The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...

.

Indications

It is used in the management of Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

 in combination with L-DOPA (levodopa

Levodopa

L-DOPA is a chemical that is made and used as part of the normal biology of some animals and plants. Some animals including humans make it via biosynthesis from the amino acid L-tyrosine. L-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine , and epinephrine collectively...

) as co-beneldopa (BAN

British Approved Name

A British Approved Name is the official non-proprietary or generic name given to a pharmaceutical substance, as defined in the British Pharmacopoeia...

), under the brand names Madopar in the UK and Prolopa in Canada, both made by Roche

Hoffmann-La Roche

F. Hoffmann-La Roche Ltd. is a Swiss global health-care company that operates worldwide under two divisions: Pharmaceuticals and Diagnostics. Its holding company, Roche Holding AG, has shares listed on the SIX Swiss Exchange....

. Benserazide is not approved for use in the US; carbidopa

Carbidopa

Carbidopa is a drug given to people with Parkinson's disease in order to inhibit peripheral metabolism of levodopa.- Pharmacology :...

 is used instead for the same purpose. These combinations are also used for the treatment of restless legs syndrome

Restless legs syndrome

Restless legs syndrome or Willis-Ekbom disease is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but can affect the arms, torso, and even phantom limbs...

.

Pharmacology

Levodopa

Levodopa

L-DOPA is a chemical that is made and used as part of the normal biology of some animals and plants. Some animals including humans make it via biosynthesis from the amino acid L-tyrosine. L-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine , and epinephrine collectively...

 is a precursor

Precursor (chemistry)

In chemistry, a precursor is a compound that participates in the chemical reaction that produces another compound. In biochemistry, the term "precursor" is used more specifically to refer to a chemical compound preceding another in a metabolic pathway....

 to the neurotransmitter

Neurotransmitter

Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

 dopamine

Dopamine

Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...

 which is administered to increase its levels in the central nervous system

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

. However, most levodopa is decarboxylated

Decarboxylation

Decarboxylation is a chemical reaction that releases carbon dioxide . Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to...

 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

Nausea

Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

 and arrhythmia, are minimized. However, benserazide cannot reduce the centrally-mediated side effects of levodopa, particularly dyskinesia

Dyskinesia

Dyskinesia is a movement disorder which consists of effects including diminished voluntary movements and the presence of involuntary movements, similar to tics or choreia. Dyskinesia can be anything from a slight tremor of the hands to uncontrollable movement of, most commonly, the upper body but...

.

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