Drugs used in Parkinsonism 123

Parkinsonism is an extrapyramidal motor
disorder, characterized by akinesia, rigidity
and tremor with secondary manifestations
such as excessive salivation, seborrhoea,
mood changes (especially depression) and
in certain patients, liver damage has been
reported. It was first described by James
Parkinson in 1817.

In parkinsonism, there is a degeneration
of dopaminergic nerve endings of the basal
ganglion (neurons in substantia nigra and
the nigrostriatal tract), which results in
deficiency of dopamine and cholinergic
overactivity. This imbalance between the
dopamine deficiency and overactivity of
cholinergic system gives rise to this motor
disorder. Thus, the rational approach to the
therapy of parkinsonism would be either to
increase the central dopaminergic activity or
to decrease the central cholinergic activity.

The drugs used in the treatment of
parkinsonism can be classified as in table 2.10.1.

LEVODOPA

Levodopa is the most effective drug
available for the treatment of parkinsonism

and used in combination with peripheral

dopa decarboxylase inhibitors. Levodopa as

such is inactive but it is the immediate

precursor of the transmitter dopamine.

When administered orally, 95 percent of the

dose is decarboxylated in the peripheral

tissues (mainly in liver). Dopamine thus

formed in peripheral system act on CVS and

other peripheral tissues and produce the

unwanted effects. Dopamine, as such, can

not be used to treat parkinsonism as it does

not cross the blood brain barrier. However,

the precursor of dopamine i.e. dopa crosses

the blood brain barrier and is converted to

dopamine in the brain and is released as a

neurotransmitter.

Pharmacological Actions

1. CNS: Levodopa does not produce any
   significant action in normal individual.
   In parkinsonism patient, it improves all
   manifestations of parkinsonism.
   Akinesia responds first, followed by
   rigidity and tremor. Other symptoms
   such as seborrhoea, sialorrhoea and
   aphonia also improve. The drug also
   improves mood, memory and patients

(Mode of Action of Drugs)

PharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamics

Chapter

1.4

Chapter

2.10 Drugs Used in Parkinsonism

Drugs Used in

Parkinsonism