(Mode of Action of Drugs)

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Chapter

1.4

Chapter

2.2

Sedative

&

Hypnotics

Sedative

&

Hypnotics

Sedative (anxiolytic) are the agents which
reduce anxiety and exert a calming effect
with little or no effect on motor or mental
functions.

Hypnotics are the drugs which produce
drowsiness and encourage the onset and
maintenance of sleep. They are classified
into different categories (Table 2.2.1.)

BARBITURATES

Barbiturates are the derivatives of
barbituric acid. They are general CNS
depressants. They can cause sedation,
hypnosis and general anaesthesia
depending upon the particular barbiturates
used and its dose.

Pharmacological Actions

CNS: Barbiturates produce depression
of central nervous system in dose dependent
manner. In small dose, barbiturates relieve
anxiety and are generally used as sedative.
In hypnotic dose, it produces sleep resem-
bling normal physiological sleep. Hypnotic
dose of barbiturates produce motor incoor-
dination.

Pain: Barbiturates do not have any an-

algesic effect.

Anaesthesia: The ultra short acting bar-

biturates produce general anaesthesia (de-

tails are given in chapter ‘General

anaesthetics’).

Anticonvulsant action: In anaesthetic

dose all barbiturates e.g. phenobarbitone,

mephobarbitone possess anticonvulsant ac-

tion. Phenobarbitone is drug of choice for

the treatment of grandmal epilepsy (details

are given in chapter ‘Antiepileptic drugs’).

CVS: In hypnotic dose, hypotension and

decrease in heart rate occurs. In toxic dose,

there is a severe decrease in blood pressure

due to ganglionic blockade.

Respiration: In higher dose, barbiturates

depress the respiration. It depresses the sen-

sitivity of respiratory centre to CO 2.

GIT: They depress the tone and motil-

ity of GIT, but thiobarbiturates may stimu-

late the intestinal smooth muscles.

Kidney: They directly depress the tubu-

lar reabsorption of sodium, reduce urine

flow and increase ADH release.