Sympathomimetics

JSS College of Pharmacy - Mysuru
SYMPATHOMIMETICS
SUBMITTED BY:
NARASIMHAMURTHY M
1ST M PHARM
DEPARTMENT OF PHARMACOLOGY
JSSCPM , MYSURU

CONTENT
Introduction
Adrenergic Receptors
Sympathomimetic drugs
 Classification
Pharmacological Actions
Adverse Effects and Contraindications
Therapeutic Uses

Introduction
• The prime function of the adrenergic or
sympathetic nervous system is to help the
human beings to adjust to stress and prepare
the body for flight or fight reactions.
• When exposed to stress, the heart rate and
stroke volume increases with the resultant
increase in cardiac output.

Adrenergic (more precisely ‘Noradrenergic’)
transmission is restricted to the sympathetic
division of the ANS. There are three closely related
endogenous catecholamines (CAs).
 Noradrenaline (NA) : It acts as transmitter at
postganglionic sympathetic sites (except sweat
glands, hair follicles and some vasodilator fibres)
and in certain area of brain.
ADRENERGIC TRANSMISSION

ADRENERGIC TRANSMISSION
 Adrenaline (Adr) : It is secreted by adrenal
medulla and may have a transmitter role in
the brain.
 Dopamine (DA) : It is a major transmitter in
basal ganglia, limbic system, CTZ, anterior
pituitary, etc. and in a limited manner in the
periphery.

Metabolism of Catecholamines
 Venillyl mandelic acid (VMA) is the main metabolite of
catecholamines excreted in urine .
 Normal value of VMA is 4-8 mg per 24 hours urine.
 Its levels are raised in pheochromocytoma, a tumour of adrenal
medulla sympathetic ganglia.
 estimation of levels of catecholamines and their metabolites in
blood and urine is of great value in the diagnosis of
pheochromocytoma.
Adrenaline COMT & MAO Vanillyl mandelic acid
Noradrenaline Metanephrine
Normetanephrine

ADRENERGIC RECEPTORS
 Adrenergic receptors are membrane bound G-protein
coupled receptors.
 Adrenergic receptors are classified into two types α
and β.
 The alpha-adrenergic receptors α1 receptor
(α1A,α1B,α1D) and α2 receptor (α2A,α2B,α2C) are
GPCRs.
 The beta-adrenergic receptors β1,β2 and β3 receptor
are GPCRs.

ADRENERGIC RECEPTORS
 Presynaptically
located α2 and β2
receptors playing
important roles in the
regulation of
neurotransmitter
release from
sympathetic nerve
ending.

Distribution of adrenergic receptors

SYMPATHOMIMETIC DRUGS
Definition
• These are drugs that partially or completely mimic
the action of to that of adrenaline or of
sympathetic stimulation is known as
sympathomimetic drugs.

Classification of sympathomimetic drugs
Direct sympathomimetics : They act directly as
agonists on α and/or β adrenoceptors— Adr, NA,
isoprenaline, phenylephrine and many others.
Indirect sympathomimetics : They act on adrenergic
neurone to release NA, which then acts on the
adrenoceptors – tyramine, amphetamine.
Mixed action sympathomimetics : They act directly
as well as indirectly—ephedrine, dopamine,
mephentermine.

CLASSIFICATION OF ADRENARGIC
DRUGS(SYMPATHOMIMETICS)

PHARMACOLOGICAL ACTIONS
• Adrenaline acts on α1 α2 β1 β2 and β3 –receptors.
1.Cardiovascular system
a) Heart : Adrenaline is a powerful cardiac stimulant. It acts
mainly by interacting with β1- receptors and produces
various effects. They are as follows:
 Increase in heart rate (positive chronotropic effect)
 Increase in myocardial contractility (positive inotropic
effect)
 Increase in conduction velocity (positive dromotropic
effect)

Increase in cardiac output.
Increase in automaticity.
Cardiac work and its oxygen requirement is
markedly increased.
b) Blood vessels and BP : Blood vessels of the
skin and mucous membranes (α1-receptors) are
constricted by adrenaline. It also constricts
renal, mesenteric, pulmonary and splanchnic
vessels, but dilates the blood vessels of skeletal
muscles and coronary vessels (β2).

Intravenous administration of adrenaline in
moderate doses produces biphasic effect.
There is an initial rise in BP due to α1 (blood
vessels) and β1 (heart) actions followed by a
fall in BP due to β2-mediated vasodilatation in
skeletal muscle.
Administration of adrenaline aftereversar α-
blocker produces only a fall in BP (β2-action).
This is referred to as vasomotor reversal.

2.Respiratory system :
Adrenaline rapidly relaxes (β2) bronchial smooth
muscle. It is potent bronchodilator but as a short
duration of action.
It inhibit the release of inflammatory mediators
from mast cells (β2). It also reduces secretions
and relieves mucosal congestion by
vasoconstrictor effect (α1).

PHARMACOLOGICAL ACTIOS
3. GIT :
• It relaxes the smooth muscle of the gut (α2 and β2). It
reduces the intestinal tone and peristaltic movements
but the effects are transient.
4. Bladder :
• It relaxes the detrusor muscle (β2) and contacts the
sphincter (α1). As a result, it may cause difficulty in
urination.

5. CNS :
• In therapeutic doses, adrenaline does not cross the
BBB ; hence, CNS effects are minimal. But in high
doses, It may causes headache, restlessness and
tremor.
6. Eye :
• Adrenaline has poor penetration through cornea
when applied topically into the eye. Hence, it is
administered as a prodrug.

7. Metabolic effects :
a) Adrenaline increases blood glucose level by :-
Stimulating hepatic glycogenolysis (β2), which is
the predominant effect.
Reducing insulin secretion through α2 action.
Decreasing uptake of glucose by peripheral
tissues.
b) It increases blood lactic acid level by stimulating
glycogenolysis in skeletal muscles.

PHARMACOKINETICS
 Adrenaline is not suitable for oral administration
because of its rapid inactivation in the GI mucosa
and liver. Adrenaline can be given subcutaneously.
 In anaphylactic shock, absorption of s.c. adrenaline is
poor; hence, it is given intramuscularly.
 In cardiac arrest, it is given intravenously. It does not
cross the BBB; is rapidly metabolized by COMT and
MAO, and the metabolites are excreted in urine.

ADVERSE EFFECTS AND CONTRAINDICATIONS
ADVERSE EFFECTS :
1. Cardiovascular system
o Heart : Tachycardia, Palpitation other Arrhythmias.
Myocardial Ischemia, Reflex bradycardia.
o Blood Vessels : Hypertension, Headache, Local
necrosis at the site of administration.
2. CNS : (Mainly in lipophilic agents)
Anxiety, Fear, Agitation, Insomnia, Irritation etc…

ADVERSE EFFECTS AND CONTRAINDICATIONS
3. Decreased effect after repeated administration :
Tachyphylaxis.
4. Skeletal muscle tremors.
CONTRAINDICATIONS :
 Adrenaline is contraindicated in hypertensive,
hyperthyroid and angina patients.
 Adrenaline should not be given during anaesthesia with
halothane (risk of arrhythmias) and to patients receiving β
blockers (marked risk in BP can occur due to unopposed a
action).

Therapeutic uses of sympathomimetic
 Hypertension (α2-agonists)
Nasal decongestant (α1-agonists)
Ophthalmic uses : Mydriasis(α1) ; Glaucoma
(α2)
Asthma and COPD (β2-agonists)
Allergic reactions
Tocolytic (β2-agonists)
Narcolepsy.

THANK YOU

Sympathomimetics

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