sympathomimetics

1. Adrenergic Drugs/Sympathomimetics
• These are the drugs that mimic the response of sympathetic or
adrenergic system.
Neurotramsmitters: Neurotransmitters are the chemical mediators
released by the neurons to transmit the signals through synapse.
Three major endogenous catecholamines are:
 Adrenaline (Adr, Epinephrine)
 Noradrenaline (NA, Norepinephrine)
 Dopamine
Adrenergic Receptors
α β
α1 α2 β1 β2 β3

2. Tyrosine
Dopa
Dopamine
Noradrenaline
Adrenaline
Synthesis:
Tyrosine hydroxylase
Amino acid decarboxylase
Dopamine β-Hydroxylase
Phenylethanolamine N-methyl transferase

4. Adrenergic drugs acts through adrenergic receptors.
Adrenergic Receptors/Adenoreceptors are of 2
types: alpha (α) & beta (β).
Receptor Tissue Response
α1 Vascular smooth muscle vasocontraction
Genitourinary tract
smooth muscle
contraction
Smooth muscle
(Sphincter, radial muscle
of iris, gland)
Contraction
(mydriasis, secretion)
Intestinal smooth muscle Relaxation
α2 Prejunctional nerve
ending
NA release
Vascular smooth muscle vasoconstriction
Alpha receptors (α)

5. Receptor Tissue Response
β1 Heart Rate, FOC,
A-V conduction
Juxtaglomerular cells Rennin release
β2 Smooth muscles
(Bronchial,
gastrointestinal,
genitourinary, uterus)
Relaxation
Skeletal muscle Glycogenolysis
K+ uptake
Liver Glycogenolysis
Gluconeogenesis
β3 Adipose tissue Lipolysis
Beta receptors (β)

7. Adrenergic drugs/Sympathomimetics
1.Direct
sympathomimetics
Adrenaline,
NorAdrenaline,
Isoprenaline,
Phenylephrine,
Xylometazoline
2.Indirect
sympathomimetics
Amphetamine, Cocaine,
Sellegilline, Entacapone
3.Mixed action
sympathomimetics
Ephedrine,
Mephentermine

9. Pressor agents Dopamine, NA, Mephentermine, Ephedrine
Cardiac
stimulant
Dobutamine, Adr, Iso
Bronchodilators Salbutamol (albuterol), Salmeterol, Terbutaline, Iso,
Adr
Nasal
decongestant
Xylometazoline, Oxymetazoline, Phenylephrine
Pseudoephedrine
CNS stimulants Amphetamine, Dexamphetamine
Anorectics Fenfluramine, Sibutramine
Uterine relaxant Ritodrine, Isoxsuprine, salbutamol, Terbutaline
Clinical classification of Adrenergic drugs

10. Adrenaline (Adr) α1+ α2 + β1+ β2+weak β3 action
Noradrenaline (NA) α1+ α2+ β1+ β2 but no β3 action
Isoprenaline (Iso) β1+ β2+ β3 action but no α
action
Pharmacological Actions:
Epinephrine (adrenaline) is a potent stimulant of both α and β
adrenergic receptors. Most of the responses are seen after injection of
epinephrine, although the occurrence of sweating, piloerection, and
mydriasis depends on the physiological state of the patient. Particularly
prominent are the actions on the heart and on vascular and other
smooth muscle.
Norepinephrine (Noradrenaline) and epinephrine both are direct
agonists on effector cells, and their actions differ mainly in the ratio of
their effectiveness in stimulating α and β2 receptors. They are
approximately equipotent in stimulating β1 receptors. Norepinephrine
is a potent αagonist and has relatively little action on β2 receptors.

11. Heart Positive ionotropic effect (increase in force of contraction)
Positive chronotropic effect (increase in heart rate)
Positive dromotropic effect (increase in heart conduction)
Respiration Bronchodilation , Nasal decongestion
Blood
vessels
Vasoconstriction
Blood
pressure
Increases
GIT Relaxation but sphincter contracts so peristalsis decreases
Eye Mydriasis (Dilation of pupils)
Uterus Non-pregnant-Contraction; Pregnant-Relaxation
Skeletal
muscle
Tremor, glycogenolysis
Metabolic Hyperglycemia, Lipolysis, Hypokalemia

12. Adverse effects:
• Adr-sc/i.m: restlessness, palpitation, anxiety,
tremor, pallor
• Adr-i.v. high dose: cerebral haemorrhage,
arrhythmias
Contraindications:
• Hypertensive, Hyperthyroidism, Angina Pectoris
• Patient receiving β-blocker.
• During anesthesia by Halothane

13. • Dopamine is the immediate metabolic precursor of
norepinephrine and epinephrine. It is a central neurotransmitter
particularly important in the regulation of movement and
possesses important intrinsic pharmacological properties.
• In the periphery, it is synthesized in epithelial cells of the
proximal tubule and is thought to exert local diuretic and
natriuretic effects.
• Dopamine is a substrate for both MAO and COMT and thus is
ineffective when administered orally.
• It doesn’t cross BBB.
• In moderate dose (0.2-1mg) it increases BP & urine flow.
Mechanism of action:
• Dopamine can activate α- and β-adrenergic receptors. It acts on
dopaminergic receptors (D1-D5) present on peripheral
mesenteric and renal vascular beds. Binding of dopamine
produces vasodilation. D2 receptors are also found on
presynaptic adrenergic neurons, where their activation interferes
with norepinephrine release.

14. Indication:
• Given as i.v. infusion to patients with cardiogenic & septic
shock.
• Severe Congestive Heart Failure
• Dose regulated by monitoring BP & urine formation.
• At high concentrations, dopamine activates vascular a1
receptors, leading to more general vasoconstriction.
Adverse Effects:
Nausea, vomiting, tachycardia, anginal pain, arrhythmias,
headache, hypertension, and peripheral vasoconstriction
may be encountered during dopamine infusion.
Contraindication:
Hypovolemic shock, depression (patients receiving MAO
inhibitors or tricyclic antidepressants)

15. Dobutamine
Mechanism of Action:
• Dobutamine is a derivative of dopamine that directly acts
on adrenergic receptors(β1).
Indications:
• Dobutamine is used to increase cardiac output in acute
congestive heart failure as well as for inotropic support
after cardiac surgery.
• It increases cardiac output and does not significantly
elevate oxygen demands of the myocardium, a major
advantage over other sympathomimetic drugs.
• It is used in pump failure (Myocardial Infarction, Cardiac
surgery, CHF)
Contraindication:
• Atrial fibrillation
• May cause tolerance

16. Ephedrine
• Mixed action adrenergic drugs
• Orally effective & long acting than Adr
• Crosses BBB so stimulation
• Used in mild chronic bronchial asthma & hypotension during
spinal anaesthesia
Amphetamine
• Synthetic compound similar to ephedrine but have more CNS
action
• Improves alertness, attention, concentration & performance
• Included in dope test (drug for abuse)
• Used in attention deficit hyperactive disorder (ADHD)
Phenylephrine
• alpha1 agonist
• used as mydriatics, decreases ocular tension
• Oral or nasal decongestant

17. Nasal Decongestants
• Topical: Oxymetazoline, Xylometazoline,
Naphazoline
• alpha2 agonist, long duration of action
• Use cautiously in hypertensive patients
• Oral: Phenylephrine, Pseudoephedrine,
Phenylpropanolamine (PPA)
• Produce vasoconstriction in mucosa & skin
• Used orally as decongestant of upper respiratory
tract, nose & eustachian tubes
• Avoided in hypertensive patients
• PPA banned in Nepal (risk of haemorrhagic stroke)

18. Indications:
1.Vascular Uses:
• Hypotensive states (shock, spinal anaesthesia, hypotensive drugs)
• Along with local anaesthetics
• Control of local bleeding
• Nasal Decongestants
2. Cardiac Use
• Cardiac arrest (drowning, electrocution, etc.) – In combination
with external cardiac massage
• Partial or complete A-V block – Isoprenaline as temporary
measure
• Congestive Heart Failure
3. Bronchial asthma
4. Allergic disorders (histamine mediated)
5. Mydriatic
• Fundus examination
• Wide angle glaucoma

19. 6. Insulin Hypoglycaemia
7. Nocturnal enuresis in children and urinary
incontinence – Amphetamine
8. Uterine relaxant – Ritoridine: to postpone labour –
Isosuxprine: threatened abortion and dysmenorrhoea
9. Central Uses
• Attention Deficit Hyperkinetic Disorders –
Amphetamine
• Narcolepsy – Amphetamine, Modafinil – Imipramine
like drugs
• Epilepsy – Amphetamines
• Parkinsonism – Amphetamine
• Obesity – Considered in severe obesity