ADRENALINE

1) Therapeutic drug action & mechanism(pharmacology)

• Sympathomimetic

• Non selective adrenoreceptor drug

• Acts on both a and b receptors but is a more potent a receptor

• Effects: i) inotrope [b₁-receptors]

ii) Vasopressor [a-receptors]; effect at higher dosages

iii) Vasodilator of skeletal muscle vasculature [b₂-receptors]

iv) Chronotrope [b₁-receptors]

v) Bronchodilation [b₂-receptors]

2) Indications

• Frequently used to aid in weaning off bypass due to its potent b₁ stimulation

• Bradycardias [heart blocks] & cardiac arrest

• Ventricular dysfunction, vasodilation, bronchoconstriction, anaphylaxis

• Drug of 1st choice in anaphylactic shock as:

i) vasopressor; elevates systolic BP due to:

a) Positive inotropic & chronotropic cardiac effect [b₁-receptors]

b) Vasoconstriction [a-receptors]

ii) antihistamine action

iii) bronchodilator [b₂-receptors]

3) Effects on organs—side effects

• May drop diastolic BP via decreasing SVR due to:

i) Vasodilation in some vessels [b₂-receptors]

4) Toxic effects/ precautions with administration

• arrhythmias

• elevated BP with secondary: cerebral haemorrhage; pulmonary oedema

• increased myocardial work load

• extravasation into sub cutaneous tissues may cause local ischaemia

• Vasoconstriction (splanchnic, renal)

5) Contraindications

• Idiopathic hypertrophic subaortic stenosis [?fixed cardiac output]

• Tetralogy of Fallot with RV outflow tract obstruction (as may constrict pulmonary vasculature exacerbating preexisting pulmonary hypertension or right ventricular dysfunction

6) Reversal, antagonism or antidote

• Very short half life

• If an adverse effect requires immediate reversal use adrenoreceptor antagonist

7) Loading dose, maintenance dose, frequency & method of administration

• 1:1000 (1mg/ml) or 1:10,000 (1mg/10ml)

• May be made up: 10mg/500 ml

• Continuous infusion eg 0.05-1mg/Kg/min

8) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• I.V. administered adrenaline has rapid onset & short duration of action

• Circulating drug is metabolised by liver & other tissues

• Majority is taken up and metabolised by sympathetic nerve endings

• Does not cross the blood-brain barrier

• Excreted in urine mainly as metabolites

9) Important drug interactions

• Should not be administered concomitantly with other sympathomimetic drugs as will exacerbate effect eg heart irritability

• Risk of arrhythmias with volatile anaesthetics

• Give with caution to patients on MAO or tricyclics as will prolong action