CARDIO: Adenosine

Question 1

ADENOSINE: INDICATIONS

Answer 1

Supraventricular Tachycardia

Question 2

ADENOSINE: MOA

Answer 2

Agonist of Adenosine Receptors (GPCRs) on Cell Surface:

• Reduces AUTOMATICITY (frequency of spontaneous depolarisations) + increases REFRACTORINESS (resistance to depolarisations)
• Transiently slows sinus rate, conduction velocity and increases AV node refractoriness
• Increasing the refractoriness of the AV node = breaks the RE ENTRY CIRCUIT
• Normal depolarisations from the SA node to resume control of the heart = CARDIOVERSION
• Duration effect = V short, rapidly taken up by cells
• Half Life = < 10 seconds

Question 3

ADENOSINE: ADVERSE EFFECTS

Answer 3

• Induce BRADYCARDIA and ASYSTOLE (interferes with SA + AV node fxn)
• Sinking feeling in chest
• Breathlessness
• Impending feeling of DOOM
• All of these effects = SHORT LIVED

Question 4

ADENOSINE: WARNINGS

Answer 4

Should not administer adenosine to a patient who will not tolerate transient bradycardia effects:

• Hypotension
• Coronary ischemia
• Decompensated heart failure
• Can induce bronchospasm in certain individuals, must be avoided in patients who suffer from COPD + ASTHMA
• Patients who have had a heart transplant, v sensitive to the effect of ADENOSINE

Question 5

ADENOSINE: INTERACTIONS

Answer 5

• Dipyramidole blocks cellular uptake of adenosine, which prolongs and potentiates its effect: dose of adenosine should be HALVED
• Theophylline, aminophylline and caffeine are competitive antagonists of adenosine receptors and reduce its effect => Patients who have taken these drugs respond poorly and may require higher doses

Question 6

ADENOSINE: EXAMPLE

Answer 6

ADENOSINE….duh!