Drug Case: Digoxin

Question 1

What class of drug is digoxin?

Answer 1

Cardiac glycoside

Question 2

What is it licensed for?

Answer 2

HF
Arrhythmias

Question 3

What HF is it licensed for?

Answer 3

Left ventricular function impaired
= backlog
= leakage of fluid

Question 4

What arrythmias is it licensed for?

Answer 4

Rate control in AF

Question 5

What is normally used to control rate?

Answer 5

BB

Question 6

How many mechanisms is there for digoxin?

Answer 6

2

Question 7

What is the 1st mechanism?

Answer 7

Increase force of myocardial contraction
= positive inotrope

Question 8

What is the 2nd mechanism?

Answer 8

Decrease conductivity at AVN
= negative inotrope

Question 9

When it is a positive inotrope?

Answer 9

Providing symptom benefit in HF

Question 10

When is it a negative inotrope?

Answer 10

Effective rate control in arrhythmias

Question 11

Why is a loading dose required?

Answer 11

Long t1/2

Question 12

How is rapid digitalisation administered?

Answer 12

In divided doses = 50% dose initial + 2md dose 4-8hrs
= this allows distribution to occur + monitor patient for signs of toxicity

Question 13

How is maintenance for AF + HF given?

Answer 13

Orally

Question 14

How is EMERGENCY loading given?

Answer 14

Intravenous infusion
= given slowly over 2hrs

Question 15

What do you do after IV loading?

Answer 15

Give digoxin oral ASAP

Question 16

What is the normal maintenance dose for AF?

Answer 16

125-250mcg

Question 17

What is the normal maintenance dose for HF?

Answer 17

62.5-125mcg

Question 18

What is digoxin available as?

Answer 18

Tablet
Elixir
IV

Question 19

What is the bioavailability of tablet?

Answer 19

63%

Question 20

What is the bioavailability of elixir?

Answer 20

75%

Question 21

In arrhythmias what can toxicity result in?

Answer 21

Formation of ventricular extrasystoles

Question 22

What do you NOT want to go below bpm wise?

Answer 22

60bpm

Question 23

What must you check first before starting digoxin?

Answer 23

Thyroid
= need a lower dose if hyperthyroidism

Question 24

What is the main problem with digoxin?

Answer 24

Narrow therapeutic window

Question 25

What are the therapeutic level?

Answer 25

1-2 mcg/L = >2 TOXIC

Question 26

When do you take the blood?

Answer 26

6hrs post dose

Question 27

How many phase distribution is digoxin?

Answer 27

2

Question 28

Describe the phase distribution of digoxin

Answer 28

Phase 1 = digoxin in serum conc Phase 2 = digoxin conc in myocardium Takes 6hrs to reach phase 2

Question 29

How is digoxin structure related to its function?

Answer 29

Lots of OH in structure = mostly renally excreted

Question 30

Because it's renally excreted what do you need to check?

Answer 30

Renal function = risk of accumulation

Question 31

What does hypokalaemia do?

Answer 31

Sensitises myocardium to actions of cardiac glycosides

Question 32

What are the signs of digoxin toxicity? SLOW AND SICK

Answer 32

Bradycardia Abdominal pain Blurred or yellow tint vision Confusion Rash

Question 33

Can you still be toxic and within the range?

Answer 33

YES

Question 34

If you can be toxin + within the range, what does this mean?

Answer 34

Always treat the patient, NOT the number

Question 35

How do you treat digoxin toxicity?

Answer 35

STOP digoxin Correct electrolyte balance DIGFab

Question 36

What is DIGFab?

Answer 36

Digoxin-specific Ab FAB fragments

Question 37

How is DIGFab given?

Answer 37

IV bolus

Question 38

When do you use DIGFab?

Answer 38

If toxic + plasma levels are >3mcg/L OR patient presents with hypokalaemia or bradycardia

Question 39

What are the interactions?

Answer 39

Medicines that... Cause hypokalaemia Increase plasma conc Decrease plasma conc Decrease excretion

Question 40

What is an example of medicine that increases plasma conc?

Answer 40

Enzyme inhibitors

Question 41

What is an example of medicine that decreases plasma conc?

Answer 41

Enzyme inducers

Question 42

What is an example of a medicine that decreases excretion?

Answer 42

Nephrotoxic medicines

Question 43

What are medicines that should not be considered with digoxin? CRASED

Answer 43

CCB Rifampicin Amiodarone St Johns Wort Erythromycin Diuretics