20.HF 2 - cardiac glycosides

Question 1

properties of cardiac glycosides

Answer 1

• from foxglove plant
• increase contractility used in HF systolic
• narrow TI because toxic + fatal
• structure: steroid ring + lactone ring + sugar residues

Question 2

action of digoxin, digitoxin

Answer 2

1. regulate cytosolic ca concentration
2. increase contractility of the cardiac muscle
3. neruohormonal inhibition
   4 extra cardiac effects:
   -kidney inhibt na/k atpase decreasing renin reliease, in sm cells enhance ca level, in cns stimulate vagal nucleus, stim chemoreceptors trigger zone

Question 3

pharacokinetics of digoxin

Answer 3

onset 10-30 min
peak effect 1-3 h
metabolized in liver and eliminated by kidney
medium lipid solubility
oral bioav. 75%
t1/2 40h
large Vd: displacement by other drugs
has a loading dose + 1 x 0.25 mg maintenance dose

Question 4

pharmacokinetics of digitoxin

Answer 4

onset 25 min - 2h
peak effect 4-12 h
liver metab. kidney elim
oral bioav. 90% more than
t1/2 168 hours
high lipid solubility + protein binding

Question 5

indication of cardiac glycosides

Answer 5

symptomatic chf NYHA 3,4
chronic decompensation
chf + afib
atrial flutter, fib
acute supraventricular tachycardias

Question 6

adverse effects of cardiac glycosides

Answer 6

-cardiac: arrythmias, bradycardia, av blocks, ecg changes
g.i: anorexia, vomiting, diarrhea, pain,
CNS: headaches, drowsiness, nerualgic pain, hallucinations
eyes: blurred visions, color vision problem, diplopia
other: gynecomastia, allergy

Question 7

drug interactions pharmacokinetics:

Answer 7

increasing absorption: neomycin, tetracyclin
decreasing absorption: cholestyramine, antacids, cytostatic, agents
increasing metabolism: ez inducers
decreasing protein binding: fenofibrate, antidiabetics

Question 8

pharmacodynamics

Answer 8

increase digitalis sensitivity: drugs that increase calcium levels,
increase AV time: Calcium antagonists, BB, drugs influencing ion levels

Question 9

antidote for digitalis intoxification:

Answer 9

digifab + potassium

Question 10

causes of digitalis intoxification

Answer 10

too high dose
relatively high dose:
- altered clearence
- enhanced sensitivity of the heart
-serum electrolyte disturbanes: hypo/hyper kalemia, hypo- mg, na, hypercalcemia, acid base imbalance
-concomitant drug admin:
anesthetics, catecholamine + sympathomimetics, antiarryhtmic agents