class 3 antiarryhtmics: K ch blockers

Question 1

MOA of K ch blockers, and drugs

Answer 1

Herg K channel: inhibitory effects is reverse use - dependent, K ch blocking effect is less marked in tachycardia, increase risk of early afterdepl. in brady cardia
effect: decrease outward K current during repol -> prolong repol, prolong QT and ERP
SLOWS PHASE 3 OF AP
drugs: amiodarone, dronedarone, sotalol, dofetilide, ibutilide, vernakalant, bretylium

Question 2

amiodarone

Answer 2

action: contains iodine -> binds proteins, 1a, 2, 4 effects, slight alpha block => - ionotropic effect
pk: oral, t1/2: 40=80 days,
MUST SCREEN: liver function test, thyroid FT, CXR, opthalmic evaluation, pulmonary FT, ECG
i: SVA-> afib, severe ventricular arrythmia TDP
AE: accumulation leading to PULM FIBROSIS, PHOTOSENSITIVITY, GREY BLUE SKIN, THYROID DYSFUNCTION, neuro, pro arrythmogenic, brady cardia, hypotension, hepatotoxicity
contraindication: sevre bradycardia, sss, thyroid dysfunction

Question 3

dronedarone

Answer 3

action: amiodarone derivative, decreases left ventricular contractility
i: Afib

Question 4

sotalol

Answer 4

action: k+ blocker + non selective bb-> decreasign hr, and av conduction
i: Afib, vfib
ae: proarrythmogenic

Question 5

dofetilide, ibutilide

Answer 5

action: block Ikr channel
dofetilide is oral, ibutilide is IV
i: Afib + conversion

Question 6

Vernakalant

Answer 6

action: block early + late Na ch, ach dep k+ ch, PROLONGS PHASE 1
admin IV
i: ventricular arrythmia ->Vfib

Question 7

bretylium

Answer 7

action: adrenergic neruon blocker, admin: I.v
i: ventricular arrythmia ->Vfib