Anti-arrhythmics Flashcards
Atropine Drug and doses
Racemic mixture of D + L hyoscyamine- only L is active
DOse is 0.015-0.02mg/kg IV or IM
0.2-0.6mg PO
3mg is needed for complete vagal blockade in adults
Atropine pharmacokinetics
Low bioavailability
Crosses placenta and blood brain barrier
Elimiation half like 2.5hrs
Atropine pharacodynamics
COmpetitics antagonist of Ach at muscarinic receptors with little action at nicotinic receptors
CV- initially can actually produce bradycardia, slows AV conduction time, dilates blood vessels at high doses
REsp- bronchodilation, increases physiological dead space, incr. rr
CNS- anticholinergic syndrome
GI- reduces gut motility and urinary tract tone
Other- mydriasis, increased IOP, reduces ADH secreiton
What is the bezold jarisch reflex?
cardioinhibitory reflex- bradycardia, vasodilation and hypotension from stimulation of cardiac receptors
Originates from inhbitoy receptors in the LV. Stimulation increases PNS and inhibits sns
Glycopyrollate drug and dosing
Charged quaternary amine
Competitice antagonist at peripheral muscarinic receptors
0.2-0.4mgIV or IM
4-10microg paeds
Glycopyrrolate pharmacokinetics
Poor oral absorprion (5% bioavailability)
Can cross placenta but not bbb
80% is excreted unchanged
Elimiation half life half an hour to an hour
Glycopyrrolate pharmacodynamics
CV- vagolytic effects last 2-3 hours
Resp- bronchodilator, increases dead space
5 x more potent than atropine at drying secretions
Other agents used in bradycardia?
Isoprenaline
adrenaline
aminophylline
Dopamine
GLucagon
Isoprenaline moa in bradycardia
B1 + B2 agonist
Can causea drop in svr due to b2 action
given IV
Adrenaline moa in bradycardia
Low dose has B chronotropic effects, increasing doses increases alpha action
Aminophylline bradycardia MOA
Non specific PDE inhibitor, increasing cAMP. Mild chronotropic effects
Dopamine MOA in bradycardia
Low dose infusion has B1 action, higher doses increase a action
increases av conduction
Glucagon moa in bradycardia ?
receptors are Gs linked and increase cAMP. 2nd/3rd line mx in B Blocker OD
Amiodarone drug and doses
Benzofuran derivative
Class 3 action- blocks K+ channels
Partial antagonist of a and b
Higher doses can depress na and ca channels
Slows rate of repolarisation and increases refractory perid- prolonging phase 3
Slows AVN automaticity and conduction
5mg/kg iv over one hour then 15mg/kg over 24 hours
orally- tds for one week then bd then od
Amiodarone pharmacokinetics
Bioavailability of 50-70%
Highly protein boud, can potentiate actions of anticoag, dioxin, calcium antagonists and B blockers as they are displaced from proteins
Elimination half life 4 hours to 52 days
Amiodarone pharacodynamics
Can cause bradycardia, hypotension and prolonged QT
Can develop pneumonitis and fibrosis
Corneal deposits
PEripheral neuropathy, LFT changes, phtosensitivity
ABdnormal thyroid fx can occur as it resembles thyroid hormone- both hyper and hypo reported
Adenosine drug and dosage
Naturally occuring purine nucleoside of adenine and d ribose
Acts on adenosine (a1) receptors in the sa and av node (Gi receptors) causing hyperpolarisation and dramatic negative chronotropy- transient heart block
A2 receptors have anti inflammatory actions
Cytoprotective properties in ischaemia
smooth muscle relaxation in coronary arteries
Dsoe: 3mg/6mg/12mg
Acts within 10s, lasts 10-20
Atropine pharmacodynamics
CV- increases myocardial blood flow
Induces AF/flutter as it decreases atrial refractory period
Decreases PVR in pulm htn
Resp- bronchospasm, increases rr+ depth
Other- can induce neuropathic pain. facial flushin. chest discomfort
DIgoxin drug and dosage
Glycoside
Directly blocks sodium/potassium/ATPase pump which increases refractory period of AV node and reduces conductivity
Indirectly acts by increasing acetylcholine release which slows conduction and prolongs refractory period
Given orally or IV
10-20 μg/kg as a loading dose 6 hourly then maintenance
Serum levels need monitoring initially (1-2 g/ml therapeutic)
Digoxin pharmacokinetics
50-70% excreted unchanged in urine, involving some active secretion
Dosing needs to be altered in renal failure
Digoxin pharmacodynamics
Digoxin side-effects are common due to the narrow therapeutic window
Gastrointestinal disturbance common including abdominal pain and nausea
Muscle weakens, headache and drowsiness can occur
Arrhythmias including heart block and ventricular bigemini
The risk of toxicity is increased in the presence of:
Hypokalaemia
Hypomagnesaemia
Hypernatraemia
Hypercalcaemia
Hypoxaemia
Renal failure
Other drugs including amiodarone, verapamil and diazepam
Magnesium indications?
Torsades, AF
MAgnesium drug and dose
2-5g IV depending on indication and levels
B blockers indications in tachycardia ?
Supraventricular arrhythmias
Calcium channel blockers indications in tachycardia
Supraventricular arrhythmias
Common calcium channel blockers used in tachycardias?
DIltazemn (30-120mg 6-8hrly) and verapamil (240-480mg in 2-3 doses)
Flecainide indication and doses
Used for all tachycardias, suppresses ventricular ectopics
Amide local anaesthetic- blocks fast na channels and slows depolarisation
100-200mg 12 hrly (can be given IV)
