Drug Monographs Flashcards
Describe Pharmacodynamics of Adenosine
- Slows conduction time through AV Node
- Naturally occuring nucleoside
- Stimulates specific adenosine receptors, causing efflux of potassium and influx of calcium in SAN, atria, and AVN
- Result is hyperpolarization of nodal tissues, slowing AV conduction and blunting SA discharge
Describe Pharmacokinetics of adenosine
- Intravenous
- Onset - rapid
- Duration - very brief
- Half-life - 6 to 10 seconds
- Duration - 1 to 2 minutes
Indications for adenosine
- Conversion of supraventricular tachycardia (SVT) / paroxysmal supraventricular tachycardia (PSVT).
Contraindications/precautions for adenosine
2 contraindications, 1 precaution
Contraindications
- Hypersensitivity
- 2nd or 3rd degree AV block, or sick sinus syndrome (without pacemaker)
Precautions
- May worsen bronchospasm in asthmatics and some patients with COPD.
Drug to drug interactions of adenosine
3 listed
- Higher than normal doses of Adenosine may be required for patients on xanthines (eg. theophylline).
- Lower than normal doses (i.e. 3 mg or less) should be used for patients on dipyridamole (Persantine) as this drug potentiates Adenosine.
- The effects of Adenosine are prolonged in patients taking Carbamazepine (anti-convulsant) and in heart transplant recipients (denervated hearts).
Adverse effects of adenosine
- Dizziness/light headedness/syncope, facial flushing, dyspnea or shortness of breath, gastroninestinal distress (nausea/vomiting), chest pain or discomfort
- Usually resolves in 1-2 mins
- Explain to the patient they will likely experience some of the above symptoms and that the symptoms are temporary
Adult dosing for adenosine
- First dose: 6 mg IV direct, given rapidly and immediately followed with 20 mL to 30 mL IV NS or RL flush
- Run ECG strip as drug is being given
- If no conversion to sinus rhythm or slowing of rhythm to diagnose underlying rhythm (e.g. atrial flutter or atrial fibrillation) in 1-2 minutes, can give a second dose: 12 mg IV direct, rapid administration followed by 20-30 mL IV NS or RL flush
- Note: Adenosine must be given very quickly and in the IV site closest to the central circulation (e.g. antecubital, external jugular, central line). It should always be immediately followed by a 20-30 cc flush of NS or RL to make sure that all of the drug is cleared from the IV tubing and delivered to the intended site.
Pediatric dosing for adenosine
- First dose:
- 0.1 mg/kg IV direct, given rapidly followed by 5-10 mL (depends on weight of child) IV NS or RL
- maximum 6 mg as a single first dose
- Second dose:
- If no conversion to sinus rhythm or slowing of rhythm to diagnose underlying rhythm (e.g. atrial flutter or atrial fibrillation) in 1-2 minutes,0.2 mg/kg IV, administered as above.
- maximum 12 mg as a single second dose
What is the likelihood of successful conversion with adenosine?
Has a > 90% successful conversion of PSVT rate when the full dose is given (Crankin et al, 1989; Garrat et al, 1989; DiMarco et al, 1990).
Describe pharmacodynamics of amiodarone
- Considered a class III anti-arrhythmic.
- Also possesses electrophysiologic characteristics of all 4 Vaughan Williams classes.
- Like Class I drugs, amiodarone blocks sodium channels at rapid pacing frequencies.
- Like class II drugs, it exerts antisympathetic activity through beta-adrenoreceptor (weak) antagonism.
- Class II type effects: negative chronotropic effect in nodal tissues.
- Class III effect: lengthens the cardiac action potential.
- In addition to blocking sodium channels, amiodarone blocks myocardial potassium channels, which contributes to slowing of conduction and prolongation of refractoriness.
- Antisympathetic action and block of calcium and potassium channels are responsible for the negative dromotropic effects on the sinus node and for the slowing of conduction and prolongation of refractoriness in the atrioventricular (AV) node.
Describe pharmacokinetics of amiodarone
Intravenous
- Onset: Minutes when used as bolus in V.Fib/pulseless VT
- Peak: 10-15 minutes
- Duration: Amiodarone has a prolonged duration of action and if used for rhythm control for other than arrest situations has a slow onset of action (1 - 2 hours)
Indications for amiodarone
- Ventricular fibrillation
- Pulseless ventricular tachycardia
- Unstable ventricular tachycardia (usually recurrent after cardioversion)
- NOTE DOSING DIFFERENCES
- Recurrent unstable VT post cardioversion
Contraindications and precautions for amiodarone
4 contraindications, 1 precaution
Contraindications
- Hypersensitivity
- Cardiogenic shock
- Marked sinus bradycardia
- 2nd or 3rd degree AV block
Precautions
- Tissue toxic if extravasation
Warnings and drug-to-drug interactions for amiodarone
Warning
- Hypotension of the most common side effect during IV infusion (~39% of patients in one trial). Slow the infusion.
- May enhance actions of B-Blocker, Ca Channel Blocker or Digoxin.
- May cause prolongation of the QT interval (>500 ms may lead to Torsade de Pointes)
Drug to drug interactions
- May enhance action of B-Blocker, Ca Channel blockers, Digoxin.
Adult dosage for amiodarone
- 300 mg IV bolus; may repeat 150 mg bolus in 10 min for ventricular fibrillation/pulseless VT.
- 150 mg IV over 10 min (150 mg in a 50 mL NS minibag run at 50 gtts/min) for recurrent unstable VT post cardioversion or unstable VT refractory to cardioversion.
Pediatric dosage for amiodarone
Trick Question!!
Safety and efficacy in children has not been established.
When should amiodarone be given in unstable VT refractory to cardioversion or recurrent VT requiring multiple cardioversions?
For unstable VT refractory to cardioversion or recurrent VT requiring multiple cardioversions, amiodarone should be administered while packaging the patient and initiating transport.
Classification of atropine
- Anticholinergic
- Antimuscarinic
Pharmacodynamics of atropine
- Parasympatholytic (inhibits stimulation from the parasympathetic nervous system)
- Vagolytic (inhibits stimulation from the vagus nerve)
- Inhibits vagal stimulation - allowing the sympathetic nervous system to dominate
- By allowing the sympathetic nervous system to dominate, impulse generation at the SA node and conduction through the AV node should increase
Pharmacokinetics of atropine
Intravenous
- Onset - 2 to 4 minutes
- Peak - 2 to 4 minutes
- Half-life - 13 to 40 hours
- Duration - 4 to 6 hours
Indications for atropine
- Restoration of cardiac rate in the presence of bradydysrhythmia
- Sinus bradycardia, less than 50 bpm - accompanied by hemodynamic compromise
- Acceptable, but controversial, in the setting of bradydysrhythmia secondary to AV blocks
- Treatment of organophosphate exposure/ingestion (high dose)
- Antidote for poisoning by certain species of mushrooms (e.g. Amanita muscaria)
Contraindications, precautions, and drug interactions for atropine
Contraindications
- Hypersensitivity to anticholinergics
- Tachycardia
Precautions
- Hepatic or renal insufficiency
- COPD - dries secretions/mucous plugging
Drug to Drug
- Antimuscurinic effects will be increased in patients taking Dysopyramide
Adult dosing for atropine
- 0.6 mg IV push - initial dose
- 0.04 mg/kg (~3 mg for most adults) = maximum (“full vagolytic”) dose
Pediatric dosing for atropine
- 0.02 mg/kg (give no less than 0.1 mg)
- Maximum or “full vagolytic” dose is 0.04 mg/kg
When giving atropine, why is it particularly imortant to give the correct dose quickly?
given in too low of a dose or too slowly may paradoxically slow the heart rate
Which bradydysrhythmias may not respond appropriately to atropine?
- Considered controversial in the setting of 2nd degree type II AV block. It may paradoxically slow the heart rate if the block is infranodal
- Not likely to be effective in ventricular escape rhythms as there is minimal parasympathetic innervation in the ventricles
How does prior administration of atropine affect patient assessment in the setting of asystole or PEA?
Atropine causes pupil dilation, therefore, assessment of pupils in the setting of asystole or PEA after Atropine has been administered may be unreliable
Pharmacodynamics of epinephrine
- α1 (Alpha 1) Effects: Vasoconstriction
- β1 (Beta 1) Effects: Increased Heartrate, Increased force of cardiac contraction
- β2 (Beta 2) Effects (moderate): Bronchodilation
- Inhibits histamine release
- +ve chronotropic, +ve dromotropic and +ve inotropic effects
Pharmacokinetics of epinephrine
Intravenous
- Onset - Immediate if given IV
- Peak - Unknown
- Half-life - Unknown
- Duration - Unknown
Intramuscular
- Onset - 5 to 15 minutes (variable onset with IM)
- Peak - Unknown
- Half-life - Unknown
- Duration - 1 to 4 hours
Inhalation
- Onset - 1 to 5 minutes (has a mostly local effect)
- Peak - Unknown
- Half-life - Unknown
- Duration - 1 to 3 hours
Indications for epinephrine
- IV/IO dose - Cardiac arrest: ventricular fibrillation, pulseless ventricular tachycardia, asystole, pulseless electrical activity
- IM, IV, IO, nebulized: Anaphylaxis
- IM dose: Bronchospasm (uncommon)
- Nebulized for severe croup
Contraindications and precautions for epinephrine
2 contraindications, 2 precautions
Contraindications
- Significant tachyarrhythmias
- See ACLS guidelines re: drug therapy in the setting of hypothermia (< 30 degrees C)
Precautions
- May cause significant dysrhythmias in patients > 35 y/o and/or cardiovascular disease
- Reduced dosage may be required for patient on MAO inhibitor as there is an increased sympathomimetic response
Drug to drug interactions and adverse effects of epinephrine
Drug to Drug Interactions
- Epinephrine is neutralized by, and may precipitate with sodium bicarbonate. Therefore, DO NOT administer in the same IV line with Bicarb unless the line has been flushed
Adverse Affects
- Tachycardia, palpitations, angina, PVC’s
- Hypertension