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beta_blocker_toxicity [2024/11/26 01:40] – jkohtsbeta_blocker_toxicity [2025/01/07 19:45] (current) – jkohts
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 ===== - Classification ===== ===== - Classification =====
-There are a number of ways to classify β-blockers. A simple functional classification is described in the table below [(31178382>[[https://pubmed.ncbi.nlm.nih.gov/31178382/|PMID: 31178382]]. Oliver E, Mayor F Jr, D'Ocon P. Beta-blockers: Historical Perspective and Mechanisms of Action. Rev Esp Cardiol (Engl Ed). 2019;72(10):853-862. doi:10.1016/j.rec.2019.04.006)].+There are a number of ways to classify β-blockers. A simple functional classification for therapeutic use is described in the table below [(31178382>[[https://pubmed.ncbi.nlm.nih.gov/31178382/|PMID: 31178382]]. Oliver E, Mayor F Jr, D'Ocon P. Beta-blockers: Historical Perspective and Mechanisms of Action. Rev Esp Cardiol (Engl Ed). 2019;72(10):853-862. doi:10.1016/j.rec.2019.04.006)].
  
 <WRAP group><WRAP column> <WRAP group><WRAP column>
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 ==== - β-adrenergic antagonism ==== ==== - β-adrenergic antagonism ====
  
-Antagonism of β-receptors can cause bradycardia and hypotension for all drugs in this class.+Excess competitive inhibition at β-adrenergic receptors primarily cause bradycardia and hypotension for all drugs in this class. There is a loss of receptor selectivity in overdose.
  
-**β1 adrenergic antagonism**\\+**β1-adrenergic antagonism**\\ 
 +β1-receptors are found primarily in cardiac tissue, and when stimulated results in increased chronotropy, inotropy, automaticity, and dromotropy. β-antagonists depress these effects, and toxicity primarily manifests as suppression of cardiac functions with bradycardia, hypotension, and cardiogenic shock. 
  
 +**β2-adrenergic antagonism**\\
 +β2-receptors are found in peripheral smooth muscle vasculature, airway smooth muscle, liver, GI tract, pancreas, uterus, and to a lesser extent cardiac tissue. When stimulated, vasodilation and bronchodilation occur. The toxic effects of β-antagonists can manifest as bronchospasm in susceptible individuals.
  
-**β2 adrenergic antagonism**\\+β-blockers may also cause hypoglycemia by inhibition of hepatic glycogenolysis and pancreatic glucagon release. Counter-regulation by adrenaline is also diminished by β-blockade, further compounding hypoglycemia.
  
- Other effects In addition to their cardiac effects, beta blocking drugs may also cause hypoglycaemia (by inhibiting glycogenolysis) and /or bronchospasm (in susceptible individuals.) 
-Propranolol and sotalol have the highest relative toxicity due to other pharmacological properties of these drugs: sodium channel blockade (propranolol) and potassium channel blockade (sotalol). 
  
  
 ==== - Features of β-blockers ==== ==== - Features of β-blockers ====
-<code> 
-Note that this section has bullets with exposition, and then subheadings with exposition. Please can you compare and we can decide how to move forward with similar situations. 
-Options: 
-  - Bullet points only for headers + description below with subheadings (like the original https://www.wikitox.org/doku.php?id=wiki:3.4.3.4.2_beta_blockers#mechanism_of_toxic_effects) 
-  - Bullet points for headers + description in bullet points 
-  - Subheadings with description, no bullet points to signpost 
-</code> 
- 
 Individual drugs in this class differ based on their unique pharmacological properties, which include: Individual drugs in this class differ based on their unique pharmacological properties, which include:
-  * **Cardioselectivity** +  * Cardioselectivity 
-    * While β1-selectivity can influence adverse effects in therapeutic use, it becomes less relevant in overdose situations because selectivity is lost at high drug concentrations. +  * Intrinsic sympathomimetic activity 
-  * **Intrinsic sympathomimetic activity** +  * Class I antiarrhythmic effects 
-    * Some β-blockers have ISA due to partial β agonism and may result in tachycardia and hypertension. This partial agonist effect rarely leads to significant problems and probably protects to some extent from the more serious class I and III antiarrhythmic effects.  +  * Class III antiarrhythmic effects 
-    * Drugs with ISA include acebutolol, pindolol, labetalol, and celiprolol. +  * Vasodilatory activity 
-  * **Class I antiarrhythmic effects** +  * Lipid solubility 
-    * The membrane-stabilizing activity of some β-blockers is due to the inhibition of fast Na+ channels (class I anti-arrhythmic activity). These effects usually only occur at high drug concentrations.  +  * Renal/hepatic clearance
-    * Propranolol has the most membrane-stabilizing activity of the β-blockers and can result in impaired AV conduction, widened QRS interval, ventricular tachyarrhythmias, coma, and seizures. +
-  * **Class III antiarrhythmic effects** +
-    * Some β-blockers block the delayed rectifier outward K+ channel which is responsible for cell repolarization. This prolongs the action potential duration and prolongs the QT interval.  +
-    * Examples of these β-blockers include sotalol and acebutolol. +
-  * **Vasodilatory activity** +
-    * The vasodilatory activity of certain β-blockers can theoretically enhance the hypotensive effects in cases of β-blocker overdose. +
-  * **Lipid solubility** +
-    * Only lipid soluble drugs will lead to direct CNS effects as they are able to penetrate the blood brain barrier, though CNS symptoms may occur secondary to cardiac effects and decreased cerebral perfusion.  +
-    * Lipid solubility alone will not lead to CNS effects and they may relate to Na+ channel blocking effects as they are particularly common with propranolol. +
-  * **Renal/hepatic clearance** +
-    * This is occasionally important in therapeutics but is largely irrelevant to overdose. +
- +
  
 **Cardioselectivity (β1-selectivity)**\\ **Cardioselectivity (β1-selectivity)**\\
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 **Renal/hepatic clearance**\\ **Renal/hepatic clearance**\\
-This is occasionally important in therapeutics but is largely irrelevant to overdose.+This is occasionally important in therapeutics but is largely irrelevant in overdose.
  
  
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 ==== - Respiratory effects ==== ==== - Respiratory effects ====
 **Bronchospasm**\\ **Bronchospasm**\\
-β-blocker overdose can result in bronchospasm as a result of β2 antagonism, particularly in individuals with underlying reactive airway disease. It is unlikely +β-blocker overdose can result in bronchospasm as a result of β2 antagonism, particularly in individuals with underlying reactive airway disease.
  
 ==== - Metabolic effects ==== ==== - Metabolic effects ====
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 <code> <code>
-Need to check this - never seen this elsewhere:+Two problems here. 
 +(1) The above are contradictory. 
 + 
 +(2) Need to check this - never seen this elsewhere:
 There are some reports of patients responding to glucose with “normal” blood glucose measurements. Therefore, it is worth giving a bolus of 50% glucose to any patient with CNS effects.  There are some reports of patients responding to glucose with “normal” blood glucose measurements. Therefore, it is worth giving a bolus of 50% glucose to any patient with CNS effects. 
 </code> </code>
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 **Propranolol**\\ **Propranolol**\\
-Propranolol is the only beta-blocker that frequently causes seizures. In one series, of those who ingested more than 2 g of propranolol, two thirds had a seizure. It also causes more severe cardiovascular effects and death more commonly than other widely used beta blocking drugs. Propranolol also appears to be over represented in beta-blocker poisoning when corrected for frequency of prescription (Reith et al 1996). This presumably relates to propranolol being taken by a younger age group for predominantly non-cardiac indications.  +Propranolol is the only beta-blocker that frequently causes seizures in overdose. It is more toxic due to its lipophilic and membrane-stabilizing properties. In one series, of those who ingested more than 2 g of propranolol, two thirds had a seizure. It also causes more severe cardiovascular effects and death more commonly than other widely used beta-blocking drugs. Propranolol also appears to be over-represented in beta-blocker poisoning when corrected for frequency of prescription [(8667464>)]. This presumably relates to propranolol being taken by a younger age group for predominantly non-cardiac indications (anxiety, stress, migraine).
-Seizures are a common and serious complication of poisoning with lipophilic beta-blockers such as propranolol and may precipitate cardiac complications.. +
-Compared with the other β-adrenergic antagonists, propranolol accounts for a disproportionate number of reported cases of self-poisoning50,204 and deaths.130,156 This may be explained by the fact that propranolol is frequently prescribed to patients with diagnoses such as anxiety, stress, and migraine who may be more prone to suicide attempts. Propranolol is more lethal because of its lipophilic and membrane-stabilizing properties+
  
 **Sotalol**\\ **Sotalol**\\
-Sotalol may frequently cause significant QT prolongation and torsade de pointes (occasionally reported with propranolol) as well as the usual manifestations of beta blockade. Other factors relate to: +Sotalol may frequently cause significant QT prolongation and torsade de pointes (occasionally reported with propranolol) as well as the usual manifestations of beta-blockade. Other factors relate to its intrinsic sympathomimetic (partial agonist) activity and lipid solubility (resulting in CNS effects).
- +
-<code> +
-  Intrinsic sympathomimetic activity (partial agonist activity) +
-  Lipid solubility (CNS effects) +
- +
-</code>+
  
  
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 ==== - Supportive ==== ==== - Supportive ====
  
-IV access with IV fluids (normal saline) should be secured as soon as possible. ECG monitoring in intensive care is indicated for all but the most trivial propranolol or sotalol poisonings. Glucose should be given to any patient with decreased consciousness or seizures regardless of a normal blood sugar.+IV access and IV fluid resuscitation (with normal saline or balanced crystalloid) should be initiated. ECG monitoring in intensive care is indicated for all but the most trivial propranolol or sotalol poisonings. Glucose should be given to any patient with decreased consciousness or seizures regardless of a normal blood sugar. 
 + 
 +<code> 
 +Again the empirical glucose administration needs to be checked. 
 +</code>
  
 ==== - Decontamination ==== ==== - Decontamination ====
  
-Syrup of ipecac should not be used to decontaminate beta-blocker poisonings under any circumstances. Gastric lavage should be considered in large ingestions of propranolol or sotalol if patients present within one hour of ingestion. Atropine should be given prior to lavage and in any patient who is vomiting. Oral activated charcoal should be given to all patients ingesting any overdose of a beta-blocking drug who present within 2 hours.+**Gastric lavage** should be considered in large ingestions of propranolol or sotalol if patients present within one hour of ingestion. Atropine should be given prior to lavage and in any patient who is vomiting.  
 + 
 +**Oral activated charcoal** should be given to all patients ingesting any overdose of a β-blocking drug who present within 2 hours. 
 + 
 +**Whole bowel irrigation** may be considered in patients who have ingested sustained-release preparations. 
 + 
 +**Induction of emesis** (e.g. with syrup of ipecac) is __contraindicated__ in β-blocker toxicity due to risk of airway compromise (from aspiration and reduced consciousness) and vagal stimulation which may worsen bradycardia. 
  
 ==== - Enhanced elimination ==== ==== - Enhanced elimination ====
 +The drugs that are water soluble are predominantly renally cleared, namely sotalol and atenolol. Among these drugs, sotalol has significant 'antiarrhythmic' effects (via K+ channel blockade) and frequently causes life-threatening poisoning.
  
-The drugs that are water soluble are predominantly renally cleared. Among these drugs, only sotalol has significant “antiarrhythmic” effects and frequently causes life threatening poisoning. Thus, haemodialysis is unlikely to be useful except perhaps for sotalol in patients with life threatening toxicity and impaired renal function.+Extracorporeal treatment with renal replacement therapies (intemittent hemodialysis preferred) can be considered in patients who have all of the following [(34112223>[[https://pubmed.ncbi.nlm.nih.gov/34112223/|PMID: 34112223]]. Bouchard J, Shepherd G, Hoffman RS, et al. Extracorporeal treatment for poisoning to beta-adrenergic antagonists: systematic review and recommendations from the EXTRIP workgroup. Crit Care. 2021;25(1):201. Published 2021 Jun 10. doi:10.1186/s13054-021-03585-7)]: 
 +  * Sotalol or atenolol toxicity 
 +  * Significant renal impairment 
 +  *__Refractory__ cardiotoxic effects (bradycardia, hypotension, recurrent polymorphic VT) 
 + 
 +<code> 
 +I have removed the argument where sotalol is the only one which should be dialyzed, in light of ExTRIP recommendation to consider atenolol also. - Review to keep changes. 
 +</code>
  
 ==== - Antidote ==== ==== - Antidote ====
  
-There are a number of drugs that will antagonize some of the cardiac effects of beta-blockers. All these treatments may be used simultaneously, if this is required+There are a number of drugs that will antagonize some of the cardiac effects of beta-blockers. All these treatments may be used simultaneously if required. 
 +  * Atropine 
 +  * Glucagon 
 +  * Isoprenaline 
 +  * Dextrose & Insulin
  
-<code> +**Atropine**\\ 
-  Atropine +This should be tried in all patients with bradycardia. It should be given prior to intubation, lavage, or any other procedure that might increase vagal tone and in patients who are nauseated or vomiting.
-  Glucagon +
-  Isoprenaline +
-  Dextrose & Insulin+
  
-</code>+**Glucagon**\\ 
 +IV glucagon had been used as antidote for beta-blocker poisoning in the past but its use has been largely superseded by HIET. Glucagon increases intracellular cAMP and activates myosin kinase independent of β-receptors. 
 +\\ 
 +  * 💊 **Glucagon** IV 5-10 mg as a bolus, then an IV infusion titrated against heart rate and blood pressure (starting at 5-10 mg/hour, or the 'reponse dose' per hour).
  
-Atropine \\ This should be tried in all patients with bradycardia. It should be given prior to intubation, lavage, or any other procedure that might increase vagal tone and in patients who are nauseated or vomiting.+**Isoprenaline** \\ 
 +Isoprenaline is a non-selective competitive β-agonist. Doses should also be titrated against cardiac parameters and the dose required may be ten or twenty fold larger than normally used. As both the agonist and antagonist are competing for the same receptors, much larger doses are needed to reach the same level of receptor occupancy. Dose requirements will fall rapidly as the β-blocking drug is metabolised.
  
-**Glucagon** \\ Glucagon had been used as antidote for beta-blocker poisoning in the past but its use has been largely superseded by insulin dextrose. The rationale for its use is that it increases cyclic AMP and activates myosin kinase independent of beta-receptors. The dose is 5 - 10 mg IV as a bolus and then an infusion titrated against heart rate and blood pressure (starting at 5 - 10 mg/hour). 
  
-**Isoprenaline**  This is a non-selective competitive beta agonist. Doses should also be titrated against cardiac parameters and the dose required may be ten or twenty fold larger than normally used. As both the agonist and antagonist are competing for the same receptors, much larger doses are needed to reach the same level of receptor occupancy. Dose requirements will fall rapidly as the beta-blocking drug is metabolised.+**HIET**\\ 
 +Patients who require inotropics support should be commenced on Dextrose & Insulin. This should be implemented in patients not responding to isoprenaline.
  
-Patients who require inotropics support should be commenced on Dextrose & Insulin.+<code> 
 +This section has been reworked 08/01. Goldfrank's has a discussion of calcium, general catecholamines (other than isoprenaline), and lipid emulsion. 
 +Do we want to include those in? 
 +Also, in what order should we include them? 
 +</code>
  
-This should be implemented in patients not responding to isoprenaline. 
  
 ==== - Treatment of specific complications ==== ==== - Treatment of specific complications ====
  
-Seizures Glucose should be given regardless of a normal blood sugar. Otherwise, they should be treated conventionally with benzodiazepines(eg diazepam). If seizures are refractory-use phenobarbitone.+**Seizures**\\ 
 +Glucose should be given regardless of a normal blood sugar. Otherwise, they should be treated conventionally with benzodiazepines (eg diazepam). If seizures are refractory, use phenobarbitone. 
 +<code>Why phenobarb instead of usual status epilepticus protocol?</code>
  
-Arrhythmias Ventricular tachycardia (torsades de pointes) may occur with sotalol or occasionally propranolol. Conventional treatment is with magnesium, isoprenaline, or cardiac pacing. Magnesium has calcium channel blocking effects and is potentially hazardous as it may further impair cardiac conduction and contractility. It should be used with great caution if at all. Isoprenaline or cardiac pacing to achieve a heart rate of 120-140 bpm is the safest option.+**Arrhythmias**\\ 
 +Ventricular tachycardia (polymorphic VT, torsades de pointes) may occur with sotalol or occasionally propranolol. Conventional treatment is with magnesium, isoprenaline, or cardiac pacing. Magnesium has calcium channel blocking effects and is potentially hazardous as it may further impair cardiac conduction and contractility. It should be used with great caution if at all. Isoprenaline or cardiac pacing to achieve a heart rate of 120-140 bpm is the safest option. 
 +<code> Unsure about this due to very high target HR, and probably should caveat with needing invasive BP monitoring? </code>
  
 ==== - Observation/disposition ==== ==== - Observation/disposition ====
  
 ===== - Prognosis ===== ===== - Prognosis =====
- +Occasional late complications/deterioration have been reported generally in patients who have had significant poisoning. It is likely that these relate to too rapid withdrawal of treatment. Long term sequelae have not been reported and no follow up is required after resolution of the clinical signs or ECG findings, unless the patient has been profoundly hypotensive.
-Occasional late complications/deterioration have been reported generally in patients who have had significant poisoning. It is likely that these relate to too rapid withdrawal of treatment. Long term sequelae have not been reported and no follow up is required after resolution of the clinical signs - ECG findings unless the patient has been profoundly hypotensive.+
  
 ===== - References ===== ===== - References =====