Ideally, the clinician should determine the specific beta-blocker involved, the quantity, and the time of the overdose. Unfortunately, these details are often not immediately available. When a history of intentional overdose is lacking, beta-blocker toxicity can go unrecognized as a cause of bradycardia and hypotension. Show Information regarding the patient's underlying medical condition may be a clinical clue to the possibility of an overdose. Hoot et al note the risk of chronic beta-blocker toxicity in patients with impaired clearance. They report such a case in a young woman with end-stage renal disease requiring peritoneal dialysis who was receiving antihypertensive treatment with atenolol, which unlike most beta-blockers is excreted primarily by the kidney, and which is poorly cleared by peritoneal dialysis. She presented with sudden onset of abdominal pain and hemodynamic instability with hypotension and relative bradycardia. [4] Initial evaluationThe initial evaluation of a comatose patient should include consideration of an occult overdose. If a patient is bradycardic and hypotensive, the clinician should consider a beta-blocker or calcium channel blocker overdose. Other associated symptoms may include hypothermia, hypoglycemia, and seizures. Hypoglycemia is relatively uncommon, but it is described in patients with unstable diabetes and in children; beta-blocking drugs may cause hypoglycemia by inhibiting glycogenolysis. Myocardial conduction delays with decreased contractility typify the acute beta-blocker ingestion. Cardiac output may diminish with resulting hypotension from bradycardia and negative inotropy. Hypotension due to the beta2-receptor blockade can be profound and jeopardize myocardial perfusion, creating a downward spiral of events. Beta-blockers that are not sustained-release formulations are all rapidly absorbed from the gastrointestinal tract. The first critical signs of overdose can appear 20 minutes postingestion but are more commonly observed within 1-2 hours. In all clinically significant beta-blocker overdoses, symptoms develop within 6 hours. Although the half-life of these compounds is usually short (2-12 h), half-lives in the overdose patient may be prolonged because of a depressed cardiac output, reduced blood flow to the liver and kidneys, or because of the formation of active metabolites. Saturation kinetics prolong elimination at the type of high plasma concentrations that typically occur with overdose. Delayed absorption from long-acting preparations can significantly increase the apparent elimination half-life. Thus, prolonged effects (>72 h) after massive overdoses are not uncommon. Asymptomatic intoxication occurs mainly in healthy persons with tolerance to these drugs who ingest beta-blockers that lack membrane-stabilizing effects or have a partial agonist effect (eg, pindolol). Individual sensitivity to beta-blockade may be significantly reduced in those patients who have tolerated therapeutic doses of up to 4 g of propranolol daily and in patients who have sustained deliberate overdoses of both practolol and propranolol without serious adverse effects. Conversely, circulatory collapse may occur in patients with preexisting cardiac failure when sympathetic drive is inhibited by even a small dose of a particular beta-blocker. Intermediate toxicity results in a moderate drop in blood pressure (systolic BP >80 mm Hg) and/or bradycardia (heart rate < 60 bpm). BradycardiaBradycardia with associated hypotension and shock (systolic BP < 80 mm Hg, heart rate < 60 bpm) defines severe beta-blocker toxicity. Patients with severe toxicity often manifest extracardiac manifestations of intoxication. Bradycardia, by itself, is not necessarily helpful as a warning sign because slowing of the heart rate and damping of tachycardia in response to stress is observed at therapeutic doses. Although case reports have documented hypotension in the absence of bradycardia, blood pressure usually does not fall before the onset of bradycardia. Bradycardia may be isolated or accompanied by mild conduction disturbances. CNS symptomsA depressed level of consciousness and seizures may occur as a result of cellular hypoxia from poor cardiac output, a direct CNS effect caused by sodium channel blocking, or even as a result of hypoglycemia. The lipid-soluble agents have increased distribution into the brain, and these agents are associated with severe CNS toxicity. Patients who have taken lipid-soluble beta-blockers, such as propranolol, frequently present with seizures after an overdose. Seizures are generalized and may be multiple but are usually brief, lasting seconds to minutes. Seizures occasionally have been reported after therapeutic use of esmolol and with overdose of alprenolol, metoprolol, and oxprenolol. Seizures are far more common after propranolol overdose. Coma may be prolonged, depending on the half-life of the agent involved and the coexisting morbidity. Long-term beta-blocker use has been linked with an acute reversible syndrome characterized by disorientation for time and place, short-term memory loss, emotional lability, a slightly clouded sensorium, and decreased performance on neuropsychometrics. [5] For example, severe memory impairment developed in an 81-year-old woman taking propranolol 20 mg 3 times per day (note that the half-life of propranolol is longer in the elderly and in females). Effects were associated with an elevated propranolol blood level (163 mcg/L) and resolved after discontinuation of the drug. BronchospasmBronchospasm is a rare complication of beta-blocker therapy or overdose but is more likely in patients who already have bronchospastic disease. Sudden fatality following administration of therapeutic doses of beta-blocker has been reported in four patients with asthma. Pulmonary edema had been reported to occur as a result of cardiac failure. Respiratory arrest has also been described with beta-blocker intoxication, especially with propranolol, and is thought to be secondary to a central drug effect.  Differential Diagnoses
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of 2 Tables Back to List Contributor Information and Disclosures Author Adhi Sharma, MD Medical Toxicology Consultant, New York City Poison Control Center Coauthor(s) Lemeneh Tefera, MD, FAAEM Attending Physician, Department of Emergency Medicine, Beth Israel Medical Center Aman Aminzay, MD Attending Physician, Department of Emergency Medicine, Beth Israel Medical Center, Albert Einstein College of Medicine Chief Editor Gil Z Shlamovitz, MD, FACEP Associate Professor of Clinical Emergency Medicine, Keck School of Medicine of the University of Southern California; Chief Medical Information Officer, Keck Medicine of USC Additional Contributors Asim Tarabar, MD Assistant Professor, Director, Medical Toxicology, Department of Emergency Medicine, Yale University School of Medicine; Consulting Staff, Department of Emergency Medicine, Yale-New Haven Hospital Acknowledgements John G Benitez, MD, MPH, FACMT, FAACT, FACPM, FAAEM, Associate Professor, Department of Medicine, Medical Toxicology, Vanderbilt University Medical Center; Managing Director, Tennessee Poison Center John G Benitez, MD, MPH, FACMT, FAACT, FACPM, FAAEM, is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Medical Toxicology, American College of Preventive Medicine, Society for Academic Emergency Medicine, Undersea and Hyperbaric Medical Society, and Wilderness Medical Society Disclosure: Nothing to disclose. David C Lee, MD Research Director, Department of Emergency Medicine, Associate Professor, North Shore University Hospital and New York University Medical School David C Lee, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Medical Toxicology, and Society for Academic Emergency Medicine Disclosure: Nothing to disclose. John T VanDeVoort, PharmD Regional Director of Pharmacy, Sacred Heart & St. Joseph's Hospitals John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists Disclosure: Nothing to disclose. Acknowledgments The authors and editors of Medscape Reference gratefully acknowledge the medical review of this article by Lada Kokan, MD. How low can your heart rate go on metoprolol?A heart rate of 55-60 is not unusual in people taking metoprolol. However, if a person had a heart rate that slow without a beta blocker, a doctor would be concerned that they would eventually develop symptoms from that slow of a heart rate.
Is bradycardia normal on betaBeta-blockers are the most common culprits in causing bradycardia, interfering with slow action potential generation and atrioventricular conduction. They target the sympathetic nervous system and have negative chronotropic and inotropic effects.
What is a dangerously low heart rate?If you have bradycardia, your heart beats fewer than 60 times a minute. Bradycardia can be a serious problem if the heart rate is very slow and the heart can't pump enough oxygen-rich blood to the body. If this happens, you may feel dizzy, very tired or weak, and short of breath.
What heart rate is too low to take propranolol?If your heart rate is lower than 50 beats per minute (while awake) after using propranolol and you are not a trained athlete, you should contact your healthcare provider immediately. A heart rate below this level can lead to fatigue or fainting and typically requires treatment.
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What is a dangerously low heart rate on beta blockers?
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