SEARCH RESULTS FOR: Beta-Blockers-Mechanism-of-Action-and-Side-Effects

Beta-Blockers-Mechanism-of-Action-and-Side-Effects

Beta-Blockers: Mechanism of Action and Side Effects Two classes of “Beta-Blockers” are used clinically: Non-cardio-selective: binds Cardio-selective: binds largely beta-1 and beta-2 receptors to beta-1 receptors Authors: Tegan Evans, Davis Maclean, Yan Yu* Reviewers:, Amanda Nguyen, P. Timothy Pollak*, Sean Spence* * MD at time of publication Beta blockers bind to beta 1 and/or beta 2-receptors of various tissues throughout body, and thus competitively inhibit binding of sympathetic adrenergic molecules (such as catecholamines from the adrenal medulla, e.g. epinephrine) to these receptors, ↓ their normal adrenergic tone Beta-2 receptor antagonism Beta-1 receptor antagonism Lungs Eyes Central nervous system Heart Kidneys ↓ cAMP (intracellular messenger) productionàcomplex, tissue-specific intracellular mechanisms resulting in a variety of effects in different tissues: Throughout body tissue Epinephrine (via cAMP) indirectly ↑ the activity of the Na+/K+ pump on cell membranes (a pump that moves 3 Na+ out of cells per 2 K+ moved into cells) Blocking epinephrine from binding the beta-2 receptor and producing cAMPà↓ activity of Na+/K+ pump à↓K+ moved into cells ↑ proportion of K+ now resides in extracellular fluid, detectable in serum (total body K+ remains the same) Hyperkalemia (see Calgary Guide: Hyperkalemia – Clinical findings) Blocking sympathetic hormonesà↓ relaxation of smooth muscle circumferentially wrapped around airways ↑ resting airway muscle toneà bronchoconstriction ↑ resistance to airflow Wheezing, dyspnea, chest tightness Exacerbation of underlying airway disease (e.g. asthma) ↓ ciliary epithelium’s production of aqueous humor (fluid that fills anterior chamber of the eye) Reduced intraocular pressure Blocking adrenergic response mediated by epinephrine and norepinephrine (e.g. the physiologic “fight- or-flight” response to stress) ↓ tremor, irritability, anxiety ↓ ability to produce adrenergic symptoms in response to hypoglycemia Hypoglycemia unawareness Coronary perfusion pressure = diastolic blood pressure in aorta – LV end diastolic pressure ↓ inotropy (contractility of cardiac muscle) ↓ chronotropy (heart rate and conduction velocity) ↓ renin releaseà↓ creation of angiotensin II & aldosterone + ↓ reabsorption of Na and H2O in nephron ↑ urinary Na+ & H2O loss ↓ total blood volume Decompensation of acute heart failure Dizziness and fatigue Hypotension (Blood pressure = cardiac output x systemic vascular resistance) ↓ O2 demand of myocardial tissue Bradycardia Inability to ↑ heart rate in response to stress (e.g. shock, sepsis) ↓ stroke volume ↓ cardiac output Beta blockers ↓ diastolic blood pressure, & thus may ↓ coronary perfusion pressure Before giving beta blockers, ensure blood pressure isn’t too low Otherwise, may worsen acute myocardial ischemia Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published Jan 14, 2021, updated Feb 7, 2021 on www.thecalgaryguide.com