Sympathomimetics MCQs

Nadolol has a half-life of 12 to 24 h and would be the best agent for beta-blockade in a patient who is undergoing a long duration surgical procedure. A single intra-operative dose should suffice the entire case. Acebutolol has a 3- to 4-h half-life. Esmolol has a 10-min half-life. It is the shortest acting Beta-blocker. Metoprolol has a 3- to 4-h half-life. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung, Pg no. 166.

Glucagon acts through cardiac glucagon receptors to stimulate the rate and force of contraction of the heart. Because this bypasses cardiac β adrenoceptors, glucagon is useful in the treatment of β-blocker-induced cardiac depression. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 757

This patient has most likely overdosed on beta blocker medications. Beta blocker overdose causes diffuse non-selective blockade of peripheral beta adrenergic receptors, causing depression of myocardial contractility, bradycardia, and varying degrees of AV block. The result is a low cardiac output state. Glucagon is the drug of choice for beta blocker overdose. Glucagon acts on G protein-coupled receptors, increasing intracellular CAMP and thus increasing the release of intracellular calcium during muscle contraction. This increases heart rate and cardiac contractility. Improvements in heart rate and blood pressure may be observed within minutes. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg. no. 192

In the periphery, cocaine it blocks uptake of NA and Adr intoadrenergic nerve endings, resulting in higher concentration of the transmitter around the receptors → sympathomimetic effect, potentiation of directly acting sympathomimetics and suppression of indirectly acting sympathomimetics. Local vasoconstriction, tachycardia, rise in BP and mydriasis are the manifestations of its sympathomimetic action.

Given clinical scenario of patient's rash, swelling, and difficulty breathing shortly after exposure to bee's stung are suggestive of anaphylaxis. In this case, start initial treatment immediately by administering epinephrine IM 1:1,000 (1 mg/mL) into the anterolateral thigh. Epinephrine injections for anaphylaxis should always be given intramuscularly in a concentration of 1:1,000 (Option B is correct) Option C: Epinephrine 1:10,000 solution used in cardiac arrest through IV route. Injecting the 1:1,000 solution into a vein can lead to cardiac arrhythmia/arrest. Option A & D: Antihistamines and corticosteroids are sometimes used as supplementary agents, but the prompt parenteral use of epinephrine is mandatory and lifesaving, thus it's treatment of choice for anaphylaxis. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung, Pg no. 147.

Of the agents given in option, only phenylephrine has the actions described. Phenylephrine is a selective alpha-1 adrenergic receptor agonist that causes marked arterial vasoconstriction when administered intravenously. The result is an increase in systemic vascular resistance and blood pressure. The induced blood pressure increase elicits a baroreceptor-mediated increase in vagal tone, which results in decreased stroke volume and a slowed heart rate. The pulse pressure, defined as the systolic pressure minus the diastolic pressure, is decreased by phenylephrine because of the reflex decrease in stroke volume and the increased afterload. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg. no. 194

This patient is hypertensive despite the use of the ACE inhibitor enalapril, an appropriate diet, and an exercise program. The physician then prescribes a second antihypertensive medication. A beta blocker was likely chosen since the use of a thiazide or loop diuretic is contraindicated in this patient due to a severe sulfa allergy. B1-selective antagonists are often used to control hypertension in patients, such as asthmatics, who might experience bronchoconstriction with nonselective beta antagonists (e.g., propranolol). Remember that beta1 receptors predominate in the heart, while B2 receptors predominate in the lungs. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 187

Explanation: Esmolol is an ultra- short-acting cardioselective beta-1 blocker. Its exceptionally short half-life (~9 minutes) is due to rapid metabolism by erythrocyte esterases . This makes it ideal for use in critical care settings (e.g., supraventricular tachycardia, perioperative hypertension) where precise, short-duration beta-blockade is required. Explanation of other options: Nadolol (Option A): A long-acting, non-selective beta-blocker. Propranolol (Option B): A non-selective beta-blocker with an intermediate half-life. Atenolol (Option D): A cardioselective beta-blocker with a longer half-life, suitable for once-daily dosing. Key Takeaways: Esmolol's short duration of action is due to metabolism by esterases in the blood. It is the beta-blocker of choice when a rapidly titratable and reversible effect is needed.