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| __NOTOC__
| | #REDIRECT [[Esmolol#Pharmacology]] |
| {{Esmolol}}
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| {{CMG}}; {{AE}} {{AZ}}
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| ==CLINICAL PHARMACOLOGY==
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| ===Mechanism of Action===
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| BREVIBLOC (Esmolol Hydrochloride) is a [[beta1]]-selective (cardioselective)[[ adrenergic]] receptor blocking agent with rapid onset, a very short duration of action, and no significant intrinsic sympathomimetic or membrane stabilizing activity at therapeutic dosages. Its elimination half-life after intravenous infusion is approximately 9 minutes. BREVIBLOC inhibits the [[beta1]] receptors located chiefly in cardiac muscle, but this preferential effect is not absolute and at higher doses it begins to inhibit [[beta2]] receptors located chiefly in the bronchial and vascular musculature.
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| ===Pharmacodynamics===
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| Clinical pharmacology studies in normal volunteers have confirmed the beta blocking activity of BREVIBLOC, showing reduction in heart rate at rest and during exercise, and attenuation of [[isoproterenol]]-induced increases in heart rate. Blood levels of BREVIBLOC have been shown to correlate with extent of beta blockade. After termination of infusion, substantial recovery from beta blockade is observed in 10-20 minutes. The acid metabolite of esmolol exhibits negligible pharmacological activity.
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| In human electrophysiology studies, BREVIBLOC produced effects typical of a [[beta blocker]]: a decrease in the [[heart rate]], increase in [[sinus cycle]]length, prolongation of the [[sinus node]] recovery time, prolongation of the AH interval during normal [[sinus rhythm]] and [[during atrial pacing]], and an increase in antegrade[[ Second degree AV block pathophysiology#Mobitz Type I|Wenckebach cycle ]]length.
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| In patients undergoing [[radionuclide angiography]], BREVIBLOC, at dosages of 200 mcg/kg/min, produced reductions in heart rate, [[systolic blood pressure]], rate pressure product, left and right ventricular[[ ejection fraction]] and [[cardiac index]] at rest, which were similar in magnitude to those produced by intravenous [[propranolol]] (4 mg). During exercise, BREVIBLOC produced reductions in [[heart rate]], rate pressure product and cardiac index which were also similar to those produced by [[propranolol]], but BREVIBLOC produced a significantly larger fall in [[systolic blood pressure]]. In patients undergoing [[cardiac catheterization]], the maximum therapeutic dose of 300 mcg/kg/min of BREVIBLOC produced similar effects and, in addition, there were small, clinically insignificant increases in the [[left ventricular end diastolic pressure]] and pulmonary [[capillary wedge pressure]]. At 30 minutes after the discontinuation of BREVIBLOC infusion, all of the hemodynamic parameters had returned to pretreatment levels.
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| The relative cardioselectivity of BREVIBLOC was demonstrated in 10 mildly asthmatic patients. Infusions of BREVIBLOC 100, 200 and 300 mcg/kg/min produced no significant increases in specific airway resistance compared to placebo. At 300 mcg/kg/min, BREVIBLOC produced slightly enhanced bronchomotor sensitivity to dry air stimulus. These effects were not clinically significant, and BREVIBLOC was well tolerated by all patients. Six of the patients also received intravenous [[propranolol]], and at a dosage of 1 mg, two experienced significant, symptomatic bronchospasm requiring [[bronchodilator]] treatment. One other[[ propranolol]]-treated patient also experienced dry air-induced[[ bronchospasm]]. No adverse pulmonary effects were observed in patients with [[COPD]] who received therapeutic dosages of BREVIBLOC for treatment of [[supraventricular tachycardia]] (51 patients) or in perioperative settings (32 patients).
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| ===Pharmacokinetics===
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| Esmolol is rapidly metabolized by hydrolysis of the ester linkage, chiefly by the esterases in the cytosol of red blood cells and not by plasma [[cholinesterase]]s or red cell membrane acetylcholinesterase. Total body clearance in man was found to be about 20 L/kg/hr, which is greater than cardiac output; thus the metabolism of esmolol is not limited by the rate of blood flow to metabolizing tissues such as the liver or affected by hepatic or renal blood flow. Esmolol has a rapid distribution half-life of about 2 minutes and an elimination half-life of about 9 minutes. | |
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| Using an appropriate loading dose, steady-state blood levels of BREVIBLOC for dosages from 50-300 mcg/kg/min are obtained within five minutes. Steady-state is reached in about 30 minutes without the loading dose. Steady-state blood levels of esmolol increase linearly over this dosage range and elimination kinetics are dose-independent over this range. Steady-state blood levels are maintained during infusion but decrease rapidly after termination of the infusion. Because of its short half-life, blood levels of esmolol can be rapidly altered by increasing or decreasing the infusion rate and rapidly eliminated by discontinuing the infusion.
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| Consistent with the high rate of blood-based metabolism of esmolol, less than 2% of the drug is excreted unchanged in the urine. Within 24 hours of the end of infusion, the acid metabolite of esmolol in urine accounts for approximately 73-88% of the dosage.
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| Metabolism of esmolol results in the formation of the corresponding free acid and [[methanol]]. The acid metabolite has been shown in animals to have negligible activity and in normal volunteers its blood levels do not correspond to the level of beta blockade. The acid metabolite has an elimination half-life of about 3.7 hours and is excreted in the urine with a clearance approximately equivalent to the [[glomerular filtration rate]]. After a 4 hour maintenance infusion of 150 mcg/kg, the plasma concentrations of esmolol are similar in subjects with normal renal function and in patients with [[ESRD]] on [[dialysis]]. The half-life of the acid metabolite of BREVIBLOC, which is primarily excreted unchanged by the kidney, is increased about 12-fold to 48 hours in patients with ESRD. The peak concentrations of the acid metabolite are doubled in ESRD.
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| [[Methanol ]]blood levels, monitored in subjects receiving BREVIBLOC for up to 6 hours at 300 mcg/kg/min and 24 hours at 150 mcg/kg/min, approximated endogenous levels and were less than 2% of levels usually associated with [[methanol toxicity]].
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| BREVIBLOC has been shown to be 55% bound to human plasma protein, while the acid metabolite is only 10% bound.<ref name="dailymed.nlm.nih.gov">{{Cite web | last = | first = | title = BREVIBLOC (ESMOLOL HYDROCHLORIDE) INJECTION [BAXTER HEALTHCARE CORPORATION] | url =http://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=595cc3d5-1306-4828-aefa-5595219ffd62 | publisher = | date = | accessdate = }}</ref>
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| ==References==
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| {{Reflist}}
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| {{FDA}}
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| | [[Category:Beta blockers]] |
| | [[Category:Cardiovascular Drugs]] |
| [[Category:Drugs]] | | [[Category:Drugs]] |