l fumarate is a long-acting selective beta2-adrenergic agonist (beta2-agonist) with a rapid onset of action. Inhaled formoterol fumarate acts locally in the lung as a bronchodilator. In vitro studies have shown that formoterol has more than 200-fold greater agonist activity at beta2-receptors than at beta1-receptors. The in vitro binding selectivity to beta2- over beta1-adrenoceptors is higher for formoterol than for albuterol (5 times), whereas salmeterol has a higher (3 times) beta2-selectivity ratio than formoterol.
Although beta2-receptors are the predominant adrenergic receptors in bronchial smooth muscle and beta1-receptors are the predominant receptors in the heart, there are also beta2-receptors in the human heart comprising 10% to 50% of the total beta-adrenergic receptors. The precise function of these receptors has not been established, but they raise the possibility that even highly selective beta2-agonists may have cardiac effects.
The pharmacologic effects of beta2-adrenoceptor agonist drugs, including formoterol fumarate, are at least in part attributable to stimulation of intracellular adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3', 5'-adenosine monophosphate (cyclic AMP). Increased cyclic AMP levels cause relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells.
In vitro tests show that formoterol fumarate is an inhibitor of the release of mast cell mediators, such as histamine and leukotrienes, from the human lung. Formoterol fumarate also inhibits histamine-induced plasma albumin extravasation in anesthetized guinea pigs and inhibits allergen-induced eosinophil influx in dogs with airway hyper-responsiveness. The relevance of these in vitro and animal findings to humans is unknown.
12.2. Pharmacodynamics
Cardiovascular effects: Healthy Subjects
The potential for QTc interval prolongation was assessed in a double-blind, single-dose, placebo- and positive-controlled crossover trial in 69 healthy subjects. The largest mean (90% upper confidence bound) differences from placebo in baseline-corrected QTcI for 2 inhalations of BEVESPI AEROSPHERE and glycopyrrolate/formoterol fumarate 72/19.2 mcg, were 3.1 (4.7) ms and 7.6 (9.2) ms, respectively, and excluded the clinically relevant threshold of 10 ms.
A dose-dependent increase in heart rate was also observed. The largest mean (90% upper confidence bound) differences from placebo in baseline-corrected heart rate were 3.3 (4.9) beats/min and 7.6 (9.5) beats/min seen within 10 minutes of dosing with 2 inhalations of BEVESPI AEROSPHERE and glycopyrrolate/formoterol fumarate 72/19.2 mcg, respectively.
Chronic Obstructive Pulmonary Disease
The effect of glycopyrrolate/formoterol fumarate on cardiac rhythm in subjects with COPD was assessed using 24-hour Holter monitoring in 2-week and 24-week trials. All treatments were administered as two inhalations twice daily. In the 2-week trial, the Holter monitoring population included 58 subjects on glycopyrrolate/formoterol fumarate 18/4.8 mcg, 58 subjects on glycopyrrolate 18 mcg, and 60 subjects on formoterol fumarate 4.8 mcg. In the 24-week trial, the Holter monitoring population included 171 subjects on BEVESPI AEROSPHERE, 160 subjects on glycopyrrolate 9 mcg, 174 subjects on formoterol fumarate 4.8 mcg, and 80 subjects on plac |
