Bisoprolol selectively blocks catecholamine stimulation of _1-adrenergic receptors in the heart and vascular smooth muscle. This results in a reduction of heart rate, cardiac output, systolic and diastolic blood pressure, and possibly reflex orthostatic hypotension. At higher doses (e.g. 20 mg and greater) bisoprolol may competitively block _2-adrenergic receptors in bronchial and vascular smooth muscle causing bronchospasm and vasodilation.
Bisoprolol is a competitive, cardioselective _1-adrenergic antagonist. Activation of _1-receptors (located mainly in the heart) by epinephrine increases heart rate and the blood pressure causing the heart to consume more oxygen. _1-adrenergic blocking agents such as bisopolol lower the heart rate and blood pressure and may be used to reduce workload on the heart and hence oxygen demands. They are routinely prescribed in patients with ischemic heart disease. In addition, _1-selective blockers prevent the release of renin, a hormone produced by the kidneys causes constriction of blood vessels. Bisoprolol is lipophilic and exhibits no intrinsic sympathomimetic activity (ISA) or membrane-stabilizing activity.
Approximately 50% of the dose is metabolized primarily metabolized by CYP3A4 to inactive metabolites. In vitro studies have shown that bisoprolol is also metabolized by CYP2D6 though this does not appear to be clinically significant. Approximately half the administered dose is excreted in unchanged in urine.
Oral, mouse: LD50 = 100 mg/kg; Skin, rabbit: LD50 = 200 mg/kg; Skin, rat: LD50 = 500 mg/kg. Symptoms of overdose include congestive heart failure (marked by sudden weight gain, swelling of the legs, feet, and ankles, fatigue, and shortness of breath), difficult or labored breathing, low blood pressure, low blood sugar, and slow heartbeat.