Bisoprolol is a cardioselective β1-adrenergic blocking agent used for secondary prevention of myocardial infarction (MI), heart failure, angina pectoris and mild to moderate hypertension. Bisoprolol is structurally similar to metoprolol, acebutolol and atenolol in that it has two substituents in the para position of the benzene ring. The β1-selectivity of these agents is thought to be due in part to the large substituents in the para position. At lower doses (less than 20 mg daily), bisoprolol selectively blocks cardiac β1-adrenergic receptors with little activity against β2-adrenergic receptors of the lungs and vascular smooth muscle. Receptor selectivity decreases with daily doses of 20 mg or greater. Unlike propranolol and pindolol, bisoprolol does not exhibit membrane-stabilizing or sympathomimetic activity. Bisoprolol possesses a single chiral centre and is administered as a racemic mixture. Only l-bisoprolol exhibits significant β-blocking activity.
Indication
For management of heart failure, angina pectoris, and mild to moderate hypertension and for secondary prevention of myocardial infarction (MI).
Pharmacology
Bisoprolol is a competitive, cardioselective β1-adrenergic antagonist. Activation of β1-receptors (located mainly in the heart) by epinephrine increases heart rate and the blood pressure causing the heart to consume more oxygen. β1-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, β1-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.
Toxicity
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.
Affected Organisms
Humans and other mammals
Biotransformation
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.
Absorption
Well absorbed. Bioavailability > 80%. Absorption is not affected by food. Peak plasma concentrations occur within 2-4 hours.
Half Life
9-12 hours; prolonged in the elderly and those with decreased renal function
Protein Binding
Binding to serum proteins is approximately 30%
Elimination
Eliminated equally by renal and non-renal pathways. Approximately 50% of the total orally administered dose is excreted unchanged in urine with the remainder appearing as inactive metabolites. Less than 2% of the dose is excreted in the feces.
