Pharmacodynamics and Receptor Profile
A key feature of bisoprolol is its high cardioselectivity. The cardioselectivity index for this drug is 75. This means it blocks \(\beta_1\)-adrenergic receptors (predominantly localized in the heart) 75 times more strongly than \(\beta_2\)-adrenergic receptors.
However, an important pharmacological principle applies to this agent: cardioselectivity is not absolute. As the administered dose increases, the selectivity of the drug decreases, and it begins to block not only target \(\beta_1\) receptors but also \(\beta_2\) receptors.
Pharmacokinetics: Absorption and Distribution
Physicochemically, bisoprolol is a lipophilic compound. This characteristic largely determines its disposition in the body:
- Absorption: The drug is readily absorbed from the gastrointestinal tract after oral administration.
- Bioavailability: Reaches high values (approximately 90%).
- First-pass effect: Unlike many other drugs, bisoprolol undergoes minimal metabolism during its initial passage through the liver, which ensures its high systemic bioavailability.
Metabolism, Elimination, and Dosing Regimen
The drug is characterized by a balanced clearance. This means its elimination from the body occurs equally through two pathways: hepatic metabolism and renal excretion.
Elimination has the following features:
- It is carried out predominantly by the kidneys.
- Exactly 50% of the administered dose is excreted unchanged.
- The remaining fraction is eliminated as inactive metabolites.
Pharmacokinetic time parameters are very convenient for patients. The half-life (\(T_{1/2}\)) ranges from 10 to 12 hours. This maintains a stable therapeutic regimen—the drug is prescribed once daily, and its absorption efficiency is completely independent of food intake.
Indications and Adverse Reactions
In medical practice, bisoprolol is prescribed for the following cardiovascular pathologies:
- Hypertension.
- Stable angina pectoris.
- Chronic heart failure (CHF) — used as part of combination therapy for mild-to-moderate disease.
Regarding side effects, special attention should be paid to the central nervous system. Because bisoprolol is a lipophilic compound, it can cross biological barriers into brain tissue, potentially causing central nervous system-related adverse effects.