Bisoprolol

Side effects

An overdose of bisoprolol can lead to fatigue, hypotension, hypoglycemia, bronchospasms, and bradycardia. Bronchospasms and hypoglycemia occur because at high doses, the drug can be an antagonist for β₂ adrenergic receptors located in the lungs and liver. Bronchospasm occurs due to the blockage of β₂ receptors in the lungs. Hypoglycemia occurs due to decreased stimulation of glycogenolysis and gluconeogenesis in the liver via β₂ receptors.

There have been no reported cases of clinically evident drug-induced liver injury associated with bisoprolol.

Cautions

Non-selective beta-blockers should be avoided in people with asthma or bronchospasm as they may cause exacerbations and worsening of symptoms. β₁ selective beta-blockers like bisoprolol have not been shown to cause an increase in asthma exacerbations, and may be cautiously tried in those with controlled, mild-to-moderate asthma with cardiac comorbidities.

A 2014 meta-analysis found that unlike non-selective beta-blockers, β₁ selective beta-blockers (bisoprolol) showed only a small impact on lung function, with patients remaining responsive to salbutamol (β₂ -agonist) rescue therapy and endorses the use of bisoprolol in select patients with controlled asthma. This was supported by a 2020 clinical trial where bisoprolol had no significant impact on bronchodilation post salbutamol administration.

Pharmacology

Mechanism of action

Bisoprolol is cardioprotective because it selectively and competitively blocks catecholamine (adrenaline) stimulation of β₁ adrenergic receptors (adrenoreceptors), which are mainly found in the heart muscle cells and heart conduction tissue (cardiospecific), but also found in juxtaglomerular cells in the kidney. Normally, adrenaline and noradrenaline stimulation of the β₁ adrenoreceptor activates a signalling cascade (Gs protein and cAMP) which ultimately leads to increased myocardial contractility and increased heart rate of the heart muscle and heart pacemaker, respectively.

Bisoprolol competitively blocks the activation of this cascade, so decreases the adrenergic tone/stimulation of the heart muscle and pacemaker cells. Decreased adrenergic tone shows less contractility of heart muscle and lowered heart rate of pacemakers.

β1-selectivity

Bisoprolol β₁-selectivity is especially important in comparison to other nonselective beta blockers. The effects of the drug are limited to areas containing β₁ adrenoreceptors, which are mainly the heart and part of the kidney. Bisoprolol, whilst β₁ adrenoceptor selective can help patients to avoid certain side-effects associated with non-selective beta-blocker activity at additional adrenoceptors (α₁ and β₂), it does not signify its superiority in treating beta-blocker indicated cardiac conditions such as heart failure but could prove beneficial to patients with specific comorbidities.

Bisoprolol has a higher degree of β₁-selectivity compared to atenolol, metoprolol and betaxolol. With a selectivity ranging from being 11 to 15 times more selective for β₁ over β₂. However, nebivolol is approximately 3.5 times more β₁-selective.

Renin-angiotensin system

Bisoprolol inhibits renin secretion by about 65% and tachycardia by about 30%.

Pharmacokinetics

After ingestion, bisoprolol is absorbed and has a high bioavailability of approximately 90% with a plasma half-life of 10–12 hours. Typically, half the circulating bisoprolol is metabolized by the liver, the rest passing unchanged through the kidneys before elimination; less than 2% may be excreted in the feces.

Bisoprolol is soluble in both lipids and water. It is classified as a beta blocker with moderate lipophilicity and hence intermediate potential for crossing the blood–brain barrier. This in turn may result in fewer effects in the central nervous system as well as a lower risk of neuropsychiatric side effects than highly lipophilic beta blockers like propranolol but greater such effects than beta blockers with low lipophilicity like atenolol.

The plasma protein binding of bisoprolol is approximately 35%, the volume of distribution is 3.5 L/kg and the total clearance is approximately 15 L/h. Bisoprolol is eliminated from the body in two ways - 50% of the substance is converted in the liver to inactive metabolites, which are then excreted in the kidneys. The remaining 50% is eliminated unchanged via the kidneys. Since elimination is equal in liver and kidney, no dose adjustment is required in patients with hepatic or renal impairment.

The pharmacokinetics of bisoprolol are linear and independent of age.

In patients with chronic heart failure, the plasma level of bisoprolol is higher and the half-life is longer than in healthy subjects when compared across studies. There is a lack of evidence directly comparing bisoprolol pharmacokinetics between healthy subjects and chronic heart failure subjects.

Chemistry

The experimental log P of bisoprolol is 1.87 to 2.2.