Pharmacology
This was previously featured in an exam
Cardiovascular
A 32 year old presents to ED with palpitations ongoing for the past 5 days. ECG demonstrates atrial fibrillation with a rate of 165 bpm with no adverse features. He has a known history of asthma. Which of the following beta-blockers is safest for a patient with a history of asthma:
Answer:
Beta-blockers can precipitate bronchospasm and should therefore usually be avoided in patients with a history of asthma. When there is no suitable alternative, it may be necessary for a patient with well-controlled asthma, or chronic obstructive pulmonary disease (without significant reversible airways obstruction), to receive treatment with a beta-blocker for a co-existing condition (e.g. heart failure or following myocardial infarction). In this situation, a cardioselective beta-blocker should be selected and initiated at a low dose by a specialist; the patient should be closely monitored for adverse effects. Atenolol, bisoprolol fumarate, metoprolol tartrate, nebivolol, and (to a lesser extent) acebutolol, have less effect on the beta2 (bronchial) receptors and are, therefore, relatively cardioselective, but they are not cardiospecific. They have a lesser effect on airways resistance but are not free of this side-effect.Beta-Blockers
Pharmacology / Cardiovascular
Last Updated: 23rd April 2020
Beta-blockers block the beta-adrenoceptors in the heart, peripheral vasculature, bronchi, pancreas and liver.
Therapeutic Effects
- Cardiovascular system
- Reduce blood pressure
- Reduce heart rate, contractility and cardiac output
- Increase AV conduction time, refractoriness and suppress automaticity
- Eye
- Reduce intraocular pressure
- Respiratory system
- Cause bronchoconstriction
Type Examples
Many beta-blockers are now available and in general they are all equally effective. There are, however, differences between them, which may affect choice in treating particular diseases or individual patients.
Sotalol hydrochloride, a non-cardioselective beta-blocker with additional class III antiarrhythmic activity, is used for prophylaxis in paroxysmal supraventricular arrhythmias. It also suppresses ventricular ectopic beats and nonsustained ventricular tachycardia. It has been shown to be more effective than lidocaine in the termination of spontaneous sustained ventricular tachycardia due to coronary disease or cardiomyopathy. However, it may prolong the QT-interval and induce torsade de pointes in susceptible patients.
Labetalol has, in addition to other beta-blocker effects, an arteriolar vasodilating action by diverse mechanisms, and thus lowers peripheral resistance. Labetalol is useful for treating hypertensive emergencies and in the treatment of hypertension of pheochromocytoma.
Esmolol hydrochloride is a relatively cardioselective beta-blocker with a very short duration of action, used intravenously for the short-term treatment of supraventricular arrhythmias, sinus tachycardia, or hypertension, particularly in the perioperative period.
Indications
Beta-blockers may be indicated in:
- Hypertension
- Pheochromocytoma (only with an alpha-blocker)
- Angina
- Secondary prevention after ACS
- Arrhythmias including atrial fibrillation
- Heart failure
- Thyrotoxicosis
- Anxiety
- Prophylaxis of migraine
- Essential tremor
- Glaucoma
Contraindications
Beta-blockers are contraindicated in people with:
- A history of asthma or bronchospasm.
- Beta-blockers can precipitate bronchospasm and should therefore usually be avoided in patients with a history of asthma. When there is no suitable alternative, it may be necessary for a patient with well-controlled asthma, or chronic obstructive pulmonary disease (without significant reversible airways obstruction), to receive treatment with a beta-blocker for a co-existing condition (e.g. heart failure or following myocardial infarction). In this situation, a cardioselective beta-blocker should be selected and initiated at a low dose by a specialist; the patient should be closely monitored for adverse effects. Atenolol, bisoprolol fumarate, metoprolol tartrate, nebivolol, and (to a lesser extent) acebutolol, have less effect on the beta2 (bronchial) receptors and are, therefore, relatively cardioselective, but they are not cardiospecific. They have a lesser effect on airways resistance but are not free of this side-effect.
- Reversible or severe COPD
- Known intolerance or hypersensitivity to beta-blockers
- Severe or symptomatic bradycardia (heart rate less than 60 beats per minute)
- Sinoatrial block, second- or third-degree heart block (unless there is a pacemaker in place)
- Severe or uncontrolled heart failure
- Severe or symptomatic hypotension (systolic blood pressure less than 90 mmHg)
- Severe peripheral arterial disease (including intermittent claudication) or Raynaud's syndrome
- Sick sinus syndrome
- Cardiogenic shock or phaeochromocytoma (without a concomitant alpha-blocker)
- Frequent episodes of hypoglycaemia
Cautions
Beta-blockers should be used with caution in people with:
- Heart failure with chronic kidney disease (CKD), hypotension, ischaemic heart disease, or less severe peripheral arterial disease
- Prinzmetal's angina
- Current or recent (within 4 weeks) exacerbation of heart failure
- First-degree atrioventricular heart block
- Portal hypertension (risk of deterioration in liver function)
- Diabetes mellitus (affects carbohydrate metabolism and symptoms of hypoglycaemia may be masked)
- COPD
- Myasthenia gravis
- Psoriasis
- Thyrotoxicosis (symptoms may be masked)
- People who wear contact lenses (reduced secretion of lacrimal fluid)
- Chronic kidney disease
Side Effects
- Deteriorating symptoms of heart failure (such as symptoms of fluid overload and fatigue)
- Hypotension and bradycardia
- Dizziness, headache, and syncope
- Nausea, vomiting, diarrhoea, and constipation
- Sexual dysfunction including erectile dysfunction and loss of libido
- Cold extremities, paraesthesia, and numbness (more common in people with peripheral arterial disease)
- Effect on carbohydrate metabolism (hypo- or hyperglycaemia in people with or without diabetes mellitus)
- Effect on metabolic and autonomic response to hypoglycaemia (possible masking of hypoglycaemia warning signs such as tremor and tachycardia)
- Fatigue and asthenia (lack of energy and strength)
- Sleep disturbance, nightmares, and depression
- Bronchospasm
- Reduction of secretion of lacrimal fluid (may affect people who wear contact lenses)
Report A Problem
Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.
Loading Form...
- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
