Dawes: Beta Blocker Drugs Flashcards
When is a beta blocker used?
When a patient is suffering from…
- Hypertension
- Angina
- Heart Failure
- Arrhythmias (AF-rate control, Atrial Flutter, SVT-termination )
- Thyrotoxicosis (symptoms)
- Migraine Prophylaxis
- Anxiety
What are the functions of adrenergic receptors?
What does activation of the beta receptors on the postsynaptic membrane result in?
What are the differences in action of between differing beta blockers?
- Selectivity (B1 or B2 - is relative and all will slightly do both)
- Elimination - Renal vs Hepatic -(lipid soluable agents)
- Half-Life - often altered so are slow release (lipophilic naturally have short T1/2)
- Solubility - Water vs Lipid
What are the specifics for the drug metoprolol?
This is a Beta-1 blocker that is lipid soluble and undergoes hepatic elimination.
What are the specifics for the drug atenolol?
This is a Beta-1 blocker than it polar and undergoes renal elimination.
What are the specifics for the drug propanolol?
This is a Beta-1 and Beta-2 blocker that is lipid soluble and undergoes hepatic elimination.
What are the specifics for the drugs carvedilol and labetalol?
These are both beta-1 and beta-2 blockers but also act as alpha blockers.
Carvedilol also acts as an antioxidant.
What are the pharmacokinetics of beta-blockers?
They are well absorbed orally and available as sustained release and iv preparations.
They have variable distribution and metabolism because of the variability they show in their lipophilicity. Propanolol and metoprolol both have high lipophilicity and therefore are eliminated by the liver, whereas, atenolol has a low lipophilicity and is eliminated by the kidneys.
Have half-lives of around 2 to 5 hours.
What does an increase in the lipophilicity mean for the drug?
As lipophilicity increases the drugs ability to cross the blood-brain-barrier also increases. This also means that it has extensive and rapid gut absorption, presystemic metabolism and high protein binding.
What is esmolol?
This is a drug that shows beta-1 selectivity, has a low lipid solubility, is eliminated by blood esterases and so is used in emergency situations (eg AAA) for rapidly lowering BP through a constant infusion.
What are the pharmacodynamic effects of beta-blockers on the CVS system?
- They are BP lowering, however, the mechanism of how this effect comes about is unclear. They do act to
- reduce cardiac output,
- reset baroreceptors,
- inhibit renin releases
- reduce sympathetic activity.
- presynaptic effects on reducing norepinephrine release.
- They are negative chronotropic as they reduce SA node firing and AV node transmission.
- Negatively inotropic acutely(need to remove excess fluid before..) but positively inotropic with chronic use
What are the pharmacodynamic effects of beta-blockers on the respiratory system?
They are beta-2 antagonists and therefore are contraindicated in asthmatics. This is because the beta-2 receptors are involved in bronchi relaxation.
Fine for COPD patients!!
What are the pharmacodynamic effects of beta-blockers on the eye?
They reduce the production of aqueous humour and therefore you may get dry eyes. As a result, this is given topically for glaucoma.
What are the pharmacodynamic effects of beta-blockers on metabolism?
It reduces glycogenolysis which is under the control of beta-2 receptors and so have hypoglycaemic events easier in diabetics - also because they have SNS block you don’t get as much of the sweating etc reducing the symptoms that warn people.