Adrenergic Antagonists Flashcards
List the classes of adrenergic antagonists
What is the effect of A-adrenergic blockers and list the categories of drugs
Sympathetic control of the vasculature is mainly due to a1-adrenergic receptors. Blockade of these receptors reduces the sympathetic tone of the blood vessels and decreases PVR.
A-adrenergic drugs fall into two (2) categories:
- Non-selective a-adrenergic blockers
- Phenoxybenzamine
- Phentolamine
- a1-selective adrenergic blockers
- Prazosin
- Terazosin
- Doxazosin
- Tamsulosin
1A. Phenoxybenzamine
An irreversible antagonist (blocks both a1 and a2 receptors).
USES
Used in Pheochromocytomas:
- prior to surgical removal of the tumor
- for chronic management of inoperable tumors
- Unsuccessful for treatment of hypertension
1B. Phentolamine
Reversible blocker of a1 and a2 receptors
USES
- Control of hypertension during preoperative preparation and surgical excision
- Diagnosis of pheochromocytoma (Phentolamine blocking test)
- Prevent dermal necrosis after extravasation of norepinephrine
- Can cause hypertensive crisis due to stimulant drug overdose
2A. Prazosin, Terazosin, Doxazosin, Tamsulosin
Selective blockers of a1-receptor with Prazosin as the prototype.
Terazosin and Doxazosin are prazosin analogs with a longer half-life and are prefered for hypertension and BPH.
Tamsulosin is selective for a1A-receptors and is prefered for treatment of BPH. Has little effect on blood pressure. A1A-receptors are predominant in the Genitourinary smooth muscle.
USES
- Treatment of hypertension (but is not the drug of choice)
- Drug of choice to treat symptoms associatd with Benign Prostatic Hyperplasia. It relaxes the smooth muscle in the bladder neck, prostate capsule and prostatic urethra improving urinary flow
CARDIOVASCULAR EFFECTS
- Lowers arterial blood pressure by relaxing both arterial and venous smooth muscle.
- The first dose produces an exaggerated hypotensive response that can resul tin syncope (fainting), headaches and dizziness. Thus the first dose must be 1/3 or 1/4 of the normal dose.
List the categories of ß-adrenergic blockers
- Non-selective ß-blockers
- Propanolol
- Nadolol
- Timolol
- ß1-selective blockers
- Atenolol
- Metoprolol
- Esmolol
- A1 and ß-blockers
- Labetalol
- Carvedilol
- Partial ß-Agonists
* Pindolol
- Non-selective ß-blockers
Block both ß1 and ß2 recpetors.
ß-adrenergic antagonists slow heart rate and decrease myocardial contractility.
Blocking ß2 receptors in the lungs can precipitate a respiratory crisis in patients with COPD or asthma. Therefore, non-selective ß blockers should be avoided in patients with asthma.
They cause decrease in glycogenolysis and gluconeogenesis
- ß1-selective blockers
Atenolol & Metoprolol
- Useful in hypertensive patients with impaired respiratory function.
- Useful in diabetic hypertensive paients who are receiving insulin or oral hypoglycemic agents.
Esmolol
- Short half-life (10 mins)
- Given IV
- Useful for rapid control of ventricular rate in patients with atrial fibrillation or atrial flutter
- A1 and ß-blockers
Labetalol
- Competitive antagonist at ß and A1 receptors
- More potent as a ß-antagonist than as an A-antagonist
- Used to treat hypertension
Carvedilol
- Simlar to labetalol
- Has antioxidant properties
- Used to treat ypertension and Chronic Heart Failure
- Partial ß-antagonists
Pindolol
- Preferential drug for individuals with diminished cardiac reserve or a propensity to bradycardia
List the uses of ß-blockers
1. Hypertension
- They lower blood pressure in hypertension by decreasing cardiac output and blocking renin release
2. Glaucoma
- Timolol is effective in diminishing intraocular pressure in glaucoma
3. Migraine
- Effective in preventing migraines
4. Hyperthyroidism
- They blunt the sympathetic stimulation that occurs in hyperthyroidism
5. Angina Pectoralis
- They decrease O2 requirement of heart muscle
- More useful to treat chronic management of stable angina (not acute angina)
6. Atrial Fibrillation
- They help to control ventricular rate
7. Myocardial Infarction
- They have a protective effect on the myocardium
8. Performance Anxiety
- Prefered treatment over Benzodiazepines (Zantax)
9. Essential Tremor
- Most commonly used drugs to treat action/resting/essential tremors
Describe the adverse effects of ß-blockers
Bronchoconstriction
- Nonselective ß-blockers result in a potentially lethal side effect in asthmatics.
- ß1-selective drugs may be less likely to evoke bronchospasm.
- The selectivity of ß blockers for ß1 receptors is modest and should be avoided if possible in patients with asthma.
Hypoglycemia
- Nonselective ß-blockers may impair recovery from hypoglycemia in insulin-dependent diabetics due to blockade of ß2 receptors in the liver.
- Also, they mask the tachycardia typically seen with hypoglycemia, denying the patient an important warning sign. Therefore, a ß1-selective blocker is preferable.
Lipid metabolism
- Blockade of ß receptors inhibits release of free fatty acids from adipose tissue.
- Both non-selective and β1-selective blockers increase TG and reduce HDL.
- Lipid levels are relatively unaffected by labetalol and partial agonists like pindolol.
CNS Effects
- Sedation
- Dizziness
- Lethargy
- Fatigue
Discuss warnings/precautions associated with ß-blockers
ß-blockers should not be withdrawn abruptly, especially in patients with Coronary Artery Disease. Instead, ß-blocker dose should be withdrawn gradually to avoid acute tachycardia, hypertension, and/or ischmia.
These affects are usually due to up-regulation of ß-receptors.
List the classes of drugs that act presynaptically
- Inhibitors of norepinephrine synthesis
* a-Methyltyrosine (Metyrosine) - Inhibitors of norepinephrine storage
- Reserpine
- Tetrabenazine
- Inhibitors of norepinephrine synthesis
Competitive inhibitor of tyrosine hydroxylase.
USES
- Used for management of malignant pheochromocytoma.
- Used in preoperative preparation of patients for resection of pheochromocytoma.
Discuss the tissues controlled by the ANS in the eye
The eye is a good example of an organ with multiple autonomic functions controlled by multiple autonomic receptors.
