Alpha Receptor Antagonists Flashcards
Phenoxybenzamine
- Action
- Clinical use
- Characteristics
- Adverse effects
- Phenoxybenzamine is a non selective alpha receptor antagonist
- Action:
Cardiovascular:
1. Prevents vasoconstriction of peripheral blood vessels by endogenous catecholamines - this can result in reflex tachycardia
2. Blocks presynaptic inhibitory alpha 2 receptors in the heart so can contribute to increased CO as more NE is released.
Epinephrine reversal:
1.. e.g., vasoconstriction (alpha 1) from E is interrupted, but vasodilation (B2) is not therefore Phenoxybenzamine with EPI decreases BP
Clinical use:
- Pheochromocytoma: before surgery to avoid hypertensive crisis
- Raynaud disease and frostbite
Characteristics:
- Irreversible: the only way to overcome the block is to synthesis new adrenoreceptors which can take more than 1 day.
- Non competitive inhibitor
- Long duration of blockage (14-48 hours)
- Lower efficacy than NE, but same potency
Adverse effects:
- Orthostatic hypotension
- Reflex tachycardia therefore b blockers should be given
- Nasal stuffiness
- Inhibition of ejaculation
- Sedation
Phentolamine
- Action
- Clinical use
- Characteristics
- Adverse effects
- Phentolamine is a non selective alpha receptor antagonist
- Action:
Cardiovascular:
1. Prevents vasoconstriction of peripheral blood vessels by endogenous catecholamines - this can result in reflex tachycardia
2. Blocks presynaptic inhibitory alpha 2 receptors in the heart so can contribute to increased CO as more NE is released.
Epinephrine reversal:
1.. e.g., vasoconstriction (alpha 1) from E is interrupted, but vasodilation (B2) is not therefore Phenoxybenzamine with EPI decreases BP
Clinical use:
- Pheochromocytoma (short term management)
- Dermal necrosis prevention
- Hypertensive crisis due to tyramine ingestion in patients on MAO-A inhibitors.
Characteristics:
- Reversible
- Competitive inhibitors
- Duration: 4h
- Do not use in patients with coronary heart disease
- Lower potency than NE but same efficacy
- Antiserotinergic actions and stimulate the M and H receptors
Adverse effects:
- Orthostatic hypotension
- Arrhythmias
- Angina
Tolazoline
- Tolazoline is a non- selective alpha receptor antagonist
Clinical use:
- Peripheral vascular disease as a vasodilator
Characteristics:
- Weak effect
- Very limited indications
- Synthetic
- Antiserotinergic actions and stimulate the M and H receptors
Prazosin
Doxazosin
Terazosin
- Action
- Clinical use
- Characteristics
- Adverse effects
- They are selective alpha 1 receptor antagonists
Clinical use:
- Hypertension
- BPH - Relieve urinary retentions, but don’t decrease prostate size
Characteristics:
- Orally active
- Short half life (have to give 3 a day for Prazosin - the other two last a little longer)
- Treatment should be started at bed time to prevent the first dose phenomenon
Adverse effects:
- 1st dose phenomenon: in the beginning of therapy, orthostatic hypotension and syncope
- Dizziness
- Palpitations
- Headache
Alfusosin
Tamsulosin
- Clinical use
- Characteristics
- Adverse effects
- These are selective alpha 1 receptor antagonists
Clinical use:
- BPH
Characteristics:
- Selective for alpha 1A receptor; which is mainly expressed along the urinary tract
Adverse effects:
- 1st dose phenomenon: in the beginning of therapy, orthostatic hypotension and syncope
- Dizziness
- Palpitations
- Headache
Urapidil
- Action
- Clinical use
- Adverse effects
- Urapidil is a selective alpha 1 receptor antagonist
Action:
- alpha 1 antagonist, weak alpha 2 agonist, 5-HT 1A agonist and B antagonist actions
Clinical use:
- Hypertension (mainly hypertensive crisis)
Adverse effects:
- 1st dose phenomenon: in the beginning of therapy, orthostatic hypotension and syncope
- Dizziness
- Palpitations
- Headache
Labetalol
Carvedilol
- Clinical use
- Characteristics
- Adverse effects
- These are selective alpha 1 receptor antagonists
Clinical use:
- Hypertension
Characteristics
- These are also used as beta blockers (beta receptor antagonist action).
Adverse effects:
- 1st dose phenomenon: in the beginning of therapy, orthostatic hypotension and syncope
- Dizziness
- Palpitations
- Headache
Yohimbine
- Action
- Clinical Use
- Characteristic
- Adverse effects
- Yohimbine is a selective alpha 1 antagonist
Action:
- Centrally it increases SY outflow
Clinical use:
- Used in ED
- Hypotension
Characteristic:
- Competitive inhibitor
Adverse effects: Do not use in: 1. Cardiovascular diseases 2. Psychiatric conditions 3. Renal dysfunction
Mirtazapine
- Action
- Clinical use
- Adverse effects
- Mirtazapine is a selective alpha 2 receptor antagonist
Action:
- Central action
Clinical use:
- Antidepressant
- Anorexia
Adverse effects:
- Weight gain
When do you not use Yohimbine?
Do not use in:
- Cardiovascular diseases
- Psychiatric conditions
- Renal dysfunction
What are the characteristics of Tolazoline?
Characteristics:
- Weak effect
- Very limited indications
- Synthetic
- Antiserotinergic actions and stimulate the M and H receptors
