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Alpha adrenergic rcptr
- Alpha 1 receptors:
- Stimulates vasoconstriction and maintenance of blood pressure
- Alpha 2 receptors:
- Found on sympathetic nerve endings - stimulation results in inhibition of release of neurotransmitter from the junction (used to reduce B/P)
Alpha Adrenergic Receptors Agonist
- Action - Mimics the effects of the sympathetic nervous system
- Primarily effects Alpha 1 Receptors
- Treatment of Shock
- Hypotensive states
- Local effects--vasoconstriction (like nasal sprays)
- Phenylephrine (Neosynephrine). Do not give to pt with high BP. In all cold/nasal meds, so just stay away from OTC meds.
Alpha Adrenergic Receptor Agonists Pharmacokinetics
- Ineffective given orally (except Phenylephrin)
- plasma half lives of 1-2 minutes
- Must be given parenterally (IV)
- Must have enough Rx "left over" to prevent IV from going dry and decreasing BP as you prepare the next administration.
SEs of Alpha Adrenergic Agonists
- Excessive increases in blood pressure
- Marked vasoconstriction in extremities, may have to use sonogram to find pulses at extremeties. Pt will probably get cold.
- Cerebral hemorrhage due to increasesd BP. Know pt Hx and watch for signs.
- Urinary retention due to decreased function of smooth muscle.
Alpha adrenerci antagonists
- Action - Blocks alpha adrenergic receptors
- Nonselective - blocks both Alpha 1 and Alpha 2 receptors; binds irreversibily- Very limited clinical use
- Selective - Blocks Alpha 1 receptors
- Treatment of BPH* (benign prostatic hypertrophy)
- Heart failure
- Examples Drugs
- Doxazosin (Cardura)
- Prazosin (Minipress)
- Terazosin (Hytrin)
- *Tamsulosin (Flomax): used for BPH ~70% men over 50yrs have this... the disorder, not the drug. Difficult to get cath. in. Have pt cough--> relaxed musclees and easier to get it in.
SEs of Alpha Bockers
- Orthostatic hypotension, esp after 1st dose
- Take at bedtime to prevent this from occurring. Tell pt to have someone available to to help to bathroom if you get up at night to pee.
- Beta 1 receptors:
- Increase heart rate, speed atrial-ventricular conduction, > strength of cardiac contraction
- Increased secretion of renin--> increased BP and fluid retention.
Basically increases whatever the heart and kidneys would normally do.
- Beta 2 Receptors:
- Relaxation of bronchial smooth muscle
- Vasodilation of blood vessels and shunting of blood in and to skeletal muscle, brain and heart. Redirecting blood from perifery to core.
Relaxation of uterine smooth muscle. Used to prevent premature birth of child. Other effects are complementary to mother and child.
- Action - Binds to and stimulates beta adrenergic receptors
- There are both selective and nonselective drugs
- Isoproterenol (Isuprel)
- Beta 1 Selective
- Dobutamine (Dobutrex): will increase BP
- Beta 2 Selective
- Albuterol (Ventolin, Provental): most popular as an inhaler. Broncodialation, but some beta 1 SEs will accompany (increase HR, BP, shakes). Has an additive effect on beta 1 receptors and decreased effect on beta 2 with excessive use.
- Metaproterenol (Alupent)
- Ritodrine (Yutopar): Used in OB to prevent premature birth
- Salmeterol (Serevent): Used in OB to prevent premature birth.
- Terbutaline (Brethine)
SEs of Beta Agonists
- Increased heart rate
- Cardiac stimulation
- Chest pain (Angina): Heart is not getting enough O2 and lead to...
- Muscle tremors
- Hyperglycemia - metabolic effects on liver and adipose tissue. Check blood sugars, espeically with diabetics and gestational onset diabetes.
- Action - Blockage of Beta 1 receptors leads to:
- Decreased heart rate
- Limits cardiac stimulation
- Slows down heart in tachycardia, so know your base lines.
- Also cannot give unles BP is within standard of care ranges. When in doubt, call the Dr.
Beta Blocker General Info
- Most in this class are nonselective and block both Beta 1 and Beta 2
- This leads to many of the adverse effects seen with these drugs
Some of these drugs are referred to as: cardioselective
and will not have many of the SEs related to brondialation.
Beta Blocker Uses
- Angina, slows heart which allows heart chambers to fill complelety, increases force of contraction
- After MI’s prevents harmful effects of sympathetic stimulation
- Cardioselective drugs produce less or no bronchoconstriction
- Treat glaucoma (by topical drop) by reducing production of aqueous humor
- Hyperthyroidism, (treats symptoms of hyerthyroidism, not the underlying cause).
- Migraine HA by dialating vessels of the brain.
- Performance anxiety by reducing heart rate --> feeling more calm.
- Alcohol withdrawal. Decreases sensations of withdrawl and decrease anxiety as described above.
SEs of Beta Blockers
- Decreased exercise tolerance
- Bronchospasm, due to action on beta1.
- Nightmares, extremely graphic.
- In diabetics:
- drugs may prevent tachycardia that typically warns patients of impending hypoglycemia
- Should avoid in those with severe allergies….blocks receptors typically used by epinephrine which means their epipen isn't going to work very well.
Examples of Beta Blockers and their uses
- Propranolol and Metoprolol:
- Anginia Pectoris
- Cardiac Dysrhythmias
- “Stage Fright”
- Migraine Headaches
- Decrease HR
- Decrease force of contraction
- Suppress impulse conduction through AV node
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