Adrenergic Antagonists Flashcards
Prazosin
• Drug class: pharmacologic class—selective alpha-1 adrenoceptor blocker; therapeutic class– antihypertensive, treatment of BPH •
Pharmacodynamics: blocks alpha-1 receptors on arterioles and veins, thereby inhibiting NE-mediated vasoconstriction and venoconstriction •
Pharmacokinetics: available po or transdermal; variable oral bioavailability (~60%), onset 2 h, duration 12-24 h; extensively metabolized in liver •
Toxicity: excessive hypotension with passing out, especially orthostatic, especially in patients on diuretics •
Interactions: additive effects with most other antihypertensives, especially diuretics •
Special considerations: start gradually, and at bedtime, to avoid first-time passing out ; male patients with BPH? •
Indications and dose/route: as monotherapy, begin with1 mg tid, advance to 20 mg per day divided tid •
Monitor: BP, weight, edema,
Tamsulosinn/Flomax™
Drug class: pharmacologic class—selective alpha-1 adrenoceptor blocker; therapeutic class– treatment of obstructive symptoms of BPH •
Pharmacodynamics: selectively blocks alpha-1 receptors, but preferentially (seen clinically) in the prostate, leading to relaxation of smooth muscles in the bladder neck and prostate, improving urine flow, and reducing obstructive symptoms of BPH •
Pharmacokinetics: completely absorbed after oral ingestion; >90% metabolized by CYP 450 enzymes; half-life about 6 hours, but duration of action up to 15 hours due to slow absorption •
Toxicity: excessive hypotension with syncope, especially orthostatic, especially in patients on diuretics, allergic reactions, decreased libido •
Interactions: additive effects with most other antihypertensives, especially diuretics •
Special considerations: rule out carcinoma of prostate before beginning treatment; do not crush or chew tablets, as that will speed up absorption; can also be used to treat spasm of ureter in patients passing kidney stones •
Indications and dose/route: for symptoms of BPH, 0.4 mg po qd or bid; similar doses for renal colic •
Monitor: BP
Atenolol/Tenormin™
Drug class: pharmacologic class— “specific” β1-adrenoceptor blocker; therapeutic class–antihypertensive, antiarrhythmic, primary and secondary prevention of MI, anti- anginal •
Pharmacodynamics: binds directly to β1-receptors, with a preference for beta-1 over beta-2, leading to lower blood pressure via several potential mechanisms (less cardiac output, less activation of the RAA system); recent evidence suggests less effective in preventing strokes than other drugs used as monotherapy for HTN •
Pharmacokinetics: available po or iv; variable oral F; onset 1-2 hours h, duration 12-24 h; can be given once per day; renally excreted (longer half-life); metoprolol has hepatic metabolism (and shorter half-life) •
Toxicity: excessive hypotension; bradycardia; heart block; can worsen severe CHF (but indicated for mild to moderate and stable CHF); worsen bronchospasm in severe asthmatics •
Interactions: additive effects with most other anti-hypertensives; additive AV block with CEB’s •
Special considerations: may be especially useful in HTN patients with exertional angina, MI, atrial fibrillation; watch out for abrupt withdrawal; may no longer be “first line” drug for essential HTN unless other indications exist (recent data); metoprolol (needs to be taken several times per day) has more data for use in patients s/p MI •
Indications and dose/route: for treatment of hypertension, 25-100 mg per day, in one or two doses •
Monitoring: BP, HR, exercise tolerance
Labetalol/Trandate™
• Drug class: pharmacologic class—mixed alpha- and beta-receptor blocker; therapeutic class– antihypertensive, treatment of stable CHF (Coreg™) •
Pharmacodynamics: reduces BP by blocking access of NE to beta-receptors and alpha-1 receptors, thereby lowering BP by several different mechanisms; patients differ in degree of beta-blockade vs alpha-blockade •
Pharmacokinetics: excellent absorption but high first-pass effect, leading to F~25%; onset 1-2 hours after po, 2-5 minutes when given iv; extensively metabolized in liver by 2D6 •
Toxicity: avoid in patients with bradycardia, heartblock, CHF, asthma, shock; use with caution in patients with cardiomyopathy, pheochromocytoma: Pregnancy Class D • Interactions: additive effects with most other antihypertensives •
Special considerations: use reduced doses in patients with impaired liver function; dizziness is most troubling early side effect; most often used for hypertensive crises (as with nitroprusside) •
Indications and dose/route: most commonly given iv with initial small boluses of 20 mg, followed by continuous infusion at 2 mg/min; not usually given po for chronic treatment; 80 mg thrice daily, or 240 mg SR once daily •
Monitor: BP, HR
Propranolol/Inderal™
• Drug class: pharmacologic class—non-specific β-adrenoceptor blocker; therapeutic class–antihypertensive, antiarrhythmic, primary and secondary prevention of MI, anti- anginal •
Pharmacodynamics: binds directly to β1-receptors and β2 receptors, leading to lower blood pressure via several potential mechanisms (less cardiac output, less activation of the RAA system); recent evidence suggests less effective in preventing strokes than other drugs; •
Pharmacokinetics: available po or iv; variable oral F; onset 1-2 hours h, duration 12-24 h; can be given once per day as LA formulation; cleared by hepatic metabolism (shorter half-life); metoprolol also cleared via hepatic metabolism (and shorter half-life) •
Toxicity: excessive hypotension; bradycardia; heart block can worsen severe CHF (but indicated for mild to moderate and stable CHF); worsen bronchospasm in severe asthmatics •
Interactions: additive effects with most other antihypertensives, additive AV block with CEB’s •
Special considerations: may be especially useful in HTN patients with exertional angina, MI, atrial fibrillation; watch out for abrupt withdrawal; may no longer be “first line” drug for essential HTN unless other indications exist (recent data); metoprolol (needs to be taken several times per day) has more data for use in patients s/p MI •
Indications and dose/route: for treatment of hypertension, 25-100 mg per day, in one or two doses •
Monitoring: BP, HR, exercise tolerance
Phentolamine mesylate/Regitine
Drug class: pharmacologic class—non-selective, competitive alpha-adrenergic receptor blocker; therapeutic class—antihypertensive drug for patients with pheochromocytoma •
Pharmacodynamics: blocks alpha-1 and alpha-2 adrenergic receptors at presynaptic and postsynaptic alpha receptors, leading to less venoconstriction and less vasoconstriction •
Pharmacokinetics: only comes in IV formulation, so F=100%; plasma half-life about 20 min after IV dose •
Toxicity: excessive hypotension with syncope, especially orthostatic, especially in patients on diuretics; allergic reactions; decreased libido •
Interactions: additive effects with most other antihypertensives, especially diuretics •
Special considerations: usual doses given iv have little effect on blood pressure of normal people, or those with essential hypotension (hence its early use to try to detect patients with a pheo, where the drop in BP can be 35/25 mm Hg or more) •
Indications and dose/route: Aid in Dx of pheo; treatment or prevention of intra-op HTN during pheo removal surgery; prevention of dermal sloughing after extravasation of NE infusion; hypertensive crisis from sympathomimetic amines (discuss tyramineMAO interaction); dose 5 mg IV, then titrate, repeat as needed •
Monitor: BP!!
