Flashcards in Phenoxybenzamine Deck (18)
What is the trade name for phenoxybenzamine?
What is the drug classification for phenoxybenzamine?
Non-selective ALPHA-adrenergic receptor antagonist
What other receptor types does phenoxybenzamine antagonize?
What are the clinical uses for phenoxybenzamine?
-given preop to patients with pheochromocytoma to prevent hypertensive episodes during surgical manipulation (tumor manipulation can cause release of large bolus of catecholamines)
-also been used in the treatment of hypertensive crisis after sympathomimetic overdose
What does phenoxybenzamine cause, as a use against pheochromocytoma?
it causes arterial pressure to decrease and postural hypotension, and a reflex increase in heart rate and CO
What is the MOA of Phenozybenzamine?
-Binds covalently to the alpha adrenergic receptor and is therefore an irreversible antagonist and long acting
-after binding to the receptor, catecholamines and sympathomimetics can no longer produce a response at that receptor
-Thus, it blocks alpha mediated vasoconstriction, resulting in a drop in arterial pressure and postural hypotension
What is generally observed with administration of phenoxybenzamine secondary to __________ activation
a reflex increase in heart rate and cardiac output is generally observed secondary to BARORECEPTOR activation and increased NE activity at Beta receptors
When taken orally, how is phenoxybenzamine absorbed?
20-30% is absorbed in its active form
What is special about the drug phenoxybenzamine regarding how it is "active"?
It is a PRO-DRUG
What is the onset, and peak of phenoxybenzamine, why does it take this amount of time?
It has a slow onset, and even with IV administration it can take about 60 minutes to peak; this is because of the molecular modifications required to make it active
What is the E1/2t after IV administration of phenoxybenzamine?
How is phenoxybenzamine metabolized/excreted?
Hepatic metabolism and renal/biliary excretion
What are the side effects of phenozybenzamine?
Nasal Congestion (nasal vasodilation)
prevents the inhibitory action of epi on secretion of insulin
also can cause: seizures, palpitations, miosis, xerostomia, and absence of ejaculation
What is something to note/consider about the drop in blood pressure in adults?
the decrease in blood pressure is minimal in healthy adults, but is increased in patients with preexisting hypotension, hypovolemia, blood loss, or when given with vasodilating drugs like volatile anesthetics
What are the contraindications to the use of Phenoxybenzamine?
Contraindicated in patients with SEVERE hypotension or hypovolemia
What can happen when Phenoxybenzamine is given to pregnant women?
when given to pregnant women, it can cause neonates to have hypotension and respiratory distress in the first 72 hrs after birth
What are the drug interactions with Phenoxybenzamine?
-Prevents the sympathomimetic response of phenylephrine
-NE only has beta 1 response when given with this drug! and EPI has an enhanced beta 2 response causing more hypotension and tachycardia