RT Book, Section
A1 Kearney, Thomas E.
A2 Olson, Kent R.
A2 Anderson, Ilene B.
A2 Benowitz, Neal L.
A2 Blanc, Paul D.
A2 Clark, Richard F.
A2 Kearney, Thomas E.
A2 Kim-Katz, Susan Y.
A2 Wu, Alan H. B.
SR Print(0)
ID 1179993042
T1 PHENTOLAMINE
T2 Poisoning & Drug Overdose, 7e
YR 2018
FD 2018
PB McGraw-Hill Education
PP New York, NY
SN 9780071839792
LK accessmedicine.mhmedical.com/content.aspx?aid=1179993042
RD 2024/04/16
AB Pharmacology.  Phentolamine  is  a  competitive  presynaptic  and  postsynaptic  alpha-adrenergic  receptor  blocker  that  produces  peripheral  vasodilation.  By  acting  on  both  venous  and  arterial  vessels,  it  decreases  total  peripheral  resistance  and  venous  return.  It  also  may  stimulate  beta-adrenergic  receptors,  causing  cardiac  stimulation.  Phentolamine  has  a  rapid  onset  of  action  (usually  2  minutes)  and  a  short  duration  of  effect  (approximately  15–20  minutes).IndicationsHypertensive  crisis  associated  with  stimulant  drug  overdose  (eg,  amphetamines,  cocaine,  or  ephedrine).  Also  an  adjunct  for  cocaine-induced  acute  coronary  syndrome  to  reverse  coronary  artery  vasoconstriction.Hypertensive  crisis  resulting  from  interaction  between  monoamine  oxidase  inhibitors  and  tyramine  or  other  sympathomimetic  amines.Hypertensive  crisis  associated  with  sudden  withdrawal  of  sympatholytic  antihypertensive  drugs  (eg,  clonidine).Extravasation  of  vasoconstrictive  agents  (eg,  epinephrine,  norepinephrine,  and  dopamine).Contraindications.  Use  with  extreme  caution  in  patients  who  have  intracranial  hemorrhage  or  ischemic  stroke;  excessive  lowering  of  blood  pressure  may  aggravate  brain  injury.Adverse  effectsHypotension  and  tachycardia  may  occur  from  excessive  doses.Anginal  chest  pain  and  cardiac  arrhythmias  may  occur.Slow  intravenous  infusion  (≤0.3  mg/min)  may  result  in  transiently  increased  blood  pressure  caused  by  stimulation  of  beta-adrenergic  receptors.Use  in  pregnancy.  FDA  Category  C.  Phentolamine  was  used  to  manage  pheochromocytoma  during  a  delivery,  with  no  adverse  effects  to  the  newborn  attributable  to  the  drug  (Introduction).Drug  or  laboratory  interactions.  Additive  or  synergistic  effects  may  occur  with  other  antihypertensive  agents,  especially  other  alpha-adrenergic  antagonists  (eg,  prazosin,  terazosin).Dosage  and  method  of  administrationParenteral.  Give  1–5  mg  IV  (children:  0.02-0.1  mg/kg  up  to  a  maximum  of  2.5  mg)  as  a  bolus;  repeat  at  5-  to  10-minute  intervals  as  needed  to  lower  blood  pressure  to  a  desired  level  (usually  90–100  mm  Hg  diastolic  in  adults  and  70–80  mm  Hg  diastolic  in  children,  but  this  may  vary  with  the  clinical  situation).  Dose  range  for  adults  with  pheochromocytoma  is  up  to  20–30  mg.  Once  hypertension  is  controlled,  repeat  every  2–4  hours  as  needed.Catecholamine  extravasation.  Infiltrate  5–10  mg  in  10–15  mL  of  normal  saline  (children:  0.1-0.2  mg/kg;  maximum,  10  mg)  into  an  affected  area  with  a  fine  (25-27-gauge)  hypodermic  needle;  improvement  is  evidenced  by  hyperemia  and  return  to  normal  temperature.FormulationsParenteral.  Phentolamine  mesylate,  5  mg  in  2-mL  vials  (lyophilized  powder  with  mannitol).  Reconstitute  with  1  mL  of  sterile  water  and  then  use  immediately  (not  to  be  stored).Suggested  minimum  stocking  levels  to  treat  a  100-kg  adult  for  the  first  8  hours  and  24  hours:  phentolamine  mesylate,  first  8  hours:  40  mg  or  eight  vials  (5  mg  each);  first  24  hours:  100  mg  or  20  vials  (5  mg  each).