| PHENOXYBENZAMINE HYDROCHLORIDE
Classifications: alpha-adrenergic antagonist; antihypertensive agent; Therapeutic: antihypertensive
Pregnancy Category: C
10 mg capsules
Long-acting alpha-adrenergic antagonist. Apparently produces noncompetitive blockade of alpha-adrenergic receptor sites
at postganglionic synapse. Alpha-receptor sites are thus unable to react to the endogenous or exogenous sympathomimetic agents
epinephrine and norepinephrine.
Blocks excitatory effects of epinephrine, including vasoconstriction, but does not affect adrenergic cardiac inhibitory
actions. It produces a "chemical sympathectomy" and it can maintain it.
Management of pheochromocytoma.
To improve circulation in peripheral vasospastic conditions such as Raynaud's acrocyanosis and frostbite sequelae, for adjunctive
treatment of shock, hypertensive crisis.
Instances when fall in BP would be dangerous; pregnancy (category C), lactation.
Marked cerebral or coronary arteriosclerosis, compensated congestive heart failure, coronary artery disease; older adults;
renal insufficiency; respiratory infections.
Route & Dosage
|Management of Pheochromocytoma
Adult: PO 10 mg b.i.d., may increase by 10 mg/d at 4-d intervals to desired response (usual range 2040 mg/d in 23 divided
Child: PO 0.2 mg/kg/d, may increase by 0.2 mg/kg/d to desired response (usual range 0.41.2 mg/kg/q68h)
- Give with milk or in divided doses to reduce gastric irritation.
- Preserve in airtight containers protected from light.
Adverse Effects (≥1%)Body as a Whole: Dizziness,
fainting, drowsiness, sedation, tiredness, weakness, lethargy, confusion, headache, shock. CNS: CNS
stimulation (large doses). CV: Postural hypotension, tachycardia,
Dry mouth. Urogenital:
Inhibition of ejaculation. Respiratory: Nasal congestion. Skin:
Allergic contact dermatitis. Special Senses: Miosis,
drooping of eyelids.
Inhibits effects of methoxamine, norepinephrine, phenylephrine;
additive hypotensive effects with antihypertensives
Variably (approximately 30%) from GI tract. Onset:
2 h. Peak:
46 h. Duration:
34 d. Distribution:
Accumulates in adipose tissue
80% in urine and bile within 24 h. Half-Life:
Assessment & Drug Effects
- Monitor BP and note pulse quality, rate, and rhythm in recumbent and standing positions during period of dosage adjustment.
Observe patient closely for at least 4 d from one dosage increment to the next; hypotension and tachycardia are most likely
to occur in standing position.
- Drug has cumulative action, thus onset of therapeutic effects may not occur until after 2 wk of therapy, and full therapeutic
effects may not be apparent for several more weeks.
Patient & Family Education
- Make position changes slowly, particularly from reclining to upright posture, and dangle legs and exercise ankles and feet
for a few minutes before standing.
- Be aware that light headedness, dizziness, and palpitations usually disappear with continued therapy but may reappear under
conditions that promote vasodilation, such as strenuous exercise or ingestion of a large meal or alcohol.
- Pupil constriction, nasal stuffiness, and inhibition of ejaculation generally decrease with continued therapy.
- Do not take OTC medications for coughs, colds, or allergy without approval of physician. Many contain agents that cause BP