Phentolamine
REGITINE
What it isShort-acting reversible nonselective alpha-1/alpha-2 antagonist used for acute catecholamine excess and vasopressor extravasation.
Why this oneRapid IV alpha blockade can reverse a catecholamine-driven hypertensive crisis or local ischemia without prolonged postoperative hypotension.
What limits itMarked hypotension and reflex tachycardia can provoke myocardial or cerebral ischemia; avoid when coronary perfusion is tenuous.
FDA-approved for
- pheochromocytoma (~1952)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Pheochromocytoma — prevention/control of hypertensive episodes (pre-op and intra-op) | Adults | 5 mg IV/IM 1 or 2 hours before surgery; repeat if necessary | 5 mg IV during surgery as indicated | Undefined |
| Prevention of dermal necrosis with IV norepinephrine | All | 10 mg added to each liter of norepinephrine solution | 10 mg per liter | Undefined |
| Treatment of norepinephrine extravasation (dermal necrosis/sloughing) | All | 5–10 mg in 10 mL saline infiltrated into the area within 12 hours | Once | Undefined |
| Diagnosis of pheochromocytoma (phentolamine blocking test) | Adults | 5 mg IV rapid injection, or 5 mg IM | Once | Once |
| Pheochromocytoma — prevention/control of hypertensive episodes (pre-op and intra-op) | Children | 1 mg IV/IM 1 or 2 hours before surgery; repeat if necessary | 1 mg IV during surgery as indicated | Undefined |
| Diagnosis of pheochromocytoma (phentolamine blocking test) | Children | 1 mg IV rapid injection, or 3 mg IM | Once | Once |
Renal Undefined
Hepatic Undefined
Positive blocking test = BP fall >35 mm Hg systolic and 25 mm Hg diastolic (IV max effect within 2 minutes; IM within 20 minutes); confirm with urinary catecholamines. Negative test does not exclude pheochromocytoma.
Instructions
- Dissolve 5 mg in 1 mL Sterile Water for Injection; use immediately, do not store reconstituted solution
- Blocking test: withhold sedatives/analgesics/non-essential drugs ≥24 hours (preferably 48 to 72 hours) and antihypertensives until BP returns to untreated hypertensive level; not for normotensive patients
- Blocking test: supine, quiet room; inject only after BP stable (readings every 10 minutes for ≥30 minutes) and venipuncture pressor response subsides
- IV test: record BP every 30 seconds × 3 minutes, then every 60 seconds × 7 minutes; IM test: every 5 minutes for 30 to 45 minutes
Available strengths
- inj 0.235 mg/mL
- drops 10 mg/mL
- sol 0.75 %
Contraindications
- MI or history of MI, coronary insufficiency, angina, or other evidence of coronary artery disease
Cautions
- MI, cerebrovascular spasm and occlusion (usually with marked hypotension)
- Blocking test largely replaced by biochemical assays — reserve for cases needing confirmation
Adverse reactions
- Acute and prolonged hypotension
- Tachycardia
- Cardiac arrhythmias
- Orthostatic hypotension
- Weakness
- Dizziness
- Flushing
- Nasal stuffiness
- Nausea
- Vomiting
- Diarrhea
Pregnancy Category C — no adequate human studies; slight fetal growth/ossification delay in rodents at 24–30× human dose; use only if benefit justifies fetal risk.
Lactation Unknown whether excreted in milk; decide whether to discontinue nursing or the drug.
Cost
| Strength | #/mo | generic $/unit | CostPlus | |
|---|---|---|---|---|
| 0.235 mg/mL | inj | per unit | not offered |
Generic entry1998
NO BOXED WARNINGS
Principal riskmarked hypotension with reflex tachycardia and ischemia
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.