PHENTOLAMINE MESYLATE
(fen-tole'a-meen)
Regitine, Rogitine

Classifications: autonomic nervous system agent; alpha-adrenergic antagonist (blocking agent), sympatholytic
Prototype: Prazosin
Pregnancy Category: C

Availability

5 mg injection

Actions

Alpha-adrenergic blocking agent structurally related to tolazoline but with more potent blocking effects. Competitively blocks alpha-adrenergic receptors, but action is transient and incomplete. Prevents hypertension resulting from elevated levels of circulating epinephrine or norepinephrine.

Therapeutic Effects

Causes vasodilation and decreases general vascular resistance and pulmonary arterial pressure, primarily by direct action on vascular smooth muscle. Through stimulation of beta-adrenergic receptors, produces positive inotropic and chronotropic cardiac effects and increases cardiac output.

Uses

Diagnosis of pheochromocytoma and to prevent or control hypertensive episodes prior to or during pheochromocytomectomy.

Unlabeled Uses

Prevention of dermal necrosis and sloughing following IV administration or extravasation of norepinephrine.

Contraindications

MI (previous or present), coronary artery disease. Safety during pregnancy (category C) or lactation is not established.

Cautious Use

Gastritis, peptic ulcer.

Route & Dosage

To Prevent Hypertensive Episode during Surgery
Adult: IV/IM 2–5 mg as needed
Child: IV/IM 1 mg or 0.1 mg/kg (max: 5 mg/dose)

To Test for Pheochromocytoma
Adult: IV/IM 5 mg
Child: IV/IM 0.1 mg/kg

To Prevent Necrosis from Norepinephrine Infusions
Adult: IV 10 mg added to each liter of IV fluid containing norepinephrine

To Treat Catecholamine Extravasation
Adult/Child: Intradermal 5–10 mg diluted in 10 mL of normal saline injected into affected area within 12 h of extravasation
Neonate: Intradermal 2.5–5 mg diluted in 10 mL of normal saline injected into affected area within 12 h of extravasation (max: dose 0.1 mg/kg or 2.5 mg total)

Administration

Note: Place patient in supine position when receiving drug parenterally. Monitor BP and pulse q2min until stabilized.

Intramuscular

Reconstitute 5 mg vial with 1 mL of sterile water for injection.

Intravenous

PREPARE: Direct: Reconstitute as for IM. May be further diluted with up to 10 mL of sterile water. Use immediately.

ADMINISTER: Direct: Give a single dose over 60 sec.

Adverse Effects (1%)

Body as a Whole: Weakness, dizziness, flushing, orthostatic hypotension. GI: Abdominal pain, nausea, vomiting, diarrhea, exacerbation of peptic ulcer. CV: Acute and prolonged hypotension, tachycardia, anginal pain, cardiac arrhythmias, MI, cerebrovascular spasm, shock-like state. Special Senses: Nasal stuffiness, conjunctival infection.

Interactions

Drug: may antagonize BP raising effects of epinephrine, ephedrine.

Pharmacokinetics

Peak: 2 min IV; 15–20 min IM. Duration: 10–15 min IV; 3–4 h IM. Elimination: Excreted in urine. Half-Life: 19 min.

Nursing Implications

Assessment & Drug Effects

Test for pheochromocytoma: (1) Withhold medications not deemed absolutely essential for at least 24 h, preferably 48–72 h; antihypertensive agents withheld until BP returns to pretreatment level (rauwolfia drugs withdrawn at least 4 wk prior to testing). (2) Keep patient at rest in supine position throughout test, preferably in quiet darkened room. (3) Take BP q10min for at least 30 min; when BP stabilizes, (4) IV administration: Record BP immediately after injection and at 30-sec intervals for first 3 min; then at 1-min intervals for next 7 min. IM administration: BP determinations at 5-min intervals for 30–45 min.

Patient & Family Education

Avoid sudden changes in position, particularly from reclining to upright posture and dangle legs and exercise ankles and toes for a few minutes before standing to walk.
Lie down or sit down in head-low position immediately if light-headed or dizzy.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug