PHENTOLAMINE MESYLATE

PHENTOLAMINE MESYLATE (fen-tole'a-meen) Regitine, Rogitine  Classifications: alpha-adrenergic antagonist; vasodilator; Therapeutic: vasodilator Prototype: Prazosin Pregnancy Category: C

Availability

5 mg injection

Action

Alpha-adrenergic blocking agent that competitively blocks alpha-adrenergic receptors, but action is transient and incomplete. Causes vasodilation and decreases general vascular resistance as well as pulmonary arterial pressure, primarily by direct action on vascular smooth muscle.

Therapeutic Effect

Prevents hypertension resulting from elevated levels of circulating epinephrine or norepinephrine.

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; peptic ulcer disease; pregnancy (category C), lactation.

Cautious Use

Gastritis.

Route & Dosage

To Prevent Hypertensive Episode during Surgery Adult: IV/IM 5 mg 1–2 h before surgery, repeat as needed Child: IV/IM 0.05–0.1 mg/kg/dose (max: 5 mg/dose) To Test for Pheochromocytoma Adult: IV/IM 5 mg Child: IV/IM 0.05–0.1 mg/kg (max: 5 mg) To Treat Extravasation Adult: Intradermal 5–10 mg diluted in 10 mL of normal saline injected into affected area within 12 h of extravasation Child: Intradermal 0.1–0.2 mg/kg diluted with normal saline injected into affected area within 12 h of extravasation

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: In urine. Half-Life: 19 min.

Nursing Implications

Assessment & Drug Effects

Test for pheochromocytoma:

• IV administration: Keep patient at rest in supine position throughout test, preferably in quiet darkened room. Prior to drug administration, take BP q10min for at least 30 min to establish that BP has stabilized before IV injection. 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: Post-injection, 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.

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