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Regitine Side Effects

Generic name: phentolamine

Medically reviewed by Last updated on Apr 6, 2023.

Note: This document contains side effect information about phentolamine. Some dosage forms listed on this page may not apply to the brand name Regitine.

Applies to phentolamine: injection powder for solution.

Serious side effects of Regitine

Along with its needed effects, phentolamine (the active ingredient contained in Regitine) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking phentolamine:


Other side effects of Regitine

Some side effects of phentolamine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common or rare

Phentolamine injected into the penis may cause tingling at the tip of the penis. This is no cause for concern.

For Healthcare Professionals

Applies to phentolamine: compounding powder, injectable powder for injection, injectable solution.


Cardiovascular side effects have included hypotension due to reduced peripheral vascular resistance. This has been a significant cardiovascular complication of phentolamine (the active ingredient contained in Regitine) therapy in some cases. Acute and prolonged hypotensive episodes with reflex tachycardia and cardiac arrhythmias have been reported. Overdosage has been characterized primarily by cardiac arrhythmias, tachycardia and severe hypotension or shock.[Ref]

If severe hypotension develops, prompt elevation of the patient's legs, infusion of IV fluids and/or volume expanders, and, if necessary, an infusion of norepinephrine (titrated to an acceptable blood pressure) is recommended. Epinephrine should not be used since it may cause a paradoxical reduction in BP.

While limited data have shown that phentolamine can attenuate the marked increases in pulmonary artery pressure and vascular resistance associated with exercise in some patients with primary pulmonary hypertension (PPH), its role in this disease is not clear. A single case of severe, worsened pulmonary hypertension has been reported after the administration of phentolamine to a young woman with PPH. Theoretically, the drug was expected to cause pulmonary arterial vasodilation and an improvement of her condition. Apparently, in patients with PPH, the pulmonary vessels become progressively unresponsive to vasodilator therapy. Phentolamine did induce decreased systemic peripheral vascular resistance in this case, which was associated with increased cardiac output, increased pulmonary blood flow, and, because of a constant pulmonary vascular resistance, increased pulmonary artery blood pressure.[Ref]

Nervous system

Nervous system side effects have included weakness and dizziness. Anxiety, headache, pupillary contraction and visual disturbances are signs of toxicity.[Ref]


Respiratory system side effects have included nasal stuffiness, probably due to peripheral vasodilation.[Ref]


Gastrointestinal side effects have included nausea, vomiting, and diarrhea.[Ref]


Genitourinary side effects among male patients who directly inject the penile cavernous body have included prolonged erections/priapism, fibrous plaque formation, severe local pain, cavernositis, urethritis, ecchymosis with hematoma, gross hematuria, and hematospermia. Urinary incompetence has not been reported, although the drug has been used to successfully treat urinary obstruction due to benign prostatic hypertrophy.[Ref]


Hepatic side effects have included transient hepatic abnormalities, manifested as elevations in liver function tests, with direct injection of phentolamine (the active ingredient contained in Regitine) and papaverine in 0.4% to 40% of men with erectile impotence.[Ref]


Metabolic side effects have included hypoglycemia. This was probably due to stimulation of insulin as a result of alpha-adrenergic blockade.[Ref]


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10. Diagnostic and Therapeutic Technology Assissment (DATTA). Vasoactive intracavernous pharmacotherapy for impotence: papaverine and phentolamime. JAMA. 1990;264:752-4.

11. Product Information. Regitine (phentolamine). Ciba-Geigy Pharmaceuticals. 2001;PROD.

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16. Kerfoot WW, Carson CC. Pharmacologically induced erections among geriatric men. J Urol. 1991;146:1022-4.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.