Regitine Side Effects

Generic Name: phentolamine

Note: This page contains side effects data for the generic drug phentolamine. It is possible that some of the dosage forms included below may not apply to the brand name Regitine.

It is possible that some side effects of Regitine may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

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

As well as its needed effects, phentolamine (the active ingredient contained in Regitine) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking phentolamine, check with your doctor immediately:

  • Dizziness
  • erection continuing for more than 4 hours, or painful erection
  • lumps in the penis

Some phentolamine side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common or rare
  • Bruising or bleeding at place of injection
  • burning (mild) along penis
  • difficulty in ejaculating
  • swelling at place of injection

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.

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.

Nervous system

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


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


Gastrointestinal side effects have included nausea, vomiting, and diarrhea.


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.


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.


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

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