Phentolamine (Injection)

Phentolamine is a vasodilator which increases blood flow in order to induce an erection in men with erectile dysfunction, or reverse local anesthetic after dental surgery.


Phentolamine injections cause blood vessels to expand in order to increase blood flow to the local area in which it is injected. It is a non-selective ?-adrenergic antagonist and works by relaxing the muscles and widening the blood vessels.

It is often used in hospital environments to control hypertensive (high blood pressure) emergencies but is best known for reversing the effects of local anesthetic administered during dental surgeries. If the mouth remains numbed after minor dental surgery, patients may accidentally chew or bite the inside of the lips or gums which can cause swelling and subsequent pain when the anesthetic eventually wears off. Furthermore, numbness can make it difficult to drink, talk or smile, and sometimes it can cause drooling. Phentolamine can help numbness to dissipate more quickly and therefore prevent these problems.

The drug can also be used to induce erections in men with erectile dysfunction. However, it should not be used as a sexual aid by men who do not have erectile dysfunction due to risk of permanent damage to the penis.

Phentolamine is only available with a doctor's prescription and is designed to be injected directly into the soft tissue in the area that requires treatment. When treating erectile dysfunction, it is injected directly into the penis. It is known in the US under brand names OraVase and Regitine.

Conditions Treated

Type Of Medicine?

  • Non-selective ?-adrenergic antagonist

Side Effects

Although phentolamine does not cause many side effects, and those which it does cause are uncommon or rare, some can be serious and need medical attention. Familiarize yourself with potential side effects so that you can recognize when to speak to your doctor.

The following should be reported to a doctor or dentist immediately:

  • Dizziness
  • Erection continuing for longer than four hours
  • Painful erection
  • Lumps in the penis

The following side effects are less serious and may not require medical attention unless they become very severe or persistent. If you have questions about them you should contact your doctor or dentist.

  • Bruising or bleeding at injection site
  • Swelling at injection site
  • Mild burning along the penis
  • Difficulty ejaculating

It's also important to note that phentolamine often causes tingling at the tip of the penis, but this is normal and is not something to be concerned about.

If you notice any other side effects not listed here, consult your doctor. You could also report new side effects to the FDA, or your doctor may do this on your behalf.


For reversal of anesthesia

If phentolamine is being used to reverse the effects of local anesthetic after dental surgery, your dentist or other healthcare professional will determine an appropriate dose and administer it themselves in a clinical environment. Usually, phentolamine is injected in the same spot as where the dental anesthesia was given.

For erectile dysfunction

If phentolamine is being used to induce an erection, you will inject it yourself at home. Your doctor will instruct you on how to safely administer the injections. The drug takes around 10 minutes to work and is usually effective for around two hours. You should not attempt intercourse more than two hours after injecting phentolamine.

0.5 to 1 mg of phentolamine is the average dose prescribed, but your doctor will instruct you on an appropriate dose based on factors personal to you, so always follow their instructions. You should not inject more than one dose in one day, or use it for more than two days in a row or more than three times each week.

Begin by cleansing the injection site with alcohol; your doctor may be able to prescribe or recommend an appropriate product for this. You should use a sterile needle for each injection. The injection should be made very slowly at the base of the penis, just below the surface of the skin. The drug should be injected very slowly, usually over the course of one to two minutes. Do not inject the medicine faster as this could cause pain.

Phentolamine injections should not hurt, other than a tingling sensation at the tip of the penis. If you do experience pain or notice bruising or swelling at the injection site, it's likely that you're injecting the medicine too deep. In this case, stop, withdraw the needle, and re-position it before continuing.

Once the injection has been administered, put pressure on the injection site. This minimizes bruising. Then, gently massage the penis (your doctor should have instructed you on this) to spread the medicine throughout the penis in order that it can work as effectively as possible. You should achieve an erection within the next 10 minutes.


Phentolamine can interact with other medicines. It is very important that you tell your doctor about all the medicines you take, including those purchased over the counter and those prescribed to you by a doctor. Be sure to mention any herbal supplements or multivitamins you take, too. It is often helpful to keep a list of all the medicines you take which you can present to each doctor, pharmacist or other healthcare professionals you see in order to avoid them administering potentially harmful medicines.

The following medicines should not be taken concurrently with phentolamine. If you do take them, your doctor will either choose not to prescribe phentolamine, or they will change the medicine you already take.

  • Asenapine (antipsychotic medication, brand names Saphris, Saphris Black Cherry)
  • Tadalafil (erectile dysfunction aid, brand names Adcirca, Cialis)

There are many other medicines which interact with phentolamine and can increase the risk of certain side effects. Where possible, your doctor may either avoid prescribing phentolamine or change some of the medicines you already take. If both medicines are deemed important, they may adjust dosages or instructions relating to the time at which you take the medicines in order to minimize the risk of harmful interactions. It is very important to follow your doctor's new instructions closely, as failure to do so could lead to serious side effects.


Risk of priapism

In rare instances, phentolamine can cause an erection to last for longer than four hours, which is a condition known as priapism. Priapism is incredibly dangerous because it can lead to the blood supply to the penis being cut off, which may cause permanent damage to the penis. To avoid priapism, only use the amount of phentolamine prescribed by your doctor. If you feel that the medicine does not provide the results you expected, do not increase the dose without consulting your doctor.

Patients with a history of priapism or sickle cell disease are at an increased risk of priapism when they use phentolamine for erectile dysfunction. They may not be able to use the medicine, or their doctor may request frequent examinations to monitor for priapism.

You should contact your doctor or seek emergency medical care if an erection lasts for longer than four hours.

Bleeding at injection site

In rare instances, phentolamine can cause bleeding at the injection site. If this occurs, patients should apply pressure to the area until the bleeding stops. They should consult a doctor immediately if the bleeding does not stop.

People with a history of bleeding problems are at an increased risk of bleeding at the place of injection when phentolamine is administered. Depending on the severity of the bleeding problem, doctors or dentists may continue to prescribe the drug. They may monitor the patient more closely to ensure other complications do not occur.

Not suitable for men without erectile dysfunction

When phentolamine is used to induce an erection, it should only be used by men who are unable to achieve an erection. It should never be used as a sexual aid by men with normal sexual function. This is because it can cause permanent damage to the penis and even lead to the loss of ability to achieve erection permanently.

Penis examination

Patients who use phentolamine regularly for erectile dysfunction should regularly examine their penis for lumps or other changes. Lumps, particularly at the injection site, and new curvature of the penis are signs that fibrosis (unwanted tissue growth) has occurred. If you notice these signs, consult your doctor as soon as possible.

Pregnancy and breastfeeding

The FDA has marked phentolamine as a pregnancy category C drug, which means it should only be used during pregnancy if the benefits of the drug far outweigh potential risks to the fetus. There have not been adequate studies into the effects of the drug in humans, and either animal trials have demonstrated a risk to the fetus, or there have not been any animal trials.

There is also little evidence as to the effects of the medicine on nursing infants if it administered to breastfeeding mothers. For this reason, patients should weigh the benefits of the drug against potential risks.

Pediatric use

The safety and efficacy of phentolamine in children aged six years or younger has not been established. For this reason, the drug is usually reserved for children over six when used to reverse dental anesthesia.


Phentolamine should be stored in the container it is provided in at room temperature and away from direct light, heat or moisture. It should not be allowed to freeze. Keep out of sight and reach of children.

If you have leftover or expired phentolamine, do not keep it. Ask your healthcare provider how to dispose of it. There may be a local medicine take-back program you could use. You should also ask your healthcare provider how to dispose of used needles safely. You should never throw used needles in the trash as they could be harmful to others.


Phentolamine is an injectable vasodilator which is commonly used to treat hypertensive emergencies in hospital settings. It is also often used to reverse local soft-tissue anesthesia after dental surgery and to induce an erection in men with erectile dysfunction.

For anesthesia reversal, phentolamine is suitable for adults and children aged 6 years and older. It is not recommended for pregnant women unless the benefits of the drug outweigh potential risks to the fetus. When used as an erectile dysfunction aid, it should only be used by men who are unable to get an erection, as others may experience serious damage to the penis.

Priapism is a major risk associated with phentolamine when it is used for erectile dysfunction. This is when an erection lasts for more than four hours, which can lead to the blood supply to the penis being cut off, and significant tissue damage. Patients can reduce the risk of this by injecting only the amount of phentolamine prescribed by their doctor. If priapism does occur, it should be reported to a doctor immediately.

When phentolamine is used to reverse anesthesia, it is administered by a dentist or other healthcare professional. When used for erectile dysfunction, it is administered at home. It is injected slowly into the base of the penis with a sterile needle. This doesn't usually hurt unless it is injected too quickly or too deep into the tissue. Mild tingling usually occurs at the tip of the penis and this is nothing to worry about.

Common side effects of phentolamine include mild bruising, bleeding or swelling at injection site, mild burning along the penis, and difficulty ejaculating, but these effects do not need medical attention unless they become severe. If priapism, dizziness, painful erection or lumps in the penis occur, medical attention must be sought.