Erectile Dysfunction Drug Interactions

Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editors: Melissa Conrad Stöppler, MD

The options to treat erectile dysfunction have increased in the past few years with the introduction of medications that can help promote an erection in males. Once thought to be due only to psychological factors, erectile dysfunction may occur because of a variety of medical conditions and in fact, it may be the initial presenting symptom of serious illness such as atherosclerosis and diabetes.

This illness often remains difficult for patients to discuss with their health care practitioners. With the advent of medications that help promote an erection and with increased advertisement of these medications in the media, the opportunity to have these discussions has improved.

In normal physiology, nerve impulses cause dilation of blood vessels in the penis due to sexual stimulation. Two cylindrical tubes, called the corpus cavernosum, that run the length of the penis fill with this increased blood volume and cause the penis to stiffen, straighten, and become erect. When the sexual stimulation is removed or when ejaculation occurs, the extra blood drains from the penis and the erection resolves.

Erectile dysfunction, previously termed impotence, is a failure of excess blood flow to engorge the corpus cavernosum and cause an erection. There are numerous potential causes and risk factors.

Examples of physiological causes of erectile dysfunction include the following:

• atherosclerotic vascular disease (or hardening of the arteries), the same diseases that can limit blood flow to the heart (angina and heart attack) and the brain [stroke and transient ischemic attack (TIA)];
  
  
• risk factors include high blood pressure, high cholesterol, diabetes, and smoking;
  
  
• other illnesses, including Parkinson's disease and multiple sclerosis;
  
  
• alcohol abuse;
  
  
• prostate cancer and its treatment;
  
  
• medication side effect; and
  
  
• trauma to the pelvis causing damage to the nerves and blood vessels that supply the penis (for example, from prolonged bicycling, where the pressure of the seat can impair blood flow to the penis and as well as compress nerves).

Erectile dysfunction may also be due to psychological conditions including depression, anxiety, and stress. Often the inability to maintain an erection is due to a combination of conditions.

Fortunately, medications are available that can help increase blood flow to the penis once sexual stimulation has occurred. Sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra) may be prescribed to help with erectile dysfunction. These medications are classified as phosphodiesterase inhibitors and work by relaxing muscles in the penis, causing blood vessels to dilate and allowing increased blood flow, but only after appropriate physical and emotional sexual stimulation.

There are some potential side effects of these medications and it is important that the patient and health care provider discuss their safe use.

• Because these medications cause blood vessels to dilate, their use with other medications such as nitrates [for example, isosorbide mononitrate (Imdur, Ismo, Monoket), isosorbide dinitrate (Isordil, Titradose, Dilatrate-SR, Isochron), nitroglycerin (Nitrostat, Nitroquick, Nitrolingual, Nitro-Dur, Minitran, Nitro-Bid and others) that cause similar reactions in the body may cause an unsafe drop in blood pressure, leading to lightheadedness and syncope, or passing out.
  
  
• Erectile dysfunction medications should not be taken with blood thinners or anticoagulation medications such as warfarin (Coumadin) and enoxaparin (Lovenox).
  
  
• Alpha-blocker medications, used to control high blood pressure [for example, doxazosin mesylate (Cardura), prazosin (Minipress)] and symptoms of an enlarged prostate tamsulosin (Flomax) can cause a drop in blood pressure; therefore, erectile dysfunction medications should not be used in conjunction with these drugs.

Since sexual intercourse is a significant physical exercise, it is important to make certain that the activity is safe. A frank discussion with a health care practitioner should occur if the patient has significant heart disease, stroke, and/or poorly controlled high or low blood pressure.

As with all prescription medications, it is important inform the health care practitioner or pharmacist if there has been a change in the patient's medications, both prescription and over-the-counter, to prevent drug interactions and side effects.

Medications like such as sildenafil (Viagra), Tadalafil (Cialis), and vardenafil (Levitra) are allowing patients to have more fulfilling sexual experiences, although they may not work for every individual. If an underlying medical condition is the cause of erectile dysfunction, addressing and treating that condition may be all that is needed. Other alternative therapies that are available include injectable medications, hormonal replacement therapy, and surgical implants. If appropriate, psychological counseling may be helpful.

The diagnosis and treatment of erectile dysfunction will occur if the patient allows the health care practitioner the opportunity to help. Often the step in making the first appointment is the hardest one.

REFERENCE: McVary KT . Male Sexual Dysfunction. Harrisons Textbook of Medicine, Chapter 49. 17th edition. 2008