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Other drug names: A-Am An-Az B C-Ch Ci-Cz D-Dh Di-Dz E F G H I-J K-L M-Mh Mi-Mz N-Nh Ni-Nz O P-Pl Pm-Pz Q-R S-Sn So-Sz T-To Tp-Tz U-V W-Z 0-9   

Sildenafil (Systemic)

Brand Names

In the U.S.-

  • Viagra

In Canada-

  • Viagra


  • Impotence therapy agent (systemic)


Sildenafil (sil-DEN-a-fil) belongs to a group of medicines that delay the enzymes called phosphodiesterases from working too quickly. The penis is one of the areas where these enzymes work. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence).

By controlling the enzyme phosphodiesterase, sildenafil helps to maintain an erection that is produced when the penis is stroked. Without physical action to the penis, such as that occurring during sexual intercourse, sildenafil will not work to cause an erection.

This medicine is available only with your doctor's prescription, in the following dosage form(s):

  • Tablets (U.S.)

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For sildenafil, the following should be considered:

Allergies- Tell your doctor if you have ever had any unusual or allergic reaction to sildenafil. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy- Sildenafil is not indicated for use in women. Sildenafil has not been studied in pregnant women. However, sildenafil has not been shown to cause birth defects or other problems in animal studies.

Breast-feeding- It is not known whether sildenafil passes into breast milk. Sildenafil is not indicated for use in women.

Older adults- Elderly people are especially sensitive to the effects of sildenafil, which may increase their chance of having side effects. Patients 65 years of age and older are started on a low dose, 25 mg, of sildenafil. The dose may be increased by a doctor as needed and tolerated.

Other medicines- Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking sildenafil, it is especially important that your health care professional know if you are taking any of the following:

  • Cimetidine (e.g., Tagamet)
  • Erythromycin (e.g., E.E.S. or Ery-Tab)
  • Itraconazole (e.g., Sporanox)
  • Ketaconazole (e.g., Nizoral)
  • Mibefradil (e.g., Posicor)
  • Ritonavir (e.g., Norvir)
  • Saquinavir (e.g., Fortovase or Invirase)-These medicines may increase the unwanted effects of sildenafil, unless lower starting doses of sildenafil are used
  • Nitrates, such as nitroglycerin (e.g., Nitrostat or Transderm-Nitro)-Sildenafil increases the lowering of blood pressure by nitrates too much and their use together is not recommended

Other medical problems- The presence of other medical problems may affect the use of sildenafil. Make sure you tell your doctor if you have any other medical problems, especially:
  • Arrhythmias (irregular heartbeat) or
  • Coronary artery disease or
  • Heart attack, history of (within the last 6 months) or
  • High blood pressure or
  • Low blood pressure or
  • Stroke, history of (within the last 6 months)-Chance of problems occurring may be increased
  • Abnormal penis, including curved penis and birth defects of the penis-Chance of problems occurring may be increased
  • Bleeding problems or
  • Retinitis pigmentosa-Chance of problems occurring may be increased. It is not known if the medicine is safe for use in these patients
  • Conditions causing thickened blood or slower blood flow, including leukemia; multiple myeloma (tumors of the bone marrow); or polycythemia, sickle cell disease, and thrombocythemia (blood problems) or
  • Priapism (history of)-Although sildenafil does not cause priapism (erection lasting longer than 6 hours), patients with these conditions have an increased risk of priapism and it could occur while using sildenafil
  • Heart or blood disease-Sexual activity increases the heart rate and blood flow and can increase the chance of problems occurring for some patients who use any type of medicine, including sildenafil, that increases sexual ability
  • Kidney problems (severe) or
  • Liver problems (severe)-Chance of problems occurring may be increased. Lower starting doses may be used and doses increased as needed and as tolerated

Proper Use of This Medicine

Special patient directions come with sildenafil. Read the directions carefully before using the medicine .

This medicine usually begins to work within 30 minutes after taking it. It continues to work for up to 4 hours, although its action is usually less after 2 hours.


The dose of sildenafil will be different for different patients. Follow your doctor's orders or the directions on the label . The following information includes only the average doses of sildenafil. If your dose is different, do not change it unless your doctor tells you to do so.

  • For oral dosage form (tablets):
    • For treatment of erectile dysfunction:
      • Adults up to 65 years of age-50 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. If needed, your doctor may increase your daily dose to 100 mg or decrease your daily dose to 25 mg.
      • Adults 65 years of age and older-25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. If needed, your doctor may increase your daily dose.
      • If you are taking protease inhibitors, such as for the treatment of HIV, your doctor may recommend a 25 mg dose and may limit you to a maximum single dose of 25 mg of Viagra in a 48 hour period


To store this medicine:

  • Keep out of the reach of children.
  • Store away from heat and direct light.
  • Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
  • Keep the medicine from freezing. Do not refrigerate.
  • Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Precautions While Using This Medicine

Sildenafil has not been studied with other medicines used for treatment of erectile dysfunction. Presently, using them together is not recommended .

Use sildenafil exactly as directed by your doctor . Do not use more of it and do not use it more often than your doctor ordered. If too much is used, the chance of side effects is increased.

If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. This condition may require prompt medical treatment to prevent tissue damage of the penis and possible permanent impotence.

Side Effects of This Medicine

Side Effects of This Medicine

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Less common
  • Abnormal vision, including blurred vision, seeing shades of colors differently than before, or sensitivity to light;  bladder pain;  cloudy or bloody urine;  dizziness;  increased frequency of urination ;  pain on urination 

  • Rare
    • Bleeding of the eye;  convulsions (seizures) ;  decreased vision or other changes in vision;  double vision;  prolonged, painful, or inappropriate erection of penis;  redness, burning, or swelling of the eye;  vision loss, temporary 

    • Note: The following rare side effects have not been completely established as being caused by sildenafil
      • Blood sugar problems (more likely with patients with diabetes mellitus), such as anxiety, behavior change similar to drunkenness, blurred vision, cold sweats, confusion, cool and pale skin, difficulty in concentrating, drowsiness, excessive hunger, fast heartbeat, headache, nausea, nervousness, nightmares, restless sleep, shakiness, slurred speech, and unusual tiredness or weakness;  bone pain;  breast enlargement;  chest pain;  chills;  confusion;  convulsions (seizures);  deafness;  decrease in amount of urine or in frequency of urination;  dizziness or lightheadedness, especially when getting up from a lying or sitting position;  dry eyes;  dry mouth;  dryness, redness, scaling, or peeling of the skin;  eye pain;  fainting or faintness;  fast, irregular, or pounding heartbeat ;  feeling of something in the eye;  groups of skin lesions with swelling;  headache (severe or continuing);  heart failure;  hives;  increase in size of pupil;  increased sweating;  increased thirst;  itching of skin;  low blood pressure ;  lower back or side pain;  migraine headache;  nausea (severe or continuing) ;  nervousness;  numbness of hands;  painful, swollen joints;  redness, itching, or tearing of eyes;  shortness of breath or troubled breathing;  skin paleness;  skin rash;  skin ulcers;  sore throat and fever or chills;  sudden weakness;  swelling of face, hands, feet, or lower legs;  twitching of muscles;  unusual tiredness or weakness;  unusual feeling of burning or stinging of skin 

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

  • More common
    • Flushing;  headache;  nasal congestion;  stomach discomfort following meals  

  • Less common
    • Diarrhea 

  • Rare
    • Anxiety 

    • Note: The following rare side effects have not been completely established as being caused by sildenafil
      • Abdominal pain;  abnormal dreams;  aches or pains of muscles;  clumsiness or unsteadiness;  cough;  diarrhea or stomach cramps (severe or continuing);  difficulty in swallowing;  ear pain;  increased amount of saliva;  increased skin sensitivity;  lack of coordination;  loss of bladder control;  mental depression ;  nausea;  numbness or tingling of hands, legs, or feet;  rectal bleeding;  redness or irritation of the tongue;  redness, soreness, swelling, or bleeding of gums;  ringing or buzzing in ears;  sensation of motion, usually whirling, either of one's self or of one's surroundings;  sexual problems in men (continuing), including failure to experience a sexual orgasm;  sleepiness;  sores in mouth and on lips;  tense muscles;  tightness of chest or wheezing;  trembling and shaking;  trouble in sleeping;  vomiting;  waking to urinate at night;  worsening of asthma 

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT