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All about: Fosamprenavir

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Some commonly used brand names are:

In the U.S.—


In Canada—



  • Antiviral


Fosamprenavir (fos-am-PREN-a-veer) is a protease inhibitor. It is used in combination with other medicines to treat patients who are infected with the human immunodeficiency virus (HIV).

HIV is the virus that causes acquired immune deficiency syndrome (AIDS). Fosamprenavir may slow down the destruction of the immune system caused by HIV. This may help delay the development of problems usually related to AIDS or HIV disease. However, this medicine will not cure or prevent HIV infection, and it will not keep you from spreading the virus to other people. Patients who are taking this medicine may continue to have the problems usually related to AIDS or HIV disease.

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

  • Oral
  • Suspension (Canada)
  • Tablets (U.S. and Canada)

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 fosamprenavir, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to fosamprenavir, amprenavir (e.g., Agenerase) or sulfa medicines. Also tell your doctor and pharmacist if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Amprenavir has not been studied in pregnant women. However, studies in animals have shown that fosamprenavir causes birth defects and other problems. Fosamprenavir should only be used during pregnancy if the benefit outweighs the potential risk. Before taking this medicine, make sure your doctor knows if you are pregnant or if you may become pregnant.

Breast-feeding—It is not known whether fosamprenavir passes into breast milk. However, breast-feeding is not recommended in patients with HIV infection because of the risk of passing the HIV virus on to the nursing infant. Mothers should not breast-feed while taking amprenavir.

Children—Studies on this medicine have been done only in adult patients, and there is no specific information comparing use of fosamprenavir in children with use in other age groups.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is not specific information comparing use of fosamprenavir in the elderly with use in other age groups.

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 fosamprenavir, it is especially important that your doctor and pharmacist know if you are taking any of the following:

  • Amiodarone (e.g., Cordarone) or
  • Lidocaine (systemic) (e.g., Xylocaine) or
  • Quinidine (e.g., Cardioquin)
  • Tricyclic antidepressants (amitriptyline [e.g., Elavil], amoxapine [e.g., Asendin], clomipramine [e.g., Anafranil], desipramine [e.g., Norpramin], doxepin [e.g., Sinequan], imipramine [e.g., Tofranil], nortriptyline [e.g., Aventyl, Pamelor], protriptyline [e.g., Vivactil], trimipramine [e.g., Surmontil]—There is a possibility that amprenavir may interfere with the removal of these medicines from the body, which could lead to serious side effects.
  • Antacids—Use of with amprenavir may keep fosamprenavir from working properly if taken close together. Antacids should be taken at least one hour before or after amprenavir.
  • Bepridil (e.g., Vascor)—Use of bepridil together with fosamprenavir can cause life-threatening reactions. Use together with caution.
  • Carbamazepine (e.g., Tegretol) or
  • Phenobarbital (e.g., Luminal) or
  • Phenytoin (e.g., Dilantin)—Use of these medicines with fosamprenavir may cause amprenavir to be less effective. Use with caution.
  • Cisapride (e.g., Propulsid)—Do not use with fosamprenavir as life-threatening reactions can occur.
  • Cyclosporine (e.g., Sandimmune) or
  • Sirolimus (rapamycin) (e.g., Rapamune)
  • Tacrolimus (e.g., Prograf)—Use with fosamprenavir may cause a high blood level of these medicines. Caution should be used.
  • Delavirdine (e.g., Rescriptor)—Use with fosamprenavir may lead to a possible resistance to delavirdine. They should not be administered together.
  • Ergot derivatives (e.g., D.H.E., Methergine, Ergotrate)—Use of these medicines with fosamprenavir can cause serious side effects. Do not use together.
  • Flecainide (e.g., Tambocor) or
  • Propafenone (e.g., Rythmol)—Do not use with fosamprenavir and ritonavir. Life-threatening reactions can occur.
  • Fluticasone (e.g., Flonase)—Using fluticasone with fosamprenavir can cause an increase in the amount of fluticasone in your body. Caution should be used and your doctor may find a substitute medicine for fluticasone if you will be using fosamprenavir for a long time.
  • HMG-CoA reductase inhibitors (atorvastatin [e.g., Lipitor] lovastatin [e.g., Mevacor], simvastatin [e.g., Zocor])—Potential for serious side effects when fosamprenavir is used together with any of these medicines. If you are on atorvastatin while on fosamprenavir, use the lowest possible dose or consider using other HMG-CoA reductase inhibitors.
  • Itraconazole (e.g., Sporanox) or
  • Ketoconazole (e.g., Nizoral)—The dose of these medicines may need to be lowered when taken together with fosamprenavir.
  • Midazolam (e.g., Versed) or
  • Triazolam (e.g., Halcion)—Use of these medicines with fosamprenavir can cause serious reactions and should not be used together.
  • Oral contraceptives (birth control pills)—Use of these medicines may cause fosamprenavir to be less effective. Alternate methods of birth control are recommended.
  • PDE5 inhibitors (sildenafil [e.g., Viagra], vardenafil [e.g., Levitra])—Use of these medicines with fosamprenavir may increase the amount of sildenafil or vardenafil in the body and may increase the chance for side effects, such as low blood pressure, changes in vision, and erection of the penis lasting more than 4 hours or being painful. Use a reduced dose of sildenafil or vardenafil.
  • Pimozide (e.g., Orap)—Use of this medicine with fosamprenavir can cause serious reactions. Do not use together.
  • Rifabutin (e.g., Mycobutin)—Use of fosamprenavir can cause increased blood levels of rifabutin. Rifabutin can cause decreased blood levels of fosamprenavir.
  • Rifampin (e.g., Rifadin)—Use of this medicine may lead to possible resistance to fosamprenavir. Do not use together.
  • Saquinavir (e.g., Forvase, Invirase)—Fosamprenavir levels may be decreased.
  • St. John's wort—This medicine can decrease the blood levels of fosamprenavir in your body. It may also result in resistance to fosamprenavir.
  • Trazodone (e.g., Desyrel)—Use of this medicine with fosamprenavir may increase the amount of trazodone in the body. Caution should be used and your doctor may reduce your dose of trazodone.
  • Warfarin (e.g. Coumadin)—Fosamprenavir may decrease your blood clotting time and make you bleed more easily.

Other medical problems—The presence of other medical problems may affect the use of fosamprenavir. Make sure you tell your doctor if you have any other medical problems, especially:

  • Bleeding problems—May be worsened by recombinant interferon alfa-2b
  • Diabetes mellitus (sugar diabetes)
  • Hemophilia—Fosamprenavir may make this condition worse.
  • Liver disease—Effects of fosamprenavir may be increased because of slower removal of fosamprenavir from the body. Your doctor may need to lower your dose of fosamprenavir.
  • Hepatitis B or
  • Hepatitis C—May increase certain concentrations of liver enzymes. Your doctor should monitor you closely.

Proper Use of This Medicine

Fosamprenavir suspension should be taken without food on an empty stomach.

Fosamprenavir tablets may be taken with or without food. However, it should not be taken with a high-fat meal. Taking fosamprenavir with a high-fat meal may decrease the amount of fosamprenavir that is absorbed by the body and prevent the medicine from working properly.

It is important to take fosamprenavir as part of a combination treatment. Your dose of medicine will be based on what other medicines you are taking, as well as your weight. Be sure to take all the medicines your doctor has prescribed for you, including fosamprenavir.

Take this medicine exactly as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. Also, do not stop taking this medicine without checking with your doctor first.

Keep taking fosamprenavir for the full time of treatment, even if you begin to feel better.

This medicine works best when there is a constant amount in the blood. To help keep the amount constant, do not miss any doses. Also, it is best to take the doses at evenly spaced times, day and night. For example, if you are to take two doses a day, the doses should be spaced about 12 hours apart. If you need help in planning the best times to take your medicine, check with your health care professional.

Only take medicine that your doctor has prescribed especially for you. Do not share your medicine with others.

Dosing—The dose of fosamprenavir 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 fosamprenavir. If your dose is different, do not change it unless your doctor tells you to do so.

  • For oral dosage form (suspension and tablets):
    • For treatment of HIV infection:
      • Adults who have not taken HIV medicines called protease inhibitors in the past (fosamprenavir alone)—1400 mg two times a day.
      • Adults who have not taken HIV medicines called protease inhibitors in the past (fosamprenavir together with ritonavir)—1400 mg fosamprenavir with 200 mg ritonavir one time per day or 700 mg fosamprenavir with 100 mg ritonavir two times a day
      • Adults who have taken HIV medicines called protease inhibitors in the past (fosamprenavir together with ritonavir)—700 mg fosamprenavir with 100 mg ritonavir two times a day
        Adults who have taken HIV medicines called protease inhibitors in the past should not take the combination of fosamprenavir with ritonavir only one time a day. Check with your doctor if you are unsure of what amounts and how many times a day you should be taking your medicines. If you are taking fosamprenavir with ritonavir and efavirenz, check with your doctor for the correct doses.
      • Children—Use and dose must be determined by your doctor.

Missed dose—If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—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. Ask your health care professional how you should dispose of any medicine you do not use. Be sure that any discarded medicine is out of the reach of children.

Precautions While Using This Medicine

Do not take any other medicines without checking with your doctor first. This includes prescription and nonprescription medicines. This also includes food supplements, herbs and vitamins. To do so may increase the chance of side effects from fosamprenavir or other medicines.

This medicine may decrease the effects of some oral contraceptives (birth control pills). To avoid unwanted pregnancy, it is a good idea to use some additional contraceptive measures while being treated with fosamprenavir.

For patients with diabetes: Amprenavir may affect blood sugar levels. If you notice a change in the results of your blood or urine sugar tests or if you have any questions, check with your doctor.

It is very important that your doctor check your progress at regular visits to make sure this medicine is working properly and to check for unwanted effects, especially increases in blood sugar.

Fosamprenavir does not decrease the risk of transmitting the HIV infection to others through sexual contact or by contamination through blood. HIV may be acquired from or spread to others through infected body fluids, including blood, vaginal fluid, or semen. If you are infected, it is best to avoid any sexual activity involving an exchange of body fluids with other people. If you do have sex, always wear (or have your partner wear) a condom (“rubber”). Only use condoms made of latex, and use them every time you have vaginal, anal, or oral sex . The use of a spermicide (such as nonoxynol-9) may also help prevent the spread of HIV if it is not irritating to the vagina, rectum, or mouth. Spermicides have been shown to kill HIV in lab tests. Do not use oil-based jelly, cold cream, baby oil, or shortening as a lubricant—these products can cause the condom to break. Lubricants without oil, such as K-Y Jelly , are recommended. Women may wish to carry their own condoms. Birth control pills and diaphragms will help protect against pregnancy, but they will not prevent someone from giving or getting the AIDS virus. If you inject drugs, get help to stop. Do not share needles or equipment with anyone. In some cities, more than half of the drug users are infected, and sharing even 1 needle or syringe can spread the virus. If you have any questions about this, check with your health care professional.

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.

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

More common

Large amount of triglyceride in the blood; severe skin rash

Less common

Abdominal pain; blurred vision; depression mood or mental changes; dry mouth; fatigue; flushed, dry skin; fruit-like breath odor; increased hunger; increased thirst; increased urination; nausea; sweating; troubled breathing; unexplained weight loss; vomiting


Back, leg, or stomach pains; bleeding gums; blistering, peeling, loosening of skin; chills; cough; dark urine; diarrhea; difficulty breathing; fever; general body swelling; itching; joint or muscle pain; loss of appetite; nosebleeds; pale skin; red irritated eyes; red skin lesions often with a purple center; sore throat; sores, ulcers, or white spots in mouth or on lips; unusual tiredness or weakness; yellowing of the eyes or 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

Itching skin; mild or moderate rash

Less common

Burning or prickling sensation around the mouth; headache

Frequency not known

Breast enlargement; obesity; increased fat deposits on face, neck, and truck; buffalo hump; fat redistribution

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

Developed: 04/02/2004
Revised: 10/28/2005

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