Protease inhibitors (PIs) for HIV


Generic Name Brand Name
atazanavir Reyataz
darunavir Prezista
fosamprenavir Lexiva
indinavir Crixivan
nelfinavir Viracept
ritonavir Norvir
saquinavir Invirase
tipranavir Aptivus

Combination medicines

Generic Name Brand Name
lopinavir and ritonavir Kaletra

Some of these medicines must be used with ritonavir. They are only approved for people who have tried other antiretroviral medicines but did not improve.

How It Works

Protease inhibitors (PIs) are antiretroviral medicines. They prevent HIV from multiplying, reducing the amount of virus in your body. When the amount of virus in the blood is kept at a minimum, the immune system has a chance to recover and grow stronger.

Why It Is Used

The use of three or more antiretroviral medicines (highly active antiretroviral therapy, or HAART) is the usual treatment for HIV infection.

The combination of medicines used for HAART will depend on your health, other conditions you might have (such as hepatitis), and results of testing. Talk to your doctor about the best treatment plan for you.

Treatment guidelines suggest the following for people with HIV:1, 2

  • When considering treatment, experts currently consider your CD4+ cell count and the presence or absence of symptoms more important than your viral load.
  • If your CD4+ cell count is below 350 cells per microliter (mcL), you should begin treatment to stabilize and increase your CD4+ cell count.
  • If your CD4+ cell count is more than 350 cells per microliter, treatment may be offered to help keep your immune system healthy and prevent AIDS.
  • If treatment is not started, your condition will be monitored with frequent CD4+ cell counts.
  • If you have symptoms of HIV or AIDS, doctors recommend starting treatment, whatever your CD4+ cell count is.
  • If you are pregnant, you should be treated to prevent your unborn baby (fetus) from becoming infected with HIV.
  • If you also have hepatitis B and are starting treatment for it, you should begin treatment for HIV as well.
Click here to view a Decision Point. Should I start antiretroviral medicines for HIV infection even though I have no symptoms?
Click here to view an Actionset. HIV: Taking antiretroviral medicines

How Well It Works

Combination therapy:

  • Reduces viral loads, which can lead to stable or increased CD4+ cell counts, a sign that the immune system is still able to fight off opportunistic infections.
  • Decreases the number and severity of opportunistic infections.
  • Reduces or prevents the occurrence of resistance to the medicines.
  • Prolongs life.

Antiretroviral therapy can also decrease symptoms of HIV infection, such as fever and weakness, and help the person gain weight.

The rate at which antiretrovirals decrease viral loads is affected by:1

  • CD4+ cell counts at the beginning of treatment.
  • Viral load at the beginning of treatment.
  • The dosage of the medicines.
  • Whether the medicines are taken exactly as prescribed.
  • Whether antiretroviral medicines have been taken before.
  • Whether any opportunistic infections are present.

Side Effects

To prevent serious medicine interactions or a decrease in medicine effectiveness, it is important to learn which medicine should not be taken with PIs and other antiretroviral medicines.

PIs may cause:

Also, each medicine may be associated with its own side effects.


Side effects of atazanavir include:

  • Increased levels of bilirubin that can make the skin, nails, and whites of the eyes appear yellow.
  • Abnormal heartbeat .
  • Headaches.
  • Pain or numbness in the arms and legs.
  • Nausea, diarrhea, abdominal cramps.
  • Rash.


Side effects of darunavir include:

  • Diarrhea and nausea.
  • Headaches.
  • Rash.
  • Liver problems.


Side effects of fosamprenavir include:

  • Appetite loss.
  • Headache.
  • Diarrhea, nausea, and vomiting.
  • Abnormal fat distribution on the body.


Side effects of indinavir include:

  • Kidney stones , reported in 5% of people who use this medicine. The risk of kidney stones can be reduced by drinking at least 48 fl oz (1.4 L) of fluid each day.
  • Mild stomach problems.
  • Dry skin and lips.
  • Loss of body hair.


Nelfinavir's most common side effect is diarrhea, which may be severe. Diarrhea can usually be controlled with nonprescription medicine such as loperamide (for example, Imodium AD) or calcium supplements, such as Tums.


Ritonavir can cause severe side effects at higher doses. But it is usually used at very low doses to help other medicines work better. At these low doses, side effects are much less common. Side effects may include:

  • Diarrhea.
  • Nausea or vomiting.
  • Loss of appetite.
  • Headache.
  • Fatigue or weakness.
  • Tingling around the mouth.
  • Changes in the way foods taste.


Saquinavir has few side effects, which may include:

  • Diarrhea.
  • Nausea.
  • Abdominal pain.
  • Rash.


Side effects of tipranavir include:

  • Diarrhea, nausea, and vomiting.
  • Belly pain.
  • Headaches.
  • Tiredness.
  • Liver problems, especially if you have liver disease.

Side effects of any combination medicine can include the side effects of any of the single medicines in the combination.

Report all side effects to your doctor at your next visit. He or she can adjust your dose or give you other medicines to reduce side effects. Some mild side effects, such as nausea, improve as your body adjusts to the medicine.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Many people think antiretroviral medicines always have severe side effects. In fact, only a few people experience severe or dangerous side effects.

Food increases the absorption of atazanavir, nelfinavir, and darunavir.3 Certain acid-reducing medicines, such as omeprazole or famotidine, should not be taken at the same time as atazanavir. Be sure to tell your doctor about any other medicines you are taking before taking protease inhibitors (PIs).

Resistance to PIs develops more frequently if these medicines are used alone or are not taken exactly as prescribed.

Ritonavir has negative interactions with many other medicines. Provide your doctor with a complete list of prescription and nonprescription medicines you are taking before you start taking ritonavir.

Lopinavir is combined with a low dose of ritonavir to inhibit the breakdown of lopinavir in the body. This delayed breakdown of lopinavir increases its effectiveness.

Lopinavir and ritonavir and most other PIs can cause a rise in cholesterol and triglyceride levels, increasing the risk of pancreatitis.

PIs are expensive. They can cost up to 2 times more than nucleoside/nucleotide reverse transcriptase inhibitors (NNRTIs).

Factors to consider when choosing a combination of medicines include:

  • The ability of the medicines to reduce your viral load.
  • The likelihood the virus will develop resistance to a certain class of medicine. If you have already been treated with a certain antiretroviral medicine, you may already know whether you are resistant to medicines in that class.
  • Side effects and your willingness to tolerate them.
  • The cost of treatment.

Do not use the nonprescription herbal supplement St. John's wort while you are taking a protease inhibitor because St. John's wort can interfere with the effectiveness of these medicines.

Talk to your doctor about whether you can eat grapefruit or drink grapefruit juice while you are taking protease inhibitors. It may increase the side effects of some of these medicines.4

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. U.S. Department of Health and Human Services (2008). Guidelines for the use of antiretroviral agents in HIV-1-infected adults and adolescents. Available online:
  2. Hammer, Scott M, et al. (2008). Antiretroviral treatment of adult HIV infection: 2008 recommendations of the International AIDS Society USA Panel. JAMA, 300 (5): 555–570.
  3. Atazanavir (Reyataz) and emtricitabine (Emtriva) for HIV infection (2003). Medical Letter on Drugs and Therapeutics, 45(1169): 90-92.
  4. Tatro DS (2004, January). Keeping up: Interactions of herbal supplements and grapefruit juice with medications used to treat HIV infection. Drug Facts and Comparisons News: 3–5.

Last Updated: April 10, 2009

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