Medical News Today: What are protease inhibitors for HIV?

By | December 3, 2018
Treatments for HIV involve taking antiretroviral drugs. Protease inhibitors are one of seven classes of antiretroviral drugs.

Antiretroviral drugs are designed to treat HIV. Different drugs have different mechanisms of action. Protease inhibitors work by blocking the activity of HIV protease, which is an enzyme that HIV needs to multiply.

A healthcare professional usually prescribes three or more drugs to treat HIV, which is called high action antiretroviral therapy (HAART), combination antiretroviral therapy (cART), or antiretroviral therapy (ART). One of these may be a protease inhibitor.

In this article, we discuss protease inhibitors, including how they work, brand names, and possible side effects.

How do protease inhibitors work?

Woman in kitchen on laptop holding prescription pill bottle and reading label
A doctor may prescribe multiple protease inhibitors to treat HIV.

When HIV enters a person’s body, it makes copies of itself by inserting its virus DNA into specific immune system cells, called CD4 cells. CD4 cells coordinate the immune system, directing it to fight off infections.

When HIV places itself inside the CD4 cells, they lose their ability to work. HIV then instructs the CD4 cells to make new HIV proteins and HIV genetic material, which it uses to create more viruses that can target more CD4 cells.

Over time, this damages the immune system by reducing the number of working CD4 cells in the body, making a person more susceptible to diseases and infections.

Protease inhibitors interfere with HIV’s ability to make new viruses inside the CD4 cells. Specifically, they block an enzyme known as protease. Protease breaks down HIV proteins, using those smaller particles to make new viruses that can mature and spread.

When a protease inhibitor blocks protease, HIV cannot break down its proteins to make new viruses. As a result, it cannot multiply, and it stops spreading.

Protease inhibitors are not a cure for HIV, but when taken in combination with other effective antiretroviral drugs, protease inhibitors can decrease HIV to undetectable levels in the body. When the virus is undetectable, it is no longer transmittable through sexual contact.

This means that a person living with HIV who adheres to an effective treatment plan can live a healthy life without risk of transmitting HIV to others.

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Protease inhibitor drug names

Many different protease inhibitors are available, and people must take them with other HIV medicines.

A healthcare provider may prescribe a protease inhibitor along with other medications; sometimes the protease inhibitor is already included in a combination HIV medicine.

The FDA-approved protease inhibitors include:

  • atazanavir, brand name Reyataz
  • darunavir, brand name Prezista
  • fosamprenavir, brand name Lexiva
  • saquinavir, brand name Invirase
  • tipranavir, brand name Aptivus

Another protease inhibitor called ritonavir (Norvir) can enhance the action of other protease inhibitors, which means a person may take it with another protease inhibitor.

Side effects of protease inhibitors

Man holding head looking ill with mug under blanket
Nausea and dizziness are potential side effects of protease inhibitors.

Protease inhibitors can have side effects, including:

  • nausea
  • vomiting
  • diarrhea
  • dizziness
  • mild red, itchy rash
  • an increase or decrease in body fat
  • high blood sugar (hyperglycemia) and diabetes
  • kidney stones, which can cause blood in the urine, painful urination, and lower back pain

Antiretroviral medications can cause immune reconstitution inflammatory syndrome (IRIS), which may happen as the immune system strengthens. IRIS can cause a flare-up of an infection that a person did not know they had.

It may also cause an overactive immune response to a past infection. This is a sign that a person’s immune system is recovering. IRIS can be mild or severe.

Some side effects of protease inhibitors may be severe. These side effects, though uncommon, require emergency medical care. They include:

  • Liver damage. Symptoms of liver damage may include jaundice, which is a yellowing of the skin or whites of the eyes, pale-colored stool, or dark-colored urine. If this happens, seek emergency medical care.
  • Gallbladder problems. Symptoms include pain on the right side of the abdomen or upper abdomen, fever, nausea, vomiting, or jaundice.
  • Heart problems.
  • Liver problems.
  • A severe rash.

A person who experiences any side effects from protease inhibitors should speak with their doctor.

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People can often manage mild side effects, and they may go away on their own. If needed, a healthcare provider can help the person find another drug that works better for them. Overall, the risks of not treating HIV are much higher than the risks of side effects from medications.

Drug interactions

Protease inhibitors can have dangerous interactions with other medications, supplements, vitamins, and herbs.

It is essential to tell a healthcare provider about any other medications or supplements before taking protease inhibitors or other HIV medications. This can help a person avoid serious interactions.

HIV and drug resistance

In some cases, HIV can become resistant to protease inhibitors. This means that the virus does not respond to the medicine any longer.

Drug resistance can happen when HIV changes, or mutates, in a person’s body. Viruses do this to try and survive. When it mutates, it may become resistant to the medicines a person is taking.

In some cases, a person may contract a drug-resistant strain of HIV. This means the type of HIV they have does not respond to certain medications

The best way to avoid HIV drug resistance is to take HIV medicines every day, precisely as a healthcare provider prescribes them. Do not skip doses, change doses, or stop taking a medication without talking to a healthcare provider.

Using a 7-day pill box, a medication reminder app, or another reminder system can remind people to take their medicines each day. If they have adverse side effects, they can talk with their healthcare provider.

Measuring treatment success

Person giving blood sample.
Tests on blood samples can help measure treatment success.

When a person is taking protease inhibitors and other antiretroviral medications, their healthcare provider will conduct specific tests to be sure their medicines are working, including:

CD4 cell counts

A CD4 cell count measures the number of CD4 cells in a blood sample. A person may have a CD4 test before starting treatment and then periodically during treatment.

A high or increasing CD4 count usually means a person’s immune system is healthy and is often a sign that the HIV medications are working as they should. A normal CD4 cell count is around 500–1,200 cells per millimeter cubed (cells/mm3).

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HIV viral loads

The viral load, or HIV RNA levels, tell a healthcare provider how much HIV is in a person’s blood. A lower viral load number means there are fewer HIV copies in the blood.

HIV treatment aims to lower the viral load to undetectable levels. This means that the HIV count is so low that the test cannot pick it up. This is an indication that the person with HIV is in good health, and that they cannot spread the disease to sexual partners.

However, even after a person reaches an undetectable viral load, they must keep taking their medicines as prescribed. It is essential to go to all checkups and appointments during treatment to measure treatment success and talk about side effects or HIV treatment questions.


Protease inhibitors are a class of antiretroviral medication that people use alongside other HIV drugs to manage HIV effectively. Protease inhibitors work by stopping the activity of HIV protease enzymes, therefore preventing HIV from multiplying.

People may take several pills each day, but many antiretroviral regimens involve taking a single tablet once per day.

There are many protease inhibitors available, including atazanavir (Reyataz), darunavir (Prezista), Fosamprenavir (Lexiva), and Saquinavir (Invirase).

HIV is a treatable condition. Taking all HIV medications as prescribed helps a person keep HIV under control. This prevents damage to the immune system and removes the risk of spreading HIV to sexual partners. Within 3 to 6 months of effective treatment, a person’s viral load is usually undetectable.

More than 150,000 people in the U.S. have HIV and do not know it. This means they are not getting the vital treatment they need.

Today’s advanced antiretroviral medicines allow people living with HIV to live long, healthy lives. Getting tested and diagnosed is the first step toward effective treatment.

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