How Do Protease Inhibitors Work?

Protease inhibitors are antiviral drugs. They interrupt the way HIV uses a healthy cell to make more virus. When HIV enters a healthy cell, its only goal is to make more viruses to infect other healthy cells. It does this by making the cell produce certain proteins the virus can use to copy itself. Two of the proteins used by the virus are reverse transcriptase and protease. The goal of the protease inhibitor is to stop the protease from helping to assemble a new virus.

protease inhibitors diagram

The diagram above shows the virus entering the cell (1), the cell making new proteins (2-3), the proteins forming a new virus (4) and the cell releasing the new virus to infect other cells (5). It also shows some steps in the process that can be interrupted by protease inhibitors and other antiviral drugs (reverse transcriptase inhibitors) that are taken along with protease inhibitors.

What can protease inhibitors do?

Protease inhibitors are the most powerful anti-HIV drugs available so far. Although many different factors affect how well any drug will work for an individual, some people who have taken protease inhibitors have had the following benefits:

  • increase in CD4 (t cell) counts, which can help fight infections

  • decrease in the amount of virus in the blood (viral load), which may slow down the disease process

  • feeling of improved overall health and ability to do more of their usual activities (ie: work, travel, socialize)

Researchers are not sure how long protease inhibitors will work in a person infected with HIV, but they have seen promising results in studies. They are hopeful that people will live longer, healthier lives because of the benefits of these new drugs.

Is this a cure?

Protease inhibitors are not called a cure because researchers do not yet know how well they will work in different people. Some people have had their viral load drop to a level that is too low for current tests to measure. Even though the virus cannot be found in their blood, doctors believe HIV is still in their bodies and that it would reproduce quickly if they stop taking the protease inhibitor. In other people, protease inhibitors may not work as well or the benefits might not last. Clinical trials are going on to help answer questions about where HIV "hides" and why people have different results with protease inhibitors.

Which protease inhibitor will I take?

There are five approved protease inhibitors: ritonavir (Norvir) and nelfinavir (Viracept) are for use by adults and children, while indinavir (Crixivan) and the two forms of saquinavir (Invirase and Fortovase) are approved for adults only. Invirase was approved in 1995, and Fortovase, a new, stronger form of saquinavir was approved in 1997. The company that makes both drugs will continue to make Invirase available to people who already take that form of saquinavir through Spring 1998. After that, it will be available to them under a limited distribution program. A decision about which drug to take should be made with a doctor who knows your individual condition, and has medical knowledge of HIV disease. By finding out about the available treatment options, you can talk to your doctor about the risks and benefits of different drug combinations.