1.   Drugs like AZT attack an enzyme known as reverse transcriptase.

2.   The three drugs are called protease inhibitors because they attack an enzyme called protease that is used by the AIDS virus, HIV, to multiply in the body.

3.   Unlike AZT and similar drugs, which target the enzyme reverse transcriptase, protease inhibitors attack another enzyme crucial to viral reproduction.

4.   The two drugs attack this enzyme at different points.

5.   Invirase slows down progression of the HIV virus, which causes AIDS, by attacking proteinase enzymes.

6.   Protease inhibitors attack an enzyme called protease which HIV needs late in its reproductive stage.

7.   The inhibitors work by attacking an enzyme called protease that is needed for reproduction by the HIV virus which causes AIDS.

8.   The inhibitors work by attacking an enzyme called protease that is needed for reproduction by HIV, the virus which causes AIDS.