How Drugs Work Disease Prevention

The first step in that process occurs when a person is exposed to HIV (usually through sexual contact or transfer of blood from an infected to a healthy person). HIV travels through the bloodstream until it comes into contact with certain types of white blood cells that contain proteins known as CD4 (cluster designation 4) receptor sites on their surface. The virus then attaches itself to the CD4 receptor and injects a protein (called the p24 protein) into the host cell s interior. The p24 protein carries the genetic information that controls reproduction of HIV. 

Once installed inside the host cell, the p24 protein attaches itself to and takes over control of the cell s own DNA. The HIV genetic code begins to function within the host cell, ordering it to produce 

The best solution that researchers have so far discovered involves the use of a type of drug known as an antiretroviral agent, that is, a chemical that interferes with the process by which the p24 protein takes over the host cell s own system of replication and reproduction. Many people who are infected with HIV are now able to live reasonably normal lives because they have access to an AIDS cocktail that contains some combination of three such antiretroviral substances. 

The structure of sulfa drug molecules, however, is very similar to that of the PABA molecule. Compare the structure of sulfanilamide, in part 2 of the diagram, with that of PABA. Notice how easily the sulfanilamide molecule can substitute for the PABA molecule in the synthesis of the bacterium s folic acid. The problem for the bacterium, however, is that folic acid produced from a sulfa drug molecule is 

Mechanism of sulfa drug action (1) Normal sequence, (2) Action of sulfa drug 

---