Kahn: It’s very important to take these medicines very precisely.

Narrator: This is Science Today. New drugs called protease inhibitors, which seem to eliminate the HIV virus from the body, have revolutionized AIDS treatment for those lucky enough to receive them. But Dr. James Kahn of the University of California, San Francisco says there’s a stiff price: besides risking serious side effects, you literally can’t afford to skip a single dose, or else there’s a strong chance the virus will become resistant to the drug.

Kahn: This is not a kind of medicine where you can skip doses, where you can take drug vacations from. You really have to embark on a lifetime commitment of this therapy.

Narrator: And sometimes, says Kahn, the virus becomes resistant anyway.

Kahn: Sometimes the drug’s simply not effective because of a poor match between the virus and the drug, sometimes the drug is given at a low dose or not in the best combination, or sometimes the person’s virus is too hearty.

Narrator: For Science Today, I’m Larissa Branin.