A number of new drugs from existing classes are being studied. Here's a brief rundown of drugs that have started trials in people:

Nucleoside Analog Reverse Transcriptase Inhibitors (NRTIs)

• Amdoxovir (DAPD): Early results from an ongoing Phase II study (in people resistant to other NRTIs) showed only a modest anti-HIV effect after two weeks on the drug.

• AVX 754: active in vitro against HIV resistant to other NRTIs. Currently in early Phase II trials.

• Elvucitabine (ACH 126,443, L- Fd4C): active in vitro against HIV that is resistant to Epivir. Currently in Phase I trials. Also active against hepatitis B virus. It may be used once a day or perhaps even once a week.

• Racivir (PSI 5004): similar to Emtriva (FTC); active against HIV and hepatitis B virus that is resistant to Epivir (3TC). Currently in Phase II trials.

Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)

• Etravirine (TMC 125): Recent study showed effectiveness in people resistant to Sustiva and Viramune; may be very strong in people who have never taken an NNRTI. Currently in Phase II trials. Taken twice a day.

• TMC278 (DAPY): shows in vitro activity against NNRTI-resistant virus; in early development.

Protease Inhibitors (PIs)

• Brecanavir (GW 640385): active in vitro against resistant virus. In Phase II trials. Taken with Norvir.

• Darunavir (TMC 114): Phase II trial showed drug to be effective in people with multi-drug resistance -- may receive FDA approval as early as this summer. Taken twice daily with Norvir (ritonavir).