Drug boosting and recycling

Even if you have used all of the available drugs, you could still put together a combination using drugs you have used previously. Sometimes you may not have developed complete resistance to all the drugs used in a previously failing combination.

Resistance to some drugs can sometimes be overcome by increasing drug levels.

This has been done for many years by using ritonavir to boost the levels of other protease inhibitors in the blood. Response to treatment is often higher with these boosted doses.

Some protease inhibitors may also boost the levels of other PIs inside cells, which is the most important concentration. For example, when atazanavir and saquinavir are both boosted by a small dose of ritonavir in the same combinations, the levels of saquinavir inside cells stays higher for longer.

Research on dual-boosted PI combinations has not shown benefits over single boosted PI combinations.

Some nukes may be able to be recycled.

Even when only a couple of drugs are new in a six- or seven-drug combination, they may work. If you have used up other options then it is worth trying regimens that include drug recycling.