How do they work?

NRTIs disrupt the process by an infected cell is forced to replicate the genetic material of an invading HIV particle, rather than its own. Effectively they confuse the process by mimicking the genetic structure of HIV DNA.

NNRTIs also disrupt the replication process, but by disabling an enzyme which controls it

Protease inhibitors block another key enzyme which HIV requires to re-produce itself.

Fusion inhibitors - a new class of drug - prevent HIV from entering target cells.

What is the best way to use them?

It has been shown that the most effect way to combat HIV is to take a combination of different antiretroviral drugs - usually three at the same time.

HIV has an extraordinary capability to mutate into new forms, giving the virus a powerful ability to develop resistance to drugs.

Blitzing the virus with a combination of drugs makes it less likely that resistance will be a problem.

However, scientists that the only way to combat HIV effectively in the longer term will be to develop new drugs which fight the infection in different ways.

How wide is access to them?

The drugs have been made widely available in the developed world.

However, they are expensive, and this, together with logistical problems concerning their distribution, has meant that they have been denied to millions of people in the developing world.

Where do the big drugs companies stand?

Many of the big pharmaceutical companies have been reluctant to lower the price of their products, arguing that it would compromise their ability to research and develop new alternatives.

However, concerted international pressure has forced a re-think.

Cheaper generic versions of expensive patented drugs are now being made available.