Friday, November 27, 1998 Published at 12:58 GMT
Health: Medical notes
Aids drugs factfile
There are several drugs which specifically target HIV at different points in its life cycle. Using them in combination has proved much more effective than prescribing them one at a time. In Europe and the US, combination therapy has resulted in a huge drop in Aids deaths and in some people have reduced the virus to undetectable levels. However, the drugs do have side effects, they do not work for all people and the effectiveness of individual drugs can wear off. And they are very expensive.
What were the first anti-HIV drugs?
The first drugs to be developed to combat HIV were AZT (also called zidovudine or Retrovir), ddI (didanosine or Videx) and ddC (zalcitabine or Hivid). These all belong to a group of drugs called nucleoside analogues or reverse transcriptase inhibitors. They prevent the production of an enzyme called reverse transcriptase which enables HIV to spread, leading to a breakdown of the patient's immune system.
AZT taken alone has been shown to reduce HIV transmission from woman to baby.
Women who avoid breastfeeding and take AZT are about 66% less likely to pass on the virus to their child.
Using combinations of drugs
Scientists noticed that people using more than one of the drugs were less likely to develop Aids, the syndrome of diseases caused when HIV has destroyed the immune system. They were therefore more likely to live longer.
In the UK, five nucleoside analogues have been licensed. In addition to AZT, ddI and ddC, doctors can also prescribe 3TC (lamivudine or Epivir) and d4T (stavudine or Zerit).
Some patients are also taking part in trials for another nuceloside analogue drug called abacavir.
Another group of drugs which stops the reverse transcriptase enzyme from working is non-nucleoside reverse transcriptase inhibitors or NNRTIs for short.
One, nevirapine, has been licensed in the US and is available in the UK. Two others are being tested.
The drugs are particularly effective for people who have not had any other anti-HIV drugs before, but they have to be taken with at least two nucleoside analogues.
Other anti-HIV drugs
There are three licensed drugs in Europe which target another enzyme which helps HIV to spread.
They are usually used in combination with nucleoside analogues. They are: indinavir (sold as Crixivan), ritonavir (trade name Norvir) and saquinavir (sold as Invirase).
Using a protease inhibitor in combination with other anti-HIV drugs can reduce the progress of HIV and the risk of death by 50% in people whose immune systems have been severely compromised. The benefits for those whose immune systems have been so severely attacked by HIV is not as noticeable.
However, combinations that contain indinavir or ritonavir can reduce the virus to almost undetectable levels in many people with HIV.
Scientists are creating more protease inhibitors.
When HIV reproduces, it can produce different strains which may be resistant to some drugs.
In some cases, the new strains can be resistant not just to one drug, but to other related drugs.
The mutation of HIV is one of the main reasons that a particular combination of drugs can lose effectiveness over time.
People are advised to change their combination of drugs if it becomes less successful at fighting HIV.
Drug-resistant HIV can be transmitted from person to person through body fluids - the same way as ordinary HIV.
Taking combination therapy
Taking the wrong dose of anti-HIV drugs or the wrong combination can be more dangerous in the long run that not taking the drugs at all.
This is because wrongly treated HIV can reproduce at very high rates and produce resistant strains very quickly.
Taking combination therapy can be very disruptive to daily life.
The drugs have to tbe taken at the right time in the right doses. Some have to be taken on an empty stomach and others on a full stomach.
It is vital that patients do not forget to take their pills as, if the level of drugs in the bloodstream drops too low, HIV may develop resistance to them.
The side effects associated with the different anti-HIV drugs vary according to the drug and the individual taking them. They can include anaemia.
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