Drugs to control the HIV virus fail because the patients are not taking them properly, experts say.

Research published in the Journal of the American Medical Association attempted to find out why HIV maintenance therapies worked for some, but not for others.

The aim of the therapies is to reduce the levels of the HIV virus in the patient to the lowest possible and reduce the risk of developing full-blown AIDS.

It was initially thought that the drugs themselves were not as effective as first hoped, or that the virus was sometimes capable of quickly changing its structure to render the drugs useless.

However, the JAMA study reveals that patients' own failure to stick to a rigid timetable of doses is more significant.

The report's authors, based in France at three urban hospitals near Paris, suggest that this should be investigated before the patient is tried on a different drug.

'Major implications'

They wrote: "These results have a major practical implication for antiretroviral drug management."

Some patients are simultaneously taking as many as three drugs, each of which has to be taken at particular times.

Some have to be taken on an empty stomach, and some with food, which, over the years, can mean havoc in the day-to-day lives of HIV-positive patients.

A spokesman for the Terence Higgins Trust said: "Doctors don't expect all their patients to take a course of antibiotics properly, and that's just over a week or a fortnight.

"HIV medication isn't just for a week, it's over a long period, and it's no surprise that some people find it hard to follow properly, particularly if you have to take different drugs at different times of the day.

"In addition, many HIV drugs have side effects such as nausea, vomiting and malaise."

He said that the key to improving success rates was developing treatments that could be taken at more convenient times, and which had fewer side effects.