The difference between success and failure
With the new combination therapies - three drugs with two different mechanisms of action - it is possible in at least 75 percent of AIDS patients to bring the number of viruses below the detection limit of 500 copies per cubic millimeter of blood. But the remaining failures have so far remained unexplained. Processes in the infected cells may be to blame - according to scientists on February 2, 1998, the first day of the 5th US conference on retroviruses and opportunistic diseases in Boston. The currently most modern drug treatment for HIV infection combines two classes of drugs: so-called nucleoside analogues, known as "&132;brakes&147"; act for the HIV enzyme reverse transcriptase, and drugs to inhibit the HIV enzyme protease.
The nucleoside analogues are sometimes administered in an inactive form. The active substance itself has no effect on HIV; it is only in the cells that a triphosphate of the substance forms the molecule that intervenes in the replication cycle of the AIDS virus.
Dr. Christine Katlama from the Hopital de la Pitie-Salpetriere in Paris has now compared the participants in two studies: subjects from the first group immediately received two such nucleoside analogues. With these alone, the number of viruses in the blood fell below the detection limit in 21 percent of the patients. However, in subjects who initially only took one drug from this &132;class&147; received, this result was registered with a subsequent other medication in only five percent of those treated.
The conclusion communicated on Monday: With some AIDS drugs, it obviously depends on whether the cells actually convert them into the effective form. Basically, these results can also simply be an indication that the HI viruses have already become resistant to the therapy.