FLT: Correction and Update

On December 21, 1990, AIDS TREATMENT NEWS mentioned FLT, an antiviral that we had listed two years ago as an important potential AIDS/HIV treatment. We said that we had found no published articles about FLT in a recent computer search, and assumed that the drug was not being developed. In fact, FLT is being developed by Lederle Laboratories (a division of American Cyanamid Company), and has already begun human trials. A number of articles have been published; we missed them because we did not know that several different spellings of the drug's chemical name are in use. (The best single name to use for a computer search is "fluorothymidine".)

Stanley A. Lang, Ph.D., project director at Lederle Laboratories, called to give us the correct information. He explained that a very early phase I trial, a single dose human study, has been finished; such studies are used to test pharmacokinetics, meaning how well the drug is absorbed, how long it stays in the body, etc. The drug was found to be very well absorbed orally, and it remains in the blood long enough that it would be used only twice daily. Now Lederle is about to start a phase I/II trial with 50 volunteers at three sites: Sloan Kettering in New York, Johns Hopkins in Baltimore, and the University of North Carolina in Chapel Hill. This trial will use five different doses, with each tested for four months.

In laboratory tests the drug has worked well against strains of HIV taken from patients. (Many earlier drug-development efforts went astray when they used the more convenient laboratory cultures of HIV in such tests; these viruses, which have been cultured for years in laboratories, are different from those found in patients.) FLT also (like most new antivirals being tested) is effective against virus strains which are resistant to AZT -- despite the fact that FLT is chemically similar to AZT.

Unfortunately, FLT also shows toxicity in animal tests, especially bone-marrow toxicity like AZT. AIDS drug expert Raymond F. Schinazi, Ph.D., was quoted in the December 13, 1990, Medical Tribune as saying that FLT "is one of the most potent compounds around. A promising drug, but it has to be used with a lot of caution."