Two medical centers are recommending against the use of injections of a papaya enzyme into discs to treat back problems.

"Our experience indicates there is no general category of patients who benefit from chymopapain injections," said Dr. Arthur Day of the University of Florida Health Science Center. "The procedure's high failure rate does not even justify its use as a last step in conservative (non-surgical) therapy."

Chymopapain was touted as a wonder drug alternative to surgery in 1982, when it was approved by the Food and Drug Administration. It is supposed to make so-called "slipped discs" return to normal by shrinking or dissolving the jelly-like material that has escaped and is pressing on a nerve.

"Although chymopapain is a substance that will make disc material shrink, injecting it into the disc itself makes little sense," said Dr. Charles A. Fager of the Lahey Clinic in Burlington, Mass. "There is no possibility that an enzyme injected into the disc space might can reach any extrusion . . . outside the disc."

Discs separate the vertebrae and act as shock absorbers. When one ruptures, the jelly-like filling seeps out. Usually, it returns inside by itself, but when it is trapped outside the disc, surgery might be necessary, the doctors said.

A survey by the American Association of Neurosurgeons, which gave chymopapain a qualified endorsement in 1983, now says its members are turning away from it. Fifty-two percent of doctors who once used it no longer do.

Most back pain, experts say, goes away by itself.