Researchers at Vanderbilt University School of Medicine in Nashville, have confirmed fears that physicians frequently expose small children to avoidable injury by overprescribing antibiotics in the chemical class known as tetracyclines.

In children up to the age of eight, the germ-killing drugs can permanently discolor the teeth - yellow, gray or brown - and deform them.

For that reason, the Food and Drug Administration for the past seven years has required supplies to warn physicians in the official prescribing instructions to withheld the tetracyclines from children in this age range unless other infection-fighting drugs are unlikely to work or may seriously endanger the patient.

Indications that many doctors don't heed the warning came initially from date on massive production of the tetracyclines in so-called pediatric dosage forms - syrups and liquids administered to patients who have difficulty swallowing capsules.

For example, the drugs committee of the American Academy of Pediatrics has reported that in the year ended June 30, 1973, the FDA certified about 15 tons of tetracyclines. An antibiotic can be sold only if the FDA certifies it to be safe and effective.

The committee saw a paradox in the continuing production of the tetracyclines in the forms that were inappropriate for young children, but that nonetheless were made specifically for them.

Until recently, however, no data were available on the frequency with which doctors prescribed the pediatric forms for young children and others, principally the elderly.

The Vanderbilt researchers - Wayne A. Ray, Charles P. Federspiel and William Schaffner - have partially filled the information gap with computerized studies of the 50,606 prescriptions for all forms of the tetracyclines filled for 27,888 ambulatory Medicaid recipients in Tennessee in a six-month period of 1975-1976.

They cite these key findings in an article in the August American Journal of Public Health and in a report to be published by the Journal of the American Medical Association:

Doctors wrote tetracycline prescriptions for 1,288 children in the under-eight age range; 82 per cent got the drugs as syrups.

Of the 2,740 prescriptions for syrups (5.4 per cent of the total of 50,606 tetracycline prescriptions), more than 55 per cent were for under-eight children; 22 per cent were for children eight through 14.

Only 8.7 per cent of the liquid tetracycline prescriptions were for individuals 15 through 59, and only 13.8 per cent for those 60 or older.

Of the 60-and-older patients who got tetracyclines, only 1.6 per cent got them in liquid form.

The researchers, after reviewing the diagnoses, said that at least three-fourths of the prescriptions for liquid tetracyclines were "inappropriate."

They also said that restrictions on these products "would decrease the strikingly large number of inappropriate prescriptions for young children," but would affect older persons "only rarely."

"The unrestricted availability of potentially harmful drugs which frequently are used incorrectly cannot be justified," the scientists wrote in the Amercian Journal of Public Health.

An FDA spokesman said last week that a panel of outside experts on anti-infective drugs considered the problem several months ago and decided that doctors excessively prescribe the tetracyclines in pediatric forms, including drops occasionally given to infants and very young children.

As a result, the spokesman said the agency, while not agreeing to ban liquid tetracyclines, plans to take three actions over an unspecified time period:

Tightening the official labeling for tetracycline liquids to emphasize that only adults - mainly the elderly - should get them.

Reminding the medical profession, probably in the FDA Drug Bulletin that goes to every doctor, to show caution and restraint in prescribing the tetracyclines in any form for under-eight children.

Halting sales of tetracycline drops.