[Studies on antibiotic skin testing].
Commercially available antibiotics for injection are supplied with test ampules. Users are instructed to dissolve them to make 300 micrograms/ml solution for intradermal pretests to avoid allergic reactions. Sometimes this concentration is too low to prevent anaphylactic reactions. In the present study, we tried to find the maximum concentration for the intradermal tests which would have high sensitivity without giving nonspecific, false positive reactions. We investigated intradermal tests with cephalothin (CET) in a patient who suffered from anaphylaxis after drip infusion with CET, although she was judged to be negative to CET by the usual intradermal test prior to the infusion. Her CET skin test was negative at a concentration of 150 micrograms/ml and positive at 300 micrograms/ml 6 weeks after anaphylaxis, but negative at 300 micrograms/ml and positive at 1000 micrograms/ml 4 and 7 years after anaphylaxis. Prick tests were always negative, even with the maximum soluble concentration of CET, 200 mg/ml. Nonspecific reactions to intradermal tests at concentrations as high as 1000 micrograms/ml were examined with 20 kinds of penicillins and cephems in 51 healthy subjects without histories of drug allergies. Very few false positive reactions were observed, except in 5 out of 24 cases with cefotiam. Intradermal tests at 3000 micrograms/ml, however, frequently resulted in nonspecific reactions. We conclude that 1000 micrograms/ml, not 300 micrograms/ml solutions should be used for intradermal tests to prevent allergic reactions to the injection of antibiotics.