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Penicilloyl-polylysine stability and clinical use over time.

BACKGROUND
The major penicillin skin test reagent, penicilloyl-polylysine, has not been commercially available since October 2004. The minimal concentration of penicilloyl-polylysine necessary for safe penicillin skin testing has not been determined.


METHODS
Penicillin skin testing was performed on 596 individuals between October 2004 and October 2006 using out-of-date commercially produced penicilloyl-polylysine as part of a complete panel of reagents. The concentration of active penicilloyl-polylysine was measured. Outcomes were compared with those for 921 individuals tested between October 2002 and September 2004 using in-date commercially produced penicilloyl-polylysine.


RESULTS
There was no significant difference in the fraction of patients who had positive skin test results using indate (5.1%) versus out-of-date (4.7%) penicilloyl-polylysine. There were four mild but no serious adverse reactions in the patients tested with the outdated reagent who were then challenged with oral penicillin class antibiotics.


CONCLUSION
Penicillin skin testing can be safely done using penicilloyl-polylysine down to a concentration of 4.29 × 10(-5) M.