Dosage considerations in patch testing with liquid allergens

This study examines reproducibility of water and ethanol drop volumes from plastic squeeze dropper bottles, examines the difference in drop volumes between commonly used liquid patch test solutions, and evaluates the volumes of water and ethanol needed to saturate Finn and IQ Chamber filter papers. 2 plastic squeeze dropper bottles recommended for use in patch testing have poor reproducibility compared to other bottles tested. 3 aqueous allergens tested (formaldehyde 1%, methylchloroisothiazolinone/methylisothiazolinone 0.01%, and dimethylol dihydroxyethyleneurea 4.5%) have drop volumes equivalent to water. Smaller drop volumes are produced by ethanol, hydrocortisone butyrate 1% in ethanol, cocamidopropyl betaine 1% a.q., and propylene glycol 30% a.q. Filter paper saturation volumes using distilled water are 16-19 micro L in standard Finn Chambers and 29-35 micro L in IQ Chambers. Ethanol saturation volumes are slightly lower. Previously recommended volumes of application for aqueous allergens of 15 micro L for standard Finn Chambers and 25 micro L for IQ Chambers (slightly below the filter paper saturation points) are appropriate. Selection of dropper bottles should consider drop volume reproducibility, differing drop volumes for different allergens, and the patch test chamber system being used.