Recommendation of appropriate amounts of petrolatum preparation to be applied at patch testing

Background: No recommendation exists on the amount of petrolatum (pet.) preparation to be applied in a Finn Chamber (R) or van der Bend Chamber. Objectives: The aim of this study was to determine the appropriate amount of pet. preparation to apply in the Finn and van der Bend chambers. Methods: 12 volunteers were patch tested with green-coloured pet. in Finn and van der Bend chambers on the back on 3 occasions. Doses were 10, 15, 20, 25, and 30 mg initially and on second and third occasion, 10 mg was removed in van der Bend Chambers and 35 mg was added. On day 2, the test sites were scored. A negative test equalled a test area not covered to 100%. A positive test meant a completely green-coloured test area. Minor and major spreading was noted. The amount of pet. preparation yielding at most 5% negative reactions and having the least number of reactions with major spreading equalled the appropriate amount. Results: For van der Bend Chambers, all doses yielded more than 5% negative reactions. For the Finn Chamber (R), 30, 25, and 20 mg pet. yielded less than 5% negative reactions and with major spreading in 60%, 40%, and 25% of test sites. Conclusions: 20 mg pet. preparation was the optimal dose for the Finn Chambers (R).