Correlation of the Vasoconstrictor Assay and Clinical Activity in Psoriasis

To the Editor.—  Cornell and Stoughton¹ reported excellent correlation in 20 of 23 instances between the vasoconstrictor assay for topical corticosteroid preparations (16 hours [57 600 s] nonoccluded application, single reading measurement) and paired comparison studies in psoriatic patients. Among those not demonstrating equivalence was 0.2% hydrocortisone valerate cream compared with 0.1% betamethasone valerate cream. No difference between the preparations could be detected clinically, but hydrocortisone valerate cream was superior in the skin blanching test.Gibson² stated that he found the best correlation between the vasoconstrictor assay and clinical efficacy in psoriasis using a modified skin blanching technique (six hours [21 600 s] occluded application, serial readings between seven hours [25 200 s] and 25 hours [90 000 s], followed by analysis of the areaunder-the-curve values produced). Stoughton and Cornell³ replied that it would be very interesting to examine hydrocortisone valerate cream using an area-under-the-curve method.We