Evaluation of the efficacy of H1 blockers by noninvasive measurement techniques

Evaluation techniques for determining the strength of action and the onset of activity of H1 receptor blockers have not yet been sufficiently standardized.

The clinical efficacy of the H1 receptor blocker loratadine was to be measured upon a wheal response subsequent to an intracutaneous injection of 0.1 ml histamine (0.1%).

In a pilot study, 10 patients were treated with the H1 receptor blocker loratadine for a period of 7 days. Various noninvasive measurement techniques, i.e. 20-MHz sonography, laser-Doppler flowmetry, chromatometry using the Lab* system and computer-assisted planimetry, were applied to provide a quantitative evaluation of the wheal and the marginal erythema. Using these quantification methods, the development of the urticarial reaction 20 min after injection and its decline were evaluated.

The urticarial reaction was reduced substantially under treatment with 10 mg loratadine over a period of 7 days. The methods we used could accurately quantify different aspects of the urticarial reaction noninvasively.

All of the chosen measurement techniques are widely recognized. For objective assessment of the urticarial reaction with high-frequency ultrasound, we recommend the measurement of the distance between skin entrance echo and fascia since the demarcation of the wheal is often impossible by ultrasound. In order to improve comparison of results of various workgroups in the future, we therefore suggest the use of the selected combination of noninvasive procedures as a standard for evaluating the efficacy of H1 receptor blockers.