Investigation of the anti-allergic activity of azelastine on the immediate and late-phase reactions to allergens and histamine using telethermography.

BACKGROUND: Due to the interest in azelastine's diverse modes of action, this study investigated its effects on immediate and late-phase cutaneous allergic reactions using visual methods and telethermography.

OBJECTIVE: The aim of the study was to investigate the effect of azelastine on the immediate and late-phase skin reactions using both planimetric evaluation of weal and erythema and a telethermographic technique.

METHODS: The study was a double-blind crossover study; medication consisted of one tablet per day for 7 days of either placebo or azelastine 4 mg. Eight allergic patients were assessed on five occasions: prior to treatment, at the end of the first 7-day treatment, after a 21-day washout period, following the second 7-day treatment period and finally following a 2-6 week washout period. Skin prick tests with timothy grass and intradermal tests with Alternaria allergens were performed on the patients' back. In addition, patients were tested with intradermal histamine as a positive control. Surfaces of weal, erythema and infiltration were calculated using computerized planimetry at 0, 20, 40 and 60 min, and 3, 6 and 8 h. Thermographic images were recorded and the thermographic area and the increase in average temperature (DeltaT) were calculated.

RESULTS: The coefficient of variation within baseline reactions ranged from 3 to 32% for weal and erythema and from 5 to 25% for thermographically recorded reactions. The stronger the reaction, the more constant the baseline was. Treatment with azelastine (4 mg/os once daily) inhibited immediate reactions to allergens by 65% (range 55-74) and to histamine by 68% (range 47-82). The late-phase reactions to allergens were less well defined and showed larger individual differences in the degree of inhibition caused by azelastine, they were inhibited by 49% (range 32-67). Late-phase reactions to histamine were less intense and could only be detected with thermography; only thermographic units showed a decrease (26%) in response to azelastine.

CONCLUSION: This study has confirmed azelastine's histamine-blocking activity. In addition, the late-phase results suggest that azelastine has anti-inflammatory activity. The reproducibility and sensitivity of the thermographic results confirm the usefulness of this technique in immunopharmacology.