Effect of topically applied local anaesthesia on histamine flare in man measured by laser Doppler velocimetry

Abstract

The direct and indirect effects of histamine on the cutaneous microvasculature were measured by laser Doppler velocimetry. Histamine (6.51 x 10(-4) M) was injected intradermally into the forearms of eight healthy subjects following treatment with a topically applied local anaesthetic cream (EMLA) or equivalent placebo. The blood flow at the injection site (0 cm) and at 1 and 2 cm proximally was measured by laser Doppler velocimetry over 80 minutes. Analysis of the changes in magnitude of the hyperaemic responses with time showed no difference at the 0 and 1 cm sites, but a marked reduction was found at the 2 cm site following EMLA treatment (p less than 0.05). At all three sites the decay of the histamine-induced hyperaemia was faster following EMLA treatment than with placebo (p less than 0.04). The experiments showed that the indirect effect of histamine on the cutaneous microvasculature in the peripheral flare around the injection site was greatly diminished by prior application of EMLA cream and this supports the neurogenic hypothesis: pre-treatment with EMLA cream did not affect the development of hyperaemia and oedema at the site of histamine injection where the mediator acts directly on the cutaneous microvasculature.

Intradermal Tests for Diagnosis of Drug Allergy are not Affected by a Topical Anesthetic Patch

“…Our study re-opens this discussion. Since the wheal responses were not affected in ours or any of the previously published studies,20,21,29,30,31 and being the wheal more likely to be used as criteria for positivity, it seems that the topical anesthesia can be reliably used. Therefore, it might be a suitable method for implementation, as long as the considered criterion for diagnosis is the wheal increase.…”

“…These results are contradictory to our findings and to those reported by Wolf et al21 as both studies evidenced no effect on flare responses. In Wolf's et al study, the flare responses were generally less than 2 cm in diameter,21 and this discrepancy in reaction sizes for Sicherer's et al study20 could explain the difference in the effects on flares responses, since EMLA® has been shown to reduce the flare in an area beyond 2 cm from the injection site of histamine using Doppler velocimetry 29. From a practical point of view, since it occurred only in tests whose flare was very large, a diminished reaction would not compromise the correct diagnosis.…”

Duodenal ulcer patients exhibit a greater skin response to histamine

“…Activation of either type of receptor can elicit maximum dilation, but the responses differ in their sensitivity to histamine, in the duration of their effect and in the mechanism of their production. In addition, the flare evoked by histamine via H1 receptors is a manifestation of an axonal reflex, as it is blocked by local anesthesia [8,20]. By contrast, activation of the H2 receptors, located on vascular smooth muscle cells, causes dilation that develops more slowly and is more sustained [8,19].…”

“…By contrast, activation of the H2 receptors, located on vascular smooth muscle cells, causes dilation that develops more slowly and is more sustained [8,19]. In addition, the flare evoked by histamine via H1 receptors is a manifestation of an axonal reflex, as it is blocked by local anesthesia [8,20]. The gastric acid secreting parietal cells, however, possess only histamine receptors type H2 [21].…”

Analgesic and anti-inflammatory effects of lignocaine-prilocaine (EMLA) cream in human burn injury

“…Local anaesthetics may alter release of inflammatory mediators, for example histamine release from mast cells in vitro [26], leukotriene B-4 and interleukin-1 release from polymorphonuclear granulocytes and mononuclear cells in vitro, respectively [27]. The flare reaction induced by trauma and injection of inflammatory mediators is diminished by local anaesthetics, in contrast with the weal and local red reaction [28][29][30]. Thus local anaesthetics block axon reflexes and sensory functions of nociceptors.…”