Vienna, Austria – A new study conducted by researchers at MedUni Vienna has revealed limited effectiveness of intramuscular adrenaline in counteracting the blood pressure drop induced by histamine, a key mediator in severe allergic reactions. The findings, published March 2 in the journal Allergy, challenge the long-held assumption that adrenaline injections are consistently effective in reversing anaphylactic shock.
The research team, led by Matthias Weiss-Tessbach and Bernd Jilma of the Department of Clinical Pharmacology, induced a controlled decrease in blood pressure in healthy volunteers through a 15-minute intravenous histamine infusion. Plasma histamine levels achieved during the infusion mirrored those observed in patients experiencing severe anaphylaxis. Participants then received either an intramuscular adrenaline injection or a placebo.
The results indicated that only a minority of participants – five out of twenty – experienced a short-lived improvement in blood pressure following the adrenaline injection. A subsequent dose of adrenaline failed to provide sustained stabilization of blood pressure. The difference in response between the adrenaline and placebo groups was described as “very small” by the researchers.
Adrenaline injections remain the primary first-line treatment for acute, severe allergic reactions, a practice largely based on clinical experience and observational data, according to the study. However, the MedUni Vienna research highlights the difficulty of conducting placebo-controlled trials in severe anaphylaxis cases, and underscores the demand for alternative or adjunctive therapies.
The study focused specifically on the hypotensive effects of histamine, alongside other anaphylactic symptoms like breathing difficulties and skin reactions. During severe allergic reactions, histamine causes blood vessel dilation and circulatory instability. By isolating this mechanism, the researchers aimed to better understand adrenaline’s impact on histamine-induced hypotension.
Research has previously established a strong correlation between plasma histamine concentrations and the occurrence of hypotension and shock in humans. A 1996 study published in PubMed found that elevated plasma histamine levels coincided with decreased mean arterial pressure, and that the body’s sympathetic nervous system response varied depending on the method used to induce histamine release. That study, which examined the effects of morphine and compound 48/80 on catecholamine release, noted that histamine receptors are present in adrenergic terminals and can inhibit norepinephrine release.
The MedUni Vienna team’s findings do not advocate for a change in current anaphylaxis treatment guidelines, but rather emphasize the need for further investigation into more effective interventions. The research suggests that while adrenaline may offer some benefit in certain cases, its efficacy in reversing histamine-induced hypotension is limited and inconsistent.
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