Background: Histamine release and vasodilation during an allergic reaction can alter the pharmacokinetics of drugs administered via the intranasal (IN) route. The current study evaluated the effects of histamine-induced nasal congestion on epinephrine pharmacokinetics and heart rate changes after IN epinephrine. Methods: Dogs received 5% histamine or saline IN followed by 4 mg epinephrine IN. Nasal restriction pressure, epinephrine concentration, and heart rate were assessed. Maximum concentration (C max), area under plasma concentration-time curve from 1 to 90 min (AUC 1-90), and time to reach C max (T max) were measured. Clinical observations were documented. Results: In the 12 dogs in this study, nasal congestion occurred at 5-10 min after IN histamine administration versus no nasal congestion after IN saline. After administration of IN epinephrine, IN histamine-mediated nasal congestion was significantly reduced to baseline levels at 60, 80, and 100 min. There were no significant differences in C max and AUC 1-90 between histamine and saline groups after IN epinephrine delivery (3.5 vs 1.7 ng/mL, p = 0.06, and 117 vs 59 ng/ mL*minutes, p = 0.09, respectively). After receiving IN epinephrine, the histamine group had a significantly lower T max versus the saline group (6 vs 70 min, respectively; p = 0.02). Following IN epinephrine administration, the histamine group showed rapidly increased heart rate at 5 min, while there was a delayed increase in heart rate (occurring 30-60 min after administration) in the saline group. Clinical observations included salivation and emesis. Conclusion: IN histamine led to more rapid epinephrine absorption and immediately increased heart rate compared with IN saline. IN epinephrine decreased histamine-induced nasal congestion.

Epinephrine is the standard of care for the treatment of severe allergy and anaphylaxis. Epinephrine is most often administered through the intramuscular (IM) route via autoinjector. The current study aimed to evaluate an alternative method of epinephrine treatment through intranasal (IN) delivery in dogs. The pharmacokinetic (PK) parameters of maximum plasma concentration (Cmax), time to reach maximum plasma concentration (Tmax), and area under the plasma concentration‐time curve from 0 to 90 minutes (AUC0–90) were observed after IN epinephrine (2, 3, 4, 5, 10, and 20 mg) and IM epinephrine via autoinjector (0.15 and 0.3 mg) for 90 minutes. Heart rate effects were measured after IN (2 and 5 mg) and IM (0.15 and 0.3 mg) epinephrine administration. IN epinephrine (5 mg) demonstrated significantly greater plasma epinephrine concentration at 1 minute as compared with IM epinephrine (0.3 mg) (1.68 ± 0.65 ng/mL vs 0.21 ± 0.08 ng/mL, P = .03). There were no significant differences in Cmax, Tmax, and AUC0–90 between 2‐mg IN and 0.15‐mg IM epinephrine or between 5‐mg IN and 0.3‐mg IM epinephrine. IN epinephrine reduced heart rate increases, as compared to IM epinephrine. IN and IM epinephrine were both well‐tolerated. Overall, IN epinephrine demonstrated advantages over IM epinephrine, including the rapid increase in plasma epinephrine and lack of increased heart rate over time.

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