Intranasal epinephrine in dogs: Pharmacokinetic and heart rate effects

Abstract 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.

to decreased airway resistance, bronchodilation, reversal of hypotension, and protective chronotropic and ionotropic cardiac effects. 1 Epinephrine is most commonly administered via intramuscular (IM) injection via an autoinjector. [4][5][6] Autoinjectors are effective in reducing anaphylactic symptoms; however, they are associated with several patient concerns and are often underused. [7][8][9] Patients and caregivers may lack confidence with autoinjectors, which can contribute to anxiety and impede autoinjector use. [10][11][12] In addition, there is potential for injuries associated with accidental injections and lacerations at the injection site, as well as the administration of expired autoinjector epinephrine. 5,7,9,13,14 Furthermore, there have been product recalls due to issues associated with autoinjector malfunction and inadequate drug delivery. 15 Lastly, cost effectiveness and autoinjector availability are potential barriers for certain patients with severe allergy. 12,16 These patient concerns may lead to lack of or delayed epinephrine treatment, which decreases the rate of survival in the event of anaphylaxis. 17 To overcome these drawbacks, alternative routes of administration and devices are needed for epinephrine delivery. The nasal cavity is an ideal site for drug delivery, particularly for medications requiring a rapid onset of action, because of the degree of vascularization and tissue permeability. 18 Intranasal (IN) administration has been explored for a wide variety of drugs, including naloxone, nalmefene, fentanyl, hydromorphone, midazolam, glucagon, and haloperidol. [19][20][21][22][23][24][25][26] For example, IN glucagon for hypoglycemia treatment and midazolam for seizure termination are used when an immediate pharmacologic intervention is required. 23 lacking. To our knowledge, only one preliminary clinical study has been conducted, which investigated epinephrine pharmacokinetic (PK) after IN versus IM administration in five participants. 27 Likewise, only two preclinical studies on IN epinephrine have been published, which were conducted in dogs with compromised cardiovascular activity during ventricular fibrillation. 28,29 We have conducted the current study in dogs to expand upon the literature knowledge base on IN epinephrine, and to provide the platform for future clinical studies.
The current study evaluated the PK profile of varying doses of epinephrine via IN administration in dogs. The study aimed to compare PK parameters, heart rate effects, and safety of IN epinephrine via nasal drops versus IM epinephrine via autoinjector.

| Animals
All animal experiments were approved by the Institutional Animal Care and Use Committee of MRIGlobal prior to dog procurement from a US Department of Agriculture (USDA)-certified vendor. Dogs aged 10 to 11 months (7.6 to 10.5 kg) from Covance Research Products were used in the study. Dogs were individually housed indoors in primary enclosures (cage banks, Shor-line) that provided floor space either meeting or exceeding specifications of the USDA Animal Welfare Act and as described in the Guide for the Care and Use of Laboratory Animals. 30,31   Dogs were housed under controlled environmental conditions with a   standard 12-hour light/dark cycle, with free access to food and water, and exercised on a regular weekly basis. Prior to epinephrine administration, dogs were shaved on the left and right chest for electrode placement and on the right thigh for IM injections.

| Experimental Design
The primary aim of these studies was to determine if escalating

| Formulation Components
The epinephrine used for IN administration was purchased from MilliporeSigma, stored at 5 ± 3°C, and protected from light. The vehicle for IN epinephrine was formulated at MRIGlobal and was based on the injectable product with appropriate modifications suitable for IN administration. In addition to water, sodium metabisulfite (SMBS) and sodium chloride, the formulation included a viscosity modifier, preservative, and buffer. The final formulation had a pH of 5.0 ± 0.5.
Autoinjectors were procured from local pharmacies and stored at room temperature (20-25°C) and protected from light.

| Dosing
For IN administration, conscious dogs (no anesthesia/sedation) were restrained by a technician, while a second technician delivered 100 µL of epinephrine in a 200-µL capacity cannula (pipette tip) that was attached to a 100-µL calibrated pipette. No dead space was present in the cannula following dose delivery.
The entire dose was delivered at a depth of three-quarters of an inch into the right nostril. For IM epinephrine administration, the autoinjector dosing procedure provided in the manufacturer's instructions was utilized.

| Sample collection
Up to 2 mL of whole blood was collected (Vacuette ® tube 4 mL K2EDTA [Greiner Bio-One]) via venous puncture from jugular or cephalic vein. Blood serum and plasma samples were separated from whole blood by centrifugation, kept on ice, and protected from light when possible during the collection, aliquoting, and transfer processes. The PK plasma samples were vortex-mixed for approximately 1 minute, followed by centrifugation and aliquoting (typically 3 × 100 μL) into amber microcentrifuge tubes containing SMBS (5 μL). Following mixing, samples were transferred to the MRIGlobal Bioanalytical Group for analysis (one aliquot per PK sample).

| Bioanalysis of plasma samples
Plasma samples were analyzed for epinephrine concentrations using a calibrator range (lower limit of quantitation to upper limit of quantitation) of either 0.4 to 10 ng/mL or 1 to 32 ng/mL.

| Safety
All dogs were monitored regularly by the veterinarian on-site for adverse events, or occurrences including illness or reaction with or without the presence of study drug, as per the USDA Veterinary Dictionary for Drug Related Affairs (VeDDRA) current guidance. 32 Specifically, adverse events were recorded in log books at approximately 1 hour before and after epinephrine administration, and throughout the duration of the study.

| Cardiovascular effects
Within 1 minute of 2-mg IN epinephrine, heart rate increased to 108 ± 10.08 beats per minute (bpm) (40% over baseline) (Figure 2A). Within the first minute following 5-mg IN epinephrine, heart rate increased to 132 ± 14.34 bpm (48% over baseline) ( Figure 2B). However, the increase was of relatively short duration, with heart rates declining to 36% over baseline within 5 minutes. The magnitude of the heart rate change observed at 5 minutes remained relatively constant over the next ministration, heart rate increased to 47% over baseline. The level of heart rate increase remained relatively constant for the next 15 minutes and began to steadily increase by 59% over baseline at 20 minutes with a further increase to 79% over baseline at 60 and 90 minutes.

| Safety
IN epinephrine (2 to 20 mg) did not result in the appearance of either immediate or sustained adverse events in dogs that were followed for 2 weeks following the last drug administration. The most common adverse events with IN epinephrine were hypersalivation and emesis ( Table 2). The most common adverse event with IM epinephrine was limping. Dogs exhibited signs of stress following IN and IM drug administration; however, all recovered within several hours, and no sustained effects were noted over the following 2 weeks. Differences in heart rate activity may also be explained by variability in epinephrine absorption and differential activation of beta-adrenergic receptors that mediate tachycardia. 35 The inconsistent pattern of plasma epinephrine concentrations and heart rate effects may be supported by the known variability in epinephrine absorption across a range of doses. 14,27 Further studies are required to understand the irregular plasma con-  [27][28][29] Two preclinical studies showed that IN epinephrine rapidly increased plasma epinephrine concentrations and improved coronary blood flow during cardiopulmonary resuscitation in dogs. 28,29 These studies required the use of higher doses of epinephrine (7.5 to 14 mg) due to the compromised cardiovascular system of the dogs during ventricular fibrillation. In these studies, an alpha-adrenergic blocker, phentolamine, was administered prior to IN epinephrine to improve epinephrine absorption. 28,29 We have also used dogs to study epinephrine PK and pharma- In the current preclinical study, IN epinephrine produced rapid epinephrine absorption and similar PK parameters overall as compared to IM epinephrine. Additionally, IN epinephrine resulted in blunted heart rate effects as compared to IM epinephrine, and was well-tolerated.

| D ISCUSS I ON
Clinical studies will further investigate IN epinephrine PK and pharmacodynamic effects. IN epinephrine may be a potential alternative therapeutic approach in the treatment of severe allergy and anaphylaxis.

E TH I C S S TATEM ENT
All animal experiments were approved by the Institutional Animal Care and Use Committee of MRIGlobal (Kansas City, MO) prior to dog procurement from a US Department of Agriculture (USDA)certified vendor.

ACK N OWLED G M ENTS
Bioanalytical results were analyzed by Dr Michael Zhuo Wang.
Writing and editorial assistance was provided by Caryne Craige, PhD, of Fishawack Communications, LLC, and was funded by Bryn Pharma, LLC.

D I SCLOS U R E S
The authors have no conflict of interest to declare.