Heat Illness, Allergic Rhinitis, Heat Injury, Sudomotor Sympathetic Dysfunction
Conditions
Keywords
H1 antihistamine, Sweating, Heat stress, Thermoregulation, M3 Muscarinic receptors, H1 receptor antagonism, M3 Muscarinic receptor blockade, Heat Illness/Injury, Allergic Rhinitis, Over-the-counter antihistamines, Allergy medication
Brief summary
Allergic rhinitis (AR) currently affects \ 25% of Canadians, and due to factors of climate change, this number is expected to increase over the coming decade. AR symptoms can significantly impact individuals' quality of life by compromising sleep, productivity, and social interactions. To alleviate AR symptoms, North Americans tend to rely on H1 antihistamine medications available over-the-counter (OTC) at most pharmacies. However, public health authorities currently suggest restraining all antihistamines during heat waves due to beliefs that M3 muscarinic receptor and H1 receptor antagonism, independent pharmacological mechanisms of H1 antihistamines, might suppress thermoregulatory responses to heat stress and increase individuals' susceptibility to heat-related illness/injury. To date, studies using supramaximal doses of antihistamines have demonstrated reductions in sweating, however these doses and administration routes are not the typical use case. Additional studies utilizing fexofenadine, a second-generation H1 antihistamine, have linked H1 receptor antagonism to reductions in skin blood flow, potentially impacting thermoregulation by reducing peripheral blood redistribution. Empirical evidence supporting OTC H1 antihistamines impacting thermoregulatory control at recommended doses is scarce. Thus, this study aims to systematically assess whether three common OTC H1 antihistamines, taken as prescribed, alter thermoregulatory responses during thermal stress.
Interventions
DRUG50 mg Diphenhydramine
Participants ingest 50mg of diphenhydramine orally \ 2 hours prior to a passive heating protocol. Participants then don a water-perfusion heat suited and lay supine on assessment table while 49℃ is circulated throughout the garment. Heating persists until participants reach a 1.5℃ increase in core temperature from baseline.
DRUG10 mg Loratadine
Participants ingest 10 mg of loratadine orally \ 2 hours prior to a passive heating protocol. Participants then don a water-perfusion heat suited and lay supine on assessment table while 49℃ is circulated throughout the garment. Heating persists until participants reach a 1.5℃ increase in core temperature from baseline.
DRUG5 mg Desloratadine
Participants ingest 5 mg of desloratadine orally \ 2 hours prior to a passive heating protocol. Participants then don a water-perfusion heat suited and lay supine on assessment table while 49℃ is circulated throughout the garment. Heating persists until participants reach a 1.5℃ increase in core temperature from baseline.
OTHERPlacebo (Sugar Pill)
Participants ingest placebo pill orally \ 2 hours prior to a passive heating protocol. Participants then don a water-perfusion heat suited and lay supine on assessment table while 49℃ is circulated throughout the garment. Heating persists until participants reach a 1.5℃ increase in core temperature from baseline.
Sponsors
Lakehead University
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
OTHER
Masking
DOUBLE (Subject, Investigator)
Masking description
Participants will be informed of the study interventions prior to experimental trials to ensure participants are able to provide informed consent. However, participants will blinded to the order of the arms (i.e., participants will not be informed which antihistamine/placebo pill they ingest for any trial). Data will remain blinded to researchers until after a third-party statistical analysis.
Intervention model description
Each participant will be asked to ingest either i) 50mg of diphenhydramine, ii) 10 mg loratadine iii) 5 mg desloratadine, or iv) placebo (sugar pill) \ 2 hours before heating protocol in a random pre-determined order over four separate experimental trials.
Eligibility
Sex/Gender
ALL
Age
19 Years to 39 Years
Healthy volunteers
Yes
Inclusion criteria
* Male or Female between ages 19 and 39 years * Fully vaccinated against COVID-19 * Able to provide informed consent * Body-mass index under 30
Exclusion criteria
* Body-mass index over 30 * Currently taking sedative or autonomic nervous system depressant medication * Hypersensitivity to diphenhydramine, loratadine, or desloratadine * History of cardiovascular disease, cancer, type 1 or 2 diabetes, chronic obstructive pulmonary disorder, or cystic fibrosis * Have smoked tobacco products less than 12 months prior to participation * Pregnant/Breastfeeding
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Local Sweat Rate | For each study arm (all completed within 4 months), measured before heating, and at every 0.25C increase in core temperature (+0.25C, +0.50C, +0.75C, +1.0C, +1.25C, and +1.5C), or every ~15 minutes of (up to ~90 minutes) and immediately after heating | Measured using ventilated sweat capsules affixed to forearm and chest |
| Whole-Body Sweat Losses | For each study arm (all completed within 4 months), measurements taken immediately before heating protocol & immediately following the heating protocol | Difference in participants' pre/post body mass |
| Skin Blood Flow | For each study arm (all completed within 4 months), measured before heating, and at every 0.25C increase in core temperature (+0.25C, +0.50C, +0.75C, +1.0C, +1.25C, and +1.5C), or every ~15 minutes of (up to ~90 minutes) and immediately after heating | Measured using laser-doppler skin blood blow sensor affixed to forearm |
| Heart Rate | For each study arm (all completed within 4 months), measured before heating, and at every 0.25C increase in core temperature (+0.25C, +0.50C, +0.75C, +1.0C, +1.25C, and +1.5C), or every ~15 minutes of (up to ~90 minutes) and immediately after heating | Measured using electrocardiogram |
| Mean Arterial Pressure | For each study arm (all completed within 4 months), measurements taken at baseline before heating, and every 10 minutes throughout heating protocol (up to ~ 90 minutes), and immediately after heating | Measured using brachial blood pressure cuff |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Thermal Comfort | For each study arm (all completed within 4 months), measured before heating, and at every 0.25C increase in core temperature (+0.25C, +0.50C, +0.75C, +1.0C, +1.25C, and +1.5C), or every ~15 minutes of (up to ~90 minutes) and immediately after heating | Self-assessments of thermal comfort using four-point analog scale where 1 is Not uncomfortable and 4 is Very uncomfortable |
| Mental Acuity | For each study arm (all completed within 4 months), measurements taken 2 hours before heating (pre-pill ingestion), 5-minutes before initiating heating, and within 5-minutes after the heating protocol | Indexed with digital Stroop test |
| Sleepiness/Fatigue level | For each study arm (all completed within 4 months), measurements taken 2 hours before heating (pre-pill ingestion), 5-minutes before initiating heating, and within 5-minutes after the heating protocol | Measured using Stanford Sleepiness Scale (min: 1, max: 7 (more fatigued)) |
| Thermal Sensation | For each study arm (all completed within 4 months), measured before heating, and at every 0.25C increase in core temperature (+0.25C, +0.50C, +0.75C, +1.0C, +1.25C, and +1.5C), or every ~15 minutes of (up to ~90 minutes) and immediately after heating | Self-assessments of thermal sensation using a 7-point analog scale where -3 is Cold and +3 is Hot. |
Countries
Canada
Contacts
Primary ContactNicholas Ravanelli, PhD
Backup ContactDouglas Newhouse, HBK
Outcome results
None listed