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| ID | Type | Description | Link |
|---|---|---|---|
| 273752 | Registry Identifier | Health Canada, Control Number |
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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.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| 50 mg Diphenhydramine | Experimental |
| |
| 10 mg Loratadine | Experimental |
| |
| 5 mg Desloratadine | Experimental |
| |
| Placebo (Sugar pill) | Placebo Comparator |
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| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| 50 mg Diphenhydramine | Drug | 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. |
| Measure | Description | Time Frame |
|---|---|---|
| Whole-Body Sweat Losses | Difference in participants' pre/post body mass | For each study arm (all completed within 4 months), measurements taken immediately before heating protocol & immediately following the heating protocol |
| Skin Blood Flow | Measured using laser-doppler skin blood blow sensor affixed to forearm | 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 |
| Heart Rate | Measured using electrocardiogram | 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 |
| Mean Arterial Pressure | Measured using brachial blood pressure cuff | 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 |
| Local Sweat Rate | Measured using ventilated sweat capsules affixed to forearm and chest | 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 |
| Measure | Description | Time Frame |
|---|---|---|
| Thermal Sensation | Self-assessments of thermal sensation using a 7-point analog scale where -3 is "Cold" and +3 is "Hot". | 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 |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Nicholas Ravanelli, PhD | Contact | 6132630361 | nravanel@lakeheadu.ca | |
| Douglas Newhouse, HBK | Contact | 8076201011 | danewho1@lakeheadu.ca |
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| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Lakehead University C.J Sanders Fieldhouse | Recruiting | Thunder Bay | Ontario | P7B5E1 | Canada |
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| ID | Term |
|---|---|
| D018882 | Heat Stress Disorders |
| D065631 | Rhinitis, Allergic |
| D014947 | Wounds and Injuries |
| D004342 | Drug Hypersensitivity |
| ID | Term |
|---|---|
| D012220 | Rhinitis |
| D009668 | Nose Diseases |
| D012140 | Respiratory Tract Diseases |
| D012130 | Respiratory Hypersensitivity |
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| ID | Term |
|---|---|
| D004155 | Diphenhydramine |
| D017336 | Loratadine |
| C121345 | desloratadine |
| D000073893 | Sugars |
| ID | Term |
|---|---|
| D005021 | Ethylamines |
| D000588 | Amines |
| D009930 | Organic Chemicals |
| D001559 | Benzhydryl Compounds |
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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.
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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.
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| 10 mg Loratadine | Drug | 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. |
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| 5 mg Desloratadine | Drug | 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. |
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| Placebo (Sugar Pill) | Other | 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. |
|
| Thermal Comfort | Self-assessments of thermal comfort using four-point analog scale where 1 is "Not uncomfortable" and 4 is "Very uncomfortable" | 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 |
| Mental Acuity | Indexed with digital Stroop test | 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 |
| Sleepiness/Fatigue level | Measured using Stanford Sleepiness Scale (min: 1, max: 7 (more fatigued)) | 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 |
| D010038 |
| Otorhinolaryngologic Diseases |
| D006969 | Hypersensitivity, Immediate |
| D006967 | Hypersensitivity |
| D007154 | Immune System Diseases |
| D064420 | Drug-Related Side Effects and Adverse Reactions |
| D064419 | Chemically-Induced Disorders |
| D001555 |
| Benzene Derivatives |
| D006841 | Hydrocarbons, Aromatic |
| D006844 | Hydrocarbons, Cyclic |
| D006838 | Hydrocarbons |
| D003533 | Cyproheptadine |
| D003986 | Dibenzocycloheptenes |
| D001567 | Benzocycloheptenes |
| D011084 | Polycyclic Aromatic Hydrocarbons |
| D010880 | Piperidines |
| D006573 | Heterocyclic Compounds, 1-Ring |
| D006571 | Heterocyclic Compounds |
| D011083 | Polycyclic Compounds |
| D002241 | Carbohydrates |