Over-the-Counter Antihistamines & Heat Stress
- Conditions
- Sudomotor Sympathetic DysfunctionHeat IllnessAllergic RhinitisHeat Injury
- Interventions
- Other: Placebo (Sugar Pill)
- Registration Number
- NCT06217367
- Lead Sponsor
- Lakehead University
- 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.
- Detailed Description
Not available
Recruitment & Eligibility
- Status
- RECRUITING
- Sex
- All
- Target Recruitment
- 16
- Male or Female between ages 19 and 39 years
- Fully vaccinated against COVID-19
- Able to provide informed consent
- Body-mass index under 30
- 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
Study & Design
- Study Type
- INTERVENTIONAL
- Study Design
- CROSSOVER
- Arm && Interventions
Group Intervention Description 5 mg Desloratadine 5 mg Desloratadine - 50 mg Diphenhydramine 50 mg Diphenhydramine - 10 mg Loratadine 10 mg Loratadine - Placebo (Sugar pill) Placebo (Sugar Pill) -
- Primary Outcome Measures
Name Time Method 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
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
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
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 Outcome Measures
Name Time Method 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".
Trial Locations
- Locations (1)
Lakehead University C.J Sanders Fieldhouse
🇨🇦Thunder Bay, Ontario, Canada