NCT06217367

Over-the-Counter Antihistamines & Heat Stress

Do Common Over-the-counter Antihistamine Medications Modify Thermoregulatory Responses During Passive Heat Stress?

• Status: Unknown
• Phase: Phase 4
• Study type: Interventional
• Enrollment: 16 (estimated)
• Sponsor: Lakehead University · Academic / Other
• Sex: All
• Age: 19 Years – 39 Years
• Healthy volunteers: Accepted

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.

Conditions

• Heat Illness
• Allergic Rhinitis
• Heat Injury
• Sudomotor Sympathetic Dysfunction

Interventions

Type	Name	Description
DRUG	50 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.
DRUG	10 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.
DRUG	5 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.
OTHER	Placebo (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.

Timeline

• Start date: 2023-12-05
• Primary completion: 2024-06-01
• Completion: 2024-06-01
• First posted: 2024-01-22
• Last updated: 2024-01-22

Locations

1 site across 1 country: Canada

Regulatory

• FDA-regulated drug study