Over-the-Counter Antihistamines & Heat Stress

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

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.

Sponsors & Collaborators

• Lakehead University

  lead OTHER

Study Design

Allocation

RANDOMIZED

Purpose

OTHER

Masking

DOUBLE

Model

CROSSOVER

Eligibility

Min Age

19 Years

Max Age

39 Years

Sex

ALL

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2023-12-05

Primary Completion

2024-06-30

Completion

2024-06-30

FDA Drug

Yes

Countries

• Canada

Study Locations