Paracetamol (Acetaminophen) Ingestion and Core Body Temperature within Normothermic and Hot Conditions at Rest

Abstract

Intravenous paracetamol (acetaminophen; ACT) administration results in dose dependent hypothermia (~4°C) within mice. However, the influence of acute oral ACT ingestion on core body temperature (Tc) in humans has not been clearly elucidated in well controlled normothermic (NORM) conditions nor during dry (DRY) and humid (HUMID) heat stress. PURPOSE: The three aims of this study were to i) identify when the peak plasma concentration occurs after acute oral ACT administration, ii) establish any precooling (PC) effect of ACT in NORM conditions and if they correlate with the peak plasma concentration, and iii) investigate if ACT mediated precooling and/or peak plasma concentration alters Tc in DRY and HUMID conditions. METHODS: Fourteen healthy, Caucasian males were randomly allocated to one of two HOT groups; DRY (120 min at 45°C, 30% r.h.) and HUMID (45 min at 45°C, 70% r.h.). Oral ingestion of ACT (20 mg.kg of LBM) was double blinded, and a standardized breakfast (0700) was consumed prior to ACT consumption to control the gastric emptying rate of ACT. All 14 participants completed a NORM (20°C, 30% r.h.) and a HOT (n = 7 in each group) condition. In the NORM condition, the PC effect of ACT was investigated. In the HOT conditions, participants entered the heat chamber when the peak plasma concentration was reached (100 min). Tc was measured every 5 min in all conditions. RESULTS: ACT significantly (p < 0.001) reduced Tc within NORM by ~0.25°C 100 min post ingestion. This precooling effect translated to a decreased mean Tc in DRY and HUMID (p < 0.05), though Tc rate of rise was unchanged. The peak PC effect was significantly correlated with the peak plasma concentration of ACT. CONCLUSION: Oral ACT ingestion elicited a significant PC effect (~0.25°C) effect in NORM, and when ACT was ingested 100 min prior to DRY and HUMID mean Tc was reduced without a change in rate of rise in Tc. Such ACT mediated increases may prove favorable during exercise heat stress.