Tramadol reduces the sweating, vasoconstriction, and shivering thresholds

Area of Science:

• Physiology
• Pharmacology
• Thermoregulation

Background:

• Tramadol is an analgesic that affects norepinephrine and serotonin reuptake and release, and activates mu-opioid receptors.
• These pharmacological actions suggest a potential influence on the body's thermoregulatory control.
• Understanding tramadol's impact on thermoregulation is crucial for clinical safety.

Purpose of the Study:

• To investigate the hypothesis that tramadol inhibits thermoregulatory control.
• To quantify the effects of tramadol on the thresholds for sweating, vasoconstriction, and shivering.
• To determine if tramadol alters the precision of thermoregulatory responses.

Main Methods:

• Eight healthy volunteers participated in a study involving four conditions: no drug, tramadol 125 mg, tramadol 250 mg, and tramadol 250 mg with naloxone.
• Thermoregulatory responses (sweating, vasoconstriction, shivering) were assessed by gradually altering core body temperature.
• Threshold core temperatures for each response were recorded and analyzed.

Main Results:

• Tramadol significantly decreased the core temperature thresholds for sweating, vasoconstriction, and shivering.
• The range between the sweating and vasoconstriction thresholds nearly doubled with high-dose tramadol, indicating reduced control precision.
• Naloxone partially reversed these thermoregulatory effects, suggesting a role for opioid receptors.

Conclusions:

• Tramadol exhibits slight thermoregulatory effects, primarily by reducing the setpoint for autonomic responses.
• The drug slightly decreases the precision of thermoregulatory control.
• Tramadol use is unlikely to cause hypothermia or facilitate fever due to its modest impact on thermoregulation.