title: pKa of fentanyl varies with temperature: implications for acid-base management during extremes of body temperature.
abstract: OBJECTIVE
  The pKa of fentanyl has not been measured previously at varying extremes of body temperature. The goal of this laboratory investigation was to test the hypothesis that the pKa of fentanyl changes with temperature.
  
  
  METHODS
  The investigation involved measuring the pKa values of aqueous fentanyl at varying temperatures.
  
  
  METHODS
  The investigation was conducted in a controlled laboratory environment.
  
  
  METHODS
  No human or animal subjects were involved.
  
  
  METHODS
  Because no live subjects were involved in the investigation, no interventions were necessary.
  
  
  RESULTS
  This paper reports the effect of temperature on the pKa of fentanyl. The pKa of aqueous fentanyl was measured at 15 degrees C, 25 degrees C, 37 degrees C, 42 degrees C, and 47.5 degrees C by potentiometric titration in 0.01 mmol/L of potassium chloride after extensive degassing. Data were analyzed using the least squares method with an appropriately fitting equation. The pKa of fentanyl was found to change in a similar manner to the neutral point of water at varying temperatures.
  
  
  CONCLUSIONS
  This finding has implications for the bioavailability of fentanyl at extremes of body temperature in association with the clinical acid-base management of the patient. Clinical implications for differing methods of intraoperative acid-base management at varying temperatures are discussed.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Thurlkill
authors.forename: David A
authors.initials: DA
authors.lastname: Cross
authors.forename: J Martin
authors.initials: JM
authors.lastname: Scholtz
authors.forename: C Nick
authors.initials: CN
authors.lastname: Pace
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology*; D000465:Algorithms; D018686:Anesthetics, Intravenous / Q000737:chemistry*; D001682:Biological Availability; D001831:Body Temperature / Q000502:physiology*; D005283:Fentanyl / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry; D011199:Potentiometry; D013696:Temperature
chemical_list: D018686:Anesthetics, Intravenous; D007093:Imidazoles; D006639:Histidine; D005283:Fentanyl