Mechanisms contributing to barbiturate intolerance in rats

Area of Science:

• Pharmacology
• Neuroscience
• Toxicology

Background:

• Barbiturates are central nervous system depressants with a narrow therapeutic index.
• Understanding drug tolerance and its mechanisms is crucial for safe and effective therapeutic use.

Purpose of the Study:

• To investigate the development and duration of barbiturate tolerance in female rats.
• To differentiate between central nervous system (CNS) and hepatic mechanisms of barbiturate tolerance.

Main Methods:

• Female rats were pretreated with barbitone (200 or 400 mg/kg/day) for 2 or 30 days.
• Subsequent challenges with barbitone or pentobarbitone assessed sleeping time and brain drug levels.
• In vitro hepatic pentobarbitone-metabolizing activity was measured at 3 and 6 weeks post-pretreatment.

Main Results:

• Pretreatment resulted in prolonged sleeping times and reduced brain barbiturate levels 3 weeks post-treatment.
• These central nervous system effects diminished by 6 weeks.
• Hepatic enzyme activity generally showed no residual effect, except for one instance of enhancement.

Conclusions:

• Barbitone administration induces a transient, non-hepatogenic central intolerance to barbiturates, linked to increased CNS sensitivity.
• This central intolerance coexists with potential hepatic tolerance, potentially altering drug efficacy and toxicity (ED50 and LD50).