Theophylline disposition in obese rats

Area of Science:

• Pharmacokinetics
• Obesity Research
• Animal Models

Background:

• Obesity can alter drug pharmacokinetics.
• Understanding these changes is crucial for effective drug dosing.
• Dietary obesity models provide a tool to study these effects.

Purpose of the Study:

• To investigate the impact of dietary-induced obesity on theophylline clearance and distribution.
• To assess the utility of a rat model for studying obesity-related pharmacokinetic alterations.
• To examine how body composition changes in obesity affect drug disposition.

Main Methods:

• Induction of obesity in Sprague-Dawley rats using a high-fat diet over several months.
• Measurement of body composition (fat volume, fat-free mass) using tritium dilution.
• Quantification of serum theophylline levels via high-performance liquid chromatography after intravenous administration.
• Calculation of total clearance and steady-state volume of distribution (Vss).

Main Results:

• Obese male rats gained up to 55% more body weight than controls.
• Theophylline clearance was similar between normal and obese male rats.
• Steady-state volume of distribution (Vss) increased proportionally with body weight.
• Limited theophylline uptake into adipose tissue was observed.
• Increased fat-free mass explained similar Vss per gram in both groups.
• Female rats did not become obese and showed lower drug clearances.

Conclusions:

• The dietary obese male rat serves as a relevant model for human theophylline pharmacokinetics.
• Obesity alters drug distribution, necessitating parameter normalization for abnormal body weights.
• Metabolic function, indicated by clearance, remained constant despite increased body and liver weights in obese males.
• This model facilitates controlled studies on obesity-related pharmacokinetic changes.