Lidocaine hydrochloride absorption from a subcutaneous site

Area of Science:

• Pharmacokinetics
• Drug Absorption
• Animal Models

Background:

• Lidocaine hydrochloride absorption is influenced by solution pH.
• Open-cell systems show pH increase due to carbon dioxide loss.
• Closed systems were designed to prevent atmospheric gas exchange.

Purpose of the Study:

• To investigate subcutaneous lidocaine hydrochloride disappearance over time in rats.
• To assess the impact of a closed absorption cell on drug solution pH.
• To determine if a simple pharmacokinetic absorption model could be derived.

Main Methods:

• Utilized a "closed" subcutaneous absorption cell on anesthetized rats.
• Monitored lidocaine hydrochloride solution over time.
• Measured changes in solution pH within the closed cell.

Main Results:

• pH shifts to higher values were observed within the closed cell.
• The observed pH changes prevented the development of a simple pharmacokinetic absorption model.
• Data suggest potential precipitation of lidocaine base due to pH shifts.

Conclusions:

• The closed absorption cell did not maintain stable pH conditions for lidocaine hydrochloride.
• Subcutaneous drug absorption studies can be complicated by unexpected solution chemistry changes.
• Further investigation is needed to understand lidocaine base precipitation in vivo.