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Lidocaine: Structure & Mechanism of Action

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Lidocaine is a common local anethetic and antiarrhythmic drug. We will learn about the structure of lidocaine and the mode of action for the drug to be able to work as intended.

Lidocaine Structure

Lidocaine is a numbing medication, or a local anesthetic, but how does it work? What happens in our bodies and on the molecular level to allow lidocaine to stop an area of our body from feeling anything?

In order to answer this question we will first need to look at the structure of lidocaine. Lidocaine, or 2-(diethylamino)-N-(2,6-dimethyl phenyl)-acetamide, is an amide, which means it contains an amine bond like with amino acids. This amide has a NH (nitrogen-hydrogen) bound to a CO (carbon-oxygen, double bond).

The structure of lidocaine, with the amide circled in red
Lidocaine structure

On the other side of the NH group is a benzene with two methyl groups on both of the ortho positions. On the other side of the CO group is a carbon which is in turn bound to another nitrogen, which has two ethane groups attached.

Mode of Action, Background

Let's briefly review how pain occurs in the body. Receptors in the body use the central nervous system to send messages to the brain, indicating pain. The receptors work by having voltage-gated channels. These channels, or gates, start an electrical signal which goes to the central nervous system, and travels to the brain to indicate pain.

The protein structure of the voltage gated channels
Voltage gated channels protein

The voltage-gated channels work by transferring sodium ions from inside the cell to outside the cell. This transferring of positive ions creates a flow of ions, making the voltage that stimulates the central nervous system.

Lidocaine Mechanism of Action

Lidocaine works by stopping the sodium ions from passing through the voltage-gated channels. So the signals for pain are stopped even before the signals are formed.

Lidocaine binds to the sodium channels. The amide on the lidocaine allows it to act like an amino acid, and interact with the active sites in the sodium channel domains. When the active site has something else interacting with it, then it cannot transfer the sodium ions.

The exact residues that lidocaine interacts with is not known, although evidence has been seen that it may interact with the residues Phe-1764 and Tyr-1771. Lidocaine interacts in a 1:1 ratio with the sodium channels. Thus, one molecule of lidocaine can block one molecule of the sodium channels.

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