Local Anaesthetics Lecture Notes

Comprehensive vocabulary flashcards covering the mechanism of action, chemical properties, clinical drugs, and administration routes of local anaesthetics based on the University of Reading School of Pharmacy lecture.

Sodium (Na+) current

An inward, depolarizing current that is one of the two major currents determining the nerve action potential.

Potassium (K+) current

An outward, hyperpolarizing current that is one of the two major currents determining the nerve action potential.

m-gate

The activation gate controlling voltage-gated $Na^+$ channels.

h-gate

The inactivation gate controlling voltage-gated $Na^+$ channels.

n-gate

The activation gate controlling $K^+$ channels.

Esters

A class of local anaesthetics, such as procaine and tetracaine, that are metabolised by plasma esterases and are generally short-acting.

Amides

A class of local anaesthetics, such as lidocaine and bupivacaine, that are metabolised by the liver and are generally longer-acting.

Hydrophilic pathway

The major mode of local anaesthetic action ($\sim 90\%$) which is use-dependent, requiring the channel to be open for drug access.

Hydrophobic pathway

The secondary mode of local anaesthetic action ($\sim 10\%$) which is non-use-dependent.

pKa of local anaesthetics

Local anaesthetics are weak bases with a $pKa$ of approximately $8-9$, meaning they are largely ionised at neutral $pH$.

Use-dependence

A phenomenon where the more a channel is open (higher frequency of action potentials), the greater the drug block becomes due to increased binding site access.

Inactivated state affinity

The preference of local anaesthetics to bind to the inactivated state of $Na^+$ channels rather than the resting state.

Cocaine

Introduced by Karl Koller in 1877; a medium-duration local anaesthetic that blocks amine uptake, now rarely used except as a spray for the upper respiratory tract.

Lidocaine (lignocaine)

A rapid-onset, medium-duration amide local anaesthetic with good tissue penetration, used for local anaesthesia and ventricular dysrhythmias.

Bupivacaine

A slow-onset, long-duration local anaesthetic with moderate tissue penetration, widely used but noted for its cardiotoxicity.

Prilocaine

A medium-duration amide local anaesthetic with no vasodilator activity; it carries a risk of methaemoglobinaemia when used in obstetric analgesia.

Surface anaesthesia

Local anaesthetic applied directly to mucous membranes (mouth, pharynx), cornea, or skin (e.g., EMLA cream).

Infiltration anaesthesia

Local anaesthetic injected directly into tissue to anaesthetize nerve endings, often used for wound stitching or minor surgery.

Nerve block anaesthesia

The injection of local anaesthetic close to a nerve trunk to anaesthetize the entire area of that nerve's distribution, such as the mandibular nerve in dentistry.

Spinal anaesthesia

Local anaesthetic injected into the subarachnoid (intrathecal) space between the 2nd and 5th lumbar vertebrae.

Epidural anaesthesia

Local anaesthetic injected directly into the epidural space; it is commonly used in obstetrics and requires larger doses than spinal anaesthesia.

Intravenous regional anaesthesia

Local anaesthetic injected into a limb where a cuff prevents systemic toxicity as the drug diffuses to the site of action.

Inflamed tissue resistance

Local anaesthetic resistance caused by acidic tissue reducing the amount of unionised drug ($B$) able to cross the membrane, resulting in less block.