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Simplicified version! Drugs Affecting the Afferent Innervation

Drugs which decrease the impulsation through afferent nerves:

-local anesthetics,

-astringent,

-covering,

-adsorbing drugs.

Drugs which stimulate the afferent innervations: irritative drugs.

Local anesthetics are the drugs which cause local anaesthesia. Local anaesthesia is the absence of sensibility in a local part of the body.

Depending on the chemical structure these drugs are divided into 2 groups :

1. Ethers: cocaine, tetracaine, benzocaine, procaine.

2. Amides: lidocaine, bupivacaine, articaine.

The mechanism of action: local anaesthetics increase the inactivation of sodium channels and, as result, decrease the action potential formation.

There are 3 types of local anesthesia:

1. Terminal (superficial, applicational) anaesthesia. It is reached by application of the drug upon the mucous membranes or skin. For this type of anaesthesia we can use cocaine, tetracaine, benzocaine and lidocaine.

2. Conduction (regional) anaesthesia is the nerve fibers' blockade after the injectional introduction of the drug directly to them. For this type of anaesthesia we can use procaine, lidocaine (1-2% solutions). Specific type of conduction anaesthesia is spinal anaesthesia.

3. Infiltration anesthesia is carried out by injectional saturation of tissues with the anesthetic solution layer by layer. For this type of anaesthesia we can use procaine, lidocaine (0.25-0.5%).

So, the most universal anesthetic is lidocaine, because it is available for any type of anesthesia

Amides are destroyed in the liver and have more prolonged action than ethers which are destroyed by the blood and tissues esterases. For example, the duration of the anesthesia caused by lidocaine is about 2 hours, by procaine is about 30-60 min.

Anesthetic drugs may be quickly absorbed from the highly vascularized tissues (face, oral cavity, throat, larynx) that may cause intoxication. To reduce this effect and to prolong the drug action the vasoconstrictors (epinephrine) are added to the anesthetic solution.

Side effects:

Severe toxicity: cocaine, tetracaine.

Allergic reactions: procaine.

Astringent drugs are those, which coagulate proteins on the surface of mucous membranes or skin, creating the albuminate panniculus, which protects them from damaging factors → decreasing of pain. One additional effect of astringent drugs is vasoconstriction → decreasing of exudation. Due to decreasing of pain and exudation astringent drugs produce anti-inflammatory activity.

Indications:

Stomatitis (inflammation of oral cavity): tannin, alumen. sage (Salvia) leaves, decoction of oak bark.

Gastritis, enteritis (inflammation of stomach and small intestine): tannalbine, bismuth subnitrate.

Dermatitis (inflammation of skin): dermatolum, xeroformum, bismuth subnitrate.

Covering drugs are those which have thick, gelic consistence, that is why they cover mucous membranes with colloidal film and protect them from damaging factors → decreasing of pain..

This group include starch, flax seeds, which we can use to treat gastritis and enteritis.

Adsorbing drugs are the small-pounded indifferent powders with large adsorptive surface, for example, activated charcoal. They adsorb different substances, including toxic ones, and protect mucous membranes from the irritation and prevent their intestinal adsorption. They are used to treat poisonings.

Irritative drugs excite the sensory nerve endings,

local effect reflex effect