**2. Local anesthetics**

In 1860, cocaine, the oldest anesthetic, was extracted from the leaves of the *Erythroxylon coca* bush. In 1884, Sigmund Freud and Karl Koller were the first to use it as an anesthetic agent during ophthalmologic procedures.

Procaine, a synthetic alternative to cocaine, was not developed until 1904. Procaine is an ester of para-aminobenzoic acid (PABA). As procaine is metabolized, PABA, a known allergen, is released as a metabolic product. The potential for severe allergic reactions limits the use of procaine and other ester-type anesthetic agents.

Tetracaine, another ester-type anesthetic, was introduced in 1930. Tetracaine is more potent than procaine, and it causes similar allergic reactions.

In 1943, an alternative class of anesthetics was discovered when Lofgren developed lidocaine. This agent is an amide derivative of diethylaminoacetic acid, not PABA; therefore, it has the benefit of a low allergic potential.

Since then, multiple amide-type anesthetics have been introduced into clinical use. Slight chemical alterations to the compounds have imparted beneficial characteristics, including increased duration and potency, to each. These compounds offer the surgeon more choices, and anesthetics can be appropriately matched to different procedures.

The lidocaine is the most widely used general-purpose local anesthetic in veterinary use. It possesses reasonably rapid onset of action, with good spreading properties. It may cause some local irritation and swelling. It is available in a variety of concentrations or injection; with and without epinephrine; and in the form of solutions, creams, jellies, sprays etc.

Duration of action is variable (depending on uptake) but will be around one hour without epinephrine, and two hours with epinephrine.

The bupivacaine has a prolonged duration of action: up to eight hours when combined with epinephrine. It is therefore used whenever long action is required.

The mepivacaine causes very little swelling and edema in the area of injection, possibly as it lacks vasodilatory action. Onset of action is faster and reliability of block greater than with prilocaine.

The prilocaine has slower onset of action, and spreads less well compared to lidocaine. The unique ability of prilocaine to cause dose-dependent methemoglobinemia limits its clinical usefulness.

Other local anesthetics are:

234 A Bird's-Eye View of Veterinary Medicine

pain, thereby facilitating surgical procedures. Many surgical procedures can be carried out

Whether or not sedation is necessary as an adjunct will depend on the species, temperament

Many operations, including some husbandry procedures and practices for experimental purposes, are performed on standing animals. Local anesthesia, enabling protracted operations in standing animals, eliminates the dangers associated with forcible casting and

The techniques are not difficult to learn and do not involve the use of expensive or

In 1860, cocaine, the oldest anesthetic, was extracted from the leaves of the *Erythroxylon coca* bush. In 1884, Sigmund Freud and Karl Koller were the first to use it as an anesthetic agent

Procaine, a synthetic alternative to cocaine, was not developed until 1904. Procaine is an ester of para-aminobenzoic acid (PABA). As procaine is metabolized, PABA, a known allergen, is released as a metabolic product. The potential for severe allergic reactions limits

Tetracaine, another ester-type anesthetic, was introduced in 1930. Tetracaine is more potent

In 1943, an alternative class of anesthetics was discovered when Lofgren developed lidocaine. This agent is an amide derivative of diethylaminoacetic acid, not PABA; therefore,

Since then, multiple amide-type anesthetics have been introduced into clinical use. Slight chemical alterations to the compounds have imparted beneficial characteristics, including increased duration and potency, to each. These compounds offer the surgeon more choices,

The lidocaine is the most widely used general-purpose local anesthetic in veterinary use. It possesses reasonably rapid onset of action, with good spreading properties. It may cause some local irritation and swelling. It is available in a variety of concentrations or injection; with and without epinephrine; and in the form of solutions, creams, jellies, sprays etc.

Duration of action is variable (depending on uptake) but will be around one hour without

The bupivacaine has a prolonged duration of action: up to eight hours when combined with

The mepivacaine causes very little swelling and edema in the area of injection, possibly as it lacks vasodilatory action. Onset of action is faster and reliability of block greater than with

and health of the farm animal, and on the magnitude of the procedure.

satisfactorily using different local anesthetics.

restraint, and prolonged recumbency.

during ophthalmologic procedures.

the use of procaine and other ester-type anesthetic agents.

and anesthetics can be appropriately matched to different procedures.

epinephrine. It is therefore used whenever long action is required.

than procaine, and it causes similar allergic reactions.

it has the benefit of a low allergic potential.

epinephrine, and two hours with epinephrine.

prilocaine.

complicated equipment.

**2. Local anesthetics** 

The proparacaine is used to anesthetize the cornea of the eye. When dropped on the cornea it has a rapid onset of action (within 1 minute) and lasts for about 15-30 minutes. It is nonirritant, and does not affect the size of the pupil.

The amethocaine is well absorbed by surfaces and is used on mucous membranes.

The procaine, an older drug with slow onset of action and poor spreading powers has been superseded by the more modern drugs.

The cocaine is the only one to cause vasoconstriction. It is now not used as a local anesthetic because of its potential for abuse.

Newer long acting local anesthetics with less cardiotoxicity, e.g. ropivacaine or lovobupivacaine, are now available for man, but are currently very expensive for veterinary use.
