local anesthetic is metabolized by the body. Vasoconstrictors are of no value in
delaying the absorption of the local anesthetic from mucous membranes (that is, topical
Cautions and Warnings of the Combination.
(1) It should be recognized that the injection of epinephrine-containing
solutions in or around fingers, toes, and the penis is not recommended.
(2) Freshly prepared combinations of vasoconstrictors and local anesthetics
are more effective than commercially premixed epinephrine-containing local anesthetic
solutions. This is because a very low pH is required to stabilize the epinephrine in these
mixtures. In general, the content of one part epinephrine to 200,000 parts of the local
anesthetic agent (is optimum) will minimize the side effects inherent with epinephrine.
Great care must be taken in calculating this dilution. Small, precisely calibrated
syringes should be used in the mixing process. It should be noted that the standard
solution of epinephrine supplied is a 1:1000 (1 to 1000) concentration in each glass
ampule. This means that 1 milliliter of the 1:1000 epinephrine solution contains 1
milligram of epinephrine. In preparing a 1:200,000 dilution, epinephrine should be
added to a local anesthetic solution on a ratio of 0.1 milliliter-20 milliliters of local
anesthetic solution. This does not apply to subarachnoid injections, in which a higher
concentration of epinephrine is required.
4-4. ANOTHER AGENT WHICH CAN AFFECT THE ACTIONS OF LOCAL
Hyaluronidase (Wydase) is sometimes used in conjunction with local
anesthetics. Hyaluronidase is an enzyme that breaks down the material that binds cells
together. Thus, when hyaluronidase is combined with local anesthetic, greater
infiltration (movement) of the local anesthetic in the tissues is made possible.
4-5. CAUTIONS AND WARNINGS ASSOCIATED WITH LOCAL ANESTHETICS
a. Precautions should be taken against the danger of confusing the various
agents with one another or mistaking different concentrations of the same drug.
b. In order to avoid intravascular (into the veins) injection, aspiration in several
planes with the plunger of the syringe should always be done before injecting the
anesthetic solution into the tissues.
c. The instillation of local anesthetic agents into the trachea and bronchi leads to
immediate absorption, which soon reach blood levels comparable to those reached by
straight intravenous injection.
d. A previously punctured vial of local anesthetic solution should never be re-