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For patients who are
allergic
to local anesthetic There are two broad
classes of injectable local anesthetic. They are the amines and the
esters. It is important to understand this when considering whether
or not you are allergic to local anesthesia, since an allergy to an ester based
anesthetic does not imply an allergy to the more important class of
amine based anesthetics. Esters Esters were the first class of local
anesthetic to be discovered (cocaine) and later to be synthesized (Novocaine). They contain such drugs as Cocaine, Procaine, Tetracaine,
Chloroprocaine and Benzocaine. Today, only benzocaine is routinely used in
dentistry, and its use is limited to topical application (applied with
a cotton swab prior to injections or for minor procedures). The others are
used today mostly in obstetrics and for producing spinal anesthesia. The
most well known dental anesthetic in this class was Novocain. Novocain was the brand
name for procaine, the very first chemically synthesized, non addictive,
injectable local anesthetic ever produced. It was invented at the end of
the 19th century. It is no longer used in dentistry partly
because it has a short duration, and partly because it is highly allergenic. High allergenicity is a trait common to all
the ester based anesthetics. In general, a patient known to be allergic to
one ester anesthetic is likely to be allergic to all ester anesthetics. The
use of ester based anesthetics can be avoided entirely since 5% lidocaine gel
(lidocaine is not an ester) works quite well as a topical anesthetic to numb the
gums before the shot is given. Amines Amines
were invented later. They include Lidocaine, mepivicaine, bupivicaine,
articaine, prilocaine and
bupivicaine. They all have the advantage of being non allergenic.
To my knowledge, there has never been a true, documented allergic
reaction to an amine anesthetic that contained no preservatives. Since dentists now use
amine based anesthetics, and no longer use ester based anesthetics, we see almost no
allergic reactions to the injectable local anesthetics. If you have suffered allergic reactions at the dentist's
office, it is most likely that the reaction was to the topical anesthetic
applied with a swab before the shot, or to the preservative used in anesthetics
containing vasoconstrictors.
Preservatives Upon occasion, a
patient may have a legitimate allergic reaction to an injected dental local
anesthetic. It is likely that he or she may in fact be allergic
only to the bisulfite preservative used to stabilize the vasoconstrictor.
If the allergic reaction was not too serious, it may be worth trying again with
either mepivicaine or prilocaine without vasoconstrictor.
Anesthetic manufactures do not use preservatives in carpules that do not
also contain vasoconstrictor. Testing
for anesthetic allergy using skin tests One of the most
commonly used skin tests used by physicians to test for general allergy is
called the
T.R.U.E.
TestŪ. This is a patch test that applies 23 allergens to the skin
contained in 12 polyester patches. One of the patches contains a mixture
of several anesthetics and is used to test for allergy to local anesthetics in general.
The mixture used includes two ester based anesthetics and one amine based
anesthetic. This mixture of anesthetics is called the "Caine
Mix", and most people are not aware that a positive T.R.U.E. patch
test does not necessarily indicate that the patient is allergic to injectable
dental anesthesia. The patient may instead be allergic to only the ester
based anesthetics (generally used only as topicals in dentistry), but not to the
amines which are injected after the topical and produce the profound anesthesia
necessary for dental surgeries. What
if you have had an allergic reaction to amine local anesthetics? If
you think you are allergic to dental anesthetics, the first thing you should do
is to visit an allergist to see if you really are allergic to the amide based
anesthetics. You could be saving yourself a LOT of difficulties in the
dental office! (Probably, you are only allergic to the
preservative used to
stabilize the vasoconstrictor, or the topical that the dentist used to swab the
area to be injected. The chances are that the use of mepivicaine or
prilocaine without vasoconstrictor will NOT cause an allergic
reaction provided that no ester based topical is used beforehand!)
The decision to administer or receive a drug that the
patient is known to be allergic to is not a trivial matter. Even
though anaphalaxis is quite rare with amine
based local anesthetics, it is still possible, and both the dentist and
patient must acknowledge and be prepared to deal with the
consequences. On the other hand, serious dental pain and poor dental
esthetics have real life consequences which may be just as bad for the
patient as the possibility of having to deal with the effects of the
allergy, no matter the consequences.
If you should decide to try dental treatment with local
anesthetic, take these precautions:
-
The dentist should always use mepivicaine or prilocaine without
vasoconstrictor. If you have suffered allergic reactions to dental
anesthesia in the past, there is a good chance that your allergic
reactions were caused by the preservatives used whenever a
vasoconstrictor is present.
-
Do not use any topical anesthetic except 5% lidocaine
gel. Benzocaine, the most popular type of topical is an ester and
is likely to stimulate an allergic reaction.
-
Take 50 mg of Benedryl, or a similar antihistamine an
hour before the dental appointment. Benedryl (diphenhydramine)
is available at pharmacies without a prescription.
How allergies work
 The signs and
symptoms of allergic reaction include:
-
generalized body rash or skin redness
-
itching, urticaria (hives)
-
broncospasm (difficulty breathing)
-
swelling of the throat
-
asthma
-
abdominal cramping
-
irregular heartbeat
-
hypotension (low blood pressure)
-
swelling of the face and lips (angioneurotic edema)
However, allergic reactions can have any degree of severity
ranging from minor itching to full blown anaphylaxis. In a very
serious anaphylactic reaction, the patient may experience serious difficulty
breathing due to closing down of the bronchioles in the lungs or swelling in the
throat area due to urticaria as well as seriously low blood pressure leading to
anaphylactic shock. This set of events, left untreated can lead to death.
Anaphylaxis is, of course the worst case scenario. Fortunately,
the majority of allergic reactions to local anesthetics are fairly mild and
are easily treated with light antihistamines like diphenhydramine (Benedryl).
In a vast majority of situations, patients who have patch tested allergic to all
modern local anesthetics can be safely injected for necessary dental work
using an anesthetic without vasoconstrictor,
provided the dentist is ready with the appropriate drugs and training necessary to combat an
anaphylactic reaction in the unlikely event one should occur. The two drugs
that you must have on hand to stabilize a patient in anaphylactic shock are as follows:
-
Epinephrine (adrenalin) 1:1000 subcutaneous injection.
This drug is standard in any emergency kit and counteracts all the serious
effects of anaphylaxis immediately. It opens the bronchioles allowing
free breathing, increases the blood pressure counteracting shock and evens
out and intensifies the heart beat. Its effects are drastic, but short
lived. The standard dose is 1 mg given in three doses five minutes
apart.
-
Benedryl (diphenhydramine) 25-50 mgm injectable. This is an
antihistamine and can also be taken in pill form an hour before the
procedure to help prevent serious allergic reaction before it begins.
Most emergency kits contain injectable diphenhydrimine which can be
administered either subcutaneously, or in the buccal fold if the dentist is
more comfortable with that route. If the patient suffers a
severe allergic reaction, call 911!! The crash team should be in your
office within a short enough period to avoid major problems provided that
you carry out standard emergency measures. Note that all measures
conform to the standard PABCD protocol that medical personnel learn
in their basic schooling:
-
The most frequent problem encountered in anaphylactic
shock is swelling in the neck area which can block breathing. This
is the primary reason for death during an anaphylactic reaction!
-
Position the patient on his or her back with the feet
elevated.
-
Maintain an airway using the chin lift-head tilt method.
In most cases, this is the only measure needed to see the patient through
the emergency! If the patient is breathing on his or her own, then the next
steps in the emergency protocol will be unnecessary.
-
If the patient is not breathing on his own, use rescue
breathing like you learned in CPR class and proceed to the next steps
in the emergency protocol.
-
circulatory collapse in anaphylaxis is a less
frequent complication, but it is absolutely essential to be prepared to
counteract it.
-
Check the carotid artery for heartbeat and use chest compressions if necessary.
-
Definitive care includes includes drugs and Defibrillation if necessary
and if an AED (Automatic External Defibrillator) is available.
The following drugs are of little use to the dentist during
the initial stages of the emergency since they are generally used by EMS personnel for longer term
stabilization of the patient. They are often included in standard
emergency kits, but are best ignored while trying to stabilize a patient in
anaphylaxis.
-
Aminophylline This drug opens
blocked breathing passages.
-
Solu-cortef IV injection. This drug is a
corticosteroid and reduces the generalized allergic inflammatory reactions
on a longer term basis. It will not act rapidly enough to reverse
anaphylaxis immediately, but is more of a long term remedy.
-
Wyamine injection. This drug is used to
counteract hypotension (low blood pressure and shock) on a prolonged basis.
The use of
Benedryl as a local
anesthetic
Surprisingly, ordinary Benadryl injection (50 mg/ml) can be
used as a local anesthetic. Properly diluted to 5 ml, mixing 4 ml
normal saline, and and with the addition of a tiny amount of epinephrine, it
can be used just like any dental local anesthetic without the danger of
allergic reaction. The major drawback is that it tends to burn on
injection, and the patient should know that this is the case before getting
the shot. Click
here for the detailed recipe.
<==Problems arising from local anesthetics
Drug testing
and local anesthetics==>
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