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Antihistamines are also considered an essential drug in the dental office. Diphenhydramine, also known as Benadryl, is an antihistamine used by many individuals. It is the typical antihistamine which one would take for mild allergic reactions i.e. hives, itching, rash.
It is routinely taken in either a tablet or liquid form. However, for an acute anaphylactic episode, the oral route of administration is not quick enough. The antihistamine needs to get into the individual’s system rapidly…there is no time to spare. For this to occur the antihistamine is given in the form of an injection. It is injected into a muscle which is rich in blood vessels so that the drug is absorbed rapidly. Such an area can be found on the under surface of the tongue. This is also where we would give epinephrine, which we discussed in the previous blog.
We will look at the different routes of administration of a drug in a future blog. For now, all you need to know is that we have to get the drug into the patient’s blood stream as fast as possible…time is of the essence.
Mode of action of Antihistamines
Histamine is released (from mast cells) when there is an allergic reaction. The histamine binds to histamine receptors (H-1) resulting in the mild symptoms of an allergic reaction, mentioned above.
Antihistamines block the action of histamine by binding to H-1 receptors…They do not inhibit the release of histamine.
The recommended dosage of intramuscular (into the tongue) Diphenhydramine is 25-50 mg’s.
Why Use an Antihistamine?
In the previous blog, posted on November 25th, we learnt that epinephrine is the first ‘line of defense’ drug that is needed to treat an acute, severe allergic reaction.
Why do we even need to administer an antihistamine?
The reason is that it helps to prevent the histaminic effects rash, hives etc. that occur during anaphylaxis when histamine is released.
Antihistamines essentially act as an adjunct to the effects of epinephrine: Epinephrine is used during the acute stage of the anaphylactic reaction and the Benadryl will help to deal with the milder allergic symptoms…One can look at this as a team effort.
In the next blog we will discuss another essential drug; Albuterol. This is administered via a ‘puffer’ which individuals inhale through their mouths.
Until next time everyone…
Dr. Robert Axelrad, Brampton’s Gentle Dentist