Antihistamine Overdose

All About Antihistamine Overdose

Antihistamine overdose is not often fatal, but it is more common than people think.  There are several types of antihistamines on the market, but all contain the ingredient called diphenhydramine, which blocks histamine from affecting the body with the symptoms of allergies, such as runny nose, itchiness, hives, and swelling of tissues.  The most common brand name for oral antihistamine is Benadryl.

Benadryl is also effective as a cough suppressant.  It is often used to treat motion sickness and has some positive effects in the treatment of mild forms of Parkinson’s disease.  The most frequent, non-allergy, use of Benadryl and its equivalents is as a sleep aid, especially in the elderly.

Even though antihistamines are considered to be very safe medications, there is a potential for very dangerous drug interactions, especially if you are already taking monoamine oxidase inhibitors.  Other conditions that could increase the risk of taking an antihistamine include glaucoma, ulcers, bladder problems, hyperthyroidism, and high blood pressure.  If you have any of these conditions, you should check with your doctor or ask your pharmacist if the antihistamine is safe for you.

Side effects of taking antihistamines are similar to the list of symptoms for antihistamine overdose.  If you experience some side effects, consider that you may be taking too much.  This may occur more often in the elderly since their bodies are more likely to absorb more of the active ingredient.

Overdose occurs in a couple of different circumstances.  Accidental overdose is more common than you would think, especially in children.  Benadryl is safe for use in children, but the dosage needs to be correct.  Most mistakes happen from using a household teaspoon instead of dosage spoon that is available from the pharmacy.  Daycare practices of giving Benadryl to children to get them to nap more easily and for a longer period of time have come to light recently in some communities.  In a small town in Montana, one child died of an antihistamine overdose at the hands of daycare provider.  It later became known that the daycare routinely gave the children antihistamine at naptime.

Another situation that often leads to antihistamine overdose is when Benadryl is used recreationally.  Use of antihistamines in high doses delivers a deliriant effect.  The effect has been described as dreaming while being awake, including visual and auditory hallucinations.  The difference between these hallucinations and those that are experienced by users of LSD is that those hallucinating on Benadryl are not able to tell the difference between the hallucinations and reality.  Habitual abuse of diphenhydramine is not common because the hallucinations are frequently unpleasant.  Also, people who are inexperienced at using hallucinogenics are likely to feel panic.

Overdose beyond the recreational range of eight to ten pills, can be very serious.  Taking 30 or more pills can lead to heart attack, coma, and death.  Symptoms of antihistamine overdose include:  agitation, blurred vision, coma, confusion, delirium, diarrhea, drowsiness, dry mouth, flushing of the face, inability to urinate, lack of sweat, fever, motor skill deficits, nausea, rapid heart rate, and unsteadiness.

If you think that someone has taken or been given an overdose of antihistamine, gather the following information before calling for help.  Determine the patient’s age and weight.  Find the bottle if you can.  Try to determine the time and amount that was taken.

As soon as possible call 911, Poison Control, or another local emergency number.  The Poison Control Center number for anywhere in the United States is 1-800-222-1222.

Once the patient is in the emergency room, their temperature, pulse, oxygenation rate, and blood pressure will be measured.  The specific symptoms of the overdose will be treated if possible.  The most common treatment will be to give the patient activated charcoal and a gastric lavage.