Benadryl overdose

                                                                Anticholinergic toxicity

I originally posted this to the ER Pulse newsletter but it is good info that should be shared.

“If the medication isn’t working I should take more right” – Random patient question

“Under no circumstance are you to take more medication that is prescribed or indicated” – Correct response by health care provider

I would like to begin this particular article with a note of thanks to everyone for the feedback on my writings and for the supply of suggestions. Even though there are a plethora of medical related subjects for me to choose from I feel that I should address the ones that are brought to me first. I try my best to use the most updated information that is available to me. Some things like body structures and processes have not changed so I feel comfortable using older models/books to present information. If you find that something I have written has been updated and I fail to express that, please let me know so I can publish a correction in the next article. It is my passion to teach and to explain things. I want it to be correct for the times. I will not be offended, that is my promise to you.

Autonomic Nervous System

The next few hundred words that you will read will be some of the most important text you will use for the rest of your career. The subject being presented in this article can be a very difficult concept to wrap your brain around. Oddly enough, it involves the gelatinous grey matter encased in your skull and the stringy connectors that come off of it. As mammals our brain maintains homeostasis maintaining all of our body processes. It changes our body function in relation to our current environment whether we are sitting with family enjoying a good meal or defending ourselves from immediate danger. Scientist today still attempt to figure out exactly how and why all these processes occur in our brain. Hopefully, this article will be helpful to you for several reasons,

  1.  It will help you better understand the complex design of the Autonomic Nervous System.
  2.  As healthcare professionals, certain medications we give affect the way this natural system works. Sometimes, our nervous system goes haywire and we need something to calm it down. Sometimes it is suppressed and we need to give it a kick start it to save a life. Even though this article is about anticholinergic toxicity I can’t with good consciousness present that information without reviewing the nervous system a bit. If you are comfortable with this material then I hope this is just a good review for you.
  3. If you struggle with this and you are giving medications that affect this system, then you are practicing blind.

So without further delay I shall introduce to thee the Autonomic Nervous System. The ANS is comprised of contradictory nerve functions that keep us working properly. The (2) parts of the system are divided as the Sympathetic and the parasympathetic. Let’s discuss the sympathetic system first. Have you ever been scared out of your wits, completely blindsided with something that causes you to lose all since of direction? When the sympathetic system is activated your heart races and pounds, blood is rushed to all of your large muscles, and your pupils widen. The bronchial smooth muscles open up your lungs to allow for more gas exchange to supply your large muscles that now have a huge demand for oxygen. …sounds like you are turning into a werewolf right? But you are not, you just feel like it. Many people refer to this as the “Flight or Fight response”.  If you are David Banner you would change into the Hulk when this system is activated. It allows you to stand and fight whatever scared you or run like crazy to get away. You also have a decrease in bowel activity, because in a survival situation, like running from a bear, who has time to stop and use the bathroom? Umm, not me. HOWEVER; with that being said it does not account for processes that already have taken place and a bear might just cause you to soil your clothes. The extra blood delivers extra oxygen to those large muscle groups while running and jumping in you desperate attempt to outrun said bear. Legal disclaimer: I am in no way telling you that running from a bear is a good or bad idea. Ok, I digress. What are some medications or drugs people can take that would stimulate the sympathetic nervous system? Cocaine is one, it belongs in the amphetamine class and a patient with cocaine on board will present as though he was being chased by a bear. Large pupils, rapid breathing, decreased bowel sounds, irritability and dry mouth. Conversations with these patients are sometimes very difficult.

Neurotransmitters: the go chemical for nerve impulse.

The actions of the nerves themselves are a result of action potentials releasing acetylcholine (neurotransmitter) into the synaptic cleft and binding with the Muscarinic receptors of intestinal, cardiac, and bronchial muscles. The Muscarinic receptor is one of (2) cholinergic receptors that react only with acetylcholine. This situation also affects the salivary and sweat glands as mentioned above a dry mouth accompanies. All these things are great for survival situations but how do we counteract this. We can’t go on forever with racing heartbeat, dry mouths, and large pupils. The contradictory system is referred to as the rest and digest or Parasympathetic system. It acts in the opposite way calming things down. The digestive system returns to normal, the heart rate returns to a normal 60-100 bpm. And the pupils return to normal size. All receptors in the parasympathetic system are cholinergic.

Now that we have a basic understanding of the difference between sympathetic and parasympathetic actions we can talk about drugs that are anticholinergic and that block the parasympathetic innervation. What should happen if we suppose someone were to ingest a toxic amount? Just imagine taking a person and shutting down the rest and digest part of the nervous system? Oh man!!! you’re in for a show. In my research of this topic it is mentioned that there are approximately 600 or so compounds with anticholinergic properties. Everything from plants to medications and many over the counter medications are in this group. One of the most common medications with this effect is….wait for it …..Wait for it….Diphenhydramine. Yes Benadryl. Benadryl toxicity causes the parasympathetic side to take a nap and just allow the crazy sympathetic to have a party.

Practice case #1

    Case Study time: Your patient arrives via ambulance and they are all wacked out. Your first reaction is to think, I think this person just did three lines of cocaine mixed with a pixy stick and washed it down with a red bull. Paints a pretty picture right? This person may be hallucinating as well so you may feel like calling for an exorcism while you wait for the persons head to spin around. But you collect yourself and regain your professionalism and look at the symptoms. Anticholinergic toxicity has a nifty little group of symptoms that may help you in this situation. In fact: anyone presenting to the ER with altered mental state, tachycardia, dry oral mucosa and decreased or absent bowel sounds should be ruled out for this condition. If you remember anything from this article remember these: Red as a beet, Dry as a bone, Hot as a hare, Blind as a bat, Mad as a hatter, and full as a flask. In our discussions why do you think these symptoms would present? Given what we have learned about how the parasympathetic system works you can ascertain the above question. A person with toxic levels of an anticholinergic compound has decreased capacity to sweat and salivate due to the blocking of the muscarinic receptors in the sweat glands. This will produce dry skin and very dry oral mucosa.( DRY AS A BONE). The person now has a rising body core temperature because they can’t sweat. Your body’s abysmal ability to compensate for the rising temperature shunts blood to the surface of the skin to dissipate the heat (RED AS A BEET). The patient will exhibit urinary retention because the detrusor muscle of the bladder is also under the influence of muscarinic management (FULL AS A FLASK). The ability to focus your eyes and accommodate is compromised (BLIND AS A BAT). Hallucinations can arise from blocking receptors in the CNS. The patient may see things in a distorted way, maybe try to slap at things we can’t visualize but seem very real to them (MAD AS A HATTER).  My eyes were opened to this condition after having two patients displaying these symptoms in the past few months. As we all know working in our field is a state of continuous learning. The more we see and talk about the more we can all learn together.

Ever thought of taking more diphenhydramine (Benadryl) because it’s not working?

Now what do we do with our patient who at first looked like a drug addict but now we find out they had taken one 25mg tablet of Benadryl every hours for the last 8 hours? The patient is not able to communicate effectively and they obviously need some intervention. First, because of the altered mental state we should do an accucheck to rule out hypoglycemia. Draw a rainbow of labs to determine other toxicities like acetaminophen and salicylates and basic metabolic function. Perform an EKG to look for potential cardiac involvement ie. Wide QRS, or QT intervals. If the patient has been having seizures you should include a serum creatine kinase level to check for Rhabdomyolysis. According to (, 2012) a medical online reference, the antihistamine called DOXYLAMINE has been known to produce Atraumatic Rhabdomyolysis. Most of the care is going to be supportive. Except in some circumstances where the patient is still able to maintain his own airway, activated charcoal can be used with caution to prevent further absorption of the drug. So here are a few medications that have anticholinergic properties. Benadryl, Dramamine, Claritin, Meclizine, Cogentin, Thorazine, Loxapine, Bentyl, Atropine, Belladonna alkaloids, Scopolamine, Amitriptyline, Tofranil, Prozac, Excedrin PM, Compoz, Norflex, Flexeril, Mushrooms: the Amanita muscaria and pantherina.  Some plants that cause anticholinergic toxicity are deadly nightshade, Jimsonweed, and Mandrake. So rule of thumb, if you don’t know what it is don’t eat it….right? Also if the patient is very agitated then instead of the staff and patient fighting for long periods of time it may be just better to sedate the person to prevent damage to either patient or staff. There have been some cases where Physostigmine was used when the patent is severely agitated or very delirious but that will be up to the physician or PA. Physostigmine is a drug that blocks acetylcholinesterase (the stuff that breaks down acetylcholine) in the CNS and the PNS increasing the concentration of the neurotransmitter (Ach) at the receptor sites and works to take over the anticholinergic blockers. Like a huge cavalry coming to the rescue (enter sound of horns here). I hope you enjoyed this article and learned from it or maybe used it to study for the CEN. Anyway have a great month and have a safe Halloween.


F.T. Fischbach, RN, BSN, MSN. & M.B. Dunning III, BS, MS, PhD. (2006) Nurses quick reference to: Common Laboratory & Diagnostic test. 4th ed. Pg. 532 Lippincott Williams & Wilkins, Philadelphia, PA.

Tintinalli, Judith, Kelen, G., Stapczynski, S.(2004)pg.1143  chapter 14,Emergency Medicine a comprehensive study guide. Sixth edition. American College of Emergency Physicians published by McGraw Hill New York, Chicago…..

Serita S. RN,BSN,MA,LNC & Bannon, A.(2007)Book of Poisons a guide for writers. How dunit series. 1st ed. Published: Writer’s Digest Books. Cincinnati, OH

Shervette RE 3rd, Schydlower, M, Lamp RM, Fearnow RG. Jimson “loco” weed abuse in adolescents. Pediatrics 1979; 63:520

UpToDate(2012)Anticholinergic poisoning. retrieved online  09/20/2012 from

  1. Fults, RN, BSN, CEN, CFRN. & P. Sturt, RN, MSN, CEN. (2005) Mosby’s Emergency Nursing Reference 3rd ed. Elselvier Mosby. pg. 666.

Adams, M.P., Josephson, D.L., and Holland, L.N. (2005) Pharmacology for Nurses, A pathophysiologic approach. Pg 129-134.

Pearson prentice hall publication, Upper Saddle River, NJ. 07458

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