January 24, 2025

Welcome back to UH EMS Institute’s Pharmacy Phriday. As we continue to review the changes and additions to the UH EMS 2025 protocols, we focus on a common antihistamine, diphenhydramine. 

Diphenhydramine is an antihistamine that is helpful in the treatment of symptoms during an allergic reaction. The antihistamine prevents the histamine responses of the body that result in signs and symptoms such as rhinitis, watery eyes, itching, rashes, swelling, wheezing, etc., by blocking H1 receptors. 

Diphenhydramine also has an anticholinergic (drying) effect on the body which helps during an allergic reaction. The anticholinergic effect is one reason diphenhydramine is helpful in dystonia or extrapyramidal symptoms (EPS) and included in the treatment when giving haloperidol.  

Additionally, diphenhydramine readily crosses the blood brain barrier affecting the CNS receptors and causes a sedative effect on the body. This is why it may be used in our protocols for the pediatric patient during behavioral emergencies. 

An additional use for diphenhydramine, cited within the 2025 protocols, includes nausea and vomiting related to motion sickness. The motion sickness created by the experience of riding in the back of the squad can complicate the patient’s illness and cause additional difficulties for the provider in caring for the patient. In some cases, the administration of ondansetron may not be effective. Diphenhydramine can act as an antiemetic, thus the UH protocols now provide the medication as an alternative treatment.  

An additional reference to the use of diphenhydramine within the 2025 protocols is its use with akathisia, a side effect that can occur with the use of metoclopramide and other antiemetic and antipsychotic medications. Akathisia is a disorder that falls on the spectrum of EPS. (View last year’s article on haloperidol.) 

Akathisia is defined as one being unable to remain still. It is a neuropsychiatric syndrome that is associated with psychomotor restlessness. With akathisia, one will generally experience an intense sensation of unease or an inner restlessness that usually involves the lower extremities, resulting in a compulsion to move. Mostly, the movement is repetitive. The individual may cross, uncross, swing, or shift from one foot to the other. To the observer, this may appear as a persistent fidget.1 Akathisia can become a safety issue for the patient and provider. 

Diphenhydramine is supplied in 50 mg/1 ml vials. Dosing of diphenhydramine under the UH Protocols is 25-50 mg IV/IO/IM for the adult patient. The pediatric dose is 1mg/kg. The presence of narcotics, alcohol and sedatives in the patient should be considered when dosing diphenhydramine as their effects can be increased. Like most medications we administer, diphenhydramine should be given as a slow IV push. The onset of diphenhydramine is usually about 10-15 minutes if given IV. The IV route is preferred in cases of dystonia and EPS. The AEMT may administer diphenhydramine, but only in cases of allergic reactions, anaphylaxis, and motion sickness. 

The most common adverse effects from the use of diphenhydramine include: 

• Anxiety 

• Drowsiness 

• Sedation 

• Palpitations 

Due to drying secretions in the body, diphenhydramine can sometimes make an asthma attack worse. Tachycardia and QT prolongation are also possible and some of the reasons caution is advised when treating a patient with a known cardiac history. Patients should be monitored carefully for these and other side effects following the administration of diphenhydramine. 

While diphenhydramine is a first-line treatment for a mild allergic reaction, it is important to remember that in the case of anaphylaxis, epinephrine is the “primary” treatment. In these situations, diphenhydramine should only be given following the use of epinephrine.   

Till next time, stay safe!  

Sincerely, 

The UH EMS-I Team 

University Hospitals 

Source: 

1. Patel J, Marwaha R. Akathisia. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519543/ 

July 12, 2024

Welcome back to UH EMS Institute’s Pharmacy Phriday. As the peak of summer arrives we will most likely begin hearing about those incidents of bee, wasp, and hornet stings again! Interaction with these insects increases as summer continues and they tend to become more aggressive, which is why it serves as a good time to review Diphenhydramine’s use in treating the allergic reactions to those stings, as well as the other indications included in the UH Protocols. 

While our focus in this article is the review of Diphenhydramine, an overwhelming point regarding an allergic reaction is recognizing the difference between a mild allergic reaction and anaphylaxis and the proper treatment. What comes to mind regarding your assessment and treatment of these patients? 

Let’s start with a quick physiology review. When an allergen, such as an insect bite, a sting, a medication, animal dander, molds, etc. is introduced into the body through ingestion, inhalation, absorption, or injection (envenomation) the body’s immune system responds to defend itself, and eliminate the foreign substance. During this protective response, one of the chemical mediators released is histamines. 

Histamines produce a wide variety of actions within various body systems, including:  

• Increased vascular permeability 

• Promotion of vasodilation and flushing 

• Decreased AV node conduction time 

• Stimulation of nerves that produce coughing 

• Smooth muscle contraction in the bronchioles and GI tract 

• Stimulation of the allergic immune response.  

In an allergic reaction, this defense mechanism is exaggerated. In anaphylaxis, the protection ceases to be a help and becomes an immediate life threat. 

Diphenhydramine is an antihistamine that helps treat symptoms during an allergic reaction. The antihistamine prevents the histamine responses of the body that result in signs and symptoms such as rhinitis, watery eyes, itching, rashes, swelling, wheezing, etc. 

Diphenhydramine also has an anticholinergic (drying) effect on the body which helps during an allergic reaction. The anticholinergic effect is also why Diphenhydramine is helpful in dystonia or extrapyramidal symptoms (EPS) and included in the treatment when giving Haldol. 

Additionally, Diphenhydramine readily crosses the blood-brain barrier affecting the central nervous system (CNS) receptors and causing a sedative effect on the body. This is why it may be used in our protocols for the pediatric patient during behavioral emergencies. 

Diphenhydramine is supplied in 50mg/1ml vials. Dosing of Diphenhydramine under the UH Protocols is 25-50 mg IV/IO/IM for the adult patient. The pediatric dose is 1mg/kg. The presence of narcotics, alcohol, and sedatives in the patient should be considered when dosing Diphenhydramine as their effects can be increased. Like most medications we administer, Diphenhydramine should be given as a slow IV push. The onset of Diphenhydramine is usually about 10-15 minutes if given IV. The IV route is preferred in cases of dystonia and EPS. The AEMT may administer Benadryl, but only in cases of allergic reactions and anaphylaxis. 

The most common adverse effects from the use of Diphenhydramine include: 

• Drowsiness 

• Sedation  

• Palpitations 

• Anxiety 

Due to drying secretions in the body, Diphenhydramine can sometimes make an asthma attack worse. Tachycardia and QT prolongation are also possible and some of the reasons caution is advised when treating a patient with a known cardiac history. Patients should be monitored carefully for these and other side effects following the administration of Diphenhydramine. 

Remember to oversee the patient for the progression of an allergic reaction to anaphylaxis. The typical allergic reaction which may seem like a “local” reaction can quickly progress to a life-threatening “systemic” reaction.  

While Diphenhydramine is a first-line treatment for a mild allergic reaction, in the case of anaphylaxis, it is not the “primary” treatment. In these situations, Diphenhydramine should only be given after Epinephrine. 

Earlier this year we reviewed a change within the OHIO EMS Scope of Practice regarding IM Epinephrine. Effective January 1, 2024, EMT-level providers can now draw up and administer Epinephrine 1 mg/ml intramuscularly using a standard syringe. As the existing Epi-Pens expire, providers can expect to see a change in the drug boxes taking place. Skill assessments should have been completed by all EMT-level providers, but if you want more training, please contact your EMS Coordinator. 

One final note: the Responsoft version of the 2024 UH protocols is now available for download. Be aware, there are two versions of the Responsoft software. Apple and older Android users can still use the Responsoft V1 software and enter the ID code 1160105. Newer Android users can download the Responsoft V2 software and use ID code 3232665. 

Till the next installment, stay safe! 

Sincerely,



The UH EMS-I Team

University Hospitals

July 7, 2023

Dear colleagues:

Welcome back to UH EMS Institute’s Pharmacy Phriday.  With the arrival of summer, it seems we start hearing about those incidents of bee, wasp, and hornet stings again!  And it serves as a good time to review Benadryl’s use in treating the allergic reactions to those stings as well as the other indications included in the UH Protocols.

While our focus in this article is the review of Benadryl, an overwhelming point regarding an allergic reaction is recognizing the difference of a mild allergic reaction to that of anaphylaxis and the proper treatment for both.  What comes to mind regarding your assessment and treatment of these patients?

Let us start with a quick physiology review.  When an allergen, be it an insect bite, a sting, a medication, animal dander, molds, etc., is introduced into the body through ingestion, inhalation, absorption, or injection (envenomation) the body’s immune system responds to defend itself and eliminate the foreign substance.  During this protective response, one of the chemical mediators released is histamines. 

Histamines produce a wide variety of actions within various body systems, including increased vascular permeability, promotion of vasodilation and flushing, decreased AV node conduction time, stimulation of nerves that produce coughing, smooth muscle contraction in the bronchioles and GI tract, and stimulation of the allergic immune response. In an allergic reaction, this defense mechanism is exaggerated.  In anaphylaxis, the protection ceases to be a help and becomes an immediate life threat.

Benadryl is an antihistamine that is helpful in the treatment of symptoms during an allergic reaction.  The antihistamine prevents the histamine responses of the body that result in signs and symptoms such as rhinitis, watery eyes, itching, rashes, swelling, wheezing, etc.

Benadryl also has an anticholinergic (drying) effect on the body, which helps during an allergic reaction.  The anticholinergic effect is a reason Benadryl is helpful in dystonia or extrapyramidal symptoms (EPS) and is included in the treatment when giving Haldol. Benadryl will affect the dopaminergic-cholinergic balance in the brain). 

Additionally, Benadryl readily crosses the blood-brain barrier affecting the CNS receptors and causes a sedative effect on the body.  This is why it may be used in our protocols for the pediatric patient during behavioral emergencies.

Benadryl is supplied in 50mg/1ml vials.  The dosing of Benadryl under the UH Protocols is 25-50 mg IV/IO/IM for the adult patient.  The pediatric dose is 1mg/kg.  The presence of narcotics, alcohol, and sedatives in the patient should be considered when dosing Benadryl, as their effects can be increased. Like most medications we administer, Benadryl should be given as a slow IV push.  The onset of Benadryl is usually about 10-15 minutes if given IV.  The IV route is preferred in cases of dystonia and EPS.  The AEMT may administer Benadryl, but only in cases of allergic reactions and anaphylaxis.

Some of the most common adverse effects from the use of Benadryl include drowsiness, sedation, palpitations, and anxiety. Due to drying secretions in the body, Benadryl can sometimes make an asthma attack worse.  Tachycardia and QT prolongation are also possible, and some of the reasons caution is advised when treating a patient with a known cardiac history.  Patients should be monitored carefully for these and other side effects following the administration of Benadryl.

Once again, remember to watch the patient carefully for the progression of an allergic reaction to one of anaphylaxis.  The typical allergic reaction, which may seem a “local” reaction, can quickly progress to a life-threatening “systemic” reaction. 

While Benadryl is the first-line treatment for a mild allergic reaction, in the case of anaphylaxis, it is not the “primary” treatment.  Benadryl should only be given following the use of Epinephrine. Anaphylaxis and Epinephrine will be the focus of our next installment of Pharmacy Phriday.

Until then, stay safe!

Sincerely,



The UH EMS-I Team

University Hospitals