March 8, 2017

How Do EpiPens Work?

EpiPen has made a splash in the headlines in recent months. Last summer, the pharmaceutical company Mylan drew widespread criticism when it was revealed that a 500% price hike had been placed on the epinephrine autoinjector. After Congressional investigations, Mylan agreed to introduce a cheaper generic version of the drug, as well as fund programs to help patients afford the costs.

An EpiPen, with its safety cover. Source: Tokyogirl79 (Wikimedia Commons)

But the damage has already been done: since the beginning of 2017, physicians have been prescribing alternatives to EpiPen at a rate 6X higher than in 2016. Without insurance, a generic version called Adrenaclick costs just $10 for a two-pack at CVS.

A young boy with anaphylaxis. 
Source: James Heilman, MD 
So how do EpiPens, and other brands of epinephrine autoinjectors, work in the first place?

Millions of people keep epinephrine autoinjectors on hand due to their risk of anaphylaxis. Anaphylaxis is a serious type of allergic reaction — most commonly to particular foods, animal stings or bites, and medications — that can start within minutes of exposure to the allergen. Symptoms include shortness of breath, throat or tongue swelling, vomiting, lightheadedness, and a drop in blood pressure.

Why such a severe reaction? In response to the the allergen, inflammatory mediators such as histamine cause contraction of smooth muscles (such as the lungs), blood vessel dilation and fluid leakage, and changes in heart rate. A person can die from anaphylaxis if their heart stops beating, or if they are unable to breathe due to swelling of the airway.

EpiPens work by rapidly injecting a dose of epipinephrine (also called adrenaline), which reverses the effects of anaphylaxis.

Epinephrine. Source: Roland Mattern (Wikimedia Commons)
Epinephrine, which plays an important role in our fight-or-flight response, relaxes the smooth muscles of the airways and lungs, and rapidly increases blood pressure by constricting blood vessels. (It's the same hormone that makes us feel like we can run a marathon when, instead, we have to sweat through a public speech to a large, scary audience.) The pen is injected directly into the thigh muscle, as the intramuscular route is faster than subcutaneous administration (like how insulin is delivered).

Have you used an epinephrine autoinjector before? What was the experience like? Let me know in the comments.