10/15/2012
I have been asked by one of our critical care pharmacists whether, in order to simplify our formulary, the subcutaneous administration of epinephrine that is now currently recommended for asthma exacerbations can be changed to intramuscular administration. I am familiar with the literature demonstrating more rapid uptake with IM administration. I also know that the most recent NHLBI guidelines continue to support SC administration for asthma. But I cannot find any good studies to support this reasoning, other than opinions that delaying absorption in asthma exacerbations may be good practice. Do you think it would be wrong for me to recommend that epinephrine be administered IM in asthma exacerbations as well? Thank you very much for your help.

Thank you for your inquiry.

I am assuming that you are referring to epinephrine administered via a syringe either from an ampule or a multidose vial.

Unfortunately, the issue is a little more complex than meets the eye because the data comparing intramuscular injection versus subcutaneous injection for epinephrine was collected using an automatic epinephrine injector (for intramuscular injection in the thigh) and not a syringe. There are very little data demonstrating that using a syringe to inject in the lateral thigh would be superior in terms of pharmacodynamic activity to injection in subcutaneous tissue or intramuscular tissue in the arm, and there of course no outcome data in asthma to compare the clinical results of injection at these sites. So, to decide to remove subcutaneous injection using those data, you would have to suggest that that injection be given by an automatic epinephrine injector.

In addition, it is more complicated because the issue is not only whether one injects subcutaneously or intramuscularly, but actually where the injections are given. In the studies comparing injection using an automatic injector, a syringe was used in the deltoid and in the subcutaneous arm tissue, and an automatic epinephrine injector was used to inject in the lateral thigh. The data on pharmacokinetic activity between injection in the deltoid muscle and injection in the subcutaneous tissue of the arm are very similar. The pharmacokinetic data differed dramatically only when one injected into the lateral thigh.

So, for a number of reasons, one cannot make a definitive judgment regarding your question based on available evidence.

Thank you again for your inquiry and we hope this response is helpful to you.

Sincerely,
Phil Lieberman, M.D.