Pharmacology: IM versus PO Meds

Thanks for the questions!

I haven’t seen great data on sub-cu vs. IM administration. The upside of sub-cu is that it hurts a little less and may have a quicker onset. The downside as I understand it is that absorption can be erratic.
I haven’t seen any evidence for benefit with a first dose IV for any condition unless they can’t take po. The only advantage is quicker time to therapeutic level, which would only potentially matter in the sickest patients (i.e. – septic shock). Even if they have a line in place, I can’t think of a reason to keep them for an extra hour or two for IV administration as opposed to giving either a dose po or just a prescription to go home with.

Mike Pallaci

Hi Laura,

Thank you for the questions!

Question 1 about subcutaneous opioids

Yes, you can use subcutaneous administration for opioids. This is less common in the emergency department and urgent care settings.
The subcutaneous route of administration is often the preferred parenteral route of administration in palliative cancer patients including subcutaneous infusions.

There are limitations, including the volume of administration, usually no more than 1.5 mL although can give more if needed. This may increase patient discomfort. Lower volumes of subcutaneous medication have less discomfort approximately 0.5 mL.
Studies comparing intramuscular to subcutaneous generally have a patient preference of subcutaneous.

Smaller needles with subcutaneous injections than intramuscular can cause less discomfort as can site of injection eg, abdomen.
Generally the absorption is similar with opioids comparing subcutaneous to intramuscular.

If immediate pain relief is needed, of course intravenous is preferred.
With chronically ill patients the absorption of subcutaneous opioids is similar to intramuscular. There is concern of critically ill patients having decreased absorption due to decreased blood flow to subcutaneous site. This can be seen with intramuscular too.

That being said, I generally will either discuss with a patient intravenous versus PO administration and do not routinely use intramuscular injection.
If you have a patient you cannot start an intravenous line on and need parenteral pain medication I would discuss both options of intramuscular and subcutaneous and use either.

Question 2

If the patient can be treated with PO antibiotics and done with evaluation there is no clear benefit to a dose of intravenous antibiotic. I often will give an initial PO dose in the emergency department or urgent care if there may be a delay in the patient picking up the prescription after discharge to allow time for prescription to be filled.

Thanks for what you do!
Sean