Refractory Anaphylaxis on a Beta-Blocker: Glucagon, High-Dose Epinephrine, or Vasopressin
A 71-year-old man on metoprolol stays hypotensive after two epinephrine doses for a wasp sting. His heart rate of 68 isn't reassuring — it's the clue to what's actually holding his pressure down.
W.H., a 71-year-old retired accountant on metoprolol for atrial fibrillation rate control, was stung by a yellow jacket at his granddaughter's birthday barbecue and within minutes had hives spreading across his chest, audible wheezing, and a blood pressure his family's own home cuff read at 74 over 40 before EMS arrived. Two intramuscular epinephrine doses on scene and en route did little to move his pressure, and he arrives in the emergency department still hypotensive, with a heart rate of 68 — not the reflex tachycardia anaphylactic shock would normally drive, but exactly the blunted response his home metoprolol would predict. He has well-controlled hypertension and type 2 diabetes besides his atrial fibrillation, manages all three with his primary care physician's help, and has never before had any reaction to an insect sting despite decades of gardening alongside his wife. She, standing at the bedside, keeps repeating that he takes ‘just a heart pill’ as though it couldn't possibly matter this much right now.
A heart rate of 68 in a patient this hypotensive is not reassuring, it's diagnostic: beta-blockade is competing directly with the epinephrine already on board, blunting both the chronotropic response that would otherwise signal how sick he is and, more urgently, part of the drug's own therapeutic effect. Glucagon works around exactly this obstruction — activating adenylate cyclase directly, downstream of the beta-receptor metoprolol is occupying, rather than trying to out-compete the blockade the way a higher epinephrine dose still has to. Whether that argues for glucagon in place of more epinephrine, or alongside it, is what's actually being decided at the bedside in the next several minutes, with his pressure still 74 over 40 and no time to try one approach, watch it fail, and only then reach for the next.
At the bedside
Give glucagon, one to five milligrams IV over five minutes, then an infusion at five to fifteen micrograms a minute — that is the AAAAI/ACAAI anaphylaxis practice parameter's own answer for the beta-blocked patient, not an improvisation. His beta-blocker is sitting on the exact receptor epinephrine needs to produce its full effect, and glucagon doesn't have to compete with that blockade — it activates adenylate cyclase directly, downstream of the beta-receptor entirely. That's a more direct fix for the actual mechanism holding his pressure at 74 over 40 than simply giving more of a drug that's already only partially working.
I don't want to abandon epinephrine on the theory that it's blocked. Its vasoconstrictive effect on blood pressure runs substantially through alpha-1 receptors, which his metoprolol doesn't touch — what's blunted is mostly the heart-rate response, which is exactly why his pulse looks so falsely reassuring at 68. Two intramuscular boluses failing doesn't mean epinephrine has failed; it means intermittent IM dosing hasn't been enough. A continuous IV infusion, titrated to his pressure, is a meaningfully different trial of the same, still-correct first-line drug.
I'm not arguing against glucagon existing as an option. I am arguing we shouldn't read two IM doses as proof epinephrine itself doesn't work here.
I don't think we have time to find out which one of you is right by trying them in sequence. Start the epinephrine infusion and give glucagon at the same time — they don't compete with each other pharmacologically, one working through alpha-1 receptors and direct cardiac stimulation, the other bypassing the beta-receptor blockade downstream. If his pressure is still where it is in ten minutes with both running, vasopressin is the next add, since it's also beta-receptor-independent. At 74 over 40, the cost of being wrong about which single drug to try first is higher than the cost of giving both.
Agreed: glucagon 1mg IV bolus given, followed by a glucagon infusion; epinephrine infusion started simultaneously, titrated to blood pressure; his pressure rises to 96/58 within fifteen minutes and continues improving over the next hour, both drugs continued through that improvement rather than sequentially withdrawn to identify which one “worked.”