Q: 45 year old female with established diagnosis of pheochromocytoma and on maintenance dose of phenoxybenzamine - presented with septic shock. Which pressors may not work on her?

Answer: Epinephrine and Norepinephrine

Phenoxybenzamine forms a permanent covalent bond with adrenergic receptors. It remains permanently bound to the receptor, preventing adrenaline and noradrenaline from binding. This causes vasodilatation, due to its antagonistic effect at the alpha-1 adrenoceptor.