Canonical Question
Immuno – Hypersensitivity
Master answer
| Adrenaline | Steroids | Antihistamines | |
|---|---|---|---|
| An endogenous catecholamine released from the mammalian post-ganglionic sympathetic nerve terminals. | Hydrocortisone and prednisone most common in treating anaphylaxis. Pharmacokinetics of hydrocortisone will be discussed here | Range of sedating and non-sedating agents. Fexofenadine will be discussed here. | |
| PD- MoA | Stabilises mast cells to prevent degranulation Low doses: Beta agonism at (inotropy and chronotropy) and causing smooth muscle relaxation (including bronchorelaxation). Higher doses: alpha effects and causes vasoconstriction. | Work by binding to the cell nucleus and switching off the transcription of various genes which encode for inflammatory mediators such as cytokines, chemokines, adhesion molecules and arachidonic acid. They also activate anti-inflammatory genes such as MAP (mitogen activated protein) and increase the expression of beta2 receptors. | Binds to H1 receptors to block the effects of the histamine released from mast cells- namely, inhibition of vasodilatation, increased vascular permeability, and contraction of non-vascular smooth muscle |
| SE | HTN, tachycardia and arrhythmias, Metabolic (glycogenolysis, lipolysis, gluconeogenesis) and can increase BMR. Can worsen PHTN(causes pulm vasoconstriction) and glaucoma. | Single dose– minimal side effects. Repeated dosing– multiple effects on virtually every organ system. CVS– HTN. CNS– psychosis, mood disorders. GIT– gastriculcers, pancreatitis. Haem– leukocytosis. ID– increased risk of infection. MSK– osteoporosis, weakening of proximal muscles, abdominal striae, easy bruising, thin skin | May cause headache or drowsiness |
| PK A | Route- IV, IM, S/C, NEB, ETT Dose- 1mg ALS, 0.1mg anaphylaxis, titrated dose for haemodynamic instability (Start at 0.01mcg/kg/min, for alpha effects) Onset to action- seconds, duration 2 mins | Route – PO, IV, inh, neb Dose– usually 200 mg IV for anaphylaxis. May require repeat dosing. | Route – PO, BA 33% Dose – 60-240mg daily in divided doses |
| D | Does not cross the BBB 50% protein bound | 90% protein bound at low concentrations, only 60-70% bound at higher. Vd 0.3-0.5L/kg | Protein binding 70% |
| M | Taken up by the sympathetic nerve terminals and metabolised via COMT and MAO circulating Adr metabolised via COMT | Hepatic to tetrahydrocortisone | Negligible metabolism in humans. |
| E | Via urine as inactive metabolites (half-life 2 min) | Elimination half-life 1.2-1.8hrs | Terminal half-life 14-15hours |
JC 2019
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2013A Q17 | Compare and contrast the mechanism of action, pharmacokinetics, and side effects of adHine, steroids, and antihistamines when used for the treatment of anaphylaxis. | historical_member | — |