What is the first-line treatment for anaphylaxis in adults?

Intramuscular epinephrine (adrenaline) is the universally recommended first-line treatment for anaphylaxis in adults, given into the anterolateral thigh, with a typical adult IM dose in the range of 0.2–0.5 mg repeated every 5–10 minutes as needed; antihistamines, corticosteroids, and inhaled beta-agonists are adjuncts and must not delay epinephrine.

First-line agent

• Intramuscular adrenaline (epinephrine) into the anterolateral thigh is the first-line treatment for anaphylaxis in all guidelines, including UK Resuscitation Council guidance.
• International guidelines concur that epinephrine is the medication of first choice in anaphylaxis because it is the only medication shown to reduce hospitalization and death.
• Adrenaline is the only drug recommended as first-line therapy in all published national anaphylaxis guidelines.
• All published guidelines clearly identify epinephrine as the first-line medication for treatment of anaphylaxis.

Dose and route

• Most UK guidance, including Resuscitation Council UK, recommends 0.5 mg IM in adults, repeated every five minutes if needed, whereas some international recommendations and auto-injector dosing strategies use 0.3 mg, particularly in community or pre-hospital settings.
• Epinephrine 1:1000 (1 mg/mL) at a dose of 0.2–0.5 mg in adults should be used, injected into a large muscle, usually the lateral thigh, with dosing repeated every 5–10 minutes as needed.
• For acute attacks, intramuscular epinephrine at a dose of 0.01 mg/kg of a 1:1000 (1 mg/mL) solution to a maximum of 0.5 mg in adults is used as the first-line agent.
• Under intensive care conditions with cardiac arrest/resuscitation, adrenaline 1:10,000 is given IV/IO at 1 mg for patients over 60 kg body weight (adults); for respiratory symptoms/shock without arrest, adrenaline 1:1000 is given intramuscularly at 0.3–0.6 mg for patients over 60 kg.

Adjunctive and second-line measures

• Diphenhydramine 1 to 2 mg/kg or 25 to 50 mg IV should be considered as second-line therapy to epinephrine, and combination of diphenhydramine with ranitidine is superior to diphenhydramine alone.
• The recommended dose of diphenhydramine as an H1a agent is 20–50 mg for adults; H1a agents are not a substitute for epinephrine.
• Short-acting inhaled β2 agonist (e.g. salbutamol) is a second-line medicine for lower respiratory tract symptoms such as bronchospasm, dyspnea, or wheezing, with a strong recommendation supporting its use.
• Glucocorticoids should not be considered first-line therapy but can help prevent protracted anaphylaxis; however, the benefit of glucocorticoids in acute management has not been established, and there is increasing evidence they may be harmful rather than simply lacking benefit.
• Supportive measures including high-flow oxygen, intravenous fluids, antihistamines, and corticosteroids may be used as adjuncts but must not delay adrenaline administration; corticosteroids are typically given as a single acute dose such as hydrocortisone 200 mg IV in adults.

Sources

• Severe Intraoperative Anaphylaxis Related to Thymoglobulin during Living Donor Kidney Transplantation — Antibodies
• Anaphylaxis Management in Acute Care Settings: A Review Based on UK Guidelines — Cureus
• Knowledge of healthcare providers in the management of anaphylaxis — The World Allergy Organization Journal
• A Clinical Practice Guideline for the Emergency Management of Anaphylaxis (2020) — Frontiers in Pharmacology
• Guideline (S2k) on acute therapy and management of anaphylaxis: 2021 update — Allergo Journal International
• Prevalence and Severity of Food Allergies Among US Adults — JAMA Network Open
• 2015 update of the evidence base: World Allergy Organization anaphylaxis guidelines — The World Allergy Organization Journal
• Global Trends in Anaphylaxis Epidemiology and Clinical Implications — The Journal of Allergy and Clinical Immunology. in Practice
• Anaphylaxis in Elderly Patients—Data From the European Anaphylaxis Registry — Frontiers in Immunology
• Drug‐induced anaphylaxis in the emergency room — Acute Medicine & Surgery
• Management and Prevention of Anaphylaxis — F1000Research
• Idiopathic Anaphylaxis — Current Treatment Options in Allergy

Decision support for clinicians, not medical advice. Answers are grounded in the published literature and every claim cites its source in the interactive view.