Allergy & Anaphylaxis

Difference between first-gen & second-gen antihistamines

First gen are more sedating (readily cross BBB) while second-gen are less sedating

Examples of first-gen antihistamines

Alimemazine. Promethazine. Chlorphenamine. Cyclizine.

Compare the sedating effects of first-gen antihistamines

Alimemazine + Promethazine > Chlorphenamine + Cyclizine

Examples of second-gen antihistamines

Acrivastine. Cetirizine. Desloratadine. Loratadine. Fexofenadine.

Antihistamines used for nausea & vomiting

Cinnarizine. Cyclizine. Promethazine.

Antihistamine used during acute migraine

Buclizine

Antihistamines for occasional insomnia

First-gen (e.g. promethazine)

Monoclonal antibody used for allergen immunotherapy

Omalizumab

When might omalizumab be used for allergen immunotherapy

When severe persistent allergic asthma can’t be adequately controlled with ICS + LABA

Side effects of omalizumab

Churg-Stauss syndrome. Hypersensitivity reactions.

Anaphylaxis Treatment Pathway in Primary Care

Use auto-injector immediately (IM adrenaline/epinephrine) → Call 999 and state anaphylaxis (CPR if needed) → Lie down & raise legs above heart → Remove trigger if possible → Repeat after 5mins if no improvement

Additional Anaphylaxis Treatment Secondary Care

High flow oxygen ASAP. IV fluids if hypotensive/shock

Drug treatment given after stabilisation of anaphylaxis

Oral non-sedating antihistamine (IM/IV chlorphenamine maleate if can’t take oral antihistamine)

What may be considered for patients with persisting respiratory problems following anaphylaxis?

Inhaled bronchodilator therapy with salbutamol and/or ipratropium bromide

Anaphylaxis Adrenaline Dose: Up to 6 months

100-150mcg

Anaphylaxis Adrenaline Dose: 6 months - 5 years

150mcg

Anaphylaxis Adrenaline Dose: 6 - 11 years

300mcg

Anaphylaxis Adrenaline Dose: Over 12 years

500mcg

!MHRA Alert! Number of autoinjectors patients should be prescribed & always carry

Two