Hypersensitivity Flashcards
Urticaria:
Itch, polymorphic, move around
CAUSES
-Allergic: suspect if predictable trigger, or other organ systems involved
-Infection
-Physical: cold, exercise, pressure
-Contact: plants, latex, animal
-Medications: penicillin, cefaclor, amoxi
-Premenstrual
-Insect bite
-Autoimmune conditions
MANAGEMENT
Avoid trigger
Cold compress
AVOID NSAIDS
Antihistamine:
Cetirizine 10mg (0.25mg/kg)
—> can give up to 4x this PRN
—> Not if <6mo
Steroid creams have NO ROLE
If severe, refractory- single oral steroid dose.
What is an ‘anaphylactoid’ reaction? Give common examples.
Now, preferred term is ‘’Non immunologic anaphylaxis’
In all ways that matter, it is anaphylaxis.
Initial mechanism different:
- Non IgE
- Non immunological
- Doesn’t require sensitisation
Eg.
Aspirin and NSAID
Contrast
Opioid
Exercise
Cold
How to reduce incidence of adverse drug reactions (ADRs):
(Type A easier to avoid than type B)
Only prescribe when necessary
Careful ADR history first
Avoid cross-reactive drugs
—> eg. b lactam/ cephalosporin
—> ACEI and ARB
Consider interactions
Adjust for renal failure
Least sensitising route (oral)
Computerised prescribing
Liase with pharmacist (incl Med rec)
“5 Rights” adhered to
Minimise interruptions during dispensing
Administer high-risk (eg. Antivenom) in safe setting
Observe for reaction
Document reactions
Alerts incl GP/ pharmacy
Give examples of antihistamine options and doses:
H1
Promethazine
—> 12.5-25mg PO TDS
—> 25-50mg IV
—> Kids: 0.25mg/kg
Cetirizine
—> 10mg PO BD
—> Kids: 0.25mg/kg
Loratidine
—> 10mg PO daily
H2 (GI)
Ranitidine
—> 150mg PO BD
—> 50mg IV
—> Kids: 2-4mg/kg
Aetiology of anaphylaxis’:
IMMUNE MEDIATED
Previous exposure/ sensitisation
Trigger —> antigen interacts with the IgE on mast cells an basophils —> massive degranulation —> release of:
-HISTAMINE
-TRYPTASE
- Leukotriene, prostaglandin, TNF alpha
NONIMMUNE
Direct degranulation from variety of mechanisms.
World Allergy Organisation diagnostic criteria for anaphylaxis:
3 criteria
Aims to capture:
1- Classic
2- Those without rash
3- Isolated collapse
ASCIA definition for anaphylaxis:
Acute onset illness with typical mucocutaneous features (erythema/ urticaria/ angioedema)
PLUS
-Resp
And/or
-Cardiovascular
And/or
-GI
OR
Any hypotension, bronchospasm or UAO where anaphylaxis possible, even if no skin features
What is the rate of crossover reactions with penicillin and cephalosporin?
Only 1-2% will cross react
Typically 1st gen cephalos:
‘FA/PHA’
Eg. Cephalexin, cefazolin
Risk factors for FATAL anaphylaxis:
Delay to adrenaline
Upright posture
Trigger:
Nuts
Stings
Penicillin
Concurrent use of:
-Aspirin
-NSAID
-ACEI
Extremes of age
Severe or poorly controlled asthma
Other preexisting heart/ lung disease
Mastocytosis
Tryptase testing
Imperfect: not always elevated, partic in food triggers.
3 samples:
ASAP
<6 hours
24 hours +
true anaphylaxis >15. Nonimmune anaphylaxis a bit less
INITIAL APPROACH TO ANAPHYLAXIS:
Remove trigger
Resus, call for help
Position for BP vs resp distress
-100% O2
-ADRENALINE IM to lateral thigh
—> 10microg/kg up to
(500microg adult, ie. 0.5ml 1:1000)
—> Repeat x2 -3 (3-5mins)
-Large bore IV access and 20ml/kg FLUID bolus
REFRACTORY:
AIRWAY:
-NEB adrenaline 5ml
BRONCHOSPASM:
-As per asthma emergency: nebs, IV salb, Mg- avoid sedatives- prop, ket!!
HYPOTENSION
-Repeat fluid boluses
-Up to 3x IM adrenaline doses
-ADRENALINE INFUSION
—> 0.1microg/kg/min titrate
-GLUCAGON
—> 1-5mg IM or IV adult then 1mg/hr
—> 20-30microg/kg child (up to 1mg)
—> partic if on BB or CCF
-SECOND PRESSOR
—> eg. Vasopressin, metaraminol
SECONDARY (not a priority):
Role not well evidenced: extrapolated from asthma/urticaria data
- STEROID:
—> HYDROCORTISONE 250mg IV adult
—> 5mg/kg child (100)
- H1:
—> DIPHENHYDRAMINE 50mg IV/IM adult
—> 1mg/kg child
—> NO promethazine: hypotension
- H2:
—> RANTIDINE 50mg PO/IV adult
—> 1mg/kg child
POST TREATMENT MX OF ANAPHYLAXIS:
-Observe min 4 hours post adrenaline
—> Longer if risk factors
-Educate re avoid trigger
-Educate re biphasic reaction
-Epipen script and education
-Action Plan
-Medical alert (if drug, latex etc. Consider report ADR, SRLS)
-Refer to allergist/immunologist
-Consider taking off beta blocker/
NSAID/ACEI (risk factors)
No evidence for routine course of steroid or antihistamine
When should Epipen junior products be prescribed?
EpiPen Junior (300microg)
= up to 20kg
EpiPen Junior (150microg)
= 20 - 50kg
Biphasic anaphylactic reaction:
Rare: 1-5%
More common with food
Usually milder than initial
Theoretically risk reduced by steroids: evidence weak.
How does anaphylaxis Mx differ in pregnancy?
It doesn’t really.
Usual L lateral/ uterine displacement during resus
OER
Continuous CTG
….everything else is the same.
