MCQs in pediatric Allergy Par- II

Q 1-3 :

A 5-year-old girl (weight ¼ 18 kg) is admitted to the paediatric ward with pneumonia. There is a past history of a mild rash after an oral antibiotic but her mother is unable to remember the name of the drug. She is commenced on intravenous co-amoxiclav. Shortly after administration of the first dose, she vomits, begins to feel unwell and looks flushed. Minutes later, she becomes tachypnoiec, hypotensive

and unresponsive.

1. What would be her appropriate emergency management?

A. 5 mg oral chlorpheniramine and if no response after 5 min administer 0.2 ml adrenaline (1:1000) into the

      right thigh muscle

B. 40 mg oral prednisolone followed immediately by 0.2 ml intravenous adrenaline (1:10,000)

C. 5 mg intravenous chlorpheniramine and 50 mg intravenous hydrocortisone, followed immediately by

0.2 ml intramuscular adrenaline (1:1000)

D. 100 mg IV Hydrocortisone, followed immediately by intramuscular Epipen (300 mcg)

E. Intramuscular Epipen (Junior e 150 mcg)

2. Which of the following is the MOST useful test in aiding the diagnosis of anaphylaxis? 

A. Serum Histamine

B. Specific IgE antibodies

C. Skin-prick testing

D. Serum tryptase

E. Coomb’s test

F. Complement levels

3. With regards to antibiotic reactions, which ONE of the following is TRUE?

A. Most antibiotic reactions are IgE mediated

B. In non-IgE mediated antibiotic reactions, there is a clear temporal link to the dose

C. The most commonly involved organ is the skin

D. Provocation testing should be undertaken in all those with a severe reaction

E. Desensitization should be used in all patients who have a severe antibiotic reaction


Answers :


1. E

The first line of treatment in anaphylaxis is administration of an intramuscular dose of Adrenaline (Epinephrine). Premade Adrenaline auto injectors (e.g. Epipen) are in common usage and provide 300 mcg and 150 mcg of Adrenaline in the Epipen and Junior Epipen respectively. A child weighing between 7 and 30 kg should be given an Epipen Junior and those more than 30 kg, the Epipen. The Epipen Junior can be used from 6 months upwards. In infants below 6 months and in situations where an Epipen or similar auto
injector device is not available, a dose of 10 mg/kg (0.01 ml/ kg) of 1:1000 solution should be injected into the thigh.

Early intramuscular Adrenaline administration is key in the treatment of anaphylaxis. Time spent attempting intravenous access, calculating drug doses and drawing up steroids or antihistamines can cause unnecessary delay that can have an adverse effect on outcome. These drugs are not effective in treating acute anaphylaxis but may be beneficial and can be given after the cardiorespiratory status is stabilized using Adrenaline and fluids. The median time to cardiac arrest from anaphylaxis is dependent on the cause.

This can be as short as 5 min in drug induced anaphylaxis, 15 min in venom e triggered anaphylaxis and 30 min in anaphylaxis resulting from food allergy.

2. D

The measurement of serum levels of mast-cell mediators can aid in the diagnosis of anaphylaxis. This can be
particularly useful if the history is not clear. Measurement of histamine is not helpful as the rise is only transient, with peak levels at 1 h following an anaphylactic reaction and
therefore easily missed.

Tryptase is a mast-cell specific protease. Serum levels peak at 1 h and remain elevated for up to 6 h. Raised serum tryptase suggests massive mast-cell degranulation (in the absence of any other predisposing conditions such as mastocytosis). Some cases of anaphylaxis do not display a rise in serum tryptase (e.g. some food-induced anaphylaxis).

These cases are thought to be due to basophilmediated histamine release. Despite this, serum tryptase
elevation is thought to be 95% sensitive and 95% specific for mast-cell mediated anaphylactic reactions.
Whilst skin-prick testing and specific IgE antibody tests (RAST) can both be used to detect specific IgE antibodies to allergens, neither is diagnostic of anaphylaxis. Additionally, their role in antibiotic allergy is limited as, if negative, antibiotic allergy cannot be ruled out.

A positive Coombs test has been seen in certain drug reactions e.g. Cephalosporins; however has no role in the acute diagnosis of anaphylaxis.

Serum complement levels have limited value in the diagnosis of anaphylaxis. It is thought that activation levels
should be measured rather than complement fractions themselves as during an anaphylactic reaction there can be a large dilutional effect.

3. C

Allergic reactions to antibiotics comprise only a small proportion of adverse drug reactions but since they are
unexpected and can be severe, they are associated with significant morbidity and mortality. Physicians should strive to evaluate the diagnosis of possible antibiotic allergy once the child has recovered and not allow them to unnecessarily carry that label into adulthood. The vast majority of children with a label of beta lactam allergy will be found to be able to take all beta lactam antibiotics without an allergic reaction.

 A good medical history is important in the assessment and diagnosis of antibiotic reactions. An incorrect diagnosis of antibiotic allergy leads to the unnecessary use of more expensive agents at substantial cost to the health service and also contributes to the emergence of resistant pathogens.

Atopy is not a risk factor for drug allergy. Allergy to antibiotics can manifest in numerous different
ways. Any organ can be affected, but the skin is most commonly involved. The reaction in the girl described was clearly amultisystemIgEmediated anaphylaxis; however such reactions are rare. Much more common are non-IgE mediated reactions consisting mainly of skin rashes. These may occur days to weeks after the initial exposure to the drug and may be relatively mild with a maculopapular rash and no mucosal
involvement or have a more severe presentation similar to Stevens Johnson syndrome. Typically while the rash of acute IgE mediated reactions last only for a few hours, the rash of non-IgE mediated reactions may continue for many days. Skin-prick testing, intradermal testing and specific IgE
antibody tests can be used to detect allergen-specific IgE antibodies in antibiotic allergy. However, other than for Penicillin, the relevant allergenic determinants are not known for most antibiotics and non-irritating concentrations of the antibiotic are used to perform the skin tests. Additionally, while the negative predictive value of skin tests for Penicillin is high, it is less so for semi-synthetic penicillins such as Amoxicillin and other non-beta lactam antibiotics. There are no validated tests for antibiotic induced non-IgE mediated, delayed skin reactions.

Drug provocation testing, also called a “graded challenge” is the administration of increasing antibiotic doses
up to the usual daily dose and may be used to confirm or rule out antibiotic allergy. These are usually performed when either there is low likelihood that the reaction was caused by the drug or when the reaction appears to be only a mild maculopapular exanthem caused either by non-IgE mechanisms or due to an underlying viral infection. They are contraindicated when there is a clear diagnosis of anaphylaxis or desquamative skin reactions. The initial dose used is often 1/10th of the full therapeutic dose and this is doubled every 30 min. There is always a risk of a significant reaction during such challenges and drug
provocation must only be attempted where equipment for cardiopulmonary resuscitation and trained staff are available and under the supervision of an allergy specialist.

For IgE mediated antibiotic reactions, desensitization can be utilized if the antibiotic in question is a necessary
part of patient treatment (e.g. in cystic fibrosis). This is a technique by which children who are highly allergic to a drug are converted to a state where they can tolerate the medication. Desensitization involves the administration (intravenous or oral) of increasing doses of the antibiotic over a period of hours until a therapeutic target dose is reached. The initial dose may be as small as 1/10,000 of the therapeutic dose and this is doubled every 15 min. If mild reactions occur, they are treated symptomatically e.g. antihistamines for urticaria. If the patient experiences a severe reaction, desensitization is discontinued and an alternative antibiotic must be sought.

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Q 4

A 7-year-old girl presents with hives, which developed after a bee sting. She has no otherNsymptoms. The hives resolve with diphenhydramine. Which of the following is the most appropriate management?

(A) Write a prescription for diphenhydramine in case she is bitten again.
(B) Provide an Epi-pen Jr (epinephrine autoinjector) to be carried at all times, as well as a prescription for
     diphenhydramine.
(C) Admit to the hospital for observation for delayed hypersensitivity symptoms.
(D) Refer her to an allergist for desensitization.
(E) Order a skin-prick test with hymenoptera venom.


Answer :


(B)

The insect order Hymenoptera includes ants, bees, and wasps. Their venom usually only causes a local reaction. About 1–4% of the population is sensitized to the venom and at risk for immediate hypersensitivity reactions.

Reactions may include urticaria, angioedema, wheezing, or hypotension. Severe reactions should be treated with IV fluids, oxygen, and epinephrine. Although the child responded well to diphenhydramine, because there was a systemic reaction, it is advisable to carry an Epi-pen Jr at all times. Only children with   life-threatening systemic reactions need to be referred for desensitization. Testing IgE or skinprick test with Hymenoptera venom is not predictive of future systemic reactions.