Drug allergy: diagnosis and medical treatment

2021-07-24 11:37 PM

Drug allergy is an excessive, abnormal, and harmful reaction to the patient's body when using or coming into contact with a drug, due to a hypersensitivity phase

A drug allergy is an adverse reaction to a drug caused by stimulation of the immune system by a drug.

Some drugs can bind directly to effector cells of the immune system (eg, mast cells) and cause mast cell degeneration with clinical symptoms of urticaria or anaphylaxis. Such symptoms are very similar to some allergic drug reactions (immunoglobulin E [IgE]) and are known as pseudo-allergic or non-allergic hypersensitivity reactions. They do not involve drug- or T-cell-specific antibodies and are therefore not truly immune-mediated responses.

A drug allergy is an excessive, abnormal, and harmful reaction to the patient's body when using or in contact with a drug (with a combination of an allergen with an antibody or an equivalent factor), due to the presence of the sensitization phase. Drug allergy is independent of dose, cross-sensitivity, with certain clinical symptoms and syndromes, often with skin manifestations and very pruritus. If the drug or its relative is used again, the allergic reaction will be more severe and possibly fatal.

Differentiate between allergies and adverse drug reactions

Idiosyncrasy: A condition in which an individual is unusual, special, and unexpected sensitivity to a drug at very low doses compared to the therapeutic dose, encountered in a small number of people, unrelated to known pharmacological effects. For example, anemia caused by phenytoin or bone marrow failure due to chloramphenicol, ...

Intolerance: This is the body's distinctive, intense reaction to a drug in normal doses, with a genetic predisposition. Clinical symptoms similar to drug poisoning occur exclusively in a small number of people, the disease does not get stronger or more dangerous when the same drug is used again. For example, taking a few drops of atropine can dilate pupils or lower blood pressure, or sleeping for 16 hours after taking an antihistamine.

Drug toxicity: occurs in any person or many people when taking a relatively large amount of drug or at low doses when the patient is old and weak, with impaired function of some organs (liver, kidney). ,...) or highly toxic drugs. For example, high doses of chlorpromazine will lower blood pressure and possibly death.

Side effect: An undesirable, predictable, drug-induced effect with a given drug, in addition to the main therapeutic effect. For example, atropine causes dry mouth. Aspirin and non-steroidal anti-inflammatory drugs cause stomach ulcers, ...

Secondary effect: The same clinical manifestations will occur in people taking the same drug at high doses, for a long time. For example pseudo-Cushing syndrome after taking corticosteroids or dysbacteriosis, fungal infection, vitamin deficiency after taking antibiotics, ...

Clinical Manifestations

Table of Clinical manifestations of drug allergy


Clinical Manifestations


Anaphylaxis, hypotension, survival, vasculitis, lymphadenopathy, serum sickness.


Urticaria, Quincke's edema, pruritic papules, contact dermatitis, photosensitivity, generalized erythema, purpura sepsis, Stevens-Johnson syndrome, Lyell's syndrome.


Shortness of breath, cystitis.


Hepatitis, liver cell damage.




Nephritis, nephrotic syndrome.


Thrombocytopenia purpura, hemolytic anemia, decreased irritability.


It is a common manifestation and is often the initial manifestation of other drug allergies, appearing and disappearing quickly. The primary lesion is a very itchy edematous papule. Acute urticaria < 6 weeks, chronic urticaria > 6 weeks.

Edema Quincke

Appears after taking the drug a few minutes or a few hours, slower than urticaria, manifests in the skin and subcutaneous tissue with clusters of swelling, 2-10cm in diameter, usually appearing in the areas of the skin with nests loose function: lips, neck, around eyes, abdomen, genitals, larynx, intestines, stomach, brain, uterus.

Quincke's edema usually has no fever, no itching, and little change in skin color.


The clinical presentation of anaphylaxis is quite diverse, usually occurring briefly after taking the drug from a few seconds to 20-30 minutes, starting with a strange feeling (restlessness, panic, fear of death, ...). Then there is the rapid appearance of symptoms in one or more organs such as cardiovascular, respiratory, digestive, skin, ... with manifestations such as tingling all over, abdominal cramps, involuntary urination and defecation. aorta, rapid, small pulse, low or unmeasured blood pressure, dyspnea. In the fulminant form, the patient is comatose, choking, cardiovascular disorders, cardiac arrest, and dies after a few minutes.


Sudden high fever, rapid deterioration in health, necrotic ulcers of the mucous membranes of the eyes, mouth, throat, genital organs; pneumonia, thrombophlebitis, sepsis, easily lead to death.

Serum disease

Due to injection of serum or heterologous proteins, appear from 2nd to 14th day after dosing. Patients with fatigue, anorexia, insomnia, nausea, joint pain, swollen lymph nodes, high fever 38°c -39°c, may have hepatitis, nephritis, may have systemic urticaria.

Contact allergic dermatitis

Usually occurs after a few hours of exposure to the drug, the patient feels intense itching, red rash, blisters, edema of the open skin areas, the area exposed to the drug.

Redness of the whole body

Redness of the whole body is a widespread or whole body redness like boiled shrimp, including 2 stages: red skin and white scales.

Pink rash button

After a few days of taking the drug, the patient has a high fever, body aches and pains, many large and small nodes appear on the skin, smooth red, painful, located in the middle of the dermis and dermis, concentrated on the extensor side. limbs, sometimes appearing on the trunk and face. Lesions change color resembling bruises and subside after a few weeks.

Erythema fixed chromosomal

Symptoms appear hours or days after taking the drug. Patients with mild fever, fatigue, skin appears red at first, then dark, on lips, extremities, trunk. The disease will appear in the same place if the next time using the same or similar drugs.

Erythema variety

After taking the drug, patients often feel tired, feverish and appear many types of skin lesions: erythema, papules, vesicles, bullae, often with target-shaped rash, acute systemic progression.

Stevens-Johnson Syndrome

This syndrome is characterized by ulceration of natural cavities (more than 2 are common in the eyes and mouth) and there are many types of skin lesions: bullae, affected skin area < 10% of body skin area, possibly accompanied by liver and kidney damage, the severe form can cause death.

Lyell's syndrome

It is the most severe toxic necrosis of the skin characterized by a positive Nikolsky sign (easily shed), with a high mortality rate. The patient is too tired, has a high fever, red patches or petechiae appear on the skin, then the epidermis separates from the skin, and when touched, it slides out in patches. Damaged skin area > 30% body skin, liver, and kidney inflammation may occur, the patient's condition is often very severe, quickly leading to death.

Diagnosis of drug allergy

There is a medication history.

Allergic reactions occur after taking the drug.

There are symptoms, syndromes of drug allergy (itching is a key sign).

History of allergies (history of drug allergies or personal, family allergies).

Laboratory tests (XN): have one test (+) or more depending on the clinical form or type of reaction (mast cell degranulation reaction, specific leukopenia, lymphocyte transformation test, RAST, etc.). ..).

Treatment of anaphylaxis

Emergency regimen for anaphylaxis (according to the Circular 08 dated May 4, 1999 of the Ministry of Health).

Treatment on the spot

Immediately stop contact with the allergen (injection, oral, topical, eye drops, nose).

Have the patient lie in place.

Drug use: adrenaline is the basic drug against anaphylaxis.

Adrenalin solution 1/1000, tube 1ml = 1mg, injected subcutaneously immediately after the appearance of anaphylaxis with the following dose: 1/2 -1 ampoules in adults. Not more than 0.3ml in children (1ml tube (1mg) + 9ml distilled water = 10ml then 0.1ml/kg injection). Or adrenaline 0.01mg/kg for both children and adults.

Continue injecting adrenaline as above 10-15 minutes until blood pressure returns to normal.

Warm, low head, high legs, monitor blood pressure every 10-15 minutes (lying on your side if vomiting occurs).

If the shock is too severe to threaten death, in addition to the subcutaneous route, adrenaline can be injected in a solution of 1/10,000 (1/10 dilution) intravenously, pumped through an endotracheal tube or injected through the cricothyroid membrane.

Other measures

Depending on the conditions of medical equipment and technical expertise of each level, the following measures may be applied:

Treatment of respiratory failure: depending on the baseline and the degree of dyspnea, the following measures can be used:

Inhale nasal oxygen give breaths.

Squeeze the oxygenated Ambu ball.

Endotracheal intubation, artificial ventilation. Tracheal opacities if glottis edema is present.

Slow intravenous infusion of diaphyllin 1mg/kg/hour or terbutaline 0.2μg/kg/min.

Can be used:

Terbutaline 0.5mg (1ml), 1 tube subcutaneously in adults and 0.2ml/10kg in children. Re-inject after 6-8 hours if no relief from shortness of breath.

Throat spray terbutaline, salbutamol 4-5 times each time, 4-5 times a day.

Establish an intravenous line: adrenaline to maintain blood pressure starts at 0.1μg/kg/min, rate adjusted according to blood pressure (2mg adrenaline/hour for 55kg adult).

Other drugs:

Methylprednisolone 1 - 2mg/kg/4 hours or hydrocortisone hemisuccinate 5mg/kg/hour intravenously (can be injected intramuscularly at baseline). Use a higher dose if the shock is severe (2-5 times more).

NaCI 0.9% 1-2 liters in adults, not more than 10ml/kg in children.

Diphenhydramine 25mg or dimedrol 10mg x 2 ampoules, intramuscular or intravenous.

Combination therapy

Take activated charcoal 1g/kg body weight if the allergen is ingested.

Compression bandage above the injection site (if the allergen is injected).


Monitor patients for at least 24 hours after blood pressure has stabilized.

After giving first aid, the femoral vein should be used.

If blood pressure is still not elevated after adequate fluid and adrenaline infusion, additional plasma, albumin (or blood if blood loss) or any available macromolecule solution may be given.

Nurses can use adrenaline under the skin according to the regimen when doctors and nurses are not present.

Some clinical forms of drug allergy

Urticaria, Quincke's edema, serum sickness, generalized erythema, various types of erythema,...): two main types of treatment:

Glucocorticoid (methyl-prednisolone, depersolon, Medrol, Celestron, dexamethasone, prednisolone,), the dose depends on the clinical form and drug type.

Mild form, for example: take prednisolone 5mg x 6-8 tablets/day x 3-5 days or Medrol 16mg x 2 tablets/day x 3-5 days.

Heavy cards, eg: depersolon 30mg or methylprednisolone (Solu-Medrol) 40mg x 2 - 4 vials/day x 3 - 5 days. Then use oral drugs: prednisolone 5mg x 6-8 tablets/day x 3-5 days or Medrol 16mg x 2 tablets/day x 3-5 days.

Antibiotic histamine Hi: chlorpheniramine, Phenergan, fexofenadine (Telfast), cetirizine (Cezil, Zyrtec), loratadine (Clarityne), desloratadine (Aeolus), levocetirizine (Xyzal).

Mild form, for example: chlorpheniramine 4mg x 2 tablets/day x 3-5 days or Telfast 180mg, take 1 tablet/day x 3-5 days.

Severe: dimedrol 10mg, IM 2 -4 ampoules x 3 - 5 days. Then use orally: chlorpheniramine 4mg x 2 tablets/day or desloratadine (Aerius), levocectirizm (Xyzal) 5mg, loratadine (Clarityne), cetirizine (Cezil, Zyrtec) 10mg x 1 tablet/day x 3-5 days.

Stevens-Johnson and Lyell Syndrome

Replenish water, electrolytes, nutrition, anti-infection (similar to bladder treatment)

Water and electrolyte replacement: 5% glucose solution 500ml - 2000ml/day or 0.9% NaCI solution: intravenous infusion for 3-5 days can be based on clinical progress and urine volume to adjust fluid volume transmission. Rely on electrolytes to replenish electrolytes.


On-site: change bed linen daily. Clean natural recesses regularly. Apply Castellani solution to the affected areas of the skin. Glycerin borate: apply to lips. Only apply hydrocortisone in the eye if there is no corneal ulceration, usually apply CB2 solution 2-4 times a day.

Systemic: use antibiotics, if possible, use antibiotics with less risk of allergic reactions based on specific mast cell breakdown or leukopenia. Usually, antibiotics of the macrolide family (low allergy) are used.

Nutrition: if there is no peptic ulcer, it is necessary to feed soup with sufficient quantity and quality (rich in protein and vitamins). If there is an erosive peptic ulcer: provide energy intravenously, it is necessary to transfer protein and fat to the patient.

Drug allergy treatment

Glucocorticoid: methyl-prednlsolon (Solu-Medrol 40mg) or depersolon 30mg x 2-4 vials/day, intravenously for the first 3-5 days, then reduce the dose by oral medication. Prednisolone 5mg x 6-8 tablets/day x 3-5 days or Medrol 16mg x 2 tablets/day x 3-5 days. Finally, prednisolone 5mg x 2-4 tablets/day x 3-5 days or Medrol 16mg x 1 tablet/day x 3-5 days.

If there is damage to the brain, heart,... can use glucocorticoid by the method of high dose, short term ("pulse therapy'' or "bolus"): methyl-prednisolone 500-1000mg: solution for infusion of NaCI solution 0 ,9% 250ml (or 5% glucose solution 250ml), intravenous infusion XXX minutes X 3 days, then reduce the dose (oral).

Antihistamine H1: dimedrol 10mg x 2-4 ampoules/day. Intramuscular injection for the first 3-5 days, then can be used orally. Chlorpheniramine 4mg x 2 tablets/day or desloratadine (Aerlus), levocectirizm (Xyzal) 5mg, loratadine (Clarityne), cetirizine (Cezil, Zyrtec) 10mg, take 1 tablet/day x 3-5 days.

Measures to limit drug allergy and anaphylaxis

Propagating the rational and safe use of drugs according to indications

Before prescribing the drug, the doctor must carefully explore the patient's allergy history, in patients with a history of allergies to drugs, foods, etc., it is very easy to have allergies when using drugs. SPV must be prevented in susceptible patients, considering the dosage, route of administration, and rate of drug absorption used in treatment and diagnosis. When a patient with a history of anaphylaxis to a drug, even mildly, tries to avoid re-administration, cross-reactions between drugs should be clearly understood.

Before injecting antibiotics (penicillin, streptomycin) must have a skin prick test, the test is negative before being injected.

Be prepared with medicine and first aid equipment for anaphylaxis.

While injecting, if there are unusual feelings (restlessness, panic, fear, ...) to stop the injection and promptly handle such as anaphylaxis.

After the injection, the patient waits 10-15 minutes to prevent SPV from occurring later.

Contents of anaphylaxis emergency medicine box

Adrenaline: 1mg - 1ml: 2 ampoules.

Distilled water: 10ml: 2 tubes.

Sterile syringe: 10ml; 2 pieces, 1ml: 2 pieces

Hydrocortisone hemisuccinate 100mg or methylprednisolone (Solumedrol 40mg or depersolon 30mg: 2 ampoules).

Alcohol, cotton, sterile gauze...

Garage rope.

First aid regimen for anaphylaxis.